Flame synthesis of novel ternary nanocatalysts Pd/CeO2[sbnd]TiO2 with promotional low-temperature catalytic oxidation properties

Abstract

One-step flame-assisted spray pyrolysis with highly-quenched premixed stagnation flame is developed to synthesize the supported palladium catalysts on the mixed ceria-titania oxides. Promotional oxygen reducibility and inherent high activity of the catalysts are discovered in contrast to the same loading palladium catalyts on either single support, and the complete methane oxidation is achieved at as low as 450 °C. Palladium valence electronic structure analysis from X-ray photoemission spectroscopy (XPS) indicates that the metal palladium is highly positively charged and electrons transfer from palladium clusters to support oxides during the flame synthesis process. Similar electron transfer can even occur during the cyclic catalytic process for the initially non-charged clusters. From the cyclic experiments, theelectrostatic interaction built up at the metal–support interface plays a major role in the superior sintering resistance for palladium-based catalysts during the combustion process. Moreover, the introduction of water vapor to the feedstock induces a negative effect on the methane oxidation at low temperatures. XPS spectra reveals that the palladium 3d binding energy varies and the interfacial electron transfer flow changes over heating–cooling cycles when exposed to water vapor. More importantly, the excellent thermal stability performances remain even under the water vapor environment.