CA2592124A1 - Metal catalysts with perm-selective coatings, methods of making same and uses thereof - Google Patents

Abstract

In various illustrative embodiments of the present invention there are provided catalysts comprising metals on supports, methods of making the same and uses thereof. In various illustrative embodiments of the present invention, there is provided a catalyst comprising: a core comprising a metal catalyst dispersed on a support, an inner shell adsorbed on the core, and an outer shell adjacent and in contact with the inner shell. In various other illustrative embodiments of the present invention, there is provided a catalyst as described herein further comprising a hydrogenation site adsorbed on, embedded in or embedded in part in the outer shell. In avrious other illustrative embodiments of the present invention, there is provided a catalyst described herein wherein the metal is a noble metal. In various other illustrative embodiments of the present invention, there is provided a method of hydrogenating unsaturated hydrocarbons comprising exposing an unsaturated hydrocarbon to a catalyst described herein.

Description

Metal Catalysts with Perm-selective Coatings, Methods of Making Same and Uses Thereof Background The world-wide reserves of conventional crude oil are steadily decreasing and heavy oil, such as those obtained from oil sands, are becoming an increase source for producing oil and oil-derived products. Heavy oil has different properties than those of conventional crude oil. In particular, heavy gas oil (HGO) produced from the oil sands contains about 50% more cyclic aromatic compounds and significantly higher concentrations of sulfur (40 000 ppm) and nitrogen than conventional crude-derived HGO. The current technology to reduce the aromatic content of oil uses conventional non-noble metal sulfide catalysts, often referred to as hydrodearomatization (HDA) catalysts. Noble metal catalysts are also known, but are sensitive to sulfur poisoning.

Summary This invention is based, in part, on protecting a metal in sulfur-resistant metal containing catalyst that are active and selective under mild operating conditions, for the removal of aromatic compounds in heavy oil derived from oil sands. Such catalysts may contain protected noble metals. The metal resides in the core of the catalyst.
The core is sometimes refered to as a catalyst and this core is covered with a coating that is permeable only to hydrogen. Larger molecules are excluded from the core do not deactive the metals. The hydrogen that can penetrate to the core, adsorbs and dissociates on the metals to form hydrogen atoms or ions that are highly reactive. The hydrogen atoms or ions can then spillover from the core through the coating to the external surface of the catalyst where other reactions, such as hydrogenation, occur.
In various illustrative embodiments of the present invention, there is provided a catalyst comprising: a core comprising a metal catalyst dispersed on a support, an inner shell adsorbed on the core, and an outer shell adjacent and in contact with the inner shell.
In various other illustrative embodiments of the present invention, there is provided a catalyst as described herein further comprising a hydrogenation site adsorbed on, embedded in or embedded in part in the outer shell.

In various other illustrative embodiments of the present invention, there is provided a catalyst described herein wherein the metal is a noble metal.
In various other illustrative embodiments of the present invention, there is provided a method of hydrogenating unsaturated hydrocarbons comprising exposing an unsaturated hydrocarbon to a catalyst described herein.

Brief Description of the Drawings Figure 1 is a schematic of an illustrative embodiment of a catalyst according to the present invention.
Figure 2 is a chart illustrating pore size distribution and adsorption isotherms of samples A1-1 (see example 1) and commercial gamma-A1203 (Alfa Aesar). Sample A1-1 is representative of all in-house prepared samples with or without platinum as described in Example 1.

Figure 3 is a chart illustrating XRD patterns of alumina samples and Pt/A12O3 catalysts. All samples were calcinated. Catalysts were reduced at 300 C for 2h with flowing H2.

Figure 4 is a chart illustrating XRD patters of reduced Pt/A12O3 catalysts obtained with slow scans (0.2 /min).
Figure 5 is a chart illustrating influence of platinum precursors on dispersion in Pt/Al203 catalysts. The dry gels were calcinated in a muffle furnace at 550 C for 2h with a heating rate of 2 C/min, and reduced to 300 C for 2h in flowing H2.

Figure 6 (a and b) are TEM images of catalyst BA-1.
Figure 7 is a chart illustrating influence of heating rate during calcination on Pt dispersion of Pt/A1203 catalysts. The dry gel was calcinated in flowing gas at a heating rate of 2 or 10 C/min.
Figure 8 is a chart illustrating influence of gas flow during calcination on Pt dispersion of Pt/A1203 catalysts. All the catalysts were calcinated in flowing air or in static air (muffle furnace at a heating rate of 2 Clmin.

Figure 9 is a chart illustrating CO2 and NO2 evolution monitored by mass spectrometry during calcination of dry gel alumina (Al-200) in flowing 02 or He (20m1/min, 10 C/min).

Figure 10 is a chart illustrating CO2 evolution monitored by mass spectrometry during calcination of Al-200, N-200 and Py-200 in flowing 02 or He (20m1/min, 10 C/min).

Figure 11 is a chart illustrating thermogravimetric analysis of Al-200, N-200 and Py-200 heated at 2 C/min in air.

Figure 12 is a chart illustrating differential thermal analysis of Al-200, N-200 and Py-200 heated at 2 C/min in air and also for N-200 heated at 2 C/min in He and at 10 C/min in air.

Figure 13 is a chart illustrating toluene hydrogenation activity of N-4, Py-4, MA-1, and BA-1 catalysts at 240 C for three different runs: (=) run 1(o) run 2, and (V) run 3. The numbers given in brackets on the x-axis are the Pt dispersions of each catalyst.
Figure 14 is a schematic illustration of chemical vapour deposition apparatus.
Figure 15 is a chart illustrating effect of deposition temperature on measured surface area of A1203 for a deposition time of lh.

Figure 16 is a chart illustrating change in measured surface area of Ni/A12O3 (~) and A1203 (o) with deposition time, at a deposition temperature of 350 C.

Figure 17 is a chart illustrating change in pore size distribution of NilA12O3 with deposition time, at a deposition temperature of 350 C.

Figure 18 is a chart illustrating amount of Si02 on Ni/A12O3 as a function of deposition time at a deposition temperature of 350 C.

Figure 19 is a chart illustrating change in H2 (s) and CO (o) uptakes on with deposition time at a deposition temperature of 350 C.

Figure 20 is a chart illustrating XRD spectra for Ni/A12O3: (a) reduced, with no deposition, (b) 3-h deposition at 350 C, before reduction, and (c) 3-h deposition at 350 C, after calcination and reduction.

Figure 21 is a chart illustrating Temperature-programmed desorption (10 C/min) of NH3 on Ni/A12O3: (a) no deposition, (b) 1-h deposition, (c) 1.5-h deposition, (d) 2-h deposition, (e) 2.5-h deposition, and (f) 3-h deposition, all at a deposition temperature of 350 C.

Figure 22 is a chart illustrating change in n-octane conversion as a function of Si02 deposition time on Ni/A12O3 during hydrocracking of n-octane at 400 C
and atmospheric pressure.

Figure 23 is a schematic illustration of the structure of Ni/A12O3 catalyst coated with Si02.

Figure 24 is an Arrhenius plot of ln k versus 1/T for the hydrogenation of toluene with spillover hydrogen. Plot shows two distinct regimes of reaction and diffusion control.
Figure 25 is a chart illustrating a change in H2 (e) and CO (o) uptakes on Ni/A1203 with deposition time at a deposition temperature of 350 C
Figure 26 is a chart illustrating a change of n-octane conversion as a function of Si02 deposition time on Ni/A1203 during hydrocracking of n-octane at 400 C and atmospheric pressure Figure 27 is a schematic illustration of Fluidized Chemical Vapour Deposition (CVFD) apparatus.

Figure 28 is a chart illustrating N2 uptake and Si02 content of Mo,,Oy/A12O3 after FCVD for 0.5h to 2h at 350 C.

Figure 29 is a chart illustrating change in H2 (=) and CO (o) uptake on Ni/A12O3 with deposition time at a deposition temperature of 350 C.

Figure 30 is a chart illustrating Si02 deposition on A1203 being more rapid than on Ni/A1203 and N2 uptake of coated A1203 decreasing faster than coated Ni/A1203.

Figure 31 is an illustration of an MoOy/Al2O3 particle before SiO2 deposition.
Figure 32 is an illustration of an MoxOy/A12O3 particle after Si02 deposition.
Figure 33 is a chart illustrating an Energy Dispersive Spectroscopy (EDS) spectra of the uncoated Mo,{Oy/A12O3 shown in Figure 31.

Figure 34 is a chart illustrating an EDS spectra of the coated Mo,tOy/Al2O3 particle shown in Figure 32.

Figure 35 is a chart illustrating 29Si MAS NMR of MoXOy/Al2O3 after FCVD for (a) 0.5h, and (b) 2.5h. Both samples were calcinated after the FCVD
process.

Figure 36 is a chart illustrating 29Si MAS NMR of MoROy/Al2O3 after FCVD for 0.5h.

Figure 37 is a chart illustrating 29Si MAS NMR of Mo,,Oy/Al2O3 after FCVD for 2.5h.

Figure 38 is a chart illustrating activity of Ni/A12O3 towards n-octane cracking.
Figure 39 is a chart illustrating the percent conversion of benzene to cyclohexane at varying temperatures using catalysts, diluents and mixtures thereof.
Figure 40 is a chart illustrating the percent conversion of toluene to methylcyclohexane at varying temperatures using catalysts, diluents and mixtures thereof.
Figure 41 is a chart illustrating the percent conversion of O-xylene to di-methylcyclohexane and trimethylcyclopentane at varying temperatures using mixtures of catalysts and diluents.
Figure 42 is a chart illustrating the percent conversion to hydrogenated species using varying amounts of diluent with Pt/gamma-A1203 at varying temperatures.
a Figure 43 is a chart illustrating the Dv(d) [cc/A/g] vs Diameter (A) for the distribution of pore size of Ni containing catalysts deposited with Si02 under varying conditions.

Figure 44 is a chart illustrating the H2 and CO uptake ( Ug) of Ni containing catalysts deposited with Si02 under varying deposition times.

Figure 45 is a chart illustrating the Mass of Si02 (g)/g of sample of Ni containing catalysts deposited with Si02 under varying deposition times.

Figure 46 is a chart illustrating the NH3 uptake ( mol/g) of Ni containing catalysts deposited with Si02 under varying deposition times.

Figure 47 is a chart illustrating the n-octane conversion (%) of Ni containing catalysts deposited with Si02 under varying deposition times.

Figure 48 is a chart illustrating the 29 Si MAS NMR data for two Ni containing catalysts coated with Si02, the lower line corresponds to the 0.5 hour coating and the higher line corresponds to the 2.5h coating.

