Dispersed Pd/alumina catalyst with finite iodine entry for boosted CO purification and dimethyl carbonate synthesis

Abstract

Sintering caused catalyst deactivation resulting from the agglomeration of active metal sites. CH3I/CO based approaches are attractive owing to their effectiveness and mildness in rejuvenating sintered catalysts. However, few investigations have been reported for their application in oxides-supported catalysts. Herein, a landscape of reversible structural transformation of Pd/γ-Al2O3 catalyst is depicted. The scenario of Pd redispersion in γ-Al2O3 is significantly different from previously reported activated carbon-supported metal catalysts. Time-controlled CH3I/CO treatment facilitates the rapid redispersion of aggregated Pd particles on γ-Al2O3 surface. The redispersion of Pd promotes the reactivity of Pd/γ-Al2O3 catalyst. For dimethyl carbonate synthesis, the space-time yield increases from 556.9 gDMC·kgcat.−1·h−1 to 1008.9 gDMC·kgcat.−1·h−1. For CO purification, 100% conversion of H2 impurities and the rise of 27.4% in selectivity are achieved. The intrinsic oxidation rate is elevated from 607.8 mmolH2·gPd−1·h−1 to 1166.5 mmolH2·gPd−1·h−1. However, complete oxidation and atomic dispersion of Pd cannot be achieved through further treatments. Combined characterizations verify the particle reconstruction of Pd and the evolution of anchoring sites on γ-Al2O3via strong metal-iodine binding. It reveals a double-edged-sword character of CH3I for Pd redispersion, wherein the excessive treatment results in re-aggregated Pd particles and inferior reactivity.