Surface characterization of zirconia, holmium oxide/zirconia and sulfated zirconia catalysts

Abstract

Zirconia-supported holmium oxide, as well as their sulfated catalysts using (NH 4) 2SO 4 were prepared by wet impregnation and calcined at different temperatures. The samples thus obtained were subjected to bulk and surface texture analysis using X-ray powder diffractometry (XRD) and N 2-sorptiometry, respectively. The surface acidic properties were characterized by in situ FT-IR spectroscopy of adsorbed pyridine molecules. The decomposition of gas phase 2-propanol molecules on the catalysts was examined at different temperatures, also using in situ FT-IR spectroscopy. The results obtained revealed that the presence of Ho 2O 3 on ZrO 2 induces the formation of cubic and/or tetragonal ZrO 2 phase at low temperatures (≤800 °C) without significant effect on the surface area. Whereas, the presence of Ho 2O 3 and sulfate ions on ZrO 2 results in the highest formation of cubic and/or tetragonal ZrO 2 phase at low temperatures and induces stabilization of the surface area. The surface of Ho 2O 3/ZrO 2 samples exposes Lewis acid and reactive basic sites, whereas the sulfated samples show at least two types of Lewis and Brönsted acid sites with enhanced acid strength. The decomposition of 2-propanol results show that the sulfate-free samples are dual functioning catalysts at 300 °C; 2-propanol molecules decompose thereon via dehydration into propene and dehydrogenation into acetone. However, the sulfated samples are found to only catalyze the dehydration into propene at all reaction temperatures applied.