Hydrogen interaction with Pd/Ce 0.8Zr 0.2O 2 nanocomposites prepared by microemulsion, coprecipitation and supercritical CO 2 treatment

Abstract

Nanocrystalline Ce 0.8Zr 0.2O 2 solid-solutions (CZ) were synthesized by microemulsion (ME80), co-precipitation (CP80) and co-precipitation followed by supercritical CO 2 post-treatment (SC80). Structural, microstructural and textural characterizations of oxides were performed and correlated with their redox properties. The results are consistent with the formation of solid solutions with high surface area ( S BET ∼ 200 m 2 g −1), constituted by nanoparticles (4–6 nm) with a fluorite type structure but different mesoporosity. Dynamic oxygen storage capacity (OSC) measurements indicate that the presence of Pd improves the extension of reduction of CZ support, with the higher low-temperature OSC capacity observed for Pd/SC80. Static kinetics measurements, confirm that Pd promotes hydrogen spillover onto CZ favoring both surface and bulk reduction of Ce(IV) to Ce(III) even at 373 K. Pd/SC80 presents considerably higher total OSC (691 versus 400–454 μmol H 2 g −1) with respect to the other samples. Significant Pd sintering was observed over Pd/ME80 only, with the consequent decrease of redox capability for Pd/ME80 catalyst. On the contrary, Pd/CP80 and Pd/SC80 samples presented highly dispersed Pd and good stability after redox cycling. These findings indicate that CP followed by thermal treatment under supercritical conditions is a promising method to synthesize materials with high low temperature OSC and promissory redox properties due to improved Pd/CZ interaction.