Gold catalysts selective hydrogenation

Table 9.2 Hydrogenation of 1,3-butadiene on gold catalysts selectivities and product distributions, with comparable results for other metals.

Claus recently reviewed the hydrogenation of a,P-unsaturated aldehydes, a process that displays very high selectivity by supported gold catalysts [215]. 

However, the removal of carbon monoxide by water-gas shift to a low level still demands its selective oxidation to the minimum concentration possible. Much research and development has been conducted during the past decades to find a gold catalyst that can do this the target is usually described by the acronym PROX (preferential oxidation), but sometimes as SCO (selective catalytic oxidation). The task is somewhat simplified by the constraints that are externally imposed the preferred feed gas, often termed idealised reformate, has the composition 1.0% CO, 1.0% 02, 75.0% H2, balance nitrogen or other inert gas, and while of course variations to this composition can be made to explore the kinetics and mechanism, and the effects of the products water and carbon dioxide can be added to observe their effects, the successful catalyst must remove almost all the carbon monoxide (to <10 ppm) and less than 0.5% hydrogen. This requirement is expressed as a selectivity based on the percentage of the oxygen consumed that is taken by the carbon monoxide this should exceed 50%, under conditions where the conversion of carbon monoxide is above 99.5%.5... 

There have been two recent studies of the hydrogenation of ethyne on gold catalysts. With 1% Au/TiC>2 made by thermally decomposing the supported complex [Au2(PPh3)6](BF4)2 and having particles of average size 4.6 nm, reaction occurred at 453 K with about 90% selectivity to ethene,... 

Studies with gold catalysts have focused on the selective reduction of nitric oxide by propene, carbon monoxide and hydrogen urea,10 methane11 and other hydrocarbons9,11,13 have also been used. NOx removal using the first three of these will now be discussed. 

In contrast to PGM catalysts, gold nanocatalysts are generally more active for CO oxidation than for H2 oxidation. In addition, gold catalysts are almost insensitive to CO2, and their activity is enhanced by moisture, the products of the two reactions. Gold catalysts are therefore strong candidates for the selective oxidation of CO in H2-rich gases [2, 35, 38,46, 52, 53,101,157,159, 183-200], a reaction needed to produce pure hydrogen for fuel cells. 

Partly because gold catalysts are active under mild conditions, they have been investigated for other selective oxidation and for selective hydrogenation reactions. Details are given in Sect. 6.2.4. 

Another advantage for gold catalysts is that they can be used to selectively catalyse this oxidation, since the selectivity for the competing hydrogen/oxygen reaction is significantly lower at ambient temperatures (see Sect. 6.4.4). 

Key Words Direct propylene epoxidation. Propylene oxide, Gold, Titanium, Propene, Au/Ti catalysts. Catalysis by gold. Titanium silicalite, TS-1, Gold/TS-1, Hydrogen peroxide, Kinetics, Design of experiments, Deposition-precipitation, Ammonium nitrate, Selective oxidation, Alkene epoxidation, Density functional theory, DFT calculations, QM/MM calculations. 2008 Elsevier B.v. 

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