Rational design of highly H2O- and CO2-tolerant hydroxyapatite-supported Pd catalyst for low-temperature methane combustion

For the first time, palladium (Pd) supported on hydroxyapatite (HAP) was synthesized by integrating ion-exchange method and single-mode microwave technology. The effect of ion-exchange time on the methane (CH4) combustion performance of Pd/HAP was investigated. It was disclosed that the dispersion and size of Pd particles on HAP is affected by ion-exchange time. When the time was 5 h (denoted as Pd/HAP-5), T-90 (the temperature for 90% CH4 conversion) over the catalyst was 400 degrees C. However, there was decrease of catalytic performance when the time was 20 h. The eminent performance of Pd/HAP-5 is ascribed to (i) ample surface PdO and active oxygen species, (ii) high Pd dispersion and reducibility, and (iii) strong CH4 adsorption. Unlike traditional Pd-based catalysts, Pd/HAP-5 shows improved performance in the presence of 5%volCO(2). Moreover, Pd/HAP is highly durable in the presence of 7 vol%H2O. Finally, we propose a reaction mechanism of CH4 combustion over the Pd/HAP.