WO2009045802A1

WO2009045802A1 - Group viii-alkaline earth metal catalysts

Info

Publication number: WO2009045802A1
Application number: PCT/US2008/077448
Authority: WO
Inventors: Sheldon Gerald Shore; Mark A. Keane; Errun Ding
Original assignee: The Ohio State University
Priority date: 2007-09-28
Filing date: 2008-09-24
Publication date: 2009-04-09

Abstract

Alkaline earth metals are used in place of Lanthanide metals to produce bimetallic catalysts containing both group VIII metals and alkaline earth metals. The bimetallic catalysts have catalytic properties comparable to other bimetallic and monometallic catalytic systems. The synthesis of various organometallic compounds containing group VIII metals such as Ni, Pd, and Pt and alkaline earth metals such as Ba and Sr are used to prepare the bimetallic catalysts.

Description

GROUP VIII-ALKALINE EARTH METAL CATALYSTS

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This research was supported by the National Science Foundation through grant

CHE 02-13491.

Cross-Referenee to Related Application

[0002] This application claims priority to prior U.S. Provisional Application

Serial No. 60/975,966, filed September 28, 2007, the disclosure of which is hereby incorporated herein by reference.

BACKGROUND

[0003] Bimetallic catalysts formed by calcinating in a reducing atmosphere certain organometallic compounds containing a group VIII metal and a Lanthanide metal (i.e.: a rare earth metal) have been shown to exhibit interesting catalytic activity. For example, the organometallic compounds [(DMF)₄Eu-Ni(CN)₄] and [(DMF)₄Eu-Pt(CN)₄], the synthesis of which is disclosed in Inorganic Chemistry (1996), 35, 5328-5334, have been prepared and have been used to form various group VIII catalysts that exhibit increased catalytic activity compared to monometallic catalysts that contain only group VIII metals. Both the J. of Molecular Catalysts A: Chemical 212 (2004) 291-300 and Catalyst Communications 3 (2002) 77-84 describe the preparation of Pd-Yb catalysts using a bimetallic organometallic compound, while the catalytic hydrogenation of phenol and hydrodechlorination of 1,2- dichlorobenzene using Pd-Yb catalysts so prepared are described in Applied Orsanometallic Chemistry (2003) 17, 493-498, Journal of Alloys and Compounds 418 (2006) 21-26, and the Journal of Catalysis 239 (2006) 486-500. Likewise, the Journal of Molecular Catalysts A: Chemical 212 (2004) 291-300 and Catalysis Communications 3 (2002) 77-84 describe preparation of similar Pd-Yb and Ni-Yb type catalysts and describe the use of these catalysts to effectively convert phenol into cyclohexanone/cyclohexanol. While group VIII- Lanthanide bimetallic catalysts have improved performance versus group VIII monometallic catalysts, and they can be prepared from bimetallic organometallic precursors, a major drawback is that Lanthanide metals are too rare and too expensive to be used regularly in commercial catalysts.

SUMMARY

[0004] In accordance with this invention, it has been surprisingly found that bimetallic catalysts having analogous compositions to group VIII-Lanthanide bimetallic catalysts, but where one or more alkaline earth metals are used in place of the Lanthanide metal, exhibit significant catalytic activity as well. Furthermore, unlike Lanthanide metals, most alkaline earth metals are both inexpensive and commonly available.

[0005] An aspect of the present invention provides for a bimetallic catalyst comprising at least one group VIII metal and at least one alkaline earth metal supported on an inorganic oxide support made by calcinating a pre-catalyst composition in a reducing atmosphere.

[0006] Another aspect of the present invention provides for a method for making a catalyst composition comprising calcinating in a reducing atmosphere an inorganic oxide support impregnated with a pre-catalyst impregnating liquid composition comprising (a) a non-aqueous solvent; (b) a group VITI metal present in the form of an oxygen-free salt; and (c) an alkaline earth metal present in the form of an oxygen-free salt.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The accompanying drawings, which are incorporated into and form part of the specification, schematically illustrate an exemplary embodiment of the present invention and, together with the general description given above and detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

[0008] Figures 1-4 show x-ray crystal structures of various organometallic compounds used to prepare catalysts associated with the present invention.

[0009] Figure 5 is a TEM image of the catalyst PdBa/SiO₂. [0010] Figure 6 shows the results of fractional dechlorination of chlorobenzene using various catalysts.

[0011] Figure 7 shows the results of fractional dechlorination of 1,2-dichlorobenzene using various catalysts.

DETAILED DESCRIPTION

[0012] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0013] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless otherwise indicated, the numerical properties set forth in the following specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from error found in their respective measurements.

General

[0014] As used herein, "inorganic oxide support" means an oxidized, refractory material. The inorganic oxide support may be present in many different physical forms including powders, granules, fused gels, films, coatings that are either used in a standalone manner or that are coated onto another substrate, or the inorganic oxide support can be pressed or fabricated into a 3 -dimensional structure that is porous or non-porous in nature. [0015] As used herein, "metal ligands" means organic molecules that complex with a metal species by physical association with a metal species using valence electrons to form dative bonding interactions.

[0016] As used herein, "non-aqueous solvents" means solvents other than water.

