Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0238—Impregnation, coating or precipitation via the gaseous phase-sublimation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/24—Chromium, molybdenum or tungsten
  • B01J23/26—Chromium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/32—Manganese, technetium or rhenium
  • B01J23/36—Rhenium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/061—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing metallic elements added to the zeolite

Definitions

• the present invention relates to a process according to t preamble of claim 1, for preparing a heterogeneous cataly comprising a support and at least one catalytically activ species bound to its surface.
• the surface of the support is optionally first pretreated.
• the catalyst reagent containi the catalytically active species or its precursor is vapo ized and the vapour is conducted to a reaction chamber wh it is contacted with the support.
• the catalyst reagent not bound to the support is then withdrawn in gaseous form fr the reaction chamber.
• the species bound to support is posttreated in order to convert it into a cata ⁇ lytically active form.
• the invention also relates to an apparatus according to t preamble of claim 15, for preparing heterogeneous catalyst
• heterogeneous catalysts have been prepared depositing catalytically active compounds from the liquid phase onto the surface of the support by means of impregna ion, precipitation or ion exchange.
• the starting materials used here comprise chemical compounds, often salts, which are soluble in known solvents.
• the solvents most frequentl employed are water and different alcohols.
• the acidity of the surface has a decisive effect on the activity of the catalyst.
• the acidi is influenced both by the type of the acid sites, for example, the Br ⁇ nstedt and Lewis type, as well as by the number of sites.
• the acid sites can be influenced by, e.g., different heat treatments, hen zeolites are treated with solvents, especially water, after a heat treatment, a definite change in the distribution of the acid sites is discernible. At least some of the acid sites then assume reversibly different forms. Thus, it is clear that the degree of acidity cannot be controlled during impregnatio or ion exchange.
• the solvent used are often contaminated with impurities that can adversely affect the activity of the catalyst.
• Reference [1] outlines a process that involves heating rhenium heptoxide to a temperature in the range from 150° 700 ⁇ C and allowing the vapour to condense on the surface of an aluminium oxide support which is maintained at a temperature below 50*C.
• the reaction is carried out at a temperature between 500 ⁇ and 600 ⁇ C, the
• the citation includes an example disclosing the preparation of a catalyst containi
• 4,362,654 and 4,380,616 comprise plac the silica support and a piece of chromium metal in a rou bottomed flask, evacuating the flask, and stirring the silica in the flask with a magnetic stirrer.
• the chromium vaporized by heating with heat resistances [3 and 4]. In this case also, the chromium adheres to the support surface in the form of small particles.
• the dispersion of the activ metal may be heterogenic and there is not yet a proper understanding of how the carbene complex is formed on the catalyst.
• reasearchers have prepared different catalysts having extremely thin layers, known as "atomic layers", of metal oxide bound to the surface of the supports [5 - 8] .
• the catalysts comprises 1 to 3 of these atomic layers.
• Reference [5] discloses the preparation of catalysts having ultra-thin L ⁇ 2 ⁇ 3, Ti ⁇ 2 Si ⁇ 2, and Nb2 ⁇ s layers on the outer surface of a zeolite (ZSM-5).
• Reference [6] describes the corresponding catalysts having a Si ⁇ 2 support.
• catalysts containing Si ⁇ 2 and Ti ⁇ 2 are prepared by contacting methyltriethoxysilane and titanium isopropoxide vapors with the hydroxyls of ZSM-5 surfaces at 473 K (200 ⁇ C) in a vacuum.
• the Zr0 2 /ZSM-5 hybrid catalyst was prepared by contacting vaporized Zr tetraoxide having a vapour pressure of 133 Pa at 473 K with ZSM-5 at the same temperature.
• the catalys thus prepared have unique properties.
• the catalysts exhibit good selectivity.
• the catalysts prepared according to reference [5] are used for selective propane preparation from CO and H2.
• the catalyst described in reference [6] is used during ethanol dehydrogenation, this catalyst being more active and selective than a catalyst prepared by impregnation or Nb2 ⁇ 5.
• the catalyst cited in reference [8] activates the formation of isopentan from methanol.
• the common feature of the methods cited in references [5] [8] is that first, a thin oxide layer is prepared on the surface of the support.
• the starting metal compound is chosen such that it does not fit into the cavities of the zeolite [5, 8].
