Morphology-selective synthesis of active and durable gold catalysts with high catalytic performance in the reduction of 4-nitrophenol

A series of novel catalysts consisting of nanosized Au particles confined in micro-mesoporous ZSM-5/SBA-15 (ZSBA) materials with platelet (PL), rod (RD), and hexagonal-prism (HP) morphologies have been synthesized in situ. These catalysts possess both SBA-15 and ZSM-5 structures and exhibit excellent stability of their active sites by confinement of the Au nanoparticles (NPs) within ZSBA. The catalysts have been characterized in depth to understand their structure-property relationships. The gold NP dimensions and the pore structure of the catalysts, which were found to be sensitive to calcination temperature and synthetic conditions, are shown to play vital roles in the reduction of 4-nitrophenol. Au/ZSBA-PL, with short mesochannels (210 nm) and a large pore diameter (6.7 nm), exhibits high catalytic performance in the reduction of 4-nitrophenol, whereas Au/ZSBA-HP and Au/ZSBA-RD, with long mesochannels and relatively smaller pore sizes, show poor catalytic activities. In the case of catalysts with different gold NP sizes, Au/ZSBA-PL-350 with an Au NP diameter of 4.0 nm exhibits the highest reaction rate constant (0.14 min(-1)) and turnover frequency (0.0341 s(-1)). In addition, the effect of the reaction parameters on the reduction of 4-nitrophenol has been systematically investigated. A possible mechanism for 4-nitrophenol reduction over the Au/ZSBA catalysts is proposed.