Pt on alumina

Vinyl chloride can be hydrogenated over a 0.5% platinum [7440-06-4], Pt, on alumina catalyst to ethyl chloride and ethane [74-84-0]. This reaction is 2ero order in vinyl chloride and first order in hydrogen. 

The extent to which small particles of Pd and Pt show evidence of oxidation after exposure to air Is also highly variable. It Is difficult to confirm the evidence of X-ray diffraction and EXAFS (25) that most particles In the 15-20A size range consist entirely of oxide. We have found that such particles usually give single crystal patterns attributable to the metals. There Is, however, considerable evidence that, in the case of Pt on alumina, the Pt crystals have a well-defined epitaxial relationship with the crystallites (20-50A diameter) of the nominally "amorphous" alumina substrate. 

Interest, because of their nonuniformity and will not be discussed further. Schmidt ( ) and Baker (11) have elaborated on the platlnum-slllca mobility question and the strength of metal-support Interactions. Sample C, Pt on alumina, was used as a reference for the H/Pt measurements, and beyond that Is of little relevance In these discussions. 

Since the initial work of Onto et al. (1) a considerable amount of work has been performed to improve our understanding of the enantioselective hydrogenation of activated ketones over cinchona-modified Pt/Al203 (2, 3). Moderate to low dispersed Pt on alumina catalysts have been described as the catalysts of choice and pre-reducing them in hydrogen at 300-400°C typically improves their performance (3, 4). Recent studies have questioned the need for moderate to low dispersed Pt, since colloidal catalysts with Pt crystal sizes of <2 nm have also been found to be effective (3). A key role is ascribed to the effects of the catalyst support structure and the presence of reducible residues on the catalytic surface. Support structures that avoid mass transfer limitations and the removal of reducible residues obviously improve the catalyst performance. This work shows that creating a catalyst on an open porous support without a large concentration of reducible residues on the Pt surface not only leads to enhanced activity and ee, but also reduces the need for the pretreatment step. One factor... 

Sinfelt et al, J Phys Chem 64 892, 1960). Another investigation is to be made at this temperature and 6.8 atm total pressure with a reactor 1 inch in diameter and 1 ft long. The catalyst used, Pt on alumina, has a bulk density of 187.5 lb/cuft. The volumetric feed rate is to be 12.3 Std cuft/min. What conversion can be expected with feeds composed of (a) 5% n-pentane and 95% hydrogen, (b) 20% n-pentane and 80% hydrogen ... 

Special attention has been paid to acid-catalyzed ring expansion. Sterba and Haensel (J19) reported that the rate of benzene formation from methyl-cyclopentane increases with increasing fluorine content of the catalyst (up to 1.0% F with 0.3% Pt on alumina). At the same time, increasing platinum content also promoted this reaction (up to 0.075% Pt with 0.77% F on alumina). This indicates the remarkable cooperative action of a dual function catalyst (119, p. 11). 

Pt on alumina and activated carbon also show high activity, whereas Pt supported on Si02-Al203 and Zr02 show moderate catalytic activity for H2 production. Lower activity has been observed for Pt supported on Ce02 and ZnO, mainly due to the deactivation caused by hydrothermal degradation of the supports. 

The 5 wt% Pt-on-alumina was a commercial catalyst (Engelhard 4462). The metal dispersion (D = 0.30) was determined from TEM pictures. Different fields were examined and about 1000 particles were counted and their size determined. The degree of dispersion was calculated from the surface average diameter (76). 

Before bismuth-promotion the Pt-on-alumina catalyst was pre-reduced in water with hydrogen. The pH was decreased to 3 with acetic acid and the appropriate amount of bismuth nitrate dissolved in water (10 - lO " M) was added into the mixed slurry in 15-20 min, in a hydrogen atmosphere. Promotion of unsupported Pt was carried out similarly. The metal composition of the bimetallic catalysts was determined by atomic absorption spectroscopy. 