[0017] As used herein, "organometallic compound" means a compound with at least one bonding interaction (covalent, dative, ionic, localized or delocalized) between one or more carbon atoms of an organic functional group, molecule or metal ligand; and a group VIII metal atom, alkaline earth metal atom, or both.

[0018] As used herein, "oxygen-free salt" means compounds or salts of group VIII metals and compounds or salts of alkaline earth metals that do not contain metal-oxygen or metal-hydroxide based bonds. As intended herein, metal-oxygen and metal-hydroxide based bonds does not include metal-oxygen bonds arising from dative bonding interactions, which includes physical association or coordination of a metal atom with an oxygen species in a metal ligand or solvent molecule (for example water, THF, DME, DMF, or DMSO).

[0019] As used herein, "reducing atmosphere" means a suitable reducing agent used under conditions that favor the reduction of group VIII metals having various oxidation states that are greater than zero.

Bimetallic Catalysts and Methods for Making

[0020] The bimetallic catalysts can be present as complexes, compositions, compounds, or mixtures that contain at least one group VIII metal species and at least one alkaline earth metal species. The bimetallic catalyst containing these metal species is adsorbed on and supported by an inorganic oxide support. Any group VIII metals are suitable for use. Preferably, group VIII metal species are selected from but not limited to Ni, Pd, Pd, and mixtures thereof. Any alkaline earth metals are suitable for use. Preferably, alkaline earth metal species are selected from but not limited to Sr, Ba, and mixtures thereof. The bimetallic catalysts are formed by preparing a pre-catalyst impregnating liquid, impregnating an inorganic oxide support with the pre-catalyst impregnating liquid, and calcinating in a reducing atmosphere the inorganic oxide support impregnated with the pre- catalyst impregnating liquid. Preparation of Pre-catalyst Impregnating Liquid

[0021] The pre-catalyst impregnating liquid is a mixture containing a non-aqueous solvent, at least one group VDI metal and at least one alkaline earth metal. The group VIII metals and the alkaline earth metals can be in the form of oxygen-free salts, or organometallic compounds, or both. The pre-catalyst impregnating liquid is made by mixing the nonaqueous solvent with at least one oxygen-free salt of a group VIII metal and at least one oxygen-free salt of an alkaline earth metal. Alternatively, the pre-catalyst impregnating liquid can be made by mixing a non-aqueous solvent with an organometallic compound containing at least one group VIII metal species and at least one alkaline earth metal species. In certain embodiments, the pre-catalyst impregnating liquid may optionally contain metal ligands capable of simultaneously coordinating to both group VIII metal species and alkaline earth metal species that are present, and which can thereby form bridging molecular structures to at least two separate metal species.

[0022] Non-aqueous solvents are used in the pre-catalyst impregnating liquid to dissolve, disperse or suspend the additional ingredients that are present in the pre-catalyst impregnating liquid to bring them into intimate contact with one another. The additional ingredients, which include oxygen-free metal salts, organometallic compounds, and optionally metal ligands, are dissolved, dispersed, or suspended in the non-aqueous solvent by mixing using any mechanical means including, for example, stirring, shaking, or sonication. For certain formulations, heat may be applied in order to dissolve, disperse or suspend the ingredients in the non-aqueous solvent, hi exemplary embodiments the nonaqueous solvent is distilled or de-gassed or is treated to have the moisture removed before being mixed with the other ingredients to form the pre-catalyst impregnating liquid. Preferably, suitable non-aqueous solvents include but are not limited to tetrahydofuran (THF), dimethlyformamide (DMF), dimethoxyethane (DME), dimethyl-sulfoxide (DMSO) or mixtures thereof.

[0023] The oxygen-free metal salts of both the group VIII metal species and the alkaline earth metal species that are used in the pre-catalyst impregnating liquid are miscible or can be dissolved or dispersed or suspended in the non-aqueous solvent, with stirring, shaking, or sonicating. In certain instances, this may also involve heating or even refluxing the non-aqueous solvent for an extended period of time. Suitable oxygen-free salts of both the group VIII metal species and the alkaline earth metal species include both air stable and air sensitive salts and also include water stable and water sensitive salts. Preferably, oxygen- free group VIII metal salts are selected from but not limited to oxygen-free salts of the group VIII metals Ni, Pd, Pt or mixtures thereof. More preferable are alkali tetracyano salts of Ni, Pd, and Pt. Even more preferable are potassium and sodium tetracyano salts of Ni, Pd, and Pt. Preferably, oxygen-free alkaline earth metal salts are selected from but not limited to oxygen-free salts of alkaline earth metals Sr, Ba or mixtures thereof. More preferable are halide salts of Sr and Ba. Even more preferable are chlorine or bromine and iodine salts of Sr and Ba.