• McDaniel has studied the state of chromium(VI) on a Philli polymerisation catalyst [9] and he has also, together with Stricklen, patented a process for preparing a CO-reduced chromyl halide silica-supported catalyst [10].
• the startin compounds chosen include Cr ⁇ 2Cl2. Cr ⁇ 2 2 and Cr ⁇ 2 Cl. Befo depositing the starting compound on the support, the surfa of the support was heated in an oxidising ambient, such as air, at a temperature within the range of 400 to 1000 ⁇ C in order to remove the hydroxyl groups on the support. After the oxidising treatment, the oxygen was purged by nitrogen or argon gas flushing.
• t reagent in the example 0.5 to 4.0 ml of chromyl chloride, was then injected into a stream of nitrogen gas conducted through the support, the reagent vapours reacting with the hydroxyl groups of the support. Unreacted reagent vapour w withdrawn from the reactor.
• the surfaces of the support particles used in heterogeneou catalysts are structurally inhomogeneous.
• the chrystalline structure of the material also complex containing, e.g., pore openings having dia ⁇ meters ranging from 0.3 to 0.7 nm.
• the surfaces of the support materia are chemically inhomogeneous containing numerous binding sites of different valencies for new atoms or molecules contacted with the surface of the support. It is difficult to control the binding of the metals or metal compounds us as reagents when following any of the conventional practic described above in references [5] to [10].
• the conventional processes also present difficulties in achieving homogeneous dispersion of the metals or the meta compounds on the support surfaces.
• the present invention aims at eliminating the drawbacks of the prior art and at providing an entirely novel technical solution for gas phase preparation of heterogeneous cata ⁇ lysts.
• the invention is based on the concept of bringing the cata lyst reagent in vapour state to the reaction chamber in an amount that at least corresponds to the amount of binding sites on the support surface. It is preferred to use an excess of reagent in relation to the available surface binding sites.
• the temperature of the support is kept high than the condensation temperature of the vapour and sufficiently high for the active species or its precursor to be chemisorbed on the surface of the support. In other words, the process aims at providing the thermal activatio energy needed for the formation of bonds between the activ species or its precursor and the surface of the support.
• the apparatus for preparing the heterogeneous catalyst according to the invention is characterised by what is stated in the characterising part of claim 15.
• the binding o the active species to the different binding sites of the surface is determined by the structural geometry of the surface atoms of the support and by the electron distribu ion (the surface energy potential).
• the chemisorpti of the active species is surface selective.
• Catalyst reagent denotes a starting material in solid, liquid or gaseous state, whose vapour contains the compon which together with the support forms the catalytically active sites on the surface of the support.
• the catalyst reagent employed can comprise any conventional reagent us for the preparation of heterogeneous catalysts, be it in t form of a gas or of a compound that can be volatilised.
• T reagent may, thus, comprise, inter alia, elemental metals, such as zinc, metal compounds, such as rhenium oxides and chromium halide compounds, and metal complexes, such as Mg(thd) 2 .
• the active species refers to the catalytically active component on the surface of the support, which can be in the form of an atom, an ion, a molecule, a chemical compou or a complex. Normally, the active species is comprised o the ion, atom or compound of a metal on the surface of th support.
• precursor denotes basic forms of the active species which may be inactive but which will yield the active species by a suitable treatment.
• the support comprises a solid material which has a rather large surface for binding the catalytically active materi or compound.
• the area of the support surface typically amounts to between 10 and 1000 m 2 /g as determined by the method.
• the support may consist of an inorganic oxide, su as silica (silica gel), aluminium oxide (alumina), thoriu oxide (thoria), zirconium oxide (zirconia), magnesium oxid
• supports are essentially catalytically inactive.
• the support used also comprise a substance which itself catalyses the desir chemical reaction.
• These supports are exemplified by the natural or synthetic zeolites. It is to be understood that, within the scope of this application, the term "support” also encompasses inactive supports having a catalytically active species bound to their surface. Thus, for instance, when bimetal catalysts are prepared, the first species may provide the support surface for the second species.
• the reaction chamber is the space, within which the support and the reagents are contacted.
• Chemisorption refers, in general, to a process, in which the gaseous, liquid or dissolved compound is bound or attached to the surface of a solid or liquid substance in such a way that a bond, essentially of a chemical nature, is formed.
• Physical adsorption is a process which, in essence, involves the physical adsorption of a substance on the surface of another substance by intermolecular force known as the van der Waals forces.
