Correlation between metal oxidation state and catalytic activity: hydrogenation of crotonaldehyde over Rh catalysts (original) (raw)

CROTONALDEHYDE HYDROGENATION ON Rh SUPPORTED CATALYSTS

Boletín de la Sociedad Chilena de Química, 2000

The vapor-phase hydrogenation of crotonaldehyde on Rh supported catalysts has been studied. The effect of some variables of preparation in catalysts prepared by the sol-gel and impregnation methods on the surface and catalytic properties were analyzed. It was found, that the porosity of the support has a small effect on the selectivity to the unsaturated alcohol and the presence of partially reducible supports such as ZrO 2 and TiO 2 , may increase the selectivity to crotyl alcohol via an enhancement of the polarization of the C=O bond as a result of surface decoration of the metal component. The presence of chlorine ions in the metal-support interfacial region, also allows, in a certain extension, a polarization of the carbonyl bond.

Liquid phase hydrogenation of crotonaldehyde over Au/CeO2 catalysts

Applied Catalysis A: General, 2009

The dependence of the catalytic properties of Pt/SiO2 catalysts for the hydrogenation of crotonaldehyde on the hydrogen pressure, the reaction temperature, the nature of the solvent and the presence of several additives were investigated. Strong deactivation of the catalysts mainly caused by decarbonylation of crotonaldehyde and irreversible adsorption of CO was observed. The initial activity of the deactivated catalysts is regained by oxidation of the adsorbed CO to CO2 by purging with air. The selectivity to crotylalcohol increased with increasing number of turnovers per metal site. This is explained with preferential blocking of the nonselective sites on the metal crystallites by CO and by a slow surface modification of the aging catalyst with organic deposits. The overall rate and the selectivity to the saturated aldehyde are markedly enhanced by an increase in hydrogen pressure and by a decrease in reaction temperature. The addition of modifiers such as potassium acetate, triphenylphosphine and thiophene had only little influence on the activity and the selectivity of the catalysts, c© 1997 Elsevier Science B.V.

Crotonaldehyde hydrogenation on supported gold catalysts

2008

Au/Nb 2 O 5 and Au/CeO 2 catalysts were studied for the selective hydrogenation of crotonaldehyde, both in liquid (batch reactor, 4 atm, 60 8C, solvent: isopropanol) and in gas (flow microreactor, 120 8C, atmospheric pressure) phases. Samples were characterized by TPR and XRD and tested for the CO oxidation reaction. Large differences in support reducibility between both catalysts were determined from the TPR results. The XRD and CO oxidation results demonstrated that the gold particles were lower than 5 nm. The dependence of the selectivity towards crotyl alcohol and of the conversion on time on stream was measured. The niobia-supported catalyst was mainly unselective, the selectivity towards crotyl alcohol value being 20% for both liquid and gas phases. The Au/CeO 2 catalyst is highly selective in gas phase (78% of selectivity towards crotyl alcohol). Under liquid phase conditions, a high selectivity level was not reached mainly due to secondary reactions. #