Palladium nanoparticles decorated on ZSM-5 derived micro-/mesostructures (MMZ) for nitrophenol reduction and MB degradation in water

Abstract

Palladium-based catalysts are promising for catalytic reduction in catalysis. The dispersion state of palladium nanoparticles (Pd NPs) impacts the catalytic performance, while the development of catalysts with highly dispersed Pd NPs is a major challenge. Herein, we developed ZSM-5 derived micro-/mesoporous silica MMZ to regulate Pd NPs size and dispersion. MMZ was synthesized by combined dissolution of ZSM-5 under basic condition and re-assembly of Al-or Si-containing species of ZSM-5 by cetyltrimethylammonium bromide (CTAB) instead of expensive carbon nanofiber reported earlier. The Pd precursor is introduced into MMZ by ultrasound assisted incipient wetness impregnation (U-IWI) strategy. Up to 1.0 wt% Pd was highly dispersed per g of MMZ without showing any X-ray diffraction lines (denoted as 1.0 Pd/MMZ), while obvious diffraction lines were noticed in the counterpart synthesized from ZSM-5 (denoted as 1.0 Pd/ZSM-5). Further calculation shows the size of Pd NPs in 1.0 Pd/MMZ is 3.5 nm, which is smaller than that in 1.0 Pd/ZSM-5. Our results also demonstrated that well-dispersed and smaller size Pd NPs corresponds to superior catalytic activity in reduction of p-nitrophenol (P-NP) and methylene blue (MB). The typical catalyst 1.0 Pd/MMZ exhibited complete reduction of P-NP and MB in water within 3 min. It is superior to 1.0 Pd/ZSM-5 catalyst with the same Pd content as well as to several reported catalysts. Furthermore, 1.0 Pd/MMZ not only keeps high catalytic activity for 6 consecutive cycles, but also exhibit long-term stability in hydrogenation reaction.