Indoor volatile organic compounds (VOCs), represented by toluene, can pose a serious threat to human health. In this work, a series of Pd/TiO 2 catalysts with different surface structures ( i.e. , dispersion/valence of Pd species, surface Ti 3+ /oxygen defect concentration and Pd-TiO 2 interactions, etc. ) was constructed by various methods. It was found that the Pd/TiO 2 catalyst prepared by one-step reduction of NaBH 4 method (Pd/TiO 2 -N) with metallic Pd particles possessed more surface Ti 3+ /oxygen defects and stronger Pd-TiO 2 interaction than Pd/TiO 2 catalysts prepared by ethylene glycol reduction loading method (Pd/TiO 2 -E) and incipient wetness impregnation method (Pd/TiO 2 -I). Further photochemical characterizations and reaction mechanism study revealed that the relatively higher concentration of Pd 0 species on Pd particles, stronger Pd-TiO 2 interaction, and more surface Ti 3+ /oxygen defects on Pd/TiO 2 -N could facilitate the generation of more reactive oxygen species (ROS) under light irradiation. The partial oxidation of toluene to benzyl alcohol/benzaldehyde/benzoic acid and the subsequent ring-opening process were found to be highly determined by the valence states of Pd particles and the concentration of surface Ti 3+ /oxygen defects. This work provides instructive insights into the construction of highly efficient Pd/TiO 2 catalysts for the removal of indoor VOCs.
A series of Pd/TiO 2 catalysts were prepared by incipient wetness impregnation method followed by atmospheric discharge plasma treatment. In order to study the influences of plasma treatment on the catalysts, the samples were characterized by XRD, TPR, TPD, XPS and TEM technologies. It was found that the plasma treatment catalysts possessed a higher acetylene conversion and ethylene selectivity compared to those of the untreated sample. The enhanced performance of the plasma treated catalyst was mainly dependent on two main effects. On one hand, the treated catalyst possessed a higher metal Pd dispersion, which resulted in the easier activation of acetylene. On the other hand, the surface electron density of metal Pd on the treated catalyst got enhanced compared to that of untreated sample, because of the stronger interaction between TiO 2 support and metallic Pd, helping the more desorption of ethylene species from the surface of catalyst.
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