High-temperature calcination improves the catalytic properties of alumina-supported Pd@ceria prepared by self assembly

摘要

The effect of varying the calcination temperature from 773 to 1073 K was examined on catalysts prepared from Pd@CeO_2, core-shell nanoparticles adsorbed on silane-functionalized γ-Al_2O_3 (Pd@CeO_2/Si-Al_2O_3). Calcining to higher temperatures increased rates per gram catalyst for the methane-oxidation reaction significantly. The Pd@CeO_2/Si-Al_2O_3 catalyst calcined to 773 K was unstable for methane-steam reforming (MSR) due to deep reduction of the catalyst while the catalyst calcined at 1073 K showed reasonable stable rates. CO adsorption, monitored using volumetric uptakes and FTIR, indicated adsorption on the Pd was suppressed following reduction at 673 K in H_2 when the catalyst had been calcined at only 773 K, but not after 1073 K. Pulse-reactor measurements demonstrated that catalysts calcined at either 773 K or 1073 K were heavily reduced under MSR reaction conditions at 673 K but that the catalyst heated to 1073 K could be re-oxidized by H _2O at this temperature, while the 773-K sample could not be. It is suggested that increasing calcination temperature modifies the structure of the ceria shell, which in turn changes the ceria redox properties.