Noble metals supported on binary γ-Al2O3-α-Ga2O3 oxide as potential low-temperature water-gas shift catalysts

Abstract

A high surface area binary Al2O3-Ga2O3 oxide (AlGa) (75% wt%/25 wt%) was prepared by a single-stage precipitation method, and then used as support for noble metal catalysts (3 wt% nominal metal content). Effect of noble metals (Os, Pd, Rh, and Pt) on the surface distribution and the type of species formed were investigated by SBET, XRD, SEM-EDS mapping, HRTEM, DRIFT-CO and XPS techniques and tested in the Water-Gas Shift (WGS) reaction carried out in a fixed bed reactor at atmospheric pressure and temperature range 160–400 °C. The activity tests revealed that the reactivity of the catalyst followed the order: Pd/AlGa > Pt/AlGa > Rh/AlGa > Os/AlGa. The Pd and Pt-based catalysts presented the light-off reaction temperature at about 280 °C while the Os and Rh-based ones were activated at 300 °C and 325 °C, respectively. For the best Pd/AlGa catalyst, the DRIFTS spectra of chemisorbed CO revealed the presence of isolated peripheral or basal palladium species suggesting the importance of those species for the WGS reaction. For the Pt/AlGa catalyst, the combined EDS mapping and HRTEM studies indicated the highest dispersion of the metal phase among the catalysts studied. In this case, the absence of a correlation between the catalyst activity and metal dispersion suggests that factors other than metal dispersion control its catalytic performance.