[0024] Similarly, the organometallic compounds that are used in the pre-catalyst impregnating liquid are miscible or can be dissolved, dispersed, or suspended within the nonaqueous solvent, with stirring, shaldng, or sonicating. In certain instances, this may involve heating or even refluxing the non-aqueous solvent for an extended period of time. Suitable organometallic compounds include both air stable and air sensitive compounds and include water stable or water sensitive compounds. The organometallic compounds also include structures where a group VIII metal species, or an alkaline earth metal species, or both of these metal species form the central core, including compounds having a structure such that the central core has a fixed ratio of group VIII-to-alkaline earth metals, which is surrounded or coordinated by organic moieties where the organic moieties are metal ligands or solvent molecules (including any non-aqueous solvent molecules), or mixtures of both. In certain exemplary embodiments, the organometallic compounds have a central core comprising a group VIII metal species and an alkaline earth metal species in a ratio from about 5:1 to about 1:5. More preferably, the central core comprises a group VIII-to-alkaline earth metal ratio of from about 1:2 to about 2:1, and even more preferably the ratio is 1:1. In other exemplary embodiments, the organometallic compounds are represented by a molecular structure [(CN)₄AB(DMF)_n], where n is from about 1 to about 4. Any group VIII metal is suitable as A and any alkaline earth metal is suitable as B. Preferably, A is selected from Ni, Pd, Pt or a mixture thereof and B is selected from Sr, Ba or a mixture thereof.

[0025] In certain embodiments the pre-catalyst impregnating liquid optionally contains metal ligands. To be useful, the metal ligands should be capable of simultaneously complexing with or coordinating to more than one metal species and should be capable of forming bridging arrangements or structures with two or more individual metal species. The metal ligands are either negatively charged, or have a molecular structure that provides a source of readily available valence electrons so that the ligands can simultaneously coordinate, via dative bonding, to both a group VIII metal species and an alkaline earth metal species that are present in the pre-catalyst impregnating liquid. Many non-aqueous solvent molecules have a molecular structure that provides a source of readily available valence electrons (for example, DMF, THF, and DME). Therefore, these types of solvent molecules can also act as metal ligands in this respect. With the ability to simultaneously coordinate to two metal species, these types of metal ligands can form bridging molecular structures with two or more metal species. Suitable metal ligands include but are not limited to CN^Cl^, _Br ⁽-⁾ _} j<-⁾ _{} N0} N}o₂, NO₃/^2"5, CO, and salts thereof.

Impregnation of Inorganic Oxide Support

[0026] Impregnating the inorganic oxide support with pre-catalyst impregnating liquid is process known as loading. This is done by combining a suitable amount of inorganic oxide support (in any of the forms previously mentioned) with a suitable amount of pre-catalyst impregnating liquid, mixing these together using mechanical means (i.e.: stirring, shaking, or sonication) or mixing these together without mechanical means (i.e.: soaking) to coat or saturate the inorganic oxide support with the pre-catalyst impregnating liquid. Excess impregnating liquid is removed by any of the techniques known to those skilled in the art including, for example, evaporating away non-aqueous solvent; decanting, draining or siphoning away excess pre-catalyst impregnating liquid; or filtering out the impregnated inorganic oxide support solids. Alternatively, pre-catalyst impregnating liquid may be deposited on or dripped onto the inorganic oxide support (in any of the forms herein mentioned). The extent of loading determines how much bimetallic catalyst forms on the inorganic oxide support, after calcination is carried out in a reducing atmosphere. One skilled in the art will undersand how the amounts and concentrations of metal salts or organometallic compounds present in the pre-catalyst impregnating liquids can be varied and how the ratio of pre-catalyst impregnating liquid to inorganic oxide support can be varied to either increase or decrease the amount of loading achieved. For example, higher loading can be achieved by using a more highly concentrated pre-catalyst impregnating liquid or by repeatedly loading an inorganic oxide substrate with additional impregnating liquid. [0027] The inorganic oxide support described in the present invention has many characteristics. The inorganic oxide support absorbs the pre-catalyst impregnating liquid, which contains the non-aqueous solvent and the various group VIII and alkaline earth metal species. Therefore, suitable inorganic oxides are insoluble in the non-aqueous solvents that are used. Suitable inorganic oxide supports are also thermally and chemically stable at the temperatures and reaction conditions experienced during the calcination step, which is carried out to form the bimetallic catalyst. The inorganic oxide support should also provide acceptable surface area, so the bimetallic catalyst species sufficiently deposits and disperses in order to exhibit effective catalytic properties. Finally, the inorganic oxide support should be both chemically and thermally stable at temperatures and reaction conditions experienced during the various catalytic conversion reactions that the bimetallic catalysts are used in. Suitable inorganic oxide supports include, but are not limited to, titanium oxide, silica, alumina, and magnesia.

Calcination

[0028] To produce the bimetallic catalysts, an inorganic oxide substrate is loaded with a suitable amount of pre-catalyst impregnating liquid containing a non-aqueous solvent and either oxygen-free salts of group VIII metals and alkaline earth metals or group VDI/alkalme earth bimetallic organometallic compounds, and optionally metal ligands. The loaded substrate then undergoes a calcination step in a reducing atmosphere. A material is calcinated by heating to high temperature, but below its melting point or fusing point, to cause a loss of moisture and a reduction. This occurs in the present invention when the inorganic oxide support that is impregnated with impregnating liquid and loaded with group VIII and alkaline earth metal species is heated in a hydrogen atmosphere. At the elevated temperatures, volatile components (including any metal ligands or non-aqueous solvent molecules that are present) are evaporated, leaving behind the metal species to undergo reduction in the hydrogen atmosphere. In one exemplary embodiment, an inorganic substrate loaded with a pre-catalyst impregnating liquid is placed in an oven, flushed with inert gas (i.e.: N₂ or He), and backfilled with a reducing atmosphere of H₂ gas. As a stream of H₂ gas is continually applied, the furnace temperature is increased from ambient temperature to a final temperature of about 250 °C to about 350 °C. The high temperature is maintained for a sufficient time to drive off volatile components and to reduce the absorbed metal species to convert them into the bimetallic catalyst. Metal Segregation

