XPS and in situ IR spectroscopic studies of CO/Rh/Al2O3 and CO/Rh/K–Al2O3 at high temperatures: probing the impact of the potassium functionalization of the support

Abstract

Potassium-functionalised alumina (6 wt.% K–Al₂O₃) was obtained by calcination at 973 K of pure alumina particles (Al₂O₃) impregnated with an aqueous solution of K₂CO₃. Both Al₂O₃ and K–Al₂O₃ were, then, impregnated with aqueous RhCl₃·3H₂O, dried at 393 K, and in situ reduced in H₂ atmosphere to obtain 1 wt.% Rh/Al₂O₃ and Rh/K–Al₂O₃ catalysts, respectively. Impacts of the potassium-functionalization on high-temperature behaviour of the Rh catalyst towards CO atmosphere were examined by (i) X-ray photoelectron spectroscopic analysis of the surface chemical composition, (ii) particle sizing of the Rh content by means of transmission electron microscopy, and (iii) in situ infrared spectroscopy of adsorbed CO. Results obtained showed the potassium-functionalization to suppress the CO-induced oxidative degradation of Rh⁰ metal particles into Rh^I, enrich the electronic density at Rh⁰ metal sites, and stabilize the Rh content against CO-assisted elimination at high temperatures. On the other hand, the presence of potassium was found not to affect the initially high dispersity of Rh⁰ metal particles on alumina despite the promoting effect on CO decomposition.