• Condensation means the liquidification or solidification of vapours and gases by cooling.
• the present process comprises three basic stages, including the pre- and posttreatment stages, which are part of the preferred embodiments of the invention, although they are not essential as far as the basic solution of the invention is concerned.
• the process parameters of the method are the temperatures and the duration of each of the given stages.
• the selection of process parameters is influenced by the actual support- reactant combination.
• all the reagents for the pre- treatment, for the binding of the catalytically active species and for the posttreatment are routed to the reacti chamber in vapour form typically one at the time.
• the vapo pressure of the vaporized catalyst reagent is maintained a a sufficiently high level and the duration of its interact ion with the surface of the support is sufficiently pro ⁇ longed that at least an equal amount or, preferably, an excess of the reagent is provided in relation to the binding sites available on the support.
• a 1.5- to 1000-fold surplus of the reagent and preferably a 2-to 100-fold surplus is normally used.
• the monolayer amount of the species can be calculate using, for instance, the BET method on the basis of the surface of the support and the molecular structure of the surface.
• reaction conditions are sought in which the gas-phase reagent (the active species its precursor) fills all or essentially all of the binding sites available to provide saturation of the surface at th prevailing temperature.
• the temperature should not be allowed to drop below the vaporization temperature of the reagent. Neiter must the reagent be allowed to condense on its rout to the reaction chamber, but the temperature of the feed piping should be kept close to the reaction temperature.
• the reagent and the temperature employed are selected in such a way that the reagent does not decompose and the decomposition products, if any, do not condense.
• a temperature gradient is formed, increasing from the reagent source towards the reaction chamber.
• the lower limit of the temperature range is determined by the condensation temperature of the evaporated reagent and the activation energy necessary for establishing the desired surface bond.
• the condensation temperature is not, by itself, an appropr ate lower limit if it is too low to provide the reagent wi the energy needed for surpassing the activation threshold.
• the upper limit is determined by the temperature at which the active species, or its precursor chemisorbed on the support, starts to show a significant rate of desorption from the binding site, i.e. when the equilibrium of the chemisorption-desorption reaction has shifted toward de ⁇ sorption.
• the reagent is selected such that the activation energy required by the chemisorption is exceeded at a temperature at which desorption is still not significant. in most cases, the activation and desorption energies are not known and, thus, the selection of suitable reactants an temperatures is determined by experimentation.
• the pretreatment, the binding and the posttreatment temperatures of the catalytically active component can differ from each other. However, it is required that limit T m in, for for each reagent used, be exceeded during each process stage.
• the temperature of the pre- treatment will influence the amount of active species or it precursor bound to the support. This is the case, for examp when chromium is bound to the surface of silica.
• the bindin temperature (>T m i n ) might then, in turn, influence the amount of the active species or its precursor chemisorbed t the support. This phenomenon can be illustrated by the preparation of the alumina-supported rhenium and the silica supported zinc catalysts. As will become evident from the following examples, the temperature is generally kept below 500*C, although this temperature does not represent an absolute upper limit.
• the reaction between the catalyst reagent vapour and the support may be carried out at elevated pressure, ambient pressure or in a vacuum.
• the process is carried out at a reduced pressure ranging from 0.1 to 100 mbar. The benefit to be gained by using reduced pressure resides in improved purit of the reaction chamber and increased diffusion rate.
• the pretreatment and posttreatment stages can, similarly, be carried out at elevated pressure, ambient pressure or reduced pressure.
• the reaction time is predominantly affected by the penetration of the vapour molecules into the pores or cavities of the support.
• the gas diffusion between the support particles constitutes an extremely fast process in comparison to the diffusion towards the inner parts of the pores.
• the reaction time should be kept long enough to all the vapour containing the active component to interact wit the binding sites of the support and to provide the desire surface saturation.
• the reaction time can be selected in the range from 0.5 to 25 hours. Usually 1 to 4 hours is enough for achieving the desired goal.
• the basic structure of the support materials of the heterogeneous catalyst are different. Thu the atoms or molecules of the vapour-phase catalytically active substance may, under the same ambient conditions, react in very different ways with different supports.
• the pretreatment stage of the support is, therefore, important. The pretreatment aims at providing the desired binding site for the catalytically active component that is to be bound to the support.
• the pretreatment can be effected by heating the support or by treating it chemically or as a combination of these two operations.
