Pd nanoparticles supported mesoporous γ-Al2O3 film as a reusable catalyst for reduction of toxic CrVI to CrIII in aqueous solution

Pd nanoparticles (NPs) were generated inside the nanocrystalline mesoporous γ-Al2O3 films of thickness ∼2 μm. The support γ-Al2O3 films were prepared from boehmite sols derived from Al-alkoxide in presence of CTAB. The BET surface area (171 m2g−1) and pore size (4.3 nm) of the undoped γ-Al2O3 films were found to be decreased to 139 m2g−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-Al2O3 films. The Pd NPs (average size ∼4.1 nm)-incorporating mesoporous γ-Al2O3 films were used as catalyst to reduce toxic CrVI compounds to non-toxic CrIII 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.

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► Mesoporous γ-Al2O3 films using CTAB were synthesized.
► Pd NPs were incorporated within the mesopores of the γ-Al2O3 films.
► Toxic CrVI was reduced to CrIII by Pd−γ-Al2O3 film catalyst.
► The film catalyst can be reused several times.