Figure 49 is a chart illustrating the BET surface area (m2/g) of Ni containing catalysts deposited with Si02 under varying deposition times.
Detailed Description Referring to Figure 1, there is an illustrative embodiment of the invention shown generally at 10. A core 12 is provided that is adsorbed on an inner shell 14.
In the examples and Figures, the core 12 is sometimes referred to as a catalyst. An outer shell 16 is adsorbed on the inner shell 14. In the examples and Figures, the outer shell 16 is sometimes referred to as a diluent. Hydrogenation sites 18 may be adsorbed, embedded or embedded in part in or on the outer shell 16 or may be absent. Catalysts of the present invention may be used to catalyze hydrogenation reactions, for example, hydrogenation of aliphatic or aromatic, unsaturated organic molecules, including, but not limited to those found in crude oil, heavy oil, bitumen and other organic molecules and mixtures used in the production of oil and oil products.
The core 12 may comprise at least one metal or metal complex of two or more metals on a support. The metal may be a noble metal. The support may be an alumina, often a gamma-alumina support. The core 12 provides highly reactive spillover hydrogen which is able to exit from the core 12 through the inner shell 14 to the outer shell 16 and the hydrogenation sites 18.
The inner shell 14 may be a silica coating that overlays, at least in part, the core such that a shape selective sulfur barrier is formed around the core 12. The inner shell 14 comprises pores that are sized so that hydrogen molecules may pass from the outer shell 16, through the inner shell 14 to the core 12 and so that hydrogen atoms and/or ions may pass from the core 12, through the inner shell 14 to the outer shell 16 and the hydrogenation sites 18.
The outer shell 16 may be acidic. The outer shell may be an acidic alumina or an acidic silica-alumina support. The support may provide a site for the opening of cyclic aromatic compounds to aid hydrogenation of the cyclic aromatic compounds.
The hydrogenation sites 18 may be conventional non-noble metal catalyst. In some embodiments, the hydrogenation sites 18 may be Ni-Mo-S particles.
The core 12 may be made by using the sol-gel method. The sol gel method may be used prepare of a core 12 that comprises pores. The sol-gel method is known in the art and may be found, for example, in Romero-Pascual et al., Journal of Solid State Chemistry, vol.
168, pp. 343-353 (2002) and Shubert et al, New J. Chem., pp. 721-724 (1998), which are herein incorporated by reference.
The sol-gel method allows the preparation of mono disperse nanosized metal oxide or metal particles in oxide matrices for many different metals and oxides. The sol-gel method can be used to produce a core 12 with uniform metal distribution, tunable particle size, high surface area, and stable dispersion. The sol gel method comprises four main steps: 1) Hydrolysis, 2) "SoP', 3) "Gel" and 4) Calcination. The resulting properties of the core 12 are sensitive to the particular processing conditions used in the sol gel method. The dispersion of the noble metal within the core 12 may vary between 1% and 100%, between 5% and 70%, between 11% and 100% or may be 80%, depending on the calcination procedure used and the noble metal precursor used. The Examples section describes sol-gel synthesis conditions of the present invention which are suitable for making a core 12 of the present invention and for use in the present invention.
Once a core 12 is prepared an inner shell 14 may be applied to the core 12 to produce a perm-selective core. Chemical vapour deposition (CVD) may be used to apply the inner shell 14 to the core 12. CVD is known in the art and examples may be found in: Niwa, M., et al., "A
Shape-Selective Platinum-Loaded Mordenite Catalyst For The Hydrocracking Of Paraffins By The Chemical Vapor-Deposition Of Silicon Alkoxide." Journal Of The Chemical Society-Faraday Transactions I, vol. 81, pp. 2757-2761, (1985); Hibino, Takashi, et al., "Shape-selectivity over HZSM-5 modified by chemical vapor deposition of silicon alkoxide." Journal of Catalysis, vol. 128, pp. 551-558, (1991); Katada, N., et al., "A continuous-flow method for chemical vapor deposition of tetramethoxysilane on gamma-alumina to prepare silica monolayer solid acid catalyst." Journal of Chemical Engineering of Japan, vol.
34, pp.
306-311, (2001). Sato, S., et al. "Catalytic and Acidic Properties of Silica-Alumina Prepared by Chemical Vapor-Deposition." Applied Catalysis, vol. 62, pp. 73-84, (1990).
CVD may be used to precisely control the pore-opening size of the pores in the core 12.
In other words the surface of the core 12 is coated such that some of the inner shell 16 is positioned, relative to the core 12, to restrict access to the pores of the core 12 in a manner that permits hydrogen atoms and/or ions and hydrogen molecules to enter and exit the pores of core 12 and does not permit some other larger compounds to enter or exit the pores.
For example, fine control of the pore-opening of NilAl2O3 using CVD for the selective chemisorption of Hz (2.9 angstroms) and exclusion of larger molecules (N2 - 3.6 angstroms and CO -3.8 angstroms) may be provided by CVD. The pore-openings of a commercial gamma-impregnated with Ni may be modified by depositing Si02 on the external surface in a fluidized bed using tetramethoxysilane (TMOS) as the Si02 precursor. The pore volume of Ni/A1203 decreases with increasing deposition time. The modal pore diameter may not change significantly and internal pore structure may not be modified. For example, a sample coated for 2.5 hours (about 14 wt% Si02), may reduce the uptake of CO and N2 by about 95% and about 87%, respectively, while the uptake of H2 remains constant. The NH3 uptake may decrease by about 80%. The Examples section describes CVD conditions of the present invention which are suitable for making an inner shell 14 of the present invention and for use in the present invention. CVD conditions may be adjusted to provide the desired deposition of the inner shell 14 on the core 12 to provide the desired characteristics of the perm-selective core.
Once an inner shell 14 is adsorbed on a core 12, an outer shell 16 may be added to the inner shell 14. This can be achieved by mechanically mixing the outer shell 16 with the perm-selected core to produce a shelled core. The mass ratio of the outer shell 16 to the perm-selective core for mixing can be 1:1, 2:1 or 4:1 or any mass ratio in between 1:1 and 4:1. The mass ratio may be selected to suit the particular desired characteristics of the shelled core. In some embodiments, the hydrogenation sites 18 may be mixed with the outer shell 16 to provide a primed outer shell. The primed outer shell may then be mixed with the perm-selective core in a desired mass ratio to provide a catalyst of the present invention. In other embodiments, the shelled core is mixed in a desired mass ratio with hydrogenation sites 18 to provide a catalyst of the present invention.

Examples Example 1 Catalyst preparation The platinum precursors were prepared by dissolving PtCl2 (Sigma-Aldrich, +99%
purity) in an aqueous solution of NH3, CH3NH2, n-butylamine or pyridine. The solvent and excess ligands were removed by open dish drying in a fume hood. The resulting Pt precursors were Pt(NH3)4C12, Pt(C5HSN)4C12, Pt(CH3NH2)4C12, and Pt(C4H9NH2)4C12. The platinum content in the Pt precursors was determined using ICP-MS (Galbraith Labs Inc.). Elemental analysis for C, H, and N content in the Pt precursors were performed using a Perkin-Elmer 2400 CHN Analyzer. Proton and carbon NMR(Bruker AMX300) were also performed to confirm the identities of the groups present in the precursor using the BBI5 probe with the sample dissolved in dimethyl sulfoxide (DMSO) or deuterated chloroform (CDC13). Pt-containing dry alumina gels were prepared using a sol-gel method similar to the procedure by Cho et al. Deionized water was mixed with aluminium tri-sec-butoxide (ATB) in an H20/ATB
molar ratio of 100, and then stirred for 30 min at room temperature. Next, a 0.1 g/ml HNO3 solution was added drop-wise to the mixture, and stirred for 10 min. During the stirring the ATB decomposed resulting in a phase containing sec-butanol forming on top of a phase containing the sol. After separating sec-butanol from the mixture, additional HNO3 solution was added to the sol until the HNO3/Al ratio reached 0.5. Finally, the Pt precursor was added to the alumina sol, which was stirred at room temperature for 1 h, and then sonicated for 30 min. The sol was then placed in the fume hood for 48 h to allow the gel to form and the solvent water to evaporate. The dry gel was further dried at 110 C for 12 h, and then at 200 C
for 2 h. The final material consisted of yellow cubic particles.

Catalyst calcination Several methods of calcination can be used. A portion of the dry gel was calcined by a one-step process. This dry gel was calcined at 550 C in one of three ways: (1) in flowing oxygen for 2 h in a U-tube flow reactor heated on the outside by an electric furnace; (2) in flowing air for 2 h in the same U-tube flow reactor or (3) in static air in a muffle furnace for 2 h. In order to investigate the influence of heating rate, two ramping rates were used-2 or C/min. The other portion of the dry gel was calcined by a two-step process.
The gel was first calcined at 550 C (2 or 10 C/min heating rate) in flowing helium for 0.5 h. After cooling to 50 C, the flow was switched to pure oxygen. The temperature was then ramped to 550 C at 2 or 10 C/min and held for 2 h.
For some of the calcinations, the exhaust gas composition was monitored during the temperature ramp using a Cirrus 200 Quadrupole Mass Spectrometer system (MKS) to determine which products were being produced during the calcination. The catalysts have been named according to the Pt precursor and the calcination treatment. For instance, Al-1 refers to a catalyst containing only alumina and calcined in oxygen at 550 C, while Py-2 refers to a catalyst prepared with a Pt-pyridine precursor and calcined in two steps with helium first and then oxygen (see Tables 1 and 2).

Catalyst characterization The N2 adsorption-desorption isotherms for the catalysts were measured on an AUTOSORB-1C (Quantachrome) instrument. All samples were evacuated at 120 C
until the outgas rate was below 15 mHg/min (or 2 Pa/min) prior to analysis. The specific surface area was calculated using the BET method. The total pore volume was determined at a relative pressure P1P = 0.99. Pore size distributions were calculated from the desorption isotherms using the Barrett, Joyner, and Halenda (BJH) method. The desorption leg of the isotherm is preferred for pore analysis because it is thermodynamically more stable than the adsorption leg due to the lower Gibb's free energy change.
H2 chemisorption measurements were carried out on the same AUTOSORB-1C
instrument. For these measurements, approximately 1.0 g of catalyst was placed in a quartz U-tube (i.d. = 10 mm), and reduced in a H2 flow of 15 ml/min at 300 C for 2 h.
After reduction, the sample cell was evacuated at 300 C for 2 h, and then cooled to 40 C for the H2 chemisorption measurement. The H2 monolayer uptake of the catalysts was calculated by extrapolating the H2 adsorption isotherm to zero pressure. The Pt particle diameter (dpt) was calculated using the formula, dp, =6V/S, where V is the volume of total metallic Pt, and S is the active Pt surface area, assuming the Pt2' ions were reduced completely and the Pt particles were spherical in shape. An adsorption stoichiometry of one hydrogen atom adsorbed per surface Pt atom (H/Pts = 1) was assumed. The percent Pt dispersion was calculated by dividing the number of exposed surface Pt atoms (as determined by H2 chemisorption) by the total amount of Pt in the catalyst.
Powder X-ray diffraction (XRD) spectra were recorded on a Multiflex X-ray diffractometer (Rigaku) using CuKal radiation (A = 1.54056 A) at 40 kV tube voltage and 40mA tube current with a scanning speed of either 0.2 or 2 /min. The XRD
patterns were referenced to the powder diffraction files (ICDD-FDP database) for identification. If possible, the average crystallite diameter of metallic Pt was calculated using Scherer's method, Dpt =KV,8cos9, where the constant K was taken as 0.9 and,8 was the full width at half maximum (FWHM) of the Pt(3 1 1) peak at 20 = 81.3 .
Transmission electron microscopy (TEM) images were recorded on an H-7000 transmission electron microscope (Hitachi) at 75 kV. The samples were ground to a fine powder, and mixed with acetone to make a suspension. A drop of the suspension was placed on a lacey carbon nickel grid, which was subsequently dried at room temperature before the measurement.

Differential thermal and thermogravimetric analyses Differential thermal and thermogravimetric analyses (DTAPTGA) were performed on three samples (A1-200, N-200, and Py-200) to examine the thermal and gravimetric changes that occur in those samples during calcination. A DSC/TGA Q600 instrument (TA
Instruments) was used for this analysis. The analysis conditions were selected so as to mimic the calcination procedure. Three different types of tests were performed as follows: (1) all samples (A1-200, N-200, and Py-200) were heated under air flow from room temperature to 550 C at 2 C/min and held at 550 C for 30 min; (2) sample N-200 was heated under air flow from room temperature to 550 C at 10 C/min and held at 550 C for 30 min and (3) sample N-200 was heated under He flow from room temperature to 550 C at 10 C/min and held at 550 C
for 30 min. Heat flow, mass loss, and differential temperatures were recorded during the analyses.

Reactivity testing Four catalyst samples, N-4, Py-4, MA-1, and BA-1 (see Table 2) were tested for reactivity in a fixed bed reactor using hydrogenation of toluene at atmospheric pressure as a model reaction. The reactor was a quartz tube with inner diameter of 7 mm.
Approximately 400 mg of catalyst was used for each run. All the catalysts particles were sieved to the same size range, 90-250 p,m. Reactions were conducted at temperatures between 60 and 270 C at 30 C intervals. A liquid hourly space velocity (LHSV) of 1 h-1 was used, with a H2 to toluene volumetric ratio of 1250. The catalysts were reduced in flowing H2 for 2 h at 300 C and then the temperature was reduced to the reaction temperature. The reactor effluent was analyzed using a gas chromatograph (Agilent 6890) equipped with a GS-GasPro PLOT column and a flame ionization detector (FID). The reactor came to steady state after approximately 30 min on stream. The steady-state compositions were used to calculate activities.
After 120 min on stream at one temperature, the temperature was increased by 30 C. Once at 270 C, the reactor was cooled to 60 C and the testing and temperature cycle repeated. One complete temperature cycle between 60 and 270 C constituted one run. Three runs were done for each of the four catalysts.