• the heat treatment can, for instance, comprise increasing the temperature of the support to the same temperature as used for binding the active component. In this case, it is preferable for temperature to be increased at a steady rate over a given period of time.
• the support may also be heated for some time, normally for between 1 min and 100 hours, preferably from between about and 30 hours, at a selected pretreatment temperature that i either higher, as high as or lower than the temperature use for binding the component.
• the suitable temperature depends on the support, on the catalytically active species to be bound, and on the binding temperature selected.
• a pretreat ⁇ ment temperature higher than the reaction temperature leads with a high probability, to a stable and reproducable surface situation in the actual reaction stage. Too high a pretreatment temperature may, however, change the desired surface structure of the support. At too low a temperature, it is not possible efficiently to remove undesired molecule of substances physically adsorbed on the surface.
• the support can b treated with a chemical substance, such as water (steam), f forming hydroxyl groups on the surface, or alternatively, with a dehydrating agent for removing hydroxyl groups.
• a chemical substance such as water (steam)
• f forming hydroxyl groups on the surface
• a dehydrating agent for removing hydroxyl groups can also be treated with a volatile metal compound, such as a magnesium or titanium compound.
• the support being heated to or maintained at the desired temperature, while subsequently contacting the surface with a chemical substance, such as steam.
• a chemical substance such as steam.
• the support is pretreated at a high temperature for removing adsorbed water. After this, the temperature of the support may possibly be changed and st allowed to interact with the surface, on which chemisorpt of new hydroxyl molecules can then proceed. The actual reaction is thus finally carried out either at the same o at another temperature.
• the surface-activated support is contacted and interacts with vapour containing the component (i.e. species of pre cursor) that is to be bound.
• the component is bound to th surface by selectively filling the available surface bind sites.
• the temperature and the durati of the process are determined experimentally for each support material, while taking the activation conditions the characteristics of the vapour containing the binding component into account.
• the binding order may vary, result being different kinds of catalysts.
• the prepared specimen can, if necessary, be subjected to post treatment.
• This may, for instance, comprise a heat treatm in which the catalyst is heated to a desired temperature which generally is at least in excess of the binding temperature.
• the heat treatment is carried out in oxidising or reducing conditions.
• the catalyst atoms may be contac with a vapour, e.g. steam, that modifies the binding surrounding.
• This modification may be necessary, e.g. when the precursor of the catalytically active species comprise a reagent molecule deposited on the surface of the support, a part of which is to be removed after the binding.
• chlorine atoms are often detrimental to the activity of the catalyst and they can b removed by steam or hydrogen sulfide treatment.
• a singl or several further species may be added by repeating the procedure described above in such a manner that a vapour containing a new species or its precursor is chosen for th actual binding reaction.
• the stages of the process can be repeated for a desired amount of new species, with the option to conduct heat treatment and/or chemical treatmen between the stages.
• the catalyst have been found to be active at lower metal loadings than previously reported in the literature. This would suggest that the metal is more evenly distributed than in the catalysts prepared from solutions. The ability to control the binding of the metal during the preparation is improved It is easier to bind several metals than from solution.
• the metal may be bound in the form of different compounds to t same support, with the necessary ligands being readily obtainable. The impurities caused by the reagents are diminished. The temperature of the process may, in some cases, be lowered.
• heterogeneous catalysts exhibiting different basic structur may be prepared.
• the catalysts used in oil refining, the metathesis catalysts and the polymerisation catalysts may b mentioned by way of example.
• the main groups of catalysts are represented by zeolite-supported zinc, alumina-supported rhenium and silica- supported chromium.
• Figure 1 shows in cross-section one possible reactor desig for carrying out the process according to the invention.
• Figures 2 and 3 depict the binding of Zn on the surface of zeolite support as a function of the binding temperature.
• Figure 4 portrays the influence of support preheating on t binding of chromium from Cr ⁇ 2Cl2 to silica.
• Figure 5 depicts the binding of chromium to silica as a function of the reaction temperature.
• Figure 6 illustrates the activity of a silica-supported chromium catalyst in comparison to a prior art catalyst.
• the test reactor used in the working examples comprises a longish reactor body 1 and a reactor chamber 4 fitted with said reactor body.
• the cover 3 is provi ded with suitable sealings, such as annular sealing rings.
• Heating elements 7, 8, 9, are mounted around the reactor body 1 for providing the necessary temperature in the different parts of the reactor.
