Effective catalytic reduction of Cr(VI) over TiO2 nanotube supported Pd catalysts

Cr(VI) is a commonly identified heavy metal pollutant in the aquatic environment. In the present study, TiO2 nanotube (TNT) supported Pd (Pd/TNT) and commercial TiO2 (P25) supported Pd (Pd/TiO2) catalysts were prepared using the photo-deposition method and Cr(VI) reduction by catalytic hydrogenation over the catalysts were investigated. Compared with P25, TNT had much higher specific surface area and surface acidity, resulting in higher Pd dispersion on the catalyst support. Given a Pd loading amount of approximately 2.0 wt.%, complete removal of Cr(VI) at an initial concentration of 1.92 mM by catalytic hydrogenation over Pd/TNT and Pd/TiO2 was achieved in 30 min and 50 min, respectively. The higher catalytic activity of Pd/TNT was attributed to the combined effect of higher Pd dispersion and higher surface acidity on TNT. Increasing the initial concentration of Cr(VI) or pH suppressed the hydrogenation reduction due to the lowered availability of the support acid sites by Cr(VI) adsorption or deprotonation. The findings indicate that catalytic hydrogenation over Pd/TNT is a promising technique to reduce Cr(VI) in aqueous solutions.

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► Cr(VI) can be effectively reduced over supported Pd catalysts by catalytic hydrogenation.
► TiO2 nanotube (TNT) has higher surface acidity than TiO2.
► Pd particles are effectively dispersed on TNT.
► Pd/TNT exhibits substantially higher catalytic activity than Pd/TiO2.
► Cr(VI) reduction rate decreases with the increase of initial Cr(VI) concentration and pH.