Results and discussion Physical properties of catalysts rahle I
Properttes of eol-Wl atumina and Pt-containing sampks before and after caktnatiaa Sample Pt prrcurstx Trc,ument Snrface wYa (m2lg) Pote volume (mllg) AI 200 Al2(h only Ikying in au at 200-C t2h) 94 0.012 Al-1 A12Oa only Oi 550 - C(2 h) 281 035 Al-2 AI20j only F(u 550'C (0,5h), 02 550 C 12h) 294 R i0 N-200 Pt(NH3)4Cl2 Urying in air at 200 C(2 h) 0 -N-t Pt(NH0;)aCh O, 550 C (2 h) 269 0.34 N-2 PttNH4)4Cl2 He 550 C(0,5h), 02 550C (2h) 262 033 Py-200 Pt{tCsHsM+Ci2 Dry'ing in air at 2ri) C {3li) 0 -Py-1 !rt(CsHst=1)4('12 04 550'C(2h) 272 0a2 Py ? Pt(CSH:N);C12 He 550-C (0.5h). O2 550'C t2h) 254 0 72 C.onturxciai y-Ai.O, - - 208 0 11 koru-: &rrcv is 15% in the sYtrface area arxl the }wm valturLL nttarummc.~nis.

Table 1 contains the surface areas and pore volumes for catalyst samples prepared using different Pt precursors and treatment procedures. The samples Al-200, N-200, and Py-200 exhibit very low surface areas (<10m2/g), which indicates that aluminium hydroxide and nitrate were not decomposed to refractory oxide A1203 after being dried in air at 200 C for 2 h. The remaining catalysts had surface areas between 254 and 281m2/g, and pore volumes between 0.30 and 0.35 ml/g. The pore size distributions were similar for all of the calcined catalysts, with mean pore diameters of 3.8 nm. These results indicate that the precursor and calcination procedure had little effect on the bulk physical structure of the catalysts.
For comparison, a commercial yA12O3 (Alfa Aesar) was characterized. The surface area of the commercial alumina is slightly lower (208m2/g) than the surface areas of the prepared catalysts, while the pore volume is similar (Table 1). Figure 2 compares the pore size distributions and adsorption isotherms of the commercial alumina and sample Al-1, which is representative of all the calcined catalysts. The in-house prepared alumina is similar to the commercial alumina in terms of its pore structure.
Based on the elemental analysis performed by ICP-MS (Galbraith Labs), the platinum content of the catalysts are as follows: 1.58% for N-batch catalysts, 1.43%
for Py-batch samples, 1.54% for MA-1, and 1.19% for BA-1. These Pt metal contents are shown in Table 2, with the Pt dispersions as determined by H2 chemisorption. The dispersions range between 11 and 106%. The metal surface areas used to calculate the dispersions are also shown in Table 2.
Dispersions above 100% may be attributed to errors in the Pt metal content, errors in the adsorbed H2 determination, or hydrogen spillover from the Pt. The Autosorb-1C
was calibrated with the Quantachrome standard reference (1%PVA1203), and had an error of 0.5%.

TaMe 2 pt dispersians of R/A1301, sampFes after rginus calcinadoo procedures Sample R precurscu Calcinaticm pracedure Heatitv, raw Pt metal Actite meal sarface Dispersion Partide (C7mik~ wnteN (4) area (m2/g) ("k) dianrctcr (nm) N-1 Pt(NHz);C'Iõ 0. 550 =C (2h) 10 1.58 1.4 35 3.2 N-2 Pt(NH3kC12. 1-Ic 5.50'C (0.5 h). Ch 550 C(2 h) 10 1.58 23 59 1.9 N-3 Pt(NH34C1+. 0Z5=.S0 C(2h) 2 1.58 4.i 105 1.1 N4 Pt(NHzkCI+_ He550^C(0.5h).C?1550 C(2h) 2 i.58 4.l 104 i.i N-5 PHNH;}yCt, Static air in muffle furoace, 550'C (2h) 2 1 58 3,3 87 1.3 N-fi Pt(NH;e l{CI3 Flowing uir, 550 C(2 h) 2 1.58 4.1 106 1.1 Py-1 Pt(C.HsN)4Cl2 (), 550 C (2 h) 10 1.43 2.2 6i3 1.8 p} -2 Pt(CsHcN)yCi2 He .5.i0'C (Ø3 h), (.)a 550 C (2 h) 10 1.43 2.0 56 2.0 Py-3 4't(C,HcN)aClz Oi 5.50'C (2h) 2 1_43 3.1 88 1.3 Py-4 Pt(C.1IiN)aCl7 lie 5.50 C (0.5 h). (?z 550 =C (2 h) 2 1.43 2.7 77 1.3 Py-5 R(C.HSN){C1Z Static air in rrwtfte fumace, 550 C (.2 h) 2 1.43 2.0 58 2.0 Py-6 pt(CsH!;N){Cii Flowing air, 550 C(2 h) 2 1.43 3.1 89 1.3 MA-1 PE(Cll; ~iF12)aC}1 Slraic air in nwtlie furnxce, 550 C(2 h) 2 1.54 ~ 2 59 1.9 BA-1 Pt(C4}{9NHj)rC.l2 Static air in nmf0e fumace, 550 C (2 h) 2 1.19 0.3d 11 9.9 Notr. (1) H2 cheme: tvption was performed after reducing ihe cntaiyxt on lire at 30(I C fcx 2 h in fiowing Hc. (2,) F:rrar is f5 % in the disperston measurements.

In general, a lower heating rate (2 C/min versus 10 C/min) results in an increased dispersion. In addition, the precursor may also significantly influence the dispersion. In this example, all comparisons are made between the same batches of catalyst.
Despite batch to batch variability, the overall trends are consistent.
The diameter of the Pt particles can be estimated from the hydrogen uptake and is given in Table 2. For all catalysts, except BA-1, the average particle sizes of Pt are less than 3.2 nm.
X-ray diffraction can also be used to estimate the particle size provided that the particles are larger than approximately 4-5 nm. Figure 3 shows the XRD spectra of the prepared catalysts and a commercial yAl2O3. The XRD pattern of aluminium oxide can be quite different depending on the preparation method and crystalline phase according to the ICDD-FDP
database. The spectra in Figure 3 indicate that the commercial yA12O3 sample and the in-house prepared samples have similar structures although the latter alumina has smaller crystalline size as indicated by the broader peaks at 29 = 67.3 . The XRD patterns of the samples are all quite similar despite different platinum particle sizes, calcination procedures, and platinum precursors. This result indicates that the alumina crystalline structure is not sensitive to these parameters, which is consistent with the BET measurements with respect to the constant pore structure and surface area.
The peaks for Pt overlap, at least partially, with alumina at most diffraction angles, except for the Pt(3 1 1) peak at 20 = 81.3 . In order to obtain accurate Pt particle size information, slow scans (0.2 /min) were performed in the range of 78-90 20.
The results are shown in Figure 4 and are consistent with the average particle size of Pt calculated from the chemisorption results. Pt is undetectable for catalysts N-5 and N-6, while Py-5 and MA-1 both have a peak at 20 = 81.3 that is too small for estimation of particle size.
The calculated average particle size of Pt in catalyst BA-1 is 23 nm, which is larger than that estimated by hydrogen chemisorption (10 nm).

Effect of platinum precursor The platinum precursors - Pt(NH3)4C12, Pt(CH3NH2)4C12, Pt(C5H5N)4C12, and Pt(C4H9NH2)4C12 - were analyzed with CHN analysis to obtain the C, H, and N
ratios contained in the catalysts. Based on the CHN analysis results, it was confirmed that the desired precursors were obtained. Carbon NMR of the Pt(C4H9NH2)4C12 precursor showed a chemical shift at 13.7 ppm and CH2 at 19.4, 32.7, and 46.1 ppm. Proton NMR of the same Pt(C4H9NH2)4C12 confirmed the presence of the CH3 and CH2 peaks in addition to the NH2 peak at ca. 5.6 ppm chemical shift. These results in addition to the CHN
analysis confirmed the presence of a (C4H9NH2) group in the precursor. Proton NMR of the Pt(C5H5N)4C12 precursor revealed an aromatic structure with the first CH at 8.9 ppm, the second at 7.5 ppm, and the third at 7.9 ppm. Combined with results of CHN analysis, these results confirmed the presence of a (C5H5N) group in the precursor.
The selection of platinum precursor was based on the hypothesis that the larger the precursor the better the resulting Pt dispersion. During calcination, platinum (oxide) atoms may agglomerate into clusters. Assuming that the agglomeration occurs as a series of binary interactions, the rate of agglomeration is related to the distance between any two platinum atoms. Thus, the ligand of the Pt(II) precursor would act as space holder for the platinum atoms. As shown in Table 2, the precursors are all nitrogen-containing molecules and soluble in water. The molecular diameters of the precursors were estimated by bond lengths and are approximately 5, 7, 12, and 13 A for Pt(NH3)4C12, Pt(CH3NH2)4C12, Pt(C5H5N)4C12i and Pt(C4H9NH2)4C12, respectively.
Figure 5 illustrates that the results were exactly the opposite of what was expected.
That is, the smaller the precursor, the better the dispersion. The results shown in Figure 5 are those taken from Table 2 for samples N-5, Py-5, MA-1, and BA-1. The Pt dispersion is strongly dependent on the precursor and increases from 11% for BA-1 (largest precursor) to 87% for N-5 (smallest precursor). These samples were calcined in a muffle furnace in static air. Although calcining in static air results in lower dispersions than flowing air, the trend of increasing dispersion with decreasing precursor size did not change with a change in the calcination procedure.

The extremely low dispersion of BA-1, obtained using Pt(C4H9NH2)4C12 as precursor, may be caused partly by the relatively poor solubility of the precursor in water. During the precursor preparation, the water solution (15 ml water, containing 0.1 g of Pt) had to be heated to 60 C in order to dissolve this precursor. The precursor did not precipitate in the sol or wet gel because of the presence of sufficient water (ca. 50 ml). The precursor, Pt(C4H9NH2)4C12, probably precipitated, however, during water removal. If the precipitate separated from the alumina gel during subsequent heat treatments, large Pt particles may be formed. TEM analysis of the reduced BA-1 catalyst (Figure 6) indicated that large Pt particles have formed. The darker particles in Figure 6(a) are on the order of 200 nm in size and are likely Pt particles or agglomerates. The lighter particles are alumina. In Figure 6(b), Pt particles are visible at the edges of the alumina particles with sizes of 10-50 nm. A homogenous Pt distribution was not obtained from this Pt precursor as the majority of the alumina particles did not contain any visible Pt particles. On all other catalysts, no Pt particles were visible, consistent with the hydrogen chemisorption and XRD results.
The chemical nature of the Pt precursors and their interaction with the support precursor (i.e., silane as precursor of silica) may also be a factor in the resulting metal dispersion. The effect of Pt precursor on the Pt dispersion and particle size has been studied over sol-gel processed Pt/Si02 by Lembacher. The studied precursors included Pt(AcAc)Z, PtC12, H2PtC16, Na2PtC16, Pt(CN)2, and Pt(NH3)4(NO3)2. PtC12 led to the highest Pt dispersion when a nitrogen-containing silane, H2NCH2CH2NH(CH2)3Si(OEt)3 (AEAPTS), was used as silica precursor. This result may stem from the strong interaction of Pt(II) and the silica precursor, while Pt(IV) cannot form a complex with nitrogen-containing molecules with a silica precursor. In this example, the Pt precursors will not react with the aluminium precursors and so anchoring of some of the Pt precursors cannot explain the different dispersions that were obtained.