[0029] Without intending to be bound, we believe the bimetallic catalysts contemplated form unique morphological structures, where the different types of metal species present may segregate and aggregate into separate phases or domains so that any single domain may only contain one type of metal. We also believe the individual domains may overlap with one another or contain defined boundaries and that, furthermore, in certain situations individual domains of the same type of metal may coalesce to form regions, films, or particles. Therefore, we contemplate embodiments of bimetallic catalysts with morphologies where the group VIII metal species are aggregated together into discrete particles that are highly dispersed on the substrate and where the alkaline earth metal species are aggregated together into discrete particles or uniform films that are highly dispersed on the substrate. It is also contemplated that in certain embodiments both group VIII metal particles and alkaline earth metal particles/films may uniformly cover the surface of the inorganic oxide support. Contemplated herein are particles of group VIII metals and alkaline earth metals having any geometrical shapes or sizes ranging from nanometers to hundreds of nanometers. We also contemplate embodiments where particles of group VIII metal species preferably have approximate diameters of from about 8 nm to about 12 nm and where particles of alkaline earth metal species preferably have approximate diameters of from about 15 nm to about 90 nm.

Methods for De-halogenating Hydrocarbons

[0030] Methods for de-halogenating hydrocarbons described herein involve removing halogen atoms from halogen-containing hydrocarbons. The methods comprise contacting a vapor of a halogen-containing hydrocarbon with any of the bimetallic catalyst compositions herein described in a reducing atmosphere. Suitable bimetallic catalysts are prepared using any of the methods herein described, which involves calcinating in a reducing atmosphere an inorganic oxide support impregnated with a pre-catalyst impregnating liquid. Methods for de-halogenating hydrocarbons which are contemplated include, but are not limited to, de- halogenation of hydrocarbons that are either singly substituted or multiply substituted with halogen atoms. In certain exemplary embodiments, the methods include de-halogenating chlorinated or brominated hydrocarbons or a mixture thereof, wherein the hydrocarbon species is single or multiply substituted with either chlorine or bromine atoms; or wherein the hydrocarbon species is multiply substituted with a mixture of both chlorine and bromine atoms. Preferably, these methods involve dehalogenating chlorobenzene (CB) and 1,2- dichlorobenzene (DCB).

Examples

Starting Materials

[0031] All manipulations were carried out on a standard high vacuum line or in a drybox under an atmosphere of dry, pure N₂ or Ar. DMF (Baker) is stirred over pretreated 4 A molecular sieves for 4-5 days in a Pyrex flask, then degassed under vacuum. The DMF is degassed a second time under vacuum and then distilled. K₂PSIi(CN)₄] *H₂O (Strem) is dried under vacuum at 150 °C for 16 h and stored in the drybox. K₂[Pd(CN)₄]OH₂O (Aldrich) is dried under vacuum at 200 °C for 0.5 h and stored in the drybox. K₂[Pt(CN)₄] (Strem) is dried under vacuum 8-10 h and, stored in the drybox. KCN (Strem), NiCl₂ (Strem), PdCl₂ (Aldrich), PtCl₂ (Strem), BaCl₂ (Strem) and SrCl₂ (Strem) are used as received.

Precursor Synthesis

[0032] The synthesis of group VΪII metal/alkaline earth metal organometallic compounds has been previously described. For example, the synthesis of [(DMF)₄Sr- Pd(CN)₄] is disclosed in Aaron M. Rath Master's thesis entitled "Study of Zirconocene Organoborane Complexes for Homogeneous Catalysis and (Pd-Ln) -Bimetallic Precursors for Heterogeneous Catalysis" (The Ohio State University - Department of Chemistry, 1999). Two different procedures (Scheme 1 and 2) for synthesizing group VIII metal/alkaline earth metal organometallic compounds are described below and either procedure can be used to product the exemplary organometallic compounds (Structures 1-6) that were used to produce the example bimetallic catalysts described herein.

[0033] Scheme (1): A 1 : 1 ratio of starting materials, BCl₂ (where B = Ba or Sr) (0.5 mmol) and K₂[A(CN)₄] (where A = Ni, Pd or Pt) (0.5 mmol) were placed into a 50 mL reaction flask in a drybox, and about 10 mL of DMF was added to the flask. The mixture was stirred at room temperature over one week. The resulting solution was filtered and a white precipitate (KCl) removed. DMF was then vacuum pumped away until a viscous oil remained. X-ray quality crystals were formed after 24 h at room temperature. Yields of approximately 85% were obtained. B = Sr, and Ba; A = Pd, Pt, and Ni; n = 3 or 4.

