Controllable synthesis of mesoporous alumina as support for palladium catalysts and reconstruction of active sites during methane combustion

Uniform mesoporous alumina (MA) nanospheres with excellent thermal stability and controllable pore size distribution were facilely obtained through ultrasonic assisted sol-gel method then taken as carriers for synthesizing a series of supported palladium catalysts. Results evidenced that the pore size distribution of MA significantly affected the catalytic performance of as-prepared catalysts. More importantly, the methane pretreatment tuned valence state of palladium species and distribution of surface oxygen species, along with promoting the adsorption of CH4 on catalysts and the generation of CH3∗ group to form methane-derived adsorbates. Moreover, the synergistic effect of PdO and surface adsorbed oxygen effectively activated CH4 and invoked the oxidation of methane-derived adsorbates, hence boosting the catalytic activity with the 90% CH4 conversion temperature (T90) decreased by 40 °C relative to the unpretreated catalyst. Noticeably, the T90 of Pd/MA(CH4) catalyst could be attained at 380 °C after subsequent long term and cyclic stability test.