Pd nanoparticles supported mesoporous γ-Al 2O 3 film as a reusable catalyst for reduction of toxic Cr VI to Cr III in aqueous solution

Abstract

Pd nanoparticles (NPs) were generated inside the nanocrystalline mesoporous γ-Al 2O 3 films of thickness ∼2 μm. The support γ-Al 2O 3 films were prepared from boehmite sols derived from Al-alkoxide in presence of CTAB. The BET surface area (171 m 2g −1) and pore size (4.3 nm) of the undoped γ-Al 2O 3 films were found to be decreased to 139 m 2g −1 and 3.5 nm respectively after incorporation of Pd NPs. The films were characterized by GIXRD, cross-sectional FESEM, and TEM. TEM/GIXRD confirmed the existence of uniformly dispersed Pd NPs inside the γ-Al 2O 3 films. The Pd NPs (average size ∼4.1 nm)-incorporating mesoporous γ-Al 2O 3 films were used as catalyst to reduce toxic Cr VI compounds to non-toxic Cr III in presence of formic acid as reducing agent at different temperatures (30, 40, 50 and 60 °C). This catalytic reduction process was monitored by UV–visible spectrometer. The rate constant value for the reduction was estimated to be 0.085 min −1 at 50 °C. The same catalytic film can be used for three consecutive cycles by simple washing with water. The catalytic property started to deteriorate after the third cycle. The original catalytic property can be restored fully after heat-treatment of the used films at 300 °C in nitrogen atmosphere.