[0034] Scheme (2): A 1 : 1 :4 ratio of starting materials, BCl₂ (where B= Ba or Sr) (0.5 mrnol), ACl₂ (where A = Ni, Pd or Pt) (0.5 mmol) and KCN (2.0 mmol) were placed into a 50 mL reaction flask in a drybox, and about 15 mL of DMF was added to the flask. The mixture was stirred at room temperature over about two weeks. The resulting solution was filtered and a white precipitate (KCl) removed. DMF was then vacuum pumped away until a viscous oil remained. X-ray quality crystals were formed after 24 h at room temperature. Yields of approximately 85% were obtained. B = Sr, and Ba; A = Pd, Pt, and Ni; n = 3 or 4.

Precursor Characterization

[0035] Analytical data for the entire series of structures 1-6 is provided in TABLE 1 below. Elemental analysis was conducted using standard methods and techniques. Single crystal X-ray diffraction data were collected using graphite monochromated Mo-Ka radiation (λ= 0.71073 A) on an Enraf-Nonius Kappa CCD diffraction system. Single crystals of the organometallic compounds (structures 1-4) were mounted on the tip of a glass fiber coated with Fomblin oil (a pentafluoropolyether) and crystallographic data were collected at 150 K. Unit cell parameters were obtained by indexing the peaks from the first 10 frames and refining employing the whole data set. AU frames were integrated and corrected for Lorentz and polarization effects using Denzo-SMN package (Nonius BV, 1999). An absorption correction was applied using the SORTAV program provided by MaXus software. The structure was solved by direct methods and refining using the SHELXTL-97 (difference electron density calculation, full matrix least-squares refinements). All non-hydrogen atoms were located and refined anisotropically. Single-crystal X-ray diffraction analysis indicated that structures 1, 2 and 4, form one-dimensional "ladder-like" structures through iso-cyanide linkages. For structure 3, single-crystal X-ray diffraction analysis confirmed that there were only bridging cyanides present in the molecule, which indicated structure 3 forms a 2- dimensional "sheet-like" structure.

TABLE 1: Analytical Date for Organometallic Compounds (Structures 1-6)

Impregnation and Substrate Loading

[0036] A typical procedure is now provided for preparing a pre-catalyst impregnating liquid and for loading the impregnating liquid onto a inorganic oxide support. This procedure can be used to prepare pre-catalyst impregnating liquids for any of the structures 1-6 described herein. In a single flask the appropriate organometallic compound is mixed with and dissolved in excess DMF. To this mix is added silica. Although DMF is present in excess, the amount and ratio of organometallic compound to silica is selected so that the desired level of loading is achieved. After stirring for 1 hour at room temperature, excess DMP is removed by applying a vacuum at room temperature. After a period of 12 hours all the DMF is removed and a white solid is left behind.

Catalyst Synthesis [0037] A typical procedure is now provided for calcinating an inorganic oxide support loaded with pre-catalyst impregnating liquid as described above, in order to form the bimetallic catalyst described herein. This procedure can be used to prepare any of the bimetallic catalysts described herein. Under ambient atmospheric conditions, the white solid described above is collected and placed into a quartz boat. The quartz boat is then put into a furnace, which is flushed with N₂ for 10 minutes and then flushed again for an additional 10 minutes with H₂. Then, as a steady stream of H₂ gas is applied, the temperature of the furnace is increased in increments of about 25 °C every 10 minutes until a final temperature of about 350 "C is reached. The approximately 350 ⁰C temperature is maintained for about 2 hours as the white solid undergoes calcination and is converted into a bimetallic catalyst. The furnace is then cooled to room temperature while being flushed with He gas. The newly formed bimetallic catalyst, in powdered form, is passivated by passing a flow of a gas mixture consisting of 1% v/v O₂ in He over the sample at room temperature for about 30 minutes.

[0038] Example 1: PdBa/SiO₂ supported bimetallic catalyst: PdBa/SiO₂ is made in the following manner. Silica is loaded with a pre-catalyst impregnating liquid containing DMF and the organometallic compound Structure 3 [(CN)₄PdBa(DMF)₃] according to the typical procedure outlined above, and is calcinated in a reducing atmosphere of H₂ gas according to the typical procedure outlined above.

[0039] Example 2: PdSiVSiO₂ supported bimetallic catalyst: PdSr/SiO₂ is made in the following manner. Silica is loaded with a pre-catalyst impregnating liquid comprising DMF and the organometallic compound Structure 4 [(CN)₄PdSr(DMF)₃] according to the typical procedure outlined above, and is calcinated in a reducing atmosphere of H₂ gas according to the typical procedure outlined above.

[0040] Comparative Example: Pd/SiO₂: Monometallic PdVSiO₂ is made in the following manner. Silica is loaded with a pre-catalyst impregnating liquid comprising DMF and Pd(C₂H₃O₂)₂ according to the typical procedure outlined above, and is calcinated in a reducing atmosphere of H₂ gas according to the typical procedure outlined above.

Catalyst Characterization [0041] Transmission electron microscopy (TEM) analysis of the exemplary bimetallic catalysts prepared above was conducted using a JEOL-2000 TEM/STEM microscope equipped with a UTW energy dispersive x-ray (EDX) detector (Oxford Instruments) operated at an accelerating voltage of 200 kV. TEM specimens of the exemplary bimetallic catalysts were prepared by ultrasonically dispersing the powdered form of the exemplary bimetallic catalysts in 2-butanol and then evaporating a drop of the resulting suspension onto a holey carbon support grid. Mean Pd particle diameters were measured and are quoted as a surface area-weighted diameter (d_s ) where: d_s and where ra,- is the number of

particles of diameter J₁- and V n. > 600- TEM-EDX elemental composition analysis was

conducted, which is known to be accurate to within ± 0.1 atom %.

