Patent Description:
Heterogeneous catalysts having noble metals supported on silica in combination with alumina and other elements are known, see e.g. U. Pat No. <CIT>. However, there is a need for additional catalyst particles with improved properties.

The present invention is directed to a heterogeneous catalyst comprising a support and gold, wherein: (i) said support comprises silica and <NUM> to <NUM> wt% titanium, (ii) said catalyst comprises from <NUM> to <NUM> wt% of gold, and from <NUM> to <NUM> wt. % of magnesium, and from <NUM> to <NUM> wt. % of at least one of cobalt or zinc, and (iii) particles of the catalyst have an average diameter from <NUM> microns to <NUM>; wherein weight percentages are based on weight of the catalyst, and wherein the average diameter is the arithmetic mean of all possible diameters.

The present invention is further directed to a method for preparing methyl methacrylate from methacrolein and methanol; said method comprising contacting a mixture comprising methacrolein, methanol and oxygen with a catalyst bed comprising particles of the heterogeneous catalyst.

All percentage compositions are weight percentages (wt%), and all temperatures are in °C, unless otherwise indicated. A "metal" is an element in groups <NUM> through <NUM> of the periodic table, excluding hydrogen, plus aluminum, gallium, indium, thallium, tin, lead and bismuth. "Titania" is titanium dioxide. Preferably, titanium is present as titania. The "catalyst center" is the centroid of the catalyst particle, i.e., the mean position of all points in all coordinate directions. A diameter is any linear dimension passing through the catalyst center and the average diameter is the arithmetic mean of all possible diameters. The aspect ratio is the ratio of the longest to the shortest diameters.

Preferably the support has a surface area greater than <NUM><NUM>/g, preferably greater than <NUM><NUM>/g, preferably greater than <NUM><NUM>/g, preferably greater than <NUM><NUM>/g, preferably greater than <NUM><NUM>/g. In portions of the catalyst which comprise little or no gold, the support may have a surface area of less than <NUM><NUM>/g, preferably less than <NUM><NUM>/g.

According to the presently claimed invention, the catalyst particle which comprises silica comprises at least <NUM> wt% titanium, preferably at least <NUM> wt%, preferably at least <NUM> wt%, preferably at least <NUM> wt%; preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%. Preferably, the catalyst particle is a silica particle comprising the aforementioned amounts of titanium. Preferably, the catalyst particle comprising titanum comprises from <NUM> to <NUM> wt% titanium; preferably at least <NUM> wt%, preferably at least <NUM> wt%, preferably at least <NUM> wt%. A catalyst support may also comprise alumina, magnesia, zirconia, boria, thoria, or mixtures thereof.

Preferably, the aspect ratio of the catalyst particle is no more than <NUM>:<NUM>, preferably no more than <NUM>:<NUM>, preferably no more than <NUM>:<NUM>, preferably no more than <NUM>:<NUM>, preferably no more than <NUM>:<NUM>, preferably no more than <NUM>:<NUM>. Preferred shapes for the particle include spheres, cylinders, rectangular solids, rings, multi-lobed shapes (e.g., cloverleaf cross section), shapes having multiple holes and "wagon wheels," preferably spheres. Irregular shapes may also be used.

Preferably, at least <NUM> wt% of the gold is in the outer <NUM>% of catalyst volume (i.e., the volume of an average catalyst particle), preferably in the outer <NUM>%, preferably in the outer <NUM>%, preferably the outer <NUM>%, preferably the outer <NUM>%. Preferably, the outer volume of any particle shape is calculated for a volume having a constant distance from its inner surface to its outer surface (the surface of the particle), measured along a line perpendicular to the outer surface. For example, for a spherical particle the outer x% of volume is a spherical shell whose outer surface is the surface of the particle and whose volume is x% of the volume of the entire sphere. Preferably, at least <NUM> wt% of the gold is in the outer volume of the catalyst, preferably at least <NUM> wt%, preferably at least <NUM> wt%. Preferably, at least <NUM> wt% (preferably at least <NUM> wt%, preferably at least <NUM> wt%, preferably at least <NUM> wt%) of the gold is within a distance from the surface that is no more than <NUM>% of the catalyst diameter, preferably no more than <NUM>%, preferably no more than <NUM>%, preferably no more than <NUM>%. Distance from the surface is measured along a line which is perpendicular to the surface.