The effect of calcination procedure on Pt dispersion A heating rate of 2 C/min under all calcination conditions resulted in higher Pt dispersions than using a heating rate of 10 C/min. Figure 7 presents the results for the catalysts derived from Pt(NH3)4C12. Samples N-1 (35% dispersion) and N-3 (105%
dispersion) were both calcined in 02 at 550 C for 2 h, while samples N-2 (59% dispersion) and N-4 (104%
dispersion) were calcined in a two-step process involving helium and then oxygen. Clearly a slower heating rate results in higher dispersions. The same trend is observed for the catalysts prepared with Pt(C5H5N)4C12 as the precursor (Py-catalysts). For example, the Pt dispersion for Py-3, heated at 2 C/min, was 88%, compared to a Pt dispersion of 63% for Py-1, which was heated at 10 C/min.
The atmosphere during calcination also affected the final Pt dispersion, but the magnitude of the effect depended on the heating rate and Pt precursor. For example, samples N-1 and N-2, were both prepared from the same precursor and heated at the same rate (10 C/min) during calcination, but had significantly different Pt dispersions (35% versus 59%).
In this case, a higher dispersion was obtained by heating in He before heating in 02.
Conversely, for samples N-3 and N-4 (Table 2), heated at 2 C/min, the Pt dispersion was the same regardless of the calcination procedure. When Pt(C5H5N)4ClZ was used as the Pt precursor, a comparison of Py-1 with Py-2, and Py-3 with Py-4 (Table 2), indicated that He pretreatment before calcination in 02 resulted in a lower Pt dispersion compared to no He pretreatment. Lembacher has shown that pretreatment in an inert atmosphere is beneficial for Pt dispersion on silica supports. For Pt/SiO2 the average particle size of Pt decreased from 22 nm to less than 3 nm by pretreating the catalyst with argon before exposure to air at 400 C.
During the one-step calcination, the Pt particles may have sintered due to local overheating caused by rapid oxidation of organic groups in the silane precursor.
Heating in a muffle furnace is a much simpler method than heating a catalyst in a flow apparatus. In these experiments, however, treatment in static air (i.e., the muffle furnace) resulted in much lower Pt dispersions than treatment in a U-tube on a flow apparatus. For example, as shown in Figure 8 and Table 2, sample N-5 was calcined in the muffle furnace and had a Pt dispersion of 87% compared to a dispersion of 106% for sample N-6, calcined in flowing air. Similar results were obtained for samples Py-5 and Py-6. Likely the water produced during the calcination was not removed quickly enough without flowing gases. The presence of water may have promoted the sintering of the Pt particles.

Calcination studies performed by mass spectrometry Mass spectrometry (MS) was used to better understand what species are being formed during the calcination. This analysis was used in conjunction with XRD
analysis. The alumina support was analyzed first, and then several samples containing Pt were analyzed. The alumina gel is soluble in water after drying at 200 C for 2 h, indicating the dry gel has the same or similar composition with the sol or wet gel except for solvent (H20) content.
In order to investigate the structure of the dry gel (A1-200 in Table 2), the XRD patterns were recorded before and after calcinations (spectra not shown). The XRD pattern of the dry gel was different from that of the sol-gel A1203 (Al-1 and Al-2). Referencing the ICDD
database, the dry gel had a similar structure to Al(OH)3, indicating the dry gel did not decompose after drying for 2 h at 200 C in air. The composition of the dry gel can be represented by A1(N03)b(OH)3-6, or more precisely Al(NO3)sOx(OH)3.6-2x because of condensation. Here, d 0.5 since the molar ratio of HNO3/Al is 0.5 during peptization. After calcination, the mass loss of the dry gel is 45 4%. From the mass loss, the value of x can be calculated. The calcined alumina samples (Al-1 and Al-2) had structures similar to a commercial yA12O3 as described previously.
Figure 9 shows the evolution of CO2 (mass 44) and NO2 (mass 46) during the calcination of the dry gel in oxygen or in helium. Masses 18 (H20) and 30 were also monitored during the experiment. During calcination water was produced from the decomposition of Al(OH)3. The water, however, condensed before the inlet to the mass spectrometer and, thus, the water signal is not reliable and not shown. The signals from masses 46 and 30 were identical in shape and, thus, mass 30 is attributed to the cracking pattern of NO2. The plots in Figure 9 are nearly identical whether the atmosphere is helium or oxygen.
In both cases, COZ is detected at temperatures between 240 and 470 C, while NO2 is detected at temperatures above 250 C. The CO2 originated from the oxidation of an organic compound in the gel produced during the hydrolysis of ATB. The organic compound is likely 2-butanol;
however, 2-butanol was not detected in the emissions. The organics were oxidized by oxygen or the produced NOx in the absence of oxygen (i.e., helium atmosphere).
Following the treatment in flowing He, the same sample was monitored during treatment in flowing 02 and no NO2 or CO2 was detected. These results suggest that complete decomposition occurred during the pre-treatment in helium and that treatment with oxygen was unnecessary.
The NO2, NO, and H2O emissions during the calcination of Pt-containing dry gels (N-200 and Py-200) were similar to that for blank alumina gel (Al-200) in either oxygen or helium. The CO2 evolution during the calcination of Al-200, N-200, and Py-200 is shown in Figure 10. The plots are similar for a helium or oxygen atmosphere. The quantity of CO2 evolved, however, depended on the presence of the precursor. Emissions of CO2 for the gel derived from Pt(NH3)4C12 (N-200) and for a blank alumina gel (Al-200) were similar. In comparison, the gel derived from Pt(C5H5N)4C12 (Py-200) produced approximately 20 times more CO2 than either N-200 or Al-200, consistent with the carbon content of the precursor.

The additional emitted CO2 came from the oxidation of the pyridine contained in the dry gel for Py-200.

Chemical reactions during calcination The composition of the alumina dry gel before calcination can be represented by Al(NO3)aOx(OH)3_a-a, 8z 0.5. The value of x can then be calculated based on mass loss during calcination. The final solid product after calcination is A1203, and the mass losses are 4 5 4%
during calcination. Thus, the reaction during calcination can be described as follows:

2A1(NOo)o.5Ox(OH)2.s-2z = A1Z03 +N02 +(2.5-2x)H20 + 0.2502 (1) The calculated value of x is between 0 and -0.8. On average, if the mass loss is 45%, x 0.4. That is, lOOg of the dry gel would produce 25g of NO2, 4.3g of 02, and 16g of H20.
Water condensation in the lines after the calcination vessel was evident. The condensed water had a yellow color and was strongly acidic (pH < 1), indicating that HNO3likely has been formed from the following reactions in the exit stream:

4NO2 + 02 +2H20 = 4HN03 (2) 3NO2 + H2O = NO + 2HN03 (3) Water vapor has been reported to enhance Pt sintering in Pt1AlZO3 during calcination and reduction. The presence of excess water vapor may have been a factor in the lower dispersions obtained when the calcination was performed in static air (muffle furnace) rather than flowing air, in which the water would have been removed and not accumulated on the surface of the catalyst. Similarly, the lower heating rate (2 C/min) may be beneficial because of the slower decomposition, and hence water evolution, of the alumina gel.
The gas flow rate and amount of catalyst was kept constant throughout the calcination tests.
The effect of the Pt precursor on dispersion may be related to the composition of the precursor. In this example, the Pt precursors with organic ligands yielded lower Pt dispersions than the precursor containing ammonia. The dry gel containing a pyridine Pt(II) ligand (Py-200) produces approximately 20 times the amount of CO2 during calcination than the dry gel containing an ammonia Pt(II) ligand (N-200). The localized heating from the oxidation of the organic ligands may have been sufficient to result in sintering of the Pt particles. Lembacher suggested that localized heating caused by rapid oxidation of the support precursor, silane, resulted in sintering in Pt/Si02 catalysts. In contrast to the work on Pt/SiO2, with Pt/A1203 He treatments before calcination in oxygen only improved the dispersion for the ammonia precursor with a heating rate of 10 C/min. The mass spectrometer results indicated that the pyridine and ammonia precursors were completely oxidized in He and a second treatment in 02 was not required. The decomposition of NO3-groups produced significant amounts of 02 and NOx which can act as oxidants. Likely these species were sufficient to completely decompose the precursors.

Results of differential thermal and thermogravimetric analyses The thermogravimetric and differential thermal analysis of samples Al-200, N-200, and Py-200 are shown in Figures 11 and 12. In agreement with the mass spectrometry results, the mass loss in an air atmosphere corresponded to decomposition within the temperature range of 200-450 C (Figure 11). The differential thermal analysis is shown for two heating rates (2 and C/min) as well as two atmospheres (helium and air) for sample N-200. More heat was evolved during the calcination of Py-200 (comparable to Py-3 with a dispersion of 88%) than for the calcination of N-200 (comparable to N-3 with a dispersion of 105%).
The largest change in heat flow occurred on sample N-200 heated in air at 10 C/min, which is consistent with the lower dispersions obtained for samples heated at 10 C/min than 2 C/min (Table 2).
These results support the theory that localized heating during calcination may contribute to sintering of the Pt resulting in lower dispersions.

Reactivity tests-toluene hydrogenation Figure 13 shows a comparison of the production of methylcyclohexane (MCH) over catalysts produced from the different precursors (N-4, Py-4, MA-1, and BA-1) at 240 C and atmospheric pressure. Three runs were performed for each catalyst and in each case, the only product was methylcyclohexane. Catalyst BA-1 had the lowest Pt dispersion (11%) and the lowest production of MCH. In contrast, catalyst N-4 had the highest Pt dispersion (104%) and the highest production rate. Catalysts Py-4 and MA-1 had intermediate Pt dispersions (77 and 59%) and intermediate activities. The activity of N-4 stayed within 2.5% of the mean activity of this catalyst. The other catalysts, however, had larger decreases in activity over time.
Conclusions Pt dispersions ranging between 11 and 106% were obtained for 1.5 wt% Pt/A12O3 catalysts prepared by sol-gel synthesis. The Pt dispersion of the catalyst was found to be strongly dependent on the platinum precursor, and a larger precursor molecule did not result in better dispersion. Specifically, in terms of highest Pt dispersion, Pt(NH3)4C12 was the best precursor followed by Pt(CH3NH2)4C12, Pt(CSH5N)4C12, and finally Pt(C4H9NH2)aC12. The latter precursor resulted in a very poor dispersion, likely because of its poor solubility. The dispersion also depended on the calcination procedure. The use of flowing gas instead of static air, and a lower heating rate (2 C/min rather than 10 C/min) resulted in higher Pt dispersions.
The presence of accumulated water (from treatment in static air or from too high a heating rate) and/or localized heating effects (dependent on the decomposition of the precursor) resulted in sintering of the Pt and lower dispersions. Pretreatment in helium before oxygen did not improve the dispersion. Toluene hydrogenation experiments indicated that higher activities and selectivities can be achieved with catalysts containing more highly dispersed Pt. Thus, it is desirable to optimize catalyst preparation to achieve high dispersion.

Example 2 This example demonstrates the use of CVD to control the pore openings of Ni/A12O3 catalysts for the selective chemisorption of H2 (2.9 A) and exclusion of larger molecules (N2, 3.6 A; CO, 3.8 A). A fluidized bed reactor was used with steam injection through an annulus of the reactor, and silicon alkoxide introduction through the bottom of the reactor was carried by an inert gas. The effect of deposition time on the subsequent adsorption of H2, CO, and N2 was investigated. The catalysts were characterized before and after modification with N2 physisorption, H2 and CO chemisorption, temperature-programmed desorption of NH3, X-ray diffraction, and inductively coupled plasma. In addition, the catalysts have been tested with a model reaction of n-octane hydrocracking to demonstrate the influence of the coating on the access to the active sites as well as on the acidity of the catalyst. The results indicate that CVD
is an appropriate method for reducing the size of the pore openings in Ni/A1203 catalysts. The modified catalysts will be useful in a catalytic reaction in which H2 is competing with larger molecules for adsorption sites.