[0042] X-ray powder diffraction (XRD) analysis of the exemplary bimetallic catalysts prepared above was collected on a Bruker D8 Advance X-ray powder diffractometer (Cu Ka radiation). Before undergoing diffraction, the samples of the exemplary bimetallic catalysts were subjected to another reductive cycle in an H₂ atmosphere at 300 °C, then loaded in 0.5 mm Lindeman glass capillaries in a glove box, and then sealed.

[0043] X-ray photoelectron spectroscopic (XPS) analyses of the exemplary bimetallic catalysts prepared above were conducted using a Kratos Axis Ultra spectrometer with monochromatized Mg Ka radiation (1253.6 eV). A sample of an exemplary bimetallic catalyst was adhered to conducting carbon tape, mounted in a sample holder, and subjected to UHV conditions (~10^"9 torr) overnight prior to analysis. A full range survey (0 - 1000 eV) and high resolution spectra (range of -30 eV) of Pd 3d_3/2/3d₅/₂, Sr 3d_5/2, Ba 3d₅/₂, Si 2p, O Is, Cl 2p_3/2 and C Is was collected. The C Is peak, centered at 284.5 eV, was used as reference to calibrate the binding energy values.

[0044] Results from the TEM analysis and the XRD were used to determine the various diameters for the group VIII metal particles and the alkaline earth metal particles which formed in preparation of the bimetallic catalysts. These results are shown in TABLE 2. The results obtained by XRD correlated with the results obtained by TEM analysis within an acceptable statistical error. [0045] As shown in TABLE 2, results of TEM analysis of the PdBaZSiO₂ bimetallic catalyst prepared in Example 1 indicate that Pd metal species in this exemplary catalyst composition are present as discrete particles with a diameter of about 12 nm and are highly dispersed on the SiO₂ substrate. Results of TEM analysis also indicate that Ba metal species in Example 1 are likewise present as discrete particles, but with diameters ranging from about 15 nm to about 90 nm. Similarly, results of TEM analysis of the PdSr/SiO₂ bimetallic catalyst prepared in Example 2 indicate that Pd metal species in this exemplary catalyst composition are present as discrete particles with a diameter of about 8 nm and are highly dispersed on the SiO₂ substrate. Likewise, results of TEM analysis show the Ba metal species in Example 2 are also present as discrete particles, but with diameters ranging from about 15 nm to about 70 nm. By comparison, results of TEM analysis for the prepared Pd/SiO₂ catalyst indicate that though the Pd metal species in the comparative example are also present as particles, the average diameter for the Pd particles in the comparative example are larger, having a mean diameter of 42 nm and a diameter range of from 2 nm to 50 nm.

[0046] Figure 5 shows a TEM image of the PdBa/SiO₂ bimetallic catalyst prepared in example 1 and is representative of the type of morphology observed for the catalysts herein described. Various areas on the image have been encircled for comparison. Areas labeled "a" and "b" correspond to regions where the larger Ba metal particles reside and these areas have limited Pd metal content. Areas labeled "c" and "d" correspond to regions rich in Pd metal particle population relative to Ba metal content. Elemental Compositional analysis of the different encircled areas are also provided in TABLE 3. Repeated mapping with TEM- EDX, over areas of about 1000-6000 nm² of the sample of PdBa/SiO₂ bimetallic catalyst as prepared in example 1, provided a wide range of Ba/Pd surface ratios (34-0.1). This suggests there is appreciable surface composition heterogeneity in the bimetallic catalyst sample. For both examples 1 and 2, the alkaline earth metals have a wider range of particle diameters than exhibited for the Pd particles. TEM-EDX analysis indicated the surface and number weighted mean Pd size was significantly lower in both the bimetallic samples PdBaZSiO₂ and PdSrZSiO₂ (examples 1 and 2) than it was for the comparative example containing only monometallic PdZSiO₂. This suggests that incorporation of alkaline earth metals into a Pd catalyst composition can aid in catalyst preparation by enhancing the dispersion of Pd particles that form on a substrate as compared to conventional PdZSiO₂ preparation methods.

TABLE 2: Pd, Sr and Ba particle diameters and ranges from TEM and XRD analysis

amean particle size refers to Pd, size range applies to both Pd and Sr, ^csize range applies to both Pd and Ba.

