STRUCTURE AND REACTIVITY OF BIMETALLIC FEIR SIO2 CATALYSTS AFTER REDUCTION AND DURING HIGH-PRESSURE CO HYDROGENATION/

Bimetallic FeIr/SiO2 CO hydrogenation catalysts have been studied by t emperature-programmed reduction, EXAFS, Mossbauer spectroscopy, and pr eviously also by infrared spectroscopy of adsorbed CO. We concentrate on the structure of a freshly reduced sample, which is selective for t he formation of hydrocarbons from CO + 3H(2), and a catalyst activated during 48 h of reaction, which produces mainly methanol. The fresh sa mple contains iron oxide and bimetallic FeIr particles with an iron-ri ch surface after reduction in H-2 at 450 degrees C. During CO hydrogen ation, a part of the oxidic iron reduces and forms, together with some of the iron that is initially alloyed an iron carbide. CO adsorption on activated FeIr/SiO2 is considerably weaker than on the freshly redu ced catalyst, while the activated catalyst also possesses a much highe r hydrogenation activity than the initially reduced system does. Struc ture models for the catalyst after reduction and during steady state C O hydrogenation at high pressure are discussed. (C) 1997 Academic Pres s.