Pd and Pd–Au nanocatalysts supported on exfoliated graphite for high throughput dehalogenation by nanocomposite membranes

Abstract

Exfoliated graphite nanoplatelets (xGnPs) are proposed as a support material in the design of hierarchical Pd-based nanocatalysts for reductive dehalogenation. xGnP-supported metallic (Pd) and bimetallic (Pd–Au) catalysts were synthesized and evaluated in experiments on dehalogenation of trichloroethylene (TCE) in batch and membrane reactors. The TCE removal of 96% was achieved with Pd–Au/xGnP-filled membranes operated at the specific permeate flux of 47.4 L m⁻² h⁻¹ bar⁻¹. Normalized reactive fluxes in flow-through dehalogenation by membranes with embedded Pd–Au/xGnP and Pd/xGnP catalysts were 14.71 ± 5.96 and 2.56 ± 1.79 m s⁻¹ M_H2⁻¹ g_Pd⁻¹ g_PSf, respectively. These values were ∼80 and ∼14 times higher than the normalized reactive flux obtained using membranes with embedded commercial Pd/Al₂O₃ catalyst. To our knowledge, this is the first report on Pd and Pd–Au catalysts on a graphene-type support for hydrodechlorination and the first demonstration of high throughput TCE dechlorination in a membrane reactor. Determined for batch reactions, the second order reaction rate constants for Pd–Au/xGnP and Pd/xGnP catalysts were 26 309 ± 6555 and 9975 ± 9506 M_H2⁻¹ s⁻¹ g_Pd⁻¹ L. These values were ∼81 and ∼31 times higher than the rate constant obtained for the commercial Pd/Al₂O₃ catalyst.