TABLE 3: TEM-EDX Compositional Analysis of PdBa/SiO₂ (encircled areas of Fig. 5)

Measurement of Catalytic Activity

[0047] The effectiveness of a catalyst can be quantified in terms of the fractional dechlorination value (xci)'

where [Cl_org] represents concentration (mol/dm³) of chlorine associated with a feed supply of chlorinated aromatic compound, and [Cl_org]_m and [Cl_org]_OH« refer to the inlet and outlet reactor streams respectively. Therefore, the larger the xa value is for a given catalyst, the better the catalyst is at de-halogenating or converting the chlorinated aromatic feed stock. However, although hydrodechlorination (HDC) refers only to the de-halogenation of chlorine containing hydrcarbons and HDC performance is quantified according to fractional dechlorination values, these experiments were conducted merely to exemplify the effectiveness of various catalyst, and HDC is only one embodiment of the various de-halogenation methods herein contemplated. Therefore, the invention and associated catalysts herein described are not limited merely to catalysts for HDC and methods for HDC. [0048] Before any hydrodechlorination (HDC) reactions were conducted, the bimetallic catalysts used were subjected to another reductive cycle in an H₂ atmosphere at 300 ^°C, in a fixed bed tubular glass reactor (i.d. = 1.25 cm) by heating (10 K min^"1) in a 60 cm³ min^"1 stream of dry H₂ (99.999%). The reduction was monitored using a Humonics (Model 520) flow meter to a final temperature of 300 ^°C that was maintained for 12 hours. This additional reduction is a catalyst activation step and should not to be confused with the calcinations step, where the initial reduction and catalyst formation occurs. The catalytic reactions were conducted in situ (after catalyst activation) with a co-current flow of the selected aromatic feed in H₂. A layer of glass beads above the catalyst bed ensured that the reactants were vaporized and reached reaction temperature before making contact with the catalyst. A Model 100 (kd Scientific) microprocessor controlled infusion pump was used to deliver the aromatic feed, via a glass/teflon air-tight syringe and teflon line at a fixed calibrated flow rate. All HDC reactions were carried out at 150 "C where isothermal operation was ensured by diluting the catalyst bed with ground glass (75 μm). Chlorobenzene (CB, obtained from Aldrich, 99.9% v/v), 1,2-dichlorobenzene (DCB, obtained from Aldrich, 99% v/v) and methanol solvent (obtained from Merck, 99.8% v/v) were used without further purification.

[0049] HDC reactions were monitored at an inlet hourly Cl/Pd mole ratio =

5 xlO³ and a contact time = 0.02 minutes. In a series of control tests, passage of each reactant in a stream of H₂ through the empty reactor, i.e. in the absence of catalyst, did not result in any detectable conversion. The reactor effluent was frozen in a liquid nitrogen trap for subsequent analysis, which was made using a Perkin-Elmer Auto System XL chromatograph equipped with a split/splitless injector and a flame ionization detector, employing a DB-I 50 m x 0.20 mm i.d., 0.33μm capillary column (J&W Scientific). The overall level of HDC was converted to mol % conversion using detailed calibration plots for each feedstock. Quantitative analysis was based on relative peak area with acetone as solvent where analytical repeatability is better than ± 1% and the detection limit typically corresponds to a feedstock conversion less than 0.1 mol %.

Catalytic Activity - Results

[0050] The bimetallic catalysts described herein were used to catalytically promote the HDC of chlorobenzene (CB) and 1,2-dichlorobenzene (DCB). The HDC of CB generated benzene as the primary product, while the HDC of DCB generated both benzene and also CB as an intermediate product. HDC performance was quantified in terms of fractional dechlorination (xa), where a larger value for xa indicated an enhanced catalytic performance or activity. Reactions were repeated with different samples from the same batch of catalysts and delivered raw data reproducibility that was better than ±5 %. HDC of both CB and DCB yielded trace amounts of cyclohexane (< 0.1% mol/mol).

[0051] Figure 6 shows a graph of the results for fractional dechlorination (xci) of CB as a function of time-on-stream using the exemplary catalysts prepared in Example 1 (PdBa/SiO₂ (A)); Example 2 (PdSr/SiO₂ (•)); and using the Comparative Example (PdZSiO₂ (■)) as a control. Figure 7 shows a graph of the results for fractional dechlorination (xo) of DCB as a function of time-on-stream using the exemplary catalysts prepared in Example 1 (PdBa/SiO₂ (A)); Example 2 (PdSr/SiO₂ (•)); and using the Comparative Example (Pd/SiO₂ (■)) as a control. With CB as the feedstock, both bimetallic catalysts PdBaZSiO₂ and PdSrZSiO₂ (as prepared in Examples 1 and 2) had fractional dechlorination (xa) activities that were an order of magnitude higher than the fractional dechlorination (xa) activity seen with PdZSiO₂ (the control catalyst). Furthermore, the enhancement in fractional dechlorination (xa) activity increased to close to two orders of magnitude for the case where the feedstock used was DCB. In separate control experiments, HDC of CB with SrZSiO₂ and HDC of CB with BaZSiO₂ were . attempted under similar reaction conditions but yielded no measureable conversion.

[0052] For every example catalyst prepared and for every exemplary catalytic reaction conducted, a temporal drop in the level of HDC was observed. This temporal drop can be expressed in terms of an empirical relationship:

(x_o - x₀) _ At

(*18* - *θ) (β + to) '

where xisn represents the fractional conversion after 18 hours and β represents a time scale fitting parameter. Conducting fit convergence of the experimental data in accordance with this empirical relationship yields a calculated value for XQ (the initial fractional HDC). The result of the fit convergence calculation and the values obtained for xo for the various exemplary catalysts tested and described herein are shown in TABLE 4. TABLE 4: Initial fractional dechlorination (xø); ratio of initial fractional dechlorination to 18 hr on-stream (xolxwfc and initial specific dechlorination rate (ro, molci h^"1 m^"2).