Preferably, the average diameter of the catalyst particle is at least <NUM> microns, preferably at least <NUM> microns, preferably at least <NUM> microns, preferably at least <NUM> microns, preferably at least <NUM> microns, preferably at least <NUM> microns; preferably no more than <NUM>, preferably no more than <NUM>, preferably no more than <NUM>. The average diameter of the support and the average diameter of the final catalyst particle are not significantly different.

Preferably, the amount of gold as a percentage of the catalyst (gold and the support) is from <NUM> to <NUM> wt%, preferably at least <NUM> wt%, preferably at least <NUM> wt%, preferably at least <NUM> wt%, preferably at least <NUM> wt%; preferably no more than <NUM> wt%, preferably no more than <NUM> wt%, preferably no more than <NUM> wt%. According to the presently claimed invention, the catalyst comprises magnesium as third element. The catalyst comprises from <NUM> to <NUM> wt% of magnesium, preferably at least <NUM> wt%, preferably <NUM> wt%; preferably no more than <NUM> wt%, preferably no more than <NUM> wt%. The catalyst comprises, in addition to the third element, at least one fourth element selected from cobalt and zinc. The catalyst comprises from <NUM> to <NUM> wt% of fourth elements, preferably at least <NUM> wt%, preferably <NUM> wt%; preferably no more than <NUM> wt%, preferably no more than <NUM> wt%.

Titanium may be added to an existing silica support, or a cogel of silica and a titanium compound could be formed. In the case of adding titanium to an existing silica support, the titanium may be in the form of a salt placed in an aqueous solution. Preferably, the solution contains an acid such as nitric acid, sulfuric acid, hydrochloric acid, acetic acid or others. Preferably, the solution contains a sulfur-containing acid, e.g., thiomalic acid, preferably a carboxylic acid, e.g., citric or oxalic acid as well. Preferably, the sulfur-containing acid is present in a concentration of <NUM> to <NUM> wt% (preferably <NUM> to <NUM>%). Preferably, the carboxylic acid is present in an amount from <NUM> to <NUM> wt% (preferably <NUM> to <NUM> wt%). Preferably, the weight ratio of sulfur to acid is <NUM>: <NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. Preferably, the support is washed with ammonium hydroxide prior to addition of gold precursor, preferably to remove chloride content to a level below <NUM> ppm in the bulk support, preferably below <NUM> ppm. The titanium compound may be in any form in which it subsequently will be precipitated onto the silica and preferably substantially converted to a titanium oxide, preferably titania (titanium dioxide) upon calcination. Suitable titanium compounds include, but are not limited to, nitrates, sulfates, oxyalates, alkyl titantates, and halides. Preferred titanium compounds are water-soluble, or if insoluble dissolved in an aqueous solution of acid in order to achieve solubility. Other titanium complexes that are water-soluble may also be utilized, such as dihydroxy bis(ammonium lactato)titanium(IV). Titanium compounds that dissolve in organic liquids such as alcohols could also be used, e.g., alkoxides. The titanium to silicon weight ratio is preferably <NUM> to 15wt% titanium. Preferably, the support is produced by precipitating on a silica particle an aluminum salt. Preferably, the resulting material is then treated by calcination, reduction, or other treatments known to those skilled in the art to decompose the metal salts into metals or metal oxides. Preferably, the gold is precipitated from an aqueous solution of metal salts in the presence of the support. Preferred gold salts include tetrachloroauric acid, sodium aurothiosulfate, sodium aurothiomalate and gold hydroxide. In one preferred embodiment, the support is produced by an incipient wetness technique in which an aqueous solution of a titanium precursor salt is added to a silica particle such that the pores are filled with the solution and the water is then removed by drying. Preferably, the resulting material is then treated by calcination, reduction, or other treatments known to those skilled in the art to decompose the metal salts into metals or metal oxides. Preferably, gold is added to titania or a titanium-modified silica support by incipient wetness, followed by drying, and preferably by calcination.