Experimental Method Apparatus. The CVD apparatus used in this work is shown in Figure 14. The fluidized bed reactor consisted of a quartz tube mounted vertically inside an electric furnace.
The reactor tube had an inside diameter of 1 cm and overall length of about 41 cm. One feature of the reactor is the attachment of an annular tube made of '/g-in.
stainless steel tubing for steam injection into the reaction zone inside the bed (Figure 14). A 1/32-in. thermocouple is also extended through the annulus to measure the temperature of the bed.
Quartz frits with openings of 15-40 micrometers were used as the distributor plate. The reactor operated at atmospheric pressure. A piston pump (Ailtech 426 HPLC pump) pumped water through an evaporator into the fluidized bed with flowing N2 (20 sccm) as the carrier.
The TMOS was pumped by a syringe infusion pump (Cole Parmer), was evaporated, and was carried to the reactor by N2 flowing at 60 sccm. The flow of N2 was controlled by a mass flow controller (Type 1179A by MKS Instruments). FieldPoint and LabView (National Instruments) were used for data acquisition and readout.
Preparation of Ni/A1203. A 25-g batch of Ni/A12O3 was prepared by the wetness impregnation method. The y-A1203 (60 mesh, Alfa Aesar) was impregnated with an aqueous solution of Ni(N03)2-6H20. The mixture was dried at room temperature for about 16 h in a fume hood and then was transferred to a muffle furnace and was treated at 80 C for 2 h followed by drying at 110 C for 10 h. The impregnated A1203 was then calcined in the muffle furnace at 550 C for 8 h. On the basis of temperature-programmed reduction, a reduction temperature of 550 C was chosen. Thus, the catalysts were reduced in flowing H2 by heating to 550 C at 10 C/min and were held at 550 C for 4 h. The resulting Ni/A12O3 catalysts had Ni loadings of 17% (Galbraith Laboratories Inc.) and a surface area of 129 m2/g ((2 m2/g). The surface area of the purchased A1203 was 208 m2/g as measured by N2 physisorption using an Autosorb-1C adsorption instrument (Quantachrome Instruments).
Silica Deposition. The Si02 deposition was performed using the CVD apparatus described above (Figure 14). One gram of Ni/A1203 was placed in the fluidized bed reactor and was fluidized with N2 (60 sccm). TMOS (1.75 mol %) was vaporized and injected into the bottom of the reactor while 14 mol % H2O was evaporated with N2 (20 sccm) as carrier gas and was injected into the annulus of the reactor. The purpose of steam injection was to suppress carbon formation and at the same time hydrolyze the TMOS.

Preliminary experiments were done using the blank A1203 support to develop the CVD
procedure. Si02 deposition experiments were done with temperatures between 150 C and 500 C. After Si02 deposition, the samples were calcined in flowing air at 500 C for 2 h to remove any traces of carbon and organic matter remaining in the catalyst caused by side reactions. The Ni catalysts were coated for times of 0.5, 1, 1.5, 2, 2.5, or 3h at 350 C and were identified according to this deposition time. That is, Ni-0 refers to an uncoated catalyst while Ni-2.5 refers to a catalyst treated in the CVD apparatus for 2.5h.
Catalyst Characterization. The characterization techniques used were N2 physisorption, H2 and CO chemisorption, X-ray diffraction (XRD), and NH3 temperature-programmed desorption (TPD). The coated samples were analyzed for H2 chemisorption before and after coating. As such, the coated samples have been reduced twice while the uncoated samples have only been reduced once. N2 physisorption was performed using an Autosorb-1C adsorption apparatus (Quantachrome Instruments) to determine surface area, pore volume, and pore size distribution. The surface area was calculated using the Brunauer, Emmett, and Teller (BET) method, while the pore volume and pore size distribution were calculated by the Barret-Joyner-Halenda (BJH) method using the desorption leg of the isotherm. The desorption leg of the isotherm is preferred for pore analysis because it is thermodynamically more stable than the adsorption leg because of the lower Gibb's free-energy change. The error in the surface area measurements is 2% on the basis of repeat analysis of the samples.
H2 and CO chemisorption were performed on a ChemBET 3000 (Quantachrome Instruments) to determine the H2 and CO uptakes before and after Si02 coating of the Ni/A12O3. All catalysts (with and without Si02 deposition) were pretreated by reduction in flowing H2 at 550 C for 4 h before the chemisorption measurements. To test whether CO can penetrate the SiO2 coating, each of the samples that were coated for 2 and 2.5 h was exposed to 60 mUmin of pure CO for 30 min at 40 C. Following the CO exposure, each of the samples was purged with flowing N2 for 1 h to remove any physically adsorbed CO. Each of the samples was tested for H2 uptake following the exposure to CO. An uncoated Ni/Al203 catalyst was also tested for H2 uptake after CO exposure to obtain a baseline for comparison.
Powder X-ray diffraction (XRD) spectra were recorded on a Rigaku Multiflex X-ray diffractometer using Cu1Ka1 radiation (y) 1.54056 A at 40 kV tube voltage and 40 mA tube current with a scanning speed of 2 lmin. The XRD patterns were referenced to the powder diffraction files (ICDD-FDP database) for identification. XRD was performed to monitor changes in the oxidation state of the Ni phase during the coating procedure.
NH3 TPD was performed using the ChemBET 3000 instrument with 10% NH3 diluted in He, before and after Si02 deposition, to determine the effect of the deposition on the acidity of the A1203 support. The NH3 was adsorbed at 40 C and desorption was performed in the temperature range of 40-550 C with a heating rate of 10 C/min.
Silicon elemental analysis of the coated Ni/A12O3 catalysts was performed using inductively coupled plasma-mass spectroscopy (ICP-MS, Galbraith Laboratories).
The ICP-MS technique used to perform the Si elemental analysis has a relative error margin of 10%.
Carbon elemental analysis was performed using a Perkin-Elmer 2400 CHN Analyzer to determine the carbon content before and after calcination of coated catalysts.
n-Octane Hydrocracking Procedure. The hydrocracking of n-octane was carried out in a quartz fixed bed reactor with 100 mg of catalyst at 400 C, a weight-hourly space velocity (WHSV) of 2.0 h-1, and H2/n-octane molar ratio of 20 under atmospheric pressure. Before reaction, the catalyst was reduced at 550 C under flowing H2 for 4 h. The reaction products were analyzed online using a gas chromatograph (Agilent 6890 GC) with a 60-m long, 0.32-mm i.d. GS-GasPro PLOT column and a flame ionization detector (FID). A mass spectrometry (Cirrus by MKS Instruments) was also used to analyze the product stream.

Results Development of CVD Procedure. The Si02 deposition procedure was developed by coating plain commercial y-A1203 with Si02 for different deposition times and temperatures.
Figure 15 illustrates the change in measured surface area with deposition temperatures 150 C, 200 C, 250 C, 300 C, 350 C, 400 C, and 500 C at a constant deposition time of 1 h. The surface area is calculated directly from the nitrogen uptake and, thus, representative of the accessibility of the pores to nitrogen. The surface area decreases as the deposition temperature increases.
The measured surface areas in Figure 15 steadily decreased until a temperature of 400 C at which point the surface area increased from 80 m2/g to 100 m2/g. With a further increase in temperature to 500 C, the surface area decreased to 83 m2/g. This increase in nitrogen adsorption at 400 C may be due to surface coverage by methoxy species and other decomposition products, which are removed from the surfaces and pores upon calcination. At deposition temperatures of 400 C and above, significant carbon formation was visible on the A1203 after the deposition. That is, the white A1203 powder turned black in color. The carbon was removed by calcination in flowing air at 500 C (the powder turned white or slightly beige in color). At deposition temperatures of 350 C and below, there was no visible carbon formation. Because of increased carbon formation at higher temperatures, a deposition temperature of 350 C was used for the silica deposition on the Ni/A1203 catalysts.
Nitrogen Physisorption on Ni/A1203. The Ni1A1203 catalysts were reduced immediately before N2 physisorption measurements. Figure 16 shows the change in measured surface area as a function of Si02 deposition time for an A1203 sample and a Ni/A1203 catalyst.
The nitrogen uptake decreased with increasing deposition time. The rate of decrease in surface area is different for the Ni/A12O3 than for the blank A1203 support. After 1.5 h of deposition, the A1203 surface area is -3 m2/g while that of Ni/A12O3 is -35 mz/g, indicating that the deposition of Si02 on the A1203 is more rapid than the deposition on Ni/A1203.
The difference in behavior is ascribed to the stronger affinity of Si02 for the alumina surface. In the case of Ni/A1203, some of the surface has likely been covered by Ni deposited on the exterior surface of the alumina particles.
The pore volumes of Ni/A1203 as a function of deposition time at 350 C are given in Table 3. Consistent with the surface area measurements, the pore volume decreased as the deposition time increased. After 2.5 h of deposition, the pore volume had decreased to essentially zero compared to a value of 0.193 cm3/g before deposition. Figure 17 shows that the pore size distribution changes as the amount of Si02 deposition increases;
that is, the pores decrease in diameter as the amount of Si02 deposition increases. The reduction in pore size may be a result of Si02 deposition within the pores since the original Ni/A1203 pores (38 A
modal pore diameter) are large enough for the silicon alkoxide molecule to penetrate the catalyst (TMOS has a kinetic diameter of 8.9 A).

Table 3. Pore Volumes of Ni/A1203 Coated with Si02 for Various Times at 350 Ca Sample ID Deposition Time (h) Average pore volume cm /g Ni-0 0 0.193 Ni-1 1.0 0.107 Ni-1.5 1.5 0.022 Ni-2 2.0 0.005 Ni-2.5 2.5 0.0007 Ni-3 3.0 0.0005 aMeasurements were performed by N2 physisorption.

Amount of Deposition and Carbon Formation. Figure 18 shows the amount of Si02, as determined by ICP-MS, deposited on Ni/A12O3 as a function of deposition time. After 1 h of deposition, the Si02 fraction was 16%. The amount of silica deposited increased to 30% after 1.5 h and then the amount deposited remained constant up to 2.5 h of deposition. The surface may have been saturated after 1.5 h with physisorbed species that hindered the growth of Si-O-Si bonds. To verify if other species were deposited on the surface, the carbon content of a Ni/A12O3 catalyst was determined by carbon, hydrogen, and nitrogen (CHN) analysis after coating the catalyst with Si02 for 2 h at 400 C. The Ni/A1203 catalyst was gray in color after the deposition, and the CHN analysis revealed a carbon content of 0.7%. This catalyst was then calcined and the carbon content was reduced to 0.2%. N2 physisorption was also performed on the same sample before and after calcination. The surface area of the sample before calcination was 50 m2/g compared to 4 m2/g after calcination.
H2 and CO Chemisorption. Figure 19 shows H2 and CO uptakes on Ni/A1203 after Si02 deposition for various times. The H2 uptake actually increased after 1 h of deposition from 398 pUg to 493 ,uUg. This increase is probably due to a further reduction of NiA12O4 within the structure during the second reduction after the coating. After 2.5 h of deposition, the average H2 uptake was 430,uUg. In contrast, the CO uptake decreased from 405 ,uUg before coating to 5.8 pLlg, after 2.5 h of deposition, indicating that the deposited silica had reduced the pore openings and that the technique was successful.
To further test the size-exclusion properties of the coated Ni/A12O3 catalysts, three catalysts were exposed to pure flowing CO for 30 min. The H2 uptakes, before and after this exposure, are listed in Table 4. The uncoated catalyst (Ni-0) was severely poisoned by exposure to CO with the H2 uptake decreasing from 398 pUg before exposure to 96 L/g after exposure (76% change). The second and third samples, coated for 2 and 2.5 h, respectively, were less affected by the exposure to CO with decreases in H2 uptakes of 68%
and 28%, respectively. These results indicate that the pores reduced the accessibility for CO.

Table 4. H2 Uptake on Ni/A12O3 after Exposure of Catalysts to 100% CO flow for 30 Min.
Ni/A1203 Was Coated with Si02 at 350 C

Sample ID Deposition time H2 uptake ( L1g) Percent change (h) Before exposure After exposure Ni-0 0 398 96 -76 Ni-2 2 441 139 -68 Ni-2.5 2.5 430 308 -28 X-ray Diffraction. The XRD spectra for Ni/A1203 at various stages in the deposition process are shown in Figure 20. After reduction (Figure 20a), the spectrum had peaks at 44.5, 51.8, and 76.4 20 corresponding to Ni and peaks at 37.3 and 67.3 20 corresponding to A1203 (matched to ICDD-FDP database). After deposition (Figure 20b), most of the Ni has been oxidized, as evidenced by peaks at 37.2, 43.3, and 62.9 28 corresponding to NiO. The peaks around 37 20 overlap; 37.2 20 is associated with NiO, 37.0 28 is associated with NiA12O4, and 37.3 20 is associated with A12O3. After deposition and reduction (Figure 20c), the XRD
spectra is very similar to the spectra of the originally reduced Ni/A12O3 catalyst (Figure 20a), except that the Ni peak intensities have decreased. This decrease is due to the silica coating.
NH3 Temperature-Programmed Desorption. Temperature programmed desorption (TPD) of NH3 on the NilA1203 catalyst was done to monitor changes in the accessibility of the acid sites on the alumina support. The TPD spectra are shown in Figure 21 for six different samples with deposition times ranging from 0 to 3 h. The total ammonia uptake was determined by integrating the area under the TPD curves, and these areas are listed in Table 5.
Two main peaks are observed in the TPD spectra around 160-180 C and 400-440 C.
These peaks correspond to weak and strong acid sites, respectively, and are consistent with the literature. The ammonia uptake decreased with increasing deposition time, indicating that the acid sites were progressively blocked. Si02 is significantly less acidic than A1203. After 0-3 h of deposition, the uptake decreased from 461 ymol/g to 4,umollg (Table 5). The NH3 uptake decreased because of coverage of the external sites on the particles as well as narrowing of the pores preventing NH3 from accessing internal sites.