• the heating elements 7, 8, can, for instance, consist of heat resistances.
• a protecting gas typically nitrogen and/or argon
• the reactor chamber 4 can be connected to a vacuum pump 24 by means of a suction pipe 25.
• the vacuum pump is also connected to the gas space defined by the reactor body 1 via a vacuum pipe 11.
• the vacuum pump used may be of a conventional membrane or pisto pump type. If necessary, a liquid nitrogen trap should be fitted between the pump 24 and the evacuated spaces for collecting condensing fumes.
• the feed pipe 12 is connected to a gas source, the reagent transport gas being fed into the pipe at the point indicated with an arrow.
• the gas flow is controlled by a regulator 17.
• the vessel 16, which is also referred to in the following as th hot source, is used for reagents that are solid or liquid a ambient temperature.
• the reagent is vaporized by heating it to the desired vaporizing temperature by means of heaters 8 and 9. By adjusting the gas flow with the aid of the regulator 17, it is possible to control the flow of the reagent vapour generated in the hot source to the reaction chamber 4.
• the second feed piping 13 is connected to two gas sources 1 and 15 used for feeding reagents that are vaporous or liqui at ambient temperature.
• Pressurised reagent is fed from the gas source 14, which typically is a gas cylinder, via a valve 18 to the feed pipe 13.
• the gas source 15 is used for reagents having a rather low vapour pressure in compariso to the reaction chamber. These reagents are normally liqu at room temperature.
• the regulators i.e. for instance th valves 19, 20, 21, control the flow of the reagents from gas source 15 to the feed pipe 13.
• the feed pipe 13 is connected before the regulator 21 to the transport gas source at the point indicated by an arrow (pipe section 26
• the transport gases used for feeding the reagents from gas sources 14 and 15 preferably comprise inert gases, such as nitrogen and/or argon.
• the reagents used for the chemical pretreatment are fed fr sources 14, 15 or 16, respectively.
• the apparatus used in the working examples further include a mass spectrometer 22 for analysing volatile reaction products from samples withdrawn through the regulator 27.
• the mass spectrometer also comprises a two-part pump arrangement 23 including a prepump and a high pressure pu
• the apparatus is used as follows:
• a suitable amount of a support material 6 is placed in the sample container 5 in the reaction chamber 4.
• the scale of the operation has been small, and usually samples weighing in a range from 3 to 10 g have b used.
• a liquid or solid reagent is placed in container 16. The reactor body 1 and the reaction chamber 4 are subsequently evacuated by feeding protecting gas via the feed conduit 10 and the feeding pipe 13 at a low flow rate
• the goal is to achieve a pressure amounting to a few millibars, e.g. 3 to 10 mbar.
• the support 6 is then pretreated.
• the heat treatment may be carried out using various heating times and temperatures; the temperature is normall in the range from about 200 to about 500 ⁇ C, whilst the heating time is about 10 to 30 hours. During this period o time the reagent in container 16 is not normally heated.
• the reactants ar fed from sources 14, 15 or 16.
• steam is conduct from source 15 by routing the protecting/transport gas flo via source 15 (valve 21 is closed and valves 20 and 19) ar opened.
• the temperature of the reagent in source 15 is increased to the desired level by the heater 9.
• Use of the heater 8 enables an increasing temperature gradient to be established between the hot source 16 and the reactor chamber 4, the temperature of the reactor chamber 4 being higher that the temperature of the hot source 16.
• the regulator 17 is next opened and reactant vapour is fed by the transport gas into the reactor chamber 4.
• the reactant is metered at a dosage larger than that required by the number of surface binding sites.
• the gaseous reagent diffuses into the support 6 in the samp container 5 and the surplus gas is withdrawn through channe 25 by means of the vacuum pump 24. A part of the gas stream flowing from the reaction chamber 4 is conducted via valve 27 to the mass spectrometer for analysis of its composition
• gaseous reagents When using gaseous reagents, these are fed from gas sources 14 and 15.
• the reagents that are gaseous at room temperatur are preferably fed from a gas cylinder 14, and liquid reagents from a liquid container 15.
• the reagents flowing through the feed pipe 13 are heated to the desired temperature by heaters 8 and 9.
• the temperature of the feed pipe is always kept higher than the condensation temperatur of the reagents.
• the process is continued until the desired surface reaction has reached a state of saturation.
• the supply of the reagen is then cut off.