Calcinations preferably are carried out at a temperature from <NUM> to <NUM>; preferably at least <NUM>, preferably no more than <NUM>. Preferably, the temperature is increased in a stepwise or continuous fashion to the ultimate calcination temperature.

In another preferred embodiment, the catalyst is produced by deposition precipitation in which a porous silica comprising titanium is immersed in an aqueous solution containing a suitable gold precursor salt and that salt is then made to interact with the surface of the inorganic oxide by adjusting the pH of the solution. The resulting treated solid is then recovered (e.g. by filtration) and then converted into a finished catalyst by calcination, reduction, or other treatments known to those skilled in the art to decompose the gold salts into metals or metal oxides.

The catalyst of this invention is useful in a process for producing methyl methacrylate (MMA) which comprises treating methacrolein with methanol in an oxidative esterification reactor (OER) containing a catalyst bed. The catalyst bed comprises the catalyst particles and is situated within the OER that fluid flow may occur through the catalyst bed. The catalyst particles in the catalyst bed typically are held in place by solid walls and by screens. In some configurations, the screens are on opposite ends of the catalyst bed and the solid walls are on the side(s), although in some configurations the catalyst bed may be enclosed entirely by screens. Preferred shapes for the catalyst bed include a cylinder, a rectangular solid and a cylindrical shell; preferably a cylinder. The OER further comprises a liquid phase comprising methacrolein, methanol and MMA and a gaseous phase comprising oxygen. The liquid phase may further comprise byproducts, e.g., methacrolein dimethyl acetal (MDA) and methyl isobutyrate (MIB). Preferably, the liquid phase is at a temperature from <NUM> to <NUM>; preferably at least <NUM>, preferably at least <NUM>; preferably no more than <NUM>, preferably no more than <NUM>. Preferably, the catalyst bed is at a pressure from <NUM> to <NUM> psig (<NUM> to <NUM> kPa); preferably no more than <NUM> kPa, preferably no more than <NUM> kPa. Preferably, pH in the catalyst bed is from <NUM> to <NUM>; preferably at least <NUM>, preferably at least <NUM>; preferably no greater than <NUM>, preferably no greater than <NUM>, preferably no greater than <NUM>, preferably no greater than <NUM>, preferably no greater than <NUM>. Preferably, the catalyst bed is in a tubular continuous reactor.

The OER typically produces MMA, along with methacrylic acid and unreacted methanol. Preferably, methanol and methacrolein are fed to the reactor containing the fixed bed in a methanol:methacrolein molar ratio from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>, preferably from <NUM>:<NUM> to <NUM>:<NUM>. Preferably, the fixed bed further comprises inert materials. Preferred inert materials include, e.g., alumina, clay, glass, silica carbide and quartz. Preferably the inert materials are in the size range for the catalyst or smaller. Preferably, the reaction products are fed to a methanol recovery distillation column which provides an overhead stream rich in methanol and methacrolein; preferably this stream is recycled back to the OER. The bottoms stream from the methanol recovery distillation column comprises MMA, MDA, methacrylic acid, salts and water. In one embodiment of the invention, MDA is hydrolyzed in a medium comprising MMA, MDA, methacrylic acid, salts and water. MDA may be hydrolyzed in the bottoms stream from a methanol recovery distillation column; said stream comprising MMA, MDA, methacrylic acid, salts and water. In another embodiment, MDA is hydrolyzed in an organic phase separated from the methanol recovery bottoms stream. It may be necessary to add water to the organic phase to ensure that there is sufficient water for the MDA hydrolysis; these amounts may be determined easily from the composition of the organic phase. The product of the MDA hydrolysis reactor is phase separated and the organic phase passes through one or more distillation columns to produce MMA product and light and/or heavy byproducts.