Table 5. Ammonia Uptake on Ni/A1203 as a Function of Si02 Deposition Time at 350 C

Sample ID Deposition time (h) Total NH3 uptake ( mol/g) Ni-0 0 461 Ni-0.5 0.5 448 Ni-1 1.0 246 Ni-1.5 1.5 224 Ni-2 2.0 143 Ni-2.5 2.5 113 Ni-3 3.0 4.1 Catalytic Performance for Hydrocracking of n-Octane. Figure 22 shows the conversion of n-octane as a function of the Si02 deposition time. The conversions shown in Figure 22 are taken after 20 min on stream. With no Si02 deposition, n-octane conversion was 29%. The maximum conversion (67%) was obtained on the Ni/A1203 catalyst coated for 0.5 h.
The conversion decreased to zero for catalysts coated for 1.5 h or longer. The product stream consisted of only one C4 species that is likely 1-butene. The stabilities of the catalysts varied.
That is, the loss of activity over 3 h on stream was 47%, 23%, and 0% for the uncoated catalyst, the catalyst coated for 0.5 h, and the catalyst coated for 1 h, respectively.
Deposition Process. The surface areas of the A1203 and Ni/A1ZO3 samples decreased with increasing deposition temperature and time (Figures 15 and 16), consistent with the results reported by Sato et al. for a Si02/Al203 system and by Fodor et al. for a Si02/MCM-41 system.
During the deposition, some additional carbonaceous material was deposited on the surface. The CHN analysis and N2 physisorption results before and after calcination are consistent with a porous layer of contamination being formed during the deposition. This layer was removed with a mild calcination, leaving behind a compact Si02 structure.
In an inert carrier gas, the thermal decomposition of silicon alkoxide tends to produce carbon and other undesired organic products. The addition of steam helps to reduce the formation of undesirable products and also helps to propagate the growth of Si-O-Si bonds so that the growth of Si02 can be faster. The carbonaceous layer likely prevented additional silica from being deposited beyond a deposition time of 1.5 h (Figure 18). Additional silica can be deposited by calcining the catalysts between deposition runs.

The silica layer narrowed the pore openings of the catalyst and prevented the penetration of the larger molecules (Figures 16, 17, and 19). That is, CO (3.8 A) and N2 (3.6 A) were excluded from the pores, while H2 (2.9 A) could still penetrate to the Ni sites. In catalyst reaction systems of noble metals using H2/CO mixture as feedstock (or H2 with CO as contaminant), the CO tends to decrease the reactivity of the noble metal by strongly adsorbing on the surface and by inhibiting further adsorption of H2. This technique may be a new way for separating H2 from CO in the reaction systems involving noble metals, thereby preserving the reactivity of noble metal catalyst against the poisoning effect of CO.
The silica precursor, TMOS, has a molecular dimension of approximately 8.9 A, which is significantly smaller than the modal pore diameter of the A1203 support (-38 A). Therefore, the TMOS likely penetrated some of the pores of the alumina creating a framework through which H2 could still penetrate. The presence of Ni in the A1203 structure influenced the deposition process (Figure 16). The silica will interact more strongly with the A1203 than the Ni. Thus, a complete shell of silica is not formed on the NiJA1203 catalyst and the measured surface area remains at 17 m2/g after 1.5 h of deposition rather than being reduced to zero as for the A1203 sample. Addition of Ni to the A1203 resulted in a decrease in surface area from 208 m2/g to 129 m2/g, indicating that the Ni is situated at the pore mouths and is blocking access to some of the internal pores. The low Ni dispersion of 1% is likely a result of some Ni being inaccessible because of this pore-mouth blocking, as well as some Ni being situated on the external surface of the particles, or some Ni being associated with the alumina in a spinel phase. Interestingly, the N2 uptake reached a minimum after 1.5 h of deposition (Figure 15), corresponding to a maximum silica uptake at 1.5 h (Figure 18), while the CO
uptake (Figure 19) and ammonia uptake (Table 5) continued to decrease up to 3 h of deposition. The activity of the catalyst (Figure 22) reached a minimum (at zero conversion) after 1.5 h of deposition.
These results may indicate that the silica shell was not uniformly formed.
That is, after 1.5 h of deposition, sufficient silica had been deposited to remove the activity of the catalyst but not to completely exclude all molecules larger than H2. Further deposition may have filled in some gaps in the coating so that ammonia and CO adsorption continued to decrease.
The N2 physisorption and ICP measurements will be less sensitive to small changes in the coating than the selective chemisorption measurements. Initial analysis of the thickness of the coating indicated that the coating could not be detected by scanning electron microsopy (SEM). The fact that the Ni peaks are still visible in the XRD spectra (Figure 20) suggests that the coating is relatively thin (<1,um). A schematic representation of the coated catalyst is given in Figure 23.
Acidity and Reactivity of Coated Ni/A1203 Catalysts. NH3 is an excellent probe molecule for the measurement of acidic properties of catalysts. The temperature-programmed desorption (TPD) results (Figure 21 and Table 5) indicated that the silica deposition significantly reduced the acid nature of the NiJA1203 catalysts. The acid sites were covered on the exterior of the particles and the pore openings were narrowed (Figure 17) so that the ammonia could not penetrate into the interior of the particles. The peaks in the TPD spectra (Figure 21) around 150 C correspond to weaker acid sites while the peaks above correspond to stronger acid sites. According to Sato and co-workers and Katada et al., the nature of acidity formed on A1203 by the deposition of Si02 is of the Bronsted type created at the interface between the Si02 and A1203. In this work, the higher temperature NH3 TPD peak shifts to higher temperatures as additional silica is deposited indicating that stronger acid sites are created by the deposition of silica on alumina, in agreement with previous work. As the layer of Si02 becomes thicker, however, the acidity declines because access to the interface is blocked.
The balance between an increase in strong acid sites and a decrease in accessibility of the Si0z/AlZ03 interface is consistent with a maximum in the n-octane conversion (Figure 22).
That is, as Si02 is deposited on the Ni/A12O3 catalyst, the number of Bronsted sites, which favor the cracking of molecules, increases because of the contribution of acidity from the Si02/Al203 interface. Further deposition of Si02 prevents access to the interface because of the large kinetic diameter (6.2 A) of n-octane and, thus, the conversion decreases. The role of Ni is to provide activated H species which reduce carbon formation. The effect of the presence of Ni on carbon formation was not directly investigated in this work, although the stability of the catalysts increased with increasing deposition time. The role of the coating may have been to limit the access of n-octane to the Ni particles, on which the hydrocarbon may crack and form carbon.

Conclusions The pore size distribution of a Ni/A12O3 catalyst was modified by depositing Si02 on the outer surface in a fluidized bed using TMOS as the Si02 precursor. The amount of deposition increased with increasing time and temperature. A temperature of 350 C was chosen for the deposition because at this temperature the rate of deposition was sufficiently fast without significant carbon formation. After 1.5 h of deposition at 350 C, the pores had been narrowed such that the measured surface area (by N2 uptake) of the Ni/Al2O3 catalyst decreased to a minimum value of 17 m2/g compared to an initial surface area of 129 m2/g. At these deposition conditions, CO uptake and NH3 uptake were also significantly reduced and continued to decrease up to a deposition time of 3 h. In contrast, the H2 uptake remained relatively constant for Si02 deposition times up to 3 h. Even after exposure to pure CO for 30 min, the H2 uptake on a Ni/A12O3 catalyst coated with Si02 for 2.5 h decreased by only 28%
compared to a decrease of 76% for an uncoated Ni/Al2O3 catalyst. NH3 TPD and n-octane hydrocracking reactions demonstrated that a deposition time of 30 min at 350 C
was optimal in terms of the number of Bronsted acids sites and accessibility to these sites.
Overall, these results indicate that the pore openings and acidity of Ni/A12O3 catalysts can be modified by the deposition of Si02 with a fluidized CVD technique.

Example 3 Sol-gel Synthesis of PtlA12O3 catalysts: effect of precursor and calcination procedure on Pt dispersion Currently there is much interest in tailored catalyst design. Sol-gel synthesis can be used to produce catalysts with uniform metal distribution, tunable particle size, high surface area, and stable dispersion. The resulting catalyst properties are sensitive to changes in the processing conditions. In this example, 2 wt% PtIA12O3 catalysts were prepared using sol-gel synthesis with various precursors including [Pt(C5H5N)4]C12 and [Pt(CõH2õ+2NH2)4]C12. After drying, calcination and reduction, the Pt particle size and dispersion were determined by TEM, XRD and H2 chemisorption.
The dispersions obtained varied between 5% and 70%. The effect of calcination procedure on the Pt dispersion depended on the precursor that was used. That is, when organic ligands were present in the precursor, the dispersion varied considerably with the calcination conditions. For example, using [Pt(C5H5N)4]C1z as a precursor, the Pt dispersion decreased from 41% to 28% when treatment in flowing He before calcination in air was removed. In contrast, the dispersions were relatively constant regardless of calcination procedure if a non-organic precursor such as [Pt(NH3)4]CI2 was used. It is possible that localized heating occurred when the organic ligands of the precursor were oxidized in air, and this temperature increase resulted in sintering of the Pt particles.

Example 4 Chemical vapor deposition of Si02 on Ni/A1203 catalysts in a fluidized-bed reactor The modification of catalyst structures can be very important for achieving high activities, selectivities, and stabilities. Chemical vapour deposition (CVD) is one method that can be used for this purpose. Fine control of the pore-opening of Ni/A12O3 for the selective chemisorption of H2 (2.9 angstroms) and exclusion of larger molecules (N2 -3.6 angstroms, NH3 - 3.6 angstroms, and CO - 3.8 angstroms) was achieved by depositing Si02 on the external surface of Ni/A1203 in a fluidized bed reactor using tetramethoxysilane (TMOS) as precursor. TMOS (1.75 mol%) was hydrolyzed with steam (14 mol%), using N2 as the carrier gas. The catalyst was characterized using N2 physisorption, H2 and CO
chemisorption, NH3 temperature-programmed desorption, and 29Si NMR. The effects of Si02 deposition time and reaction temperature were investigated. The surface areas and the pore volumes of Ni/A12O3 decreased as the deposition time increased. For a sample coated for 2.5 hours (0.31 g Si02 per g of sample), CO and N2 uptakes reduced significantly while H2 uptake remained constant.
This result was an indication that the Ni sites were still accessible to H2 while CO and N2 were excluded. Similarly the NH3 uptake diminished to near zero for a sample coated for 3 hours (0.37 g Si02 per g of sample). The reduction in acidity was ascribed to the covering of acid sites on the external surface by the Si02 coating and reduced penetration into the pores by NH3 because of the reduced size of the pore-openings. The activity of the coated catalysts was tested for n-octane hydrocracking. The catalyst coated for 30 minutes showed the maximum conversion towards n-octane cracking, while the catalysts coated for 1.5 hours or longer showed no reactivity due to decreased acidity and narrowing of pores for n-octane penetration.
An investigation of the microstructure of the Si02 coating using 29Si NMR
suggests that the coating contains at least two layers of Si after 30 minutes of coating.

