Gold catalysts for low temperature water-gas shift reaction: effect of ZrO2 addition to CeO2 support.

New gold catalysts supported on ceria modified by addition of ZrO2 have been synthesized and tested in the water-gas shift reaction (WGSR) at low temperature, where they displayed better catalytic activity than gold supported on pure ceria, following the trend: AuCe50Zr50 > AuCe80Zr20 > AuCe. Morphologic, textural, structural and spectroscopic characterisation showed that the addition of zirconia to ceria leads to the formation of mixture of tetragonal ceria–zirconia phases. Moreover, depending on the zirconia amount, a different Au dispersion is observed. Au agglomerates (10–20 nm) and nanoparticles (about 2.5 nm) have been detected by HRTEM on AuCe80Zr20, while only nanoparticles have been found on AuCe50Zr50. FTIR spectroscopy of CO adsorbed at 120 K showed also the presence of Au clusters, more abundant on AuCe50Zr50 than on AuCe80Zr20. However, at low temperature the best catalytic activity of AuCe50Zr50 is correlated not only to the abundance of gold clusters and nanoparticles, but also to the effect of ZrO2 addition that influences the acid/base surface properties of ceria, as successfully demonstrated by adsorption and surface reaction of acetone vapor at room temperature. FTIR measurements performed before and after reaction showed that the carbonate-like species have the lowest stability on the AuCe50Zr50 surface. This feature, along with the presence of a high gold dispersion, makes AuCe50Zr50 the best catalyst in terms of activity and stability