A feed consisting of <NUM> wt% methacrolein, <NUM> ppm inhibitor, and a balance of methanol was fed at a rate of <NUM>/hr to a <NUM>/<NUM>" (<NUM>) stainless steel tubular reactor containing a short front section of borosilicate glass beads followed by <NUM> of catalyst. Catalyst #<NUM> was utilized. A gas containing <NUM>% oxygen in nitrogen was also feed to the reactor at a rate sufficient to obtain <NUM>% O<NUM> in the vent. The reactor was operated at <NUM> and 160psig (<NUM> kPa). The product of the reactor was sent to a liquid-vapor separator and the vapor was sent to a condenser with liquid return and non-condensable gases going to the vent. Results are described in the below table.

Catalyst #<NUM> was prepared by the incipient wetness technique using <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> support as the starting material and adding titanium to the support material. Specifically <NUM> of titanium isopropoxide along with <NUM> of glacial acetic acid were added in very small droplets to the catalyst in rotating equipment to ensure even distribution of the solution to the support material. The solution was at <NUM> when added. The modified support material was then dried under slight vacuum at <NUM> for 4hrs and then calcined in air at ambient pressure by ramping the temperature at <NUM> per minute from ambient to <NUM>, held for <NUM> hr and then ramped at <NUM> per minute up to <NUM> and held for <NUM> hr, then ramped at <NUM> per minute to <NUM> and held for 1hr and finally ramped at <NUM> per minute to <NUM> and held for 4hrs. Gold was then added to the support by incipient wetness technique utilizing <NUM> of sodium aurothiosulfate in <NUM> of deionized water at <NUM>. The resulting catalyst was dried and calcined in air using the same heating profile as above. Analysis with a scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS) of the catalyst clearly indicates that an eggshell deposition of both Ti and Au exists with the Au preferentially located only where Ti was deposited. The Ti and Au eggshell thickness was found to be approximately 50microns or less. With an estimated loading of 10mol% in the outer 50microns of the <NUM> diameter catalyst, the local loading of titanium is estimated as up to 40mol% as Ti/(Ti+Si).

A feed solution of <NUM> was prepared comprising 10wt% methacrolein, 200ppm inhibitor and a balance of methanol, and placed in a <NUM> Parr@ reactor which served as a gas disengagement vessel. The vessel liquid was maintained at a temperature of approximately <NUM>. The liquid feed was pumped at <NUM>/min from the gas-disengagement vessel into the bottom of the vertically-oriented fixed bed reactor. Air and nitrogen gas was mixed to obtain <NUM>. 8mol% oxygen and mixed with the liquid feed prior to entering the fixed bed reactor. The fixed bed reactor was a jacketed ¼" (<NUM>) stainless steel tube maintained at <NUM> using an external heater. The reactor itself was packed with <NUM> glass beads to fill approximately <NUM> inches (<NUM>) of the tube, then catalyst. The remaining void at the top of the reactor was filled with <NUM> glass beads. Liquid and gas exiting the top of the reactor were sent to a condenser and non-condensable gases were vented, while the liquid was recycled back into the gas-disengagement vessel.

Catalyst #<NUM> was prepared by the following steps. First, a support material was prepared by impregnating magnesium nitrate hexahydrate to the incipient wetness point of <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material. The sample was then dried at <NUM> for 1hr, followed by calcination at <NUM> for 4hrs with a ramping rate of <NUM> per minute between different temperature settings. A quantity of <NUM> of titanium isopropoxide and <NUM> of acetic acid were mixed to provide a titanium precursor solution and <NUM> of the titanium precursor solution was then impregnated to the above mentioned calcined Mg-SiO<NUM>. The sample was then dried at <NUM> for 1hr, followed by calcination at <NUM> for 6hrs with a ramping rate of <NUM> per minute between different temperature settings. Gold deposition was achieved by impregnating a solution containing <NUM> of sodium gold thiosulfate and <NUM> of deionized water to the incipient wetness point of <NUM> of the above described support material. The sample was then dried at <NUM> for 1hr followed by calcination at <NUM> for <NUM> hrs. The resulting sample contained a total of <NUM>. 7wt% Mg and 4wt%Ti on Si with <NUM>. 5wt%Au loaded on that material. The sample was not assessed to determine if eggshell deposition existed.

