Insight into the degradation mechanism of mixed VOCs oxidation over Pd/UiO-66(Ce) catalysts: Combination of operando spectroscopy and theoretical calculation

Abstract

Herein, Pd/UiO-66(Ce) catalysts were successfully synthesized by N2H4, H2, and NaBH4 reduction methods with UiO-66(Ce) as support. The best catalyst was selected via utilizing o-xylene as the probe molecule, and its degradation performance of mixed VOCs was further investigated. It was found that the reduction methods greatly influenced the size of Pd nanoparticles, the state of surface Pd, and the support structure in the catalysts, which in turn affected their catalytic performance. Among them, Pd/UiO-66(Ce)-Na exhibited the best o-xylene degradation activity (T90 = 192 °C) due to its smaller average Pd particle size (Pd Average = 2.93 nm) and higher surface Pd0 content (Pd0/Pdtotal = 0.79). The performance and interaction of Pd/UiO-66(Ce)-Na catalyst for degradation of mixed VOCs (o-xylene and toluene/benzene) were investigated by DFT adsorption energy calculation, in situ DRIFTS and GC–MS. Results suggested that the single adsorption energy of o-xylene was −1.20 eV, while in the system with toluene/benzene, the adsorption energy decreased to −0.78 and −0.6 eV, respectively. This showed the competitive adsorption effect between benzene and o-xylene was stronger than that between benzene and o-xylene. Finally, combined with in situ DRIFTS and GC–MS, the degradation path of mixed components was analyzed and studied systematically, and the mechanism of intermolecular interaction of benzene in the degradation process of mixed components was further revealed.