Hydrogenation surface catalysts

The intermediate m hydrogenation formed by reaction of the unsaturated ester with the hydrogenated surface of the metal catalyst not only can proceed to the saturated fatty acid ester but also can dissociate to the original ester having a cis double bond or to its trans stereoisomer Unlike polyunsaturated vegetable oils which tend to reduce serum cholesterol levels the trans fats produced by partial hydrogenation have cholesterol raising effects similar to those of saturated fats... 

The available surface area of the catalyst gready affects the rate of a hydrogenation reaction. The surface area is dependent on both the amount of catalyst used and the surface characteristics of the catalyst. Generally, a large surface area is desired to minimize the amount of catalyst needed. This can be accomphshed by using either a catalyst with a small particle size or one with a porous surface. Catalysts with a small particle size, however, can be difficult to recover from the material being reduced. Therefore, larger particle size catalyst with a porous surface is often preferred. A common example of such a catalyst is Raney nickel. 

The earliest attempts to prepare deuterated steroids were carried out by exchange reactions of aliphatic hydrogens with deuterium in the presence of a surface catalyst. Cholesterol, for example, has been treated with platinum in a mixture of deuterium oxide and acetic acid-OD, and was found to yield... 

Regardless of detail, the experimental facts are clear process conditions that favor formation of hydrogen-poor catalysts favor migration and isomerization. Table 1 is a convenient summary of this concept. Hydrogen availability refers to hydrogen concentration at the catalyst surface. Additives that retard the rate of reduction increase hydrogen availability and retard isomerization they may also block sites with enhanced activity for migration (53). 

The first two methods have the advantage that no modification of the homogeneous catalyst is needed. Surface hydrogen-bonded catalysts are limited to cationic complexes, while physical entrapment is more widely applicable. However, both methods are very sensitive to the solvent properties of the reaction medium. The chemical methods of immobilization require modification of the ligand, and this may be quite laborious. In the case of irreversible catalyst deacti-... 

Production of hydrogen from an inexhaustible somce, water, by a cheaper route has been under extensive investigation in recent years (Koca and Sahin, 2003). The requirement for the photoproduction of hydrogen using a semiconductor is the need for a hydrogen evolution catalyst on a semiconductor surface as reported by marty... 

H2 and then CO2 pressure were applied, forming a GXL. The fluorinated catalyst then partitioned off of the fluorinated silica support and into the CO2-expanded organic phase. The reaction was assumed to occur in the expanded liquid phase in which reactants (styrene, hydrogen) and catalyst (fluorinated Wilkinson s catalyst) are homogeneously present. After the reaction was completed, the pressure was released and the catalyst then partitioned back onto the silica surface. 

Steric approach control, 67 Steric strains, 71 Steric strain control, 69 Steroid hydrogenation, 111 5/3-Stigmast-22-en-3-one, 130 Stigmasterol, 266 Sulfur dichloride, 459 Sulfur tetrafluoride, 459, 472 Sulfur tetrafluoride fluorination, 471 Surface catalysts, 157... 

Tests on the activity of LP-produced Fe-based nanopowders for liquefaction of a sub-bituminous coal under high (688 K, 1 h of reaction) and low (658 K, 0.25 h of reaction) severity conditions have been reported.38 The catalysts tested were Fe7C3 (92 m2 g 1 (BET), particle size = 17 nm (XRD))and Fe XS (42 m2 g 1 (BET), particle size = 14 nm (XRD).38 For comparison, a commercial superfine iron oxide catalyst (SFIO, supplied by Mach I, Inc.) whose major phase has been identified in one study as y-Fe20339 (surface area = 195 m2 g 1 (BET), particle diameter = 3 nm (XRD)) and in other study as the ferrihydrite40 was also evaluated under similar conditions. The coal liquefaction experiments were carried out in 50 cm3 horizontal microautoclave reactors loaded with 3 g of sub bituminous Black Thunder coal and 5 g of tetralin used as hydrogen donor. Catalyst loadings of 0.7% and 1.4% of as-received coal... 

Analysis of Fractions. Surface areas and pore size distributions for both coked and regenerated catalyst fractions were determined by low temperature (Digisorb) N2 adsorption isotherms. Relative zeolite (micropore volume) and matrix (external surface area) contributions to the BET surface area were determined by t-plot analyses (3). Carbon and hydrogen on catalyst were determined using a Perkin Elmer 240 C instrument. Unit cell size and crystallinity for the molecular zeolite component were determined for coked and for regenerated catalyst fractions by x-ray diffraction. Elemental compositions for Ni, Fe, and V on each fraction were determined by ICP. Regeneration of coked catalyst fractions was accomplished in an air muffle furnace heated to 538°C at 2.8°C/min and held at that temperature for 6 hr. 

Air and Hydrogen. Pd catalysts prepared on high surface-area supports cause catalytic ignition of H2/air or solvent/air mixtures2,3 Pd on charcoal, when thoroughly dry, is extremely pyrophoric.4... 

Fe2+. Because peroxide decomposition was slowest under the same conditions at which benzoic acid decomposition was highest, it is important to consider the efficiency of hydroxyl radical formation from peroxide decomposition. With the surface catalyst, either hydroxyl radical is not readily available to benzoic acid and is scavenged by other species, or the mineral-catalyzed decomposition of hydrogen peroxide involves additional, nonhydroxyl radical-forming pathways for peroxide decomposition. 

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