Catalyst #<NUM> was prepared by the following steps. First, a support material was prepared by Clariant Corporation utilizing a titanitium salt on Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material. Gold deposition was achieved by impregnating a solution containing <NUM> of sodium gold thiosulfate and <NUM> of deionized water to the incipient wetness point of <NUM> of the above described support material. The sample was then dried at <NUM> for 1hr followed by calcination at <NUM> for <NUM> hrs.

Catalyst #<NUM> was prepared by incipient wetness of <NUM> sodium gold thiosulfate dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-20C silica support material. The sample was dried at <NUM> for <NUM> hr followed by calcination at <NUM> for <NUM> hr. Gold loading was approximately uniform in the catalyst. This catalyst does not have an egg-shell gold loading.

Catalyst #<NUM> was prepared by incipient wetness of <NUM> of sodium aurothiomalate (I) with <NUM> DI water to make an aqueous solution and then placed on <NUM> titania spheres (Norpro) support material. The sample was dried at <NUM> for <NUM> hr followed by calcination at <NUM> for <NUM> hours with a temperature ramp of <NUM>/min.

Catalyst #<NUM> was prepared by incipient wetness of <NUM> sodium gold thiosulfate dissolved, <NUM> of mercaptosuccinic acid, and <NUM> of citric acid monohydrate in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material which had been previously treated to add approximately <NUM>. 6wt%Ti, present as titanium oxide, to the support material. The catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

The TEM work was done at Dow Chemical using a FEI Themis field emission gun (FEG) transmission electron microscope (TEM). The TEM was operated at an accelerating voltage 200keV. STEM images were collected at <NUM> x <NUM> or <NUM> x <NUM> image size. The Themis has Bruker AXS XFlash energy dispersive x-ray spectrometer (EDS) detector with an energy resolution of 137eV/channel for elemental identification and quantitative analysis.

Catalyst <NUM>, and other STEM images of fresh and aged catalysts have clearly indicated that gold nanoparticles are almost exclusively located in-between or in close proximity to titanium oxide particles which stabilize the gold nanoparticles, significantly decrease or for practical purposes eliminate the movement of the gold on the surface and thus significantly reduce the agglomeration and growth of these nanoparticles over time.

A rapid catalyst aging technique was developed to test the catalysts. In this technique, catalysts were aged at <NUM> in a solution of 4wt% methacrylic acid, 6wt% water and a balance of methanol for 10days.

Catalyst <NUM> aged by this technique was compared with a <NUM> sample of Catalyst <NUM> aged for <NUM> hours in an adiabatic fixed bed reactor operated in recycle mode with air and liquid feed entering the bottom of the vertically aligned <NUM>-inch OD (<NUM>-inch ID) {<NUM> OD (<NUM> ID)} x <NUM> inch (<NUM>) insulated 316SS reactor. The average temperature in this reactor was approximately <NUM> and the average pressure was approximately <NUM> psig. Fresh Catalyst <NUM> has an average gold nanoparticle size of approximately <NUM>. When the catalyst was aged at test conditions (<NUM> in a solution of 4wt% methacrylic acid, 6wt% water and a balance of methanol for 10days) the average gold nanoparticle size grew to approximately <NUM>. When the catalyst was aged in the <NUM> reactor for <NUM> hours, the average size also grew to <NUM>. Deactivation over this time frame in the <NUM> reactor system is estimated to be approximately <NUM>%. Catalyst aged by the test technique appears to have deactivated by approximately <NUM>%.

The table below demonstrates the reduction in average gold nanoparticle growth which may be accomplished by the addition of Ti salts as well as those of <NUM>rd elements comprising magnesium (added to increase activity) and <NUM>th elements consisting of Co, or Zn (added to further reduce gold nanoparticle size). For instance, Catalyst <NUM> and Catalyst <NUM> were aged under test conditions as described above. The gold nanoparticle size began at approximately <NUM> for both catalysts and grew to approximately <NUM> in the case of Catalyst <NUM> which was Au-Si versus approximately <NUM> in the case of Catalyst <NUM> which was Au-Ti-Si.