• the temperature and the pressure are returned to normal (STP). If necessary, the catalyst is removed from the apparatus in an atmosphere of protecting gas.
• the zeolite support was comprised of a mixture of a HZSM-5 type zeolite and silica.
• the zeolite was prepared as follows: 2300 g of tetra-propy ammonium bromide, 100 g of sodium aluminate, 2760 g of sil gel (Ludox), 114 g of sodium hydroxide and 18500 g of wate were transferred into an autoclave, the temperature was increased to 165 ⁇ C, and the chemicals were allowed to reac for 144 h. The mixture was then rapidly cooled to ambient temperature, after which the product was recovered and was with 150 1 water. The product obtained was dried for 24 h 120 ⁇ C and calcined for 15 h at 540 ⁇ C.
• the sodium-containin zeolite was ion exchanged with a 5 % w/w ammonium nitrate solution.
• the ion exchanged product was dried for 24 h at 120'C.
• the zeolite was calcined for 15 h at 540 # C.
• the support materials, silica and the y-aluminium oxide we of commercial quality.
• the following reagents were used: metallic zinc, zinc chloride (ZnCl2). chromium chloride (Cr ⁇ 2Cl2). rhenium heptoxide (R ⁇ 2 ⁇ 7), aluminium chloride (AICI3), titanium chloride (TiCl4) and magnesium dipivaloyl-methane [Mg(thd)2]»
• the materials were of commercial grade, except for the last one, which was synthesized as described in the publication Hammon, G.S. et al., Inorg Chem 2 (1963), p 73.
• the surface of the metallic zinc was treated with hydro chloric acid in order to remove the surface layer before use. Otherwise, the reagents were not pretreated.
• the amounts of elements bound to the supports were determin by means of atomic absorption spectrometry (Al, Ti, Cr, Zn) fluorescence spectroscopy (Zn), polarimetric titration (Cl) or neutron activation analysis (Re).
• Al, Ti, Cr, Zn fluorescence spectroscopy
• Cl polarimetric titration
• Re neutron activation analysis
• XPS or ESCA X-ray induced photo- electron spectroscopy
• XRD X-ray diffraction analysis
• This example illustrates the binding of a metal in elemen state to the surface of the support. Further, the impact the reaction temperature on the amount of metal bound to surface is considered in the example.
• the zinc/zeolite catalyst is used in oil refining, e.g., catalysing the conversion of butane to aromatic compounds
• the Zn concentrations in the preapared catalysts were bet 0.03 and 10 % w/w.
• the binding of Zn as a function of the reaction temperatu is depicted in Figure 2.
• the Figure shows only the result obtained after 2 hours 1 preheating. Extension of the pre ⁇ heating period to 24 hours did not increase the binding o zinc to any larger extent.
• the logarithm of the ratio of atoms to Si ⁇ 2+Al2 ⁇ 3 atoms was calculated for Figure 2.
• Th Zn concentration of the catalyst was measured giving the amount of Zn atoms per zeolite weight unit. From the known BET surface of the zeolite the number of surface molecules was calculated. As a reference, the number of Zn atoms or ZnO molecules in an atom or molecule layer completely covering the surface (monolayer, ML) was calculated.
• the binding of the zinc is influenced by the adsorption, the formation of a chemical bond and the desorption.
• the minimum temperatur is represented by the condensation temperature of zinc, 390°C.
• the binding of zinc is also substantially decreased when the temperature rises above 500°C, which possibly is caused by the fact that the desorption of zinc is faster than at binding temperatures below 500°C.
• the maximum temperature of the process in accordance with the inventio is, in this case, about 500 ⁇ C.
• vapour pressure of a metal is low (e.g. less than 0. mbar) within the temperature range used for the preparatio of a catalyst, more volatile inorganic metal compounds or organo metal compounds can be employed.
• zinc/zeolite catalysts were also prepared starting from zinc chloride.
• the binding temperature was in the ran from 355 ⁇ C to 455 ⁇ C.
• a steam treatment was effected in ord to reduce the amount of the chloride ion residue on the catalyst.
• hydrogen sulphide may, for instance, be used as well.
• catalysts were provided having zinc contents in the order of 1 % w/w.
• Figure 3 depicts the binding of zinc from ZnCl2 to zeolite as a function of the reaction temperature.
• the activity of the zeolite-supported zinc catalysts was evaluated by testing the catalysts for the conversion of n-butane into aromates and for aromate selectivity.