[0053] The results obtained for fractional dechlorination as shown in Figures 6-7, and the results of the calculations as shown in TABLE 3 indicate that with the control catalyst (Pd/SiO₂), HDC of CB exceeds HDC of DCB under identical conditions. However, this is not the case for both PdBaZSiO₂ and PdSr/SiO₂ (Examples 1-2). Surprisingly, catalytic reactivity for both these exemplary bimetallic catalysts towards CB versus DCB is not as different as is seen with Pd/SiO₂. This indicates that these bimetallic catalysts exhibit a high HDC efficiency. Also, the ratio of initial to final fractional HDC (xolxish) for both PdBaZSiO₂ and PdSrZSiO₂ is lower than it is for PdZSiO₂, indicating that these bimetallic catalysts are less susceptible to deactivation compared to monometallic catalysts like PdZSiO₂, and they also appear to retain higher fractional HDC with time-on-stream than does PdZSiO₂.

[0054] While the present invention has been illustrated by the description of embodiments thereof, and the embodiments have been described in some detail, it is not the intention of the applicant to restrict or limit the scope of the appended claims to such detail. Additional advantages and modifications will appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made without departing from the spirit or scope of the general inventive concept.

Claims

What is claimed:

1) A catalyst comprising the reaction product obtained by calcinating in a reducing atmosphere an inorganic oxide support impregnated with a pre-catalyst impregnating liquid comprising: a. a non-aqueous solvent; b. a group VIII metal; and c. an alkaline earth metal.

2) The catalyst of claim 1, wherein the group VIII metal and the alkaline earth metal are present in the pre-catalyst impregnating liquid in the form of oxygen-free salts.

3) The catalyst of claim 1, wherein the group VIII metal and the alkaline earth metal are present in the pre-catalyst impregnating liquid in the form of at least one organometallic compound.

4) The catalyst of claim 3, wherein the group VIU metal and the alkaline earth metal are present in the same organometallic compound.

5) The catalyst of claim 1, wherein the group VIII metal is selected from Ni, Pd, Pt or a mixture thereof; and the alkaline earth metal is selected from Sr, Ba or a mixture thereof.

6) The catalyst of claim 1, wherein the inorganic oxide support is selected from titania, silica, alumina, or magnesia.

7) The catalyst of claim 1, wherein the non-aqueous solvent is selected from dimethlyformamide, dimethoxyethane, dimethlysulfoxide or a mixture thereof.

8) The catalyst of claim 1, wherein the pre-catalyst impregnating liquid further comprises a metal ligand, the metal ligand capable of coordinating to both the group VIII metal and the alkaline earth metal to form a bridging structure.

9) The catalyst of claim 8, wherein the metal ligand is CN^".

10) The catalyst of claim 4, wherein the organometallic compound further comprises a repeat unit structure having a molecular formula: [(CN)₄AB(DMF)_n], wherein; a. A is a group VIII metal selected from Ni, Pd, or Pt; and b. B is an alkaline earth metal selected from Sr or Ba.

11) The catalyst of any of previous claims 1-10, wherein: a. the group VIII metal is aggregated into discrete particles; and b. the alkaline earth metal is aggregated into discrete particles; and wherein the discrete particles of group VIII metal and the discrete particles of alkaline earth metal are distributed on the surface of the inorganic oxide support.

12) The catalyst of claim 11, wherein the discrete particles of the group VIII metal have a mean diameter from about 8 nm to about 12 nm; and the discrete particles of the alkaline earth metal have a diameter from about 15 nm to about 90 nm.

13) A method for making a catalyst comprising calcinating in a reducing atmosphere an inorganic oxide support impregnated with a pre-catalyst impregnating liquid composition comprising: a. a non-aqueous solvent; b. a group VIII metal present in the form of an oxygen-free salt; and c. an alkaline earth metal present in the form of an oxygen-free salt.

14) The method of claim 13, wherein the group VITl metal and the alkaline earth metal are present in the pre-catalyst impregnating liquid in the form of at least one organometallic compound.

15) The method of claim 14, wherein the organometallic compound comprises a repeat unit having the molecular formula: [(CN)₄A-B(DMF)_n], wherein; a. A is a group VIII metal selected from Ni, Pd, or Pt; and b. B is an alkaline earth metal selected from Sr or Ba.

16) The method of either claim 13, wherein the group VIII metal is selected from Ni, Pd, Pt or a mixture thereof and the alkaline earth metal is selected from Sr, Ba or a mixture thereof.

17) The method of claim 16, wherein the inorganic oxide support is selected from titania, silica, alumina, or magnesia. 18) The method of claim 17, wherein and the non-aqueous solvent is selected from dimethlyformamide, dimethoxyethane, dimethlysulfoxide or a mixture thereof.

19) The method of claim 13, wherein the pre-catalyst impregnating liquid further comprises a metal ligand, the metal ligand capable of coordinating to both the group VIII metal and the alkaline earth metal to form a bridging structure.

20) A method for de-halogenating halogenated hydrocarbons comprising: contacting a vapor of halogenated hydrocarbons with the catalyst of any of the previous claims 1- 10 in a reducing atmosphere.

21) The method of claim 20, wherein the halogenated hydrocarbons are chlorinated hydrocarbons or brominated hydrocarbons or a mixture thereof.