The oxidation reactions were performed in a 200 cm glass reactor, equipped with gas distributer, condenser, thermometer, measuring and reference electrodes. The mixing frequency of the magnetic stirrer was 1500 min 75 mg Pt or 450 mg Pt-on-alumina catalyst was prereduced in nitrogen atmosphere at 60 °C with 3.67 g or 3.00 g 1-phenylethanol, respectively. The solvent composition was 35 cm water +... 

It seems that the reason of deactivation of the unpromoted Pt-on-alumina catalyst is the over-oxidation of the Pt° active sites, due to the high rate of oxygen... 

Improved yields of adamantane up to 65% were achieved by using superacidic systems [HF-SbF5, CF3S020H-B(0S02CF3)3, various solid superacids]40"42 and chlorinated Pt on alumina.43 More recently near-quantitative isomerization with conjugate superacids promoted by 1-haloadamantanes as the source of 1-ada-mantyl cation and sonication was reported.44... 

Pt on alumina catalyst. h Methylcyclohexane pressure, atm. c Hydrogen pressure, atm. 

The Octafining process (114—116) was developed and commercialized by Adantic Richfield and Engelhard in the eady 1960s. The first-generation catalyst was prepared by mixing equal amounts of a silica—alumina cracking catalyst with Pt on alumina. The Pt content of the mixture was about 0.5 wt %. The EB approach to equilibrium was 88%, with an 80% selectivity to xylenes. Reaction conditions consist of temperature of 425-480°C pressure of 1.14—2.51 MPa H2/hydrocarbon ratio < 10 1 (preferably 4—6 1) and LHSV = 0.6-1.6/h. An equilibrium mixture of xylenes is produced. To maintain... 

A. L. Boehm an, S. Niksa, and R. J. Moffatt, A Comparison of Rate Earnfor CO Oxidation Over Pt on Alumina, SAE 930252, Society of Automotive Engineers, Warrendale, Pa., 1993. 

X-Rav Absorption Fine Structure. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure spectra (EXAFS) were obtained for a series of Sn/Pt on alumina or silica samples (45,46). The data suggest the possibility of Pt/Sn alloy formation, but do not provide conclusive proof for this. 

Particle migration (up to 8nm particles migrated over 25 nm at 773 K) was also observed for Pt on alumina [43]. The two major mechanisms of sintering of supported Pt crystallites appeared to be (i) short-distance, direction-selective migration of particles followed by either collision and coalescence or by direct transfer of atoms between the two approaching particles, or (ii) localized direct ripening between a few immobile, adjacent particles. 

For the hydrogenation of a-functionalized ketones, the Pt on alumina system, modified with cinchonidine or its simple derivative 10,11-dihydro-O-methyl-cinchonidine, is the best catalyst [43, 44, 46]. This so-called Orito system [47] is... 

Hydrogenation of ben/ene idilule solulion of cyclohexane in benzene) by 2 percent Pt on alumina 84,95... 

Matrix effects arc large for low energy radiation prtxiuccd in a heavy matrix (for example, the Ka line of oxygen in molybdenum oxide). On the other hand, they are very weak under inverse conditions (for example, Pt on alumina). 

Discrete (qualitative) variables, which describe non-continuous variation, e.g. type of catalyst (Pd on Carbon or Pt on Alumina), type of solvent (carbon tetrachloride or hexane), type of equipment (reactor A, reactor B). 

When one or several experimental variables are discrete, we cannot rely on a geometrical interpretation of smooth and continuous response functions. A change of catalyst, e.g. Pd on carbon to Pt on alumina, may well change the influence of other continuous variables. 

Some hydrogenations were carried out in the presence of two modifiers, a vinca type producing, for example, the (S) enantiomer and a cinchona type producing the (R) enantiomer in excess. The catalysts used were Pd black and Pd on titania in the hyirogenation of isophorone, and Pt on carbon, Pt on alumina and Adams Pt in the hydrogenation of ethyl pyruvate. The amount of vinca alkaloid was kept constant, while the amount of the other was increased in each experiment. The results are shown in Figure 5, 6 and 7. 

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