• the t were carried out in a microreactor at ambient pressure and at temperatures ranging from 450 to 500 # C.
• the quantity o the catalyst batch loaded in the reactor was 5.0 g and the feed rate of n-butane into the reactor was 5 g/h.
• the reaction was monitored with the help of gas chromatography a sample being taken after each five hours 1 run at 450*C constant temperature.
• Reference catalysts were prepared by the dry impregnation technique, which involved impregnating 0.5 ml zinc nitrate solution into each g of an H-ZSM5-zeolite/silica support. Said catalysts were drie at 115 ⁇ C for 12 h, and subsequently calcined at 540*C for 4 hours. The catalysts prepared by impregnation contained 0.15 and 1.4 % w/w, respectively, of zinc.
• the catalysts produced in accordance with the invention achieve an equal or higher degree of conversion than is obtained with the reference catalyst, while the selectivity to aromatic compounds is at least at an equal level. Both the conversion and the aromat selectivity are on an industrially applicable level.
• the Re/alumina combination is a well-known metathesis catalyst which can be used, e.g., for catalysing the dispro portionation of propene to ethene and butene.
• rhenium was bound to the surface of y-alumina from rhenium heptoxide, which i a solid substance at ambient temperature.
• the catalysts were prepared using coarse-grain alumina as support. R ⁇ 2 ⁇ 7 (Aldrich Chemicals Co., purity: 99.9 %) was volatilized by heating it at 160 ⁇ C. The preheating of the support and the binding of the rhenium were carried out a 3 mbar nitrogen pressure. The reaction temperature was mai tained in the range from 175 to 360 ⁇ C, an increasing temperature gradient being formed from the hot source towards the reaction chamber. The rhenium heptoxide vapour was contacted with the support for 225 minutes. The rheni content of the prepared catalyst was determined. Table 3 gives the pretreatment and reaction temperatures.
• the table indicates that a long pretreatment at high temperatures decreases the amount of rhenium binding to th support. The largest amounts of rhenium are bound to the surface of alumina without any heat pretreatment.
• Test were further carried out to study the influence of a Mg(thd)2 addition on the support's capability to sorb rhe ⁇ nium.
• the alumina was first heated at 475 ⁇ C for 18 hours, then cooled to 240 ⁇ C and, subsequently, contacted with fum of Mg(thd)2 that had been volatilized at a temperature ranging from 75 ⁇ C to 85 ⁇ C.
• 0.36 % rhenium was bound to the support from rhenium heptoxide.
• the rhenium content was 0.12 %.
• the amount of Re bound to the support was tripled by the Mg(thd)2 treatment.
• the amount of Re bound to the support was rather small in all the tests ( ⁇ 0.65 %) in comparison to conventional Re metathesis catalysts that can have a Re content of up to 15 %.
• the activity of the prepared catalysts were assessed on basis of propene conversion. The results indicated that the Re activities on a weight basis were at least as high as those of conventional catalysts, andin several cases muc higher. Thus, in the case of the catalyst 4.2, the propene conversion per weight unit of Re was as high as over 6 % an in the case of catalyst 4.8 even exceeded 15 %.
• Silica-supported chromium is a known Phillips-type polymeri sation catalyst.
• the following example will show in more detail, how the preheating and the reaction temperatures influence the binding of chromium in the process according to the invention.
• Chromyl chloride, Cr ⁇ 2C_-2 was used as a starting coumpound for the chromium.
• a silica support (Crosfield Catalysts EP 10 silica gel) the amount of which was 4 to 5.5 g, was pre ⁇ heated at 100 ⁇ C to 360 ⁇ C in a nitrogen gas atmosphere at a pressure of 3 to 4 mbar for 17 to 20 hours. After the pre ⁇ heating the temperature was adjusted to the actual process temperature. Chromyl chloride was evaporated and reacted with the silica at 175, 270 and 365'C temperatures. The reaction time was in excess of 1.5 hours, typically 2.5 hours.
• Table 4 gives the test operating conditions of three Cr catalyst tests: Table 4. Operating conditions of Cr catalyst tests
• the Cr ⁇ 3 layer completely covered the surface of the sili support and was calculated to contain about 0.16 g chromi per 1 g silica. This corresponds to a molar content of approx. 0.003 mol chromium.
• the reagent used in the tests exceeded the aviable binding sites on the support by abou 30- to 70-fold.
