FTIR study of the low-temperature water-gas shift reaction on Au/Fe2O3 andAu/TiO2 catalysts

An FTIR and quadrupole mass spectroscopic study of the water-gas shift (WGS ), the reverse WGS reactions, and the adsorption of the individual molecule s involved has been carried out on Au/Fe2O3 and Au/TiO2 catalysts. The chem isorptions and the reactions on the two catalysts have been compared with t he aim of gaining a better understanding of the role played by the two phas es present in these catalysts and of the synergistic interplay between them in gold catalysts tested for a low-temperature water-gas shift reaction. E vidences are reported that Hz is dissociated already at room temperature on both the catalysts on gold sites, giving rise to hydrogen atoms that can r eact with adsorbed oxygen atoms or spillover on the supports where they can reduce the support surface sites. It is shown that CO is adsorbed molecula rly on different surface sites, on the support cations, on Au-0 sites expos ed at the surface of small three-dimensional particles and also on Audelta- sites exposed at the surface of negatively charged clusters. The CO formed in the reverse WGS reaction appears chemisorbed only on the Au-0 sites. Th e support sites and the Audelta- sites, where the CO appears as more strong ly bonded, are present but not accessible to the CO formed by CO2 reduction , probably because these sites are covered by water. Water and OH groups ar e adsorbed on the supports, on gold sites, and at the interface between the m. The effects of CO coadsorption on water dissociation and of Hz dissociat ion on CO2 reduction have been evidenced. The close similarity of the catal ytic activity of the two examined samples indicates that the active sites f or hydrogen dissociation and for water-CO reactive interactions are located at the surface of the metallic gold small particles where the reaction can take place by a red-ox regenerative mechanism. (C) 1999 academic Press.