Comprehensive investigation of Pd/ZSM-5/MCM-48 composite catalysts with enhanced activity and stability for benzene oxidation

ZSM-5/MCM-48 composite materials with various acidities have been successfully assembled on zeolite seeds via a two-step crystallization process. The characterization results reveal that the ZSM-5 seeds are present in the framework of the resulting composite materials with its content gradually increasing with the Si/Al molar ratio, and Al atoms prefer the tetrahedral coordination in composite products. The amount of strong acid sites increases as the Si/Al molar ratio decreases, while that of weak acid sites is almost unchanged. The activity tests demonstrate that the catalytic activity of Pd-loaded ZSM-5/MCM-48 composite catalysts is much higher than that of Pd/ZSM-5 and Pd/MCM-48, and all these catalysts are active and stable in the total oxidation of benzene. Both Pd0 and Pd2+ are responsible for the oxidation reaction, and the catalytic activity is closely related to the support acidity, the CO2 desorption capability and the Pd dispersion. This research thus indicates that the novel composite materials have promised as active Pd-supported catalysts in the elimination of volatile organic compound (VOCs).