Support material was prepared by incipient wetness <NUM> of C<NUM>K<NUM>O<NUM>Ti*<NUM><NUM>O dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material. The support was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours. The resulting support contained approximately <NUM>. Catalyst #<NUM> was prepared by incipient wetness <NUM> sodium gold thiosulfate dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material which had been previously treated to add approximately <NUM>. 0wt%Ti, present as titanium oxide, to the support material. The catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

Catalyst #<NUM> was prepared by incipient wetness <NUM> sodium gold thiosulfate dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material which had been previously treated to add approximately <NUM>. 3wt%Ti, present as titanium oxide, to the support material. The catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

Support material was prepared by incipient wetness of <NUM> Mg (NO<NUM>)<NUM>*<NUM><NUM>O dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material which had been previously treated to add approximately <NUM>. 6wt%Ti, present as titanium oxide, to the support material. The support was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

Catalyst #<NUM> was prepared by incipient wetness <NUM> sodium gold thiosulfate and <NUM> of zinc acetate dehydrate dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of support material. The catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

A feed solution of <NUM> was prepared comprising 10wt% methacrolein, 200ppm inhibitor and a balance of methanol, and placed in a <NUM> Parr@ reactor which served as a gas disengagement vessel. The vessel liquid was maintained at a temperature of approximately <NUM>. The liquid feed was pumped at <NUM>/min from the gas-disengagement vessel into the bottom of the vertically-oriented fixed bed reactor. Air and nitrogen gas was mixed to obtain <NUM>. 8mol% oxygen and mixed with the liquid feed prior to entering the fixed bed reactor. The fixed bed reactor was a jacketed ¼" <NUM>. (<NUM>) stainless steel tube maintained at <NUM> using an external heater. The reactor itself was packed with <NUM> glass beads to fill approximately <NUM> inches (<NUM>) of the tube, then catalyst. The remaining void at the top of the reactor was filled with <NUM> glass beads. Liquid and gas exiting the top of the reactor were sent to a condenser and non-condensable gases were vented, while the liquid was recycled back into the gas-disengagement vessel.

Catalyst #<NUM> was prepared by incipient wetness <NUM> sodium gold thiosulfate dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material which had been previously treated to add approximately <NUM>. 6wt%Ti, present as titanium oxide, to the support material. The catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours. <NUM> of this Au-Ti-Si catalyst was then subjected to incipient wetness of <NUM> of magnesium acetate tetrahydrate and <NUM> zinc acetate dihydrate dissolved in <NUM> of water. The resulting catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

Catalyst #<NUM> was prepared by incipient wetness <NUM> sodium gold thiosulfate and <NUM> of cobalt acetate tetrahydrate dissolved in <NUM> of water to make an aqueous solution and then placed on <NUM> of Fuji Silysia Chemical, Ltd. CARiACT Q-<NUM> silica support material which had been previously treated to add approximately <NUM>. 6wt%Ti, present as titanium oxide, to the support material. The catalyst was then placed inside a box oven with constant air purging of <NUM> liters per hour at room temperature for <NUM> hour and then the calcined at <NUM> with a temperature increase ramp of <NUM>/min and a hold time at <NUM> of <NUM> hours.

Claim 1:
A heterogeneous catalyst comprising a support and gold, wherein: (i) said support comprises silica and <NUM> to <NUM> wt% titanium, (ii) said catalyst comprises: from <NUM> to <NUM> wt% of gold, and from <NUM> to <NUM> wt.% of magnesium, and from <NUM> to <NUM> wt.% of at least one of cobalt or zinc, and (iii) particles of the catalyst have an average diameter from <NUM> microns to <NUM>; wherein weight percentages are based on weight of the catalyst, and wherein the average diameter is the arithmetic mean of all possible diameters.