Surface structure and selectivity control in the CO + H2 reaction over FeRu Bimetallic catalysts

The structures of ruthenium and iron-ruthenium catalysts supported on alumina and on Cab-O-Sil were investigated by X-ray diffraction, photoelectron spectroscopy, temperature-programmed reduction, CO and O2 chemisorption and temperature-programmed desorption of hydrogen chemisorbed at various temperatures. Turnover frequencies and selectivities revealed in the CO + H2 reaction were correlated with the structures of the catalysts. It was established that carbon monoxide hydrogenation, being a structure-sensitive reaction, is primarily influenced by the particle size and by the addition of iron to ruthenium. As a secondary effect, the bonding mode of the surface hydrogen (activated chemisorption), which depends on the dispersion, support, calcination and addition of iron to ruthenium, greatly influences the catalyst selectivity. Weakly bonded hydrogen results in the formation mainly of methane, whereas substantial olefin formation is caused by hydrogen depletion. A mechanism for these effects and a possible interpretation of the promoter effect, which plays an important role in industrial catalysts, are given.