Example 5 Controlled pore-opening of Ni/A1203 using chemical vapor deposition in a micro fluidized-bed reactor Chemical vapor deposition (CVD) provides an efficient technique to precisely control the pore-openings of porous catalysts. In this example, the fine control of the pore-opening of NilA12O3 using CVD for the selective chemisorption of H2 (2.9 angstroms) and exclusion of larger molecules (N2 - 3.6 angstroms and CO - 3.8 angstroms) is shown.
The pore-openings of a commercial gamma-A1203 impregnated with Ni were modified by depositing Si02 on the external surface in a fluidized bed using tetramethoxysilane (TMOS) as the Si02 precursor. TMOS (1 mol%) was hydrolyzed with steam(10 mol%), using N2 as the carrier gas. The effect of deposition time was investigated. The catalysts were characterized using N2 physisorption, H2 and CO chemisorption, and NH3 temperature-programmed desorption (TPD).
The surface areas measured by N2 physisorption and the pore volumes of the NilA12O3 samples decreased as the deposition time increased. The modal pore diameter, however, did not change significantly, indicating that the internal pore structure was not modified. For a sample coated for 2.5 hours (about 14 wt% SiO2), the uptakes of CO and N2 were reduced by 95% and 87%, respectively, while the uptake of H2 remained constant. This result was an indication that the Ni sites were still accessible to H2 while CO and N2 were excluded. Similarly, the NH3 uptake decreased by 80%. The reduction in acidity was ascribed to the covering of acid sites on the external surface by the silica coating, and reduced penetration into the pores by NH3 because of the reduced size of the pore-openings.

Example 6 Diffusion-controlled hydrogen spillover from modified Pt/gamma-A1Z03:
application to toluene hydrogenation Spillover is defined as the activation of species on a surface followed by the transport of those active species on an adjoining surface, which under the same conditions will not be able to activate that species. Hydrogen spillover is very important in the sense that dihydrogen (H2) can be activated on a catalyst surface to produce very reactive H species for reaction to increase the activity, selectivity, or stability of the catalyst. Surface diffusion can significantly control the rate of a reaction involving hydrogen spillover, especially when the reaction proceeds at a very rapid rate. The migration of the activated H species can play a very important role in the overall reaction kinetics.
In this example, hydrogen spillover has been demonstrated in the temperature range of 90-240 C at atmospheric pressure using toluene hydrogenation as a model reaction and modified Pt/gamma-A1203. The Pt/gamma-A1203 catalysts were modified by coating with Si02. Only H2 (kinetic diameter - 2.9 angstroms) could access the Pt sites, while toluene molecules (kinetic diameter of 6.7 angstroms) were excluded. The kinetics of the reaction were studied in the temperature range of 120-240 C to determine whether the reactions were influenced by diffusion. The theoretical model of Freeman and Doll was applied to the experimental data to obtain an estimate of the diffusion coefficients for H2 spillover from the modified Pt/gamma-A1203. A reaction mechanism was proposed.
A differential reactor was used for the reactions. The modified Pt/gamma-A1203 (40 mg) catalysts were mechanically mixed with various diluents (zeolite 13X and gamma-A1203) in a ratio of 1:1 in the reactor operating at atmospheric pressure. The reaction temperature was varied from 90 - 240 C to demonstrate H2 spillover from the modified Pt/gamma-catalyst. To study the reaction kinetics the reaction temperature was varied between 120-240 C. Toluene mole fraction was varied between 0.08 and 0.19, while H2 mole fraction was varied from 0.26 to 0.60.
The degree of conversion depended on the type of diluent, with the more acidic diluent, zeolite 13X, showing a higher conversion of toluene. Neither the modified Pt/gamma-A1203 nor the diluents alone were active towards aromatic hydrogenation. Therefore it was concluded that H2 spillover was responsible for the reactivity. The reactions were determined to be diffusion-controlled with activation energy EA of 12 kJlmol in the range of 120-180 C.
For 210-240 C the activation energy increased to 86 kJlmol suggesting a change in mechanism, possibly reaction control. Figure 24 depicts the change in reaction rate constant with temperature. The model of Freeman and Doll, which provides a relationship between diffusion-controlled rate constant kd, and diffusion coefficient D, was applied to the experimental data to estimate the D as well as the activation energy for diffusion, Ed,: In the range of 120-180 C, D values were between 7.1x10-3 and 1.3x10-2 m2/s, the average surface residence time was 2.2x10-15 s. Edt~ was 15 kJ/mol, which is of the same magnitude as EA and confirms diffusion-controlled reaction. The reactions were tested to see whether Eley-Rideal (ER) mechanism played any role in the mechanisms. The proposed mechanism involved the dissociation of H2 on Pt, followed by the surface migration of the activated H
to attack adsorbed toluene on the diluent surface, and the surface reaction of spillover H with the adsorbed toluene. No reaction between adsorbed species and gas phase species (ER
mechanism) occurred.

Example 7 Evidence of H2 Spillover from Pt1A1203 with Protected Active Sites Spillover involves the activation of species and transport of those active species from one surface to another surface on which the active species will not form under the same conditions. In H2 spillover, dihydrogen (H2) is dissociated into very reactive H atoms (or ions) for reaction. Hydrogen spillover from modified Pt/A12O3 catalysts has been demonstrated using toluene hydrogenation at atmospheric pressure in the temperature range of 90 - 240 C, as a model reaction. The Pt/A12O3 catalysts were modified so that only H2 could access the Pt sites. The modified Pt/A1203 catalysts were then mechanically mixed with various diluents (zeolite 13X, gamma-A1203, W03/A1203 and Si02). A 1:1 weight ratio of Pt/A12O3 and diluents showed toluene conversion with methylcyclohexane as the only product in all cases.
The degree of conversion depended on the type of diluent, with the most acidic diluent, zeolite 13X, showing the highest conversion of approximately 20% at 180 C. Neither the modified Pt/A12O3 nor the diluents alone were active towards toluene hydrogenation when tested under the same conditions. In addition, in the absence of Pt, toluene conversion was not observed.
Therefore, hydrogen spillover from the modified Pt/A12O3 catalysts was responsible for the hydrogenation of toluene in this reaction system.

Example 8 Evidence of H2 Spillover from Pt1A1203 With Protected Active Sites Spillover applies to the activation of species and transport of those active species from one surface to another in which the second surface does not adsorb or form the active species under the same conditions. Hydrogen spillover from PtlA12O3 catalyst with protected active sites, in which the pores have been narrowed to restrict access to reactant molecules except H2, was demonstrated using the hydrogenation of toluene at atmospheric pressure in the temperature range of 90 - 240 C. The Pt/A12O3 with narrowed pores (hereby called NP-Pt/A1203) was mechanically mixed with various diluents (zeolite 13X, gamma-A1203, Ti02, W03/A1203 and Si02). Neither NP-Pt/A12O3 nor the diluents alone were active towards toluene hydrogenation when tested under the same conditions. A 1:1 weight ratio of NP-Pt/A1203 and diluents showed toluene conversion with methylcyclohexane as the only product in all cases.
The degree of conversion depended on the type of diluent, with the most acidic diluent, zeolite 13X, showing the highest conversion of about 20% at 150 C. The confirmation of methylcyclohexane as the only product was evidence of toluene hydrogenation caused by H2 activation on Pt sites located inside the NP-Pt/A1203 catalyst, and subsequent spillover of highly reactive atomic hydrogen (H), interparticle migration to toluene molecules adsorbed on the diluent. In the absence of Pt, toluene conversion was not observed. The role of the diluent was to provide the sites for toluene adsorption. Therefore spillover hydrogen from Pt was responsible for the conversion of toluene on NP-Pt/A12O3 and diluent mixtures.

Example 9 Characterization of Si02 deposition on Ni/A1203 and Mo03/Al203 catalysts The modification of catalyst structures can be very important for achieving high activities, selectivities, and stabilities. Chemical vapor deposition (CVD) is one method that can be used for this purpose. Fine control of the pore-opening of Ni/Al2O3 for the selective chemisorption of H2 (2.9 angstroms) and the exclusion of larger molecules (N2-3.6 angstroms, NH3-3.6 angstroms, and CO-3.8 angstroms) was demonstrated by depositing Si02 on the external surface of Ni/A12O3 in a fluidized bed reactor. N2 physisorption, H2 and CO
chemisorption, and NH3 TPD were used to characterize the catalysts to investigate the effect of deposition time and temperature. The CVD technique was also applied to Mo03/A12O3 catalysts to study the mechanism, microstructure, and thickness of the Si02 deposition using solid state 29Si NMR, ToF-SIMS, and ICP-MS. The activity of the coated Ni/Al2O3 catalysts for n-octane cracking was tested to see the effect of amount of Si02 deposition on acidity and reactivity.
The Ni1A1203 (17% Ni loading) and Mo03/A12O3 (10% Mo loading) catalysts were prepared by wet impregnation using Ni(N03)2=6H20 and (NH4)6Mo7O24=4H20 respectively as precursors. Si02 was deposited on the catalysts using the hydrolysis of tetramothoxysilane (TMOS, 1-1.75%) with steam (10-14%) in a fluidized bed reactor at atmospheric pressure using N2 as a carrier gas. The cracking of n-octane was performed in a fixed bed reactor at 400 C and atmospheric pressure.
The BET surface areas and the pore volumes of the Ni/A12O3 and MoO3/A1203 catalysts decreased as the deposition time increased. For the Ni/Al2O3 catalyst coated for 2.5 hours (0.31 g Si02 per g of sample), CO uptake reduced significantly while H2 uptake remained constant, as shown in Figure 25. This result was an indication that the Ni sites were still accessible to H2 while CO was excluded. Similarly the NH3 uptake diminished to near zero for a sample coated for 3 hours (0.37 g Si02 per g of sample). The reduction in acidity was ascribed to the covering of acid sites on the external surface by the Si02 coating and reduced penetration into the pores by NH3 because of the reduced size of the pore-openings.
Figure 26 shows the conversion of n-octane as it changes with SiO2 deposition time during n-octane hydrocracking on Ni/A12O3. The catalyst coated for 30 minutes showed the maximum conversion towards n-octane cracking, while the catalysts coated for 1.5 hours or longer showed no reactivity due to decreased acidity and narrowing of pores for n-octane penetration.
The 29Si NMR of the coated Mo03/Al2O3 catalysts suggested that the coating contained at least two layers of Si after 30 minutes of coating. ToF-SIMS results also suggested a thin layer of Si02 (2-3 monolayers), or an uneven distribution of Si02 on the surface which is due to the rough surface topology of the particles. Both positive and negative ToF-SIMS spectra revealed the presence of SiOXH (x=1,2,3) and CmHn (m,n=1,2,3, etc) fragments which indicated that silanols and methoxy species are produced during the hydrolysis of TMOS.
The mechanism of Si02 deposition was proposed to be first the adsorption of Si-OCH3 species on the substrate, followed by hydrolysis to form silanol and methanol, and the oxidation of the silanol to form the Si-O-Si network.

Example 10 Kinetics of Toluene Hydrogenation on Modified gamma-A1203 Supported Catalysts with H2 Spillover Hydrogen spillover from modified gamma-A1203 supported metal catalysts was demonstrated in the range of 90 - 240 C at atmospheric pressure using toluene hydrogenation as the model reaction. The catalysts were modified by Si02 deposition so that only H2 (kinetic diameter, k.d., 2.7 angstroms) could access the metal sites, while toluene molecules (k.d. 6.7 angstroms) were excluded. A mechanical mixture of the modified catalysts and zeolite 13X or c-A1203 was active for toluene hydrogenation, with approximately 20%
conversion for 13X
and 8% for c-A1203 at 180 C. Neither the modified catalysts nor the diluents alone were active. On the metal surface, H2 is activated into highly reactive H, which then spills over onto the diluent for reaction with adsorbed toluene molecules. The kinetics of the reaction was studied in the range of 120-240 C using the 13X diluent. The reactions were modeled using a power law model of the type r=kPTPH' and a Langmuir-Hinshelwood type mechanistic model.
The order of the reaction with respect to toluene, n, ranged from -3 to 0.8.
For H2, the order m ranged from 0.8 to 1.7. The activation energy, EA, of approximately 45 kJ/mol suggests a kinetics controlled reaction. The proposed mechanism involves activation of H2 on the metal surface followed by the migration of the activated H to the diluent, competitive adsorption of toluene and H on the diluent, and sequential addition of adsorbed H to the toluene to form the product.

