Platinum-alumina preparation

Fig. 5. Electron micrograph of 2.5% (w/w) platinum/alumina catalyst. Prepared by impregnation with chloroplatinic acid, reduced in hydrogen at 210°C. Micrograph obtained by thin sectioning. The black dots are platinum particles. (X 100,000). Reproduced with permission from R. L. Moss, Platinum Metals Rev. 11 (4), 1 (1967) and British Crown Copyright.

Some experimental data obtained by Smith et al. (18) will be used to illustrate the method of approach. These data were obtained with a pressurized all glass flow reactor at a temperature of 399°. The catalyst used was 0.05% platinum on -alumina prepared by impregnating the alumina with chloroplatinic acid. The chlorine introduced by this method of impregnation was removed to reduce the acidity of the catalyst so that the isomerization of cyclohexene to methyl cyclopentane was suppressed. The amount of conversion was varied by changing the amount of catalyst in the reactor. The catalyst bed in the reactor consisted of 15 ml of crushed vycor (60-100 mesh) in which the desired amount of finely crushed (100-200... 

In this work, we investigated the preparation of bimetallic Pt-Re catalysts by surface redox reaction between hydrogen adsorbed on a parent monometallic platinum/alumina catalyst and the cation of the second metal (Re) according to the following reaction ... 

Bimetallic platinum-rhenium catalysts can be prepared in aqueous acid medium, under hydrogen flow, by a redox reaction between hydrogen activated on a parent platinum-alumina catalyst and the perrhenate ion ReO4. ... 

Figure 4.35 Mossbauer spectra at 25°C on catalyst samples B-H20 and B-lr prepared by contacting platinum-alumina catalyst (sample B of Figures 4.32 and 4.33) in its final reduced form with, respectively, water and a chloroiridic acid solution (3,41). (The platinum and iridium contents of sample B-lr are the same as those of sample D of Figure 4.32.) (Reprinted with permission from Academic Press, Inc.)...

Ethanol oxidation was studied under lean conditions on platinum/alumina catalysts modified by rhodium and/or lanthanum oxide. The results on alumina support suggest that the formation of bimetallic Pt-Rh particles enhances the production of acetaldehyde, particularly after oxidizing thermal aging of the Pt-Rh/alumina catalyst prepared by coimpregnation. The addition of lanthanum oxide to alumina allows to avoid the formation of Pt-Rh alloy after high temperature treatment and therefore induces a decrease of the production of acetaldehyde. 

Several platinum-alumina catalysts were prepared on low acidity aluminas such as A, B, and D listed in Table II. Practically all of the data obtained with such catalysts fell on a single selectivity curve correlating % conversion to MO with % selectivity to MO formation. Selectivity was found to be quite high, as illustrated by the following results for platinum on low acidity alumina ... 

A catalyst was prepared on the strongly acidic alumina E, using exactly the same preparation procedure used to make the platinum-low acidity alumina compositions. This catalyst was evaluated under the standard conditions and gave results very similar to those obtained with the commercial platinum-alumina reforming catalysts. At a conversion to MO of 8%, the selectivity to MO formation was 31%. 

An earlier study using this same compound, DMMP, led to a mathematical model of the deactivation process. Graven et a/. studied the oxidation of DMMP vapor in a stream of air, or nitrogen, over platinum-alumina catalysts. A commercial catalyst and a number of laboratory-prepared catalysts were investigated over a range of temperatures from 573-773 K, residence times from 0.15 to 2.7 seconds. The average catalyst particle sizes varied from 0.31 to 2.4 mm. They found that the fresh catalyst showed a very high activity, but after a few hours on stream it deactivated to the point that measurable quantities of DMMP vapor appeared in the effluent.. The reaction products over the deactivated catalyst were methanol and phosphorus acid. 

Shelimov, B.N., Lambert, J.-F., Che, M., Didillon, B. (1999). Initial Steps of the Alumina-Supported Platinum Catalyst Preparation a Molecular Study by i spt NMR, UV-Visible, EXAFS and Raman Spectroscopy. Journal of Catalysis, Vol.185, No.2, (July 1999), pp. 462-478, ISSN 0021-9517... 

Mang, T., B. Breitscheidel, and P. Polanek, Adsorption of platinum complexes on silica and alumina Preparation of non-uniform metal distributions within support pellets. Applied Catalysis A General, 106(2), 1993. 

From the two different preparation processes the coprecipitation route does not give the best catalytic activity, due to the fact that these samples have alkaline impurities. The sol-gel method is preferable and leads to very adive catalysts. For the CO + O2 reaction, the LaCoOa catalyst prepared via the sol-gel route showed a temperature of half conversion 100 K lower than for a 2% platinum alumina catalyst (8). 