• the preheating temperature determines the number of OH- groups in silica and thus the number of binding sites.
• Th chromyl chloride molecule can bind either to one or two hydroxyl groups releasing one or two molecules of HC1, respectively.
• the highest chromium concentrations were fo after preheating at 270 ⁇ C. Reaction temperatures for chro chloride between 150 and 330 # C did not have a major effec on the chromium concentration.
• the average Cr concentration as a function of the pretrea ment temperature is shown in Figure 5.
• Figure 6 shows the influence of the reaction temperature the binding of chromium.
• the ratio between the catalytically active metal and the support molecules was calculated.
• the figure also include an indication of the respective amounts of chromium and chromium oxide covering the silica surface in the form of a monolayer.
• the preheating temperature is raised ab 480*C, the Cr concentrations were less than 0.02 %, irrespective of whether the reaction temperatures were 175, 270 or 360 ⁇ C.
• the pretreatment should generally be conducted at a temperatur of at least 400 ⁇ C, preferably at a temperature in the rang from 600 to 800 ⁇ C.
• test 6.1 following the preheating step, the support was treated with steam for 75 min at 360 ⁇ C, after which the chromyl chloride was added.
• a new water vapour (steam) treatment was conducted at 270 C C followed by the introduction of 0.13 mol of titanium chloride (TiCl4) per unit weight (g) of the support into th same reaction space at the same temperature for 184 minutes Finally, a further steam treatment was performed for 75 minutes.
• test 6.2 following the pretreatmen , the support was acted with titanium chloride (5 mmol per g of support) at 270*C for 8.3 min.
• a water vapour treatment was the perfo for 15 minutes at the same temperature prior to the introduction of chromyl chloride into the reaction chambe
• a Cr-containing silica catalyst was prepared described in Example 5 above.
• the product thus prepared w reacted with titanium chloride at 270*C for 8.3 min.
• the amount of titanium chloride used corresponded to 9.5 mmol Ti/g of support.
• test 6.4 following the pretreatment, the support was first reacted with aluminium chloride (AICI3) at 270 ⁇ C fo 150 minutes. The amount of aluminium corresponded to 2.4 mmol Al per unit weight (g) of the support. Steam was the introduced into the reactor chamber for 75 minutes. The chromyl chloride was added as explained in Example 5.
• AICI3 aluminium chloride
• the catalysts prepared contained 0.016 to 0.47 % w/w chromium, 0.32 to 6.2 % w/w titanium and 0.49 % w/w aluminium.
• Example 7 The catalyst activity of Cr/silica-based catalysts
• the catalysts prepared according to Examples 5 and 6 were fluidized in dry air and heated first to 200 to 250 ⁇ at which temperature they were held for 4 h, after which they were finally activated by calcination at an elevated temperature (580 to 780 ⁇ C) for about 5 h.
• the calcined material was cooled to 300 ⁇ C and the air atmosphere was replaced by an oxygen-free nitrogen atmosphere.
• the catalysts thus treated were used in the polymerizatio of ethene.
• the reaction temperature was 105 ⁇ C and the tot pressure 4000 kPa.
• the hydrocarbon diluent in the polymer ization process was isobutane.
• the results are shown in Table 5, below. Table 5. Activities of Cr and Ti containing catalysts in polymerization of ethene.
• the catalysts have a very high activity even in those cases where the metal content is low.
• the X-axis indicates the percentage of chromi in the catalysts
• the Y-axis gives the amount of polyethylene formed per weight of the catalyst on an hourl basis.
• the lines drawn at an angle of 45" to the X-axis indicate the amount of polyethylene formed per hour in relation to the weight of the chromium on the catalyst.
• the McDaniel and Stricklen catalysts contain about 1 % Cr.
• Figure 6 shows that, calculated on the basis of PE-convers per unit catalyst weight, the present Cr catalyst attains almost as high an activity at lower Cr loadings as the bes prior art catalysts.
• the known catalysts have been subjected to a separate reducing treatment. From a calculation of the catalyst activity on the basis of the amount of chromium, it appear that the catalysts prepared according to the invention ar considerably more active that the prior art catalysts. Th addition of titanium increases the activity of Cr+Ti cata lysts. Since the catalysts is retained in the product aft the reaction, a decrease in the amount of Cr will provide a valuable additional benefit for catalysts prepared according to the invention.

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