Example 11 Characterization of Si02 deposition on Ni/A1203 and MNOy/A12O3 catalysts The modification of catalyst structures can be very important for achieving high activities, selectivities, and stabilities. Chemical vapor deposition (CVD) is one method that can be used for this purpose. Silica (SiO2) was deposited onto the external surface of Ni/A1203 and Mo,,Oy/Al2O3 samples using chemical vapor deposition in a fluidized bed (FCVD).
Tetramethyl oxysilane (TMOS) was used as silica precursor and was hydrolyzed with steam and nitrogen carrier gas at atmospheric pressure. The resulting deposit was characterized using various techniques including N2 physisorption, inductively coupled plasma (ICP), and solid state 29Si nuclear magnetic resonance (NMR). Due to the ferromagnetic behavior of Ni, the Ni/A12O3 was not used for NMR experiments. MoXOy/Al2O3 was used for NMR
experiments.
The Ni/A1203 catalysts with Si02 deposition were used for n-octane cracking to determine the effect of deposition on the cracking activity and the results compared to the activity of an uncoated Ni/A12O3 catalyst.

Si02 Formation:

Si(OCH3)4 (g) + 2H20 (g) 4 Si02 (s) + 4CH3OH (g) (overall reaction) Mechanism of Si02 formation by TMOS hydrolysis:

=A1-OH + Si(OCH3)4 4 =Al-O-Si(OCH3)3 + CH3OH [1] (adsorption) =Si-OCH3 + H20 4 =Si-OH + CH3OH [2] (hydrolysis) =Si-OH + OH-Si= 4 =Si-O-Si- + H20 [3] (condensation) =Si-OCH3 + OH-Si- 4 -Si-O-Si=_ + CH3OH [4] (condensation) EXPERIMENTAL
Catalyst preparation:

- Ni/Al2O3 (17% Ni loading) - wet impregnation of gamma-A1203 with Ni(N03)=6H20 - Mo,,Oy/Al2O3 (32% Mo loading) - wet impregnation of gamma-A1203 with (NH4)6Mo7O24=4H20 - Calcination at 550 C for 2 hours, 2 C/min ramping rate - Si02 deposition - TMOS (1-1.75%) hydrolyzed with steam (10%) at 350 C and atmospheric pressure, followed by calcination at 500 C in air.

Characterization (before and after Si02 deposition) Figure 27 illustrates a Schematic of the apparatus used for FCVD.
- SEM/EDX - morphology/composition; gold-coated - N2, H2 and CO chemisorption to determine the number of active sites - 29Si NMR - Si02 microstructure and bonding characteristics Amount of deposition and shape-selectivity:
Figures 28, 29 and 30 illustrate the results.

- NZ uptake of Mo,,Oy/Al2O3 decreases with increasing deposition time.

- Amount of deposition for Mo,,Oy/Al2O3 increases at the rate of 0.3 g/h of Si02 per g of sample for first 0.5 h, and then slows down to 0.025 g/h of Si02 per g of sample for more than 0.5 h of coating.

- H2 uptake of Ni/A12O3 remains almost constant as the deposition time increases.
- CO uptake however, decreases with increasing deposition time, indicating a better selective chemisorption of H2 (kinetic diameter, k.d. of 2.7 A) than CO

(k.d. of 3.8 A).

- Surface area of Ni/A12O3 and R-A1203 decrease with increasing deposition time.
Surface area of R-A1203 decreases more rapidly than Ni/Al2O3. Bonding between R-A1203 and Si02 is stronger than that of Ni and Si02.

Energy Dispersive Spectroscopy:
Figures 31 and 32 illustrate the particles and spots selected for energy dispersive spectroscopy (EDS). Figures 33 and 34 illustrate the results of the EDS for each particle shown in Figures 31 and 32.

Several spots were selected for EDS

Spots measured by EDS on MoXOy/Al2O3 particles in Figure 32 Element 1 2 3 4 5 6 7 0 48.3 43.0 38.4 28.7 46.4 26.5 36.3 Al 37.1 41.4 43.8 18.6 19.5 37.7 36.9 Si 14.6 15.6 17.7 9.0 6.3 11.2 14.1 Mo 0.0 0.0 0.0 43.7 27.8 24.6 12.7 AI:Si 2.5 2.7 2.5 2.1 3.1 3.4 2.6 Mo:Si 0.0 0.0 0.0 4.9 4.4 2.2 0.9 - Concentration of each species varies at different points on the surface.
- Mo is not uniformly distributed on the particle.
- Concentration of Si on the surface correlates more with Al than with Mo concentration. That is, AI:Si ratio varies between 2.1 and 3.4, while Mo:Si ratio varies between 0 and 4.9.
29Si NMR:
Figures 35, 36 and 37 illustrate the results.
Si(4Si) -110 ppm Si(3Si, Al) -105 ppm Si(2Si, 2Al) -100 ppm Si(3Si, H) -100 ppm Si(2Si, Al, H) -95 ppm Si(Si, 3A1) -95 ppm - Chemical shifts increase to a higher field as Si concentration increases.

- Bonding characteristics of Si on A1203 coated for 2.5 hours consistently shows deposition thickness of at least a bilayer, without the presence of a monolayer.
- At least 2 monolayers are present after 0.5 h deposition (10% Si02 deposition) due to the presence of -109 ppm chemical shift. Low shift signal is also present (-94 ppm) indicative of a monolayer.

- Deposition of Si02 on Mo,,Oy/A12O3 greater extent of non-uniformity than A1203.

n-Octane Cracking:
Figure 38 illustrates the results.
- Maximum activity for n-octane cracking observed for 0.5 h coating.
- Activity for n-octane cracking decreases with increasing deposition time.
- Cracking activity enhanced by the acid sites created at the Al-O-Si-OH
interface.
- Interface of AI-O-Si-OH is covered as deposition amount increases, leading to decrease in reactivity - In addition, as the deposition time increases, the pore-opening decreases in size relative to size of n-octane molecule resulting in decrease in n-octane penetration and loss of reactivity CONCLUSIONS
- Pore characteristics can be changed using FCVD.
- At least two Si monolayers can be achieved after 0.5 hr coating.

- SiO2 deposition may not be uniform for both A12O3 and MoROy/Al2O3, but Mo,{Oy/A12O3 shows greater extent of non-uniformity.

- Shape-selectivity is achievable by depositing Si on Ni/A1203.

- ICP and physisorption results showed that the deposition increased rapidly initially at a rate of 0.3 g/h Si02 per g of sample, and reached a plateau as deposition time increased. The decrease in deposition with time may be attributed to coverage of surface by methoxy (-OCH3) and other organic species that can be removed by calcination.

- N2 uptake decreased with increasing deposition time as a result of narrowing of pores to N2 penetration.

Example 12 Evidence of H2 Spillover from Pt/gamma-A1203 with protected Metal Active Sites Reactions:

Benzene hydrogenation:

/ I
+ 3H2 --~-\

Toluene hydrogenation:

+ 3H2 -O-xylene hydrogenation:

(trace) 2 + 6H2 -~- +

Reactivity Tests:
- Catalyst with protected metal sites only - Pt loading -0.8% (measured by ICP) - Diluent only (acidity: Zeolitel3X > gamma-A1203> Si02) - Catalysts with protected metal sites + diluent, 1:1 mass ratio - 50 mg catalyst (undiluted) - 0.6 mlJhhydrocarbon, 30 mL/min H2 flow - 1 atm, 90 -240 C
Effect of Amount of Diluent:
- Diluent-catalyst ratio of 1:1, 2:1, 4:1 RESULTS
Benzene Hydrogenation:
Figure 39 graphically illustrates the results.

- Synergism observed with bifunctional modified Pt/gamma-A1203 + diluents.
- Reactivity increases with increasing diluent acidity (Zeolite 13X >
gamma-A1203) - Diluent shows no reactivity in the absence of noble metal. Spillover works!

Toluene Hydrogenation:
Figure 40 graphically illustrates the results.

- Synergism observed with bifunctional modified Pt/gamma-A1203 + diluents.
- Reactivity increases with increasing diluent acidity (Zeolitel3X >
gamma-A1203 > Si02).

O-xylene Hydrogenation:
Figure 41 graphically illustrates the results.

> Synergism observed with bifunctional modified Pt/gamma-A1203 + diluents.
> Reactivity decreases in order: Benzene > Toluene > O-xylene.
Effect of Diluent Amount:
Figure 42 graphically illustrates the results.
- Reactivity increases with increasing diluent amount.
> Optimal diluent-catalyst ratio is 2:1 CONCLUSIONS

- Spillover hydrogen can migrate from modified Pt/gamrna-A1203 catalyst and react with species adsorbed on diluent > Mixture of modified Pt/gamma-A1203 and the most acidic diluent(Zeolitel3X) gives highest conversion - Reactivity decreases with increasing aromatic substituents (benzene >
toluene >
o-xylene) - Optimal diluent-catalyst ratio is 2:1 Example 13 Chemical Vapour Deposition of Si02 on Ni/A1203 catalyst in a fluidized-bed reactor EXPERIMENTAL METHODS
FCVD:

- Reduction of Ni1A1203 at 550 C for 4 hours in ChemBET 3000 > Hydrolysis of silicon alkoxide at latm, 350 C
> 1-2 mol% tetramethyl-oxysilane (TMOS), 10 mol% steam - 1-3 hours deposition time > Calcination in dry air at 500 C for 2 hours Si(OCH3)4 + 2H20 4Si02 + 4CH3OH

- Characterization: H2 + CO chemisorption, N2 physisorption, NH3, TPD, ICP, SEM, NMR
- Fluidized bed reactor - quartz tube, 1 cm ID, 41 cm length Mechanism of Deposition:

=AL-OH + Si(OCH3)4 a =Al-O-Si(OCH3)3 + CH3OH

-Si-OCH3 + H20 <=> =Si-OH + CH3OH (Hydrolysis) =Si-OH + OH-Si=_ a -Si-O-Si= + H20 (Condensation) -Si-OCH3 + OH-Si= ~#* =Si-O-Si= + CH3OH (Condensation) RESULTS:
Pore Size Distribution:
Figure 43 graphically illustrates the results.

- Pore sizes decrease as Si02 deposition increases Deposition Time:
Figure 44 graphically illustrates the results.

- CO (3.8 Angstroms) uptake decreases with increasing duration of deposition.
HZ (2.9 Angstroms) uptake remains almost constant.

Amount of Deposition:
Figure 45 graphically illustrates the results.

- SiO2 deposition increases with increasing deposition time - 37% deposition after 3h.
- Si Content measured by ICP-MS (Galbraith Labs).
Total Acidity:
Figure 46 graphically illustrates the results.

- SiO2 deposition covers acid sites and narrows pore openings. NH3 uptake decreases with increasing Si02 deposition.

- Acidity is created by induced effect of -Al-O-Si-OH species.
n-Octane Cracking:

Figure 47 graphically illustrates the results.
- Maximum reactivity for n-octane cracking observed after 0.5h coating.
- Si02 monolayer on gamma-A1203 increases Bronsted acidity.
29Si MAS NMR:

Figure 48 graphically illustrates the results.

- 29Si chemical shift of -122 3 ppm indicates Si(OSi)4 network - at least 2 layers of Si02.

N2 Uptake:

Figure 49 graphically illustrates the results.

- Deposition is more rapid on plain A1203 compared to Ni (17%) loaded A1203.
CONCLUSIONS

- Selective chemisorption of H2 and rejection of larger molecules (CO, NH3) is possible on Ni/A12O3 coated with Si02.

- A deposition time of 2 hours at 350 C is sufficient to block majority of pores to CO adsorption.

- At least 2 layers of Si02 are present after 0.5h of deposition.

Claims (4)

1. A catalyst comprising: a core comprising a metal catalyst dispersed on a support, an inner shell adsorbed on the core, and an outer shell adjacent to and in contact with the inner shell.

2. The catalyst of claim 1 further comprising a hydrogenation site adsorbed on, embedded in or embedded in part in the outer shell.

3. The catalyst of claim 1 or 2 wherein the metal is a noble metal.

4. A method of hydrogenating unsaturated hydrocarbons comprising exposing an unsaturated hydrocarbon to a catalyst of any one of claims 1 to 3.