The present work was undertaken to examine this possibility by trying a new method of low-temperature catalyst preparation. The method studied involves the adsorption of metal precursors on supports and the reduction by sodium tetrahydroborate solution for the preparation of supported platinum catalysts. The adsorption and reduction of platinum precursors are carried out at room temperature and the highest temperature during the preparation is 390 K for the removal of solvent. The activities of the catalysts prepared were examined for liquid-phase hydrogenation of cinnamaldehyde under mild conditions. Our attention was directed to not only total activity but also selectivity to cinnamyl alcohol, since it is difficult for platinum to hydrogenate the C=0 bond of this a, -unsaturated aldehyde compared to the C=C bond [2]. We examined the dependence of the catalytic activity and selectivity on preparation variables including metal precursor species, support materials and reduction conditions. In addition, the prepared catalysts were characterized by several techniques to clarify their catalytic features. The activity of the alumina-supported platinum catalyst prepared by the present method was briefly reported in a recent communication [3]. 

Takenaka ct al. studied the activity of various catalysts for carbon monoxide methanation in the absence of carbon dioxide [342]. From the different active species on a silica carrier, 5 wt.% ruthenium, 10wt% nickel and 10 wt.% cobalt were significantly more active than iron, palladium or platinum, each prepared with an active species content of 10 wt.%. Then Takenaka tested nickel, ruthenium and cobalt catalysts on different carrier materials, namely, alumina, silica, titania and zirconia. The formulations most active were nickel/zirconia and mthenium/ titania catalysts. The best performing catalyst was the 5 wt.% mthenium/titania, which converted the carbon monoxide apart from less than 20 ppm from a feed mixture containing 60 vol.% hydrogen, 15 vol.% carbon dioxide, 0.9 vol.% steam, 0.5 vol.% carbon monoxide, with a balance of helium at 220 °C. The space velocity was rather high at 300 L (hgcat) -... 

Schubert U., Egger C., Rose K., Alt C. Metal-complexes in inorganic matrices. 3. catalytic activity of Rh(CO)Cl(Pr3)2 heterogenised by the sol-gel method. J. Mol. Catal. 1989b 55 330-339 Seker E., Gulari E. Improved N2 selectivity for platinum on alumina prepared by sol-gel technique... 

The authors are collaborating in an extensive joint study in which the preparation, characterisation and function of a range of supported platinum catalysts is being evaluated. In part, this study will compare platinum catalysts prepared using conventional supports (e.g. silica, alumina) with those using less conventional supports (e.g. molybdena) or those prepared by less conventional methods (e.g. metal vapour deposition). The restricted object of the present paper is to compare the conventional Pt/silica prepared within this programme with the standard reference silica-supported Pt codenamed EUROPT-1 for which full preparation and characterisation details have been published (refs. 1-5). 

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

Rapoport s findings have been confirmed in the authors laboratory where the actions of carbon-supported catalysts (5% metal) derived from ruthenium, rhodium, palladium, osmium, iridium, and platinum, on pyridine, have been examined. At atmospheric pressure, at the boiling point of pyridine, and at a pyridine-to-catalyst ratio of 8 1, only palladium was active in bringing about the formation of 2,2 -bipyridine. It w as also found that different preparations of palladium-on-carbon varied widely in efficiency (yield 0.05-0.39 gm of 2,2 -bipyridine per gram of catalyst), but the factors responsible for this variation are not knowm. Palladium-on-alumina was found to be inferior to the carbon-supported preparations and gave only traces of bipyridine,... 

Catalytic processes frequently require more than a single chemical function, and these bifunctional or polyfunctional materials innst be prepared in away to assure effective communication among the various constitnents. For example, naphtha reforming requires both an acidic function for isomerization and alkylation and a hydrogenation function for aromati-zation and saturation. The acidic function is often a promoted porous metal oxide (e.g., alumina) with a noble metal (e.g., platinum) deposited on its surface to provide the hydrogenation sites. To avoid separation problems, it is not unusual to attach homogeneous catalysts and even enzymes to solid surfaces for use in flow reactors. Although this technique works well in some environmental catalytic systems, such attachment sometimes modifies the catalytic specifici-... 

A mixed solution of platinum and ruthenium precursors was prepared by adding H2PtCl6 and RuClj at a certain ratio to de-ionized water. The solution was in negnated on y-alumina of size 300-... 

Bimetallic clusters of platinum and iridium can be prepared by coimpregnating a carrier such as silica or alumina with an aqueous solution of chloroplatinic and chloroiridic acids (22,34). After the Impregnated carrier is dried and possibly calcined at mild conditions (250°-270 C), subsequent treatment in flowing hydrogen at elevated temperatures (300 -500°C) leads to formation of the bimetallic clusters. 

Glassy carbon electrodes polished with alumina and sonicated under clean conditions show activation for the ferrl-/ ferro-cyanlde couple and the oxidation of ascorbic acid. Heterogeneous rate constants for the ferrl-/ ferro-cyanlde couple are dependent on the quality of the water used to prepare the electrolyte solutions. For the highest purity solutions, the rate constants approach those measured on platinum. The linear scan voltammetrlc peak potential for ascorbic acid shifts 390 mV when electrodes are activated. 

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