Metal—support interaction of Rh4  Rb13 carbonyl clusters impregnated on Ti- and Zr-oxide-containing silica and their catalytic activities in the conversion of COH2 to ethanol

Abstract

Abstract Rh4  Rh13 carbonyl clusters were impregnated onto Zr- and Ti-oxide-containing silica to provide highly dispersed Rh catalysts with a strong metal—support interaction, and exhibiting high activities for ethanol production in an atmospheric pressure COH2 reaction. The in situ i.r. and x.p.s. studies suggested that the precursor clusters such as Rh6(CO)2−15, Rh7(CO)3−16 and Rh13(CO)23Hn−5−n (n = 2 or 3) had reacted with surface OH (the acid sites of Ti- and Zr-oxide-containing silica) to form hydrido carbonyl clusters such as Rh6(CO)15H− and Rh13(CO)23H2−3. The apparent electronic states of the adsorbed carbonyl species and the reduced form formed from impregnated Rh4(CO)12, were studied by x.p.s. The behaviour of the adsorbed carbonyl species towards O2, NO and H2 is discussed. Some particular adsorbed cluster species were generated in the reaction of under a controlled atmosphere of CO and H2O, the i.r. bands of which resembled those of the original carbonyl clusters used. The kinetic experimental results revealed that ZrO2 and TiO2 on silica prevented Rh aggregation, and play a multifunctional modifying role with Rh to enhance CO dissociation and improve the selectivity for ethanol formation in the reaction of COH2 over the resulting catalysts.