Catalytic benzene oxidation by biogenic Pd nanoparticles over 3D-ordered mesoporous CeO2

Pd nanoparticles (NPs)-based catalysts were synthesized, characterized and used to catalyze the oxidation of volatile organic compound (VOC) pollutants. A biogenic method was employed to synthesize Pd NPs with tunable sizes by using Cacumen platycladi (CP) leaf extract as a reducing agent. The Pd NPs were then anchored over a support which was made from KIT-6-templated three-dimensionally ordered mesoporous (3DOM) CeO2 (i.e., kit-CeO2) to form xPd/kit-CeO2 catalysts with various Pd loadings (x denotes Pd loading, wt%). The physicochemical properties such as morphology, structure and elemental distribution of the xPd/kit-CeO2 catalysts and the support were comprehensively characterized. The BET surface areas of the support and catalysts varied in the range of 105–109 m2/g. In the benzene oxidation catalyzed by 0.5Pd/kit-CeO2, the temperature required for 90% benzene conversion was significantly reduced to 187 °C, compared with the published results. Furthermore, the 0.5Pd/kit-CeO2 showed stable catalytic activity after being used for 150 h in on-stream reaction. Besides, density functional theory calculation indicated that the synergetic effects of Pd NPs and the kit-CeO2 support would facilitate the activation of benzene adsorbed on Pd NPs prior to oxidation. The catalytic performance of 0.5Pd/kit-CeO2 correlated well with the features of CP leaf extract, high Pd0 concentration, abundant oxygen adspecies, low temperature reducibility, and strong interactions between Pd NPs and kit-CeO2 support. The biogenic method is better than the chemical method to synthesize Pd NPs with higher catalytic activity while the kit-CeO2 is better than the commercial CeO2 and KIT-6-templated transition metal oxides (e.g., Fe2O3 and Co3O4) as a supporting material.