Cobalt-promoted palladium confined in HZSM-5 zeolite for toluene storage and oxidation capacity in humid environment

Abstract

Although oxide-zeolite bifunctional catalysts with storage and oxidation capacity was efficient for VOCs removal, the inevitable moisture in the air usually harms the catalysts performance. Herein, cobalt was in situ confined with palladium in HZSM-5 by a one-pot hydrothermal method and significantly improved the storage and oxidation abilities in humid air. The optimal Pd0.90Co0.10@Z5 catalyst showed a considerable toluene storage capacity of 76.8 mg/g (100 ppm toluene/humid air, GHSV=60,000 h−1), and the best oxidation activity (600 ppm toluene/humid air, GHSV=60,000 h−1, TOFPd = 15.5 × 10−3 s−1 at 200 °C). Pd0.90Co0.10@Z5 formed an intrapenetrated mesoporous structure with the smallest Pd clusters of dAV=2.6 nm. The synergistic effect between palladium and cobalt promoted electron transfer and Pd0.90Co0.10@Z5 had the highest Pd2+/Pd0 ratio of 3.50. Co2+ can activate water to form Co(OH)3 and provide an additional ·OH oxidation pathway, ·OH and reactive oxygen species (O*) together promote the deep oxidation of intermediates. This work provides a novel approach that bimetallic collaboration combined with porous zeolite can improve the catalytic performance and water resistance.