Promoting effect of trace amount of Pd for p-CNB hydrogenation in Pd-Au/TiO2 bimetallic catalyst

Pd-Au bimetallic catalysts supported on TiO2 with traces of Pd for p-chloronitrobenzene (p-CNB) hydrogenation were prepared by the deposition-precipitation method. It is found that the ultra-low loading of Pd can improve significantly the catalytic activities of Pd-Au/TiO2 bimetallic catalyst compared with Au/TiO2. The minimal loading of Pd favors the Au dispersion and leads the Au NPs with small size. The existence of a large number of Au/Pd interfaces and the interaction between Au and Pd make Au NPs surface electron-enriched (Au delta-) and the Pd positively charged (Pdn+). The synergetic effect of Au delta-, Pdn+, and Pd0 improves the catalytic performance of 0.01 %Pd-0.5 %Au/TiO2. For 0.01 %Pd-0.5 %Au/TiO2, the p-CNB conversion is 99.9 %, with p-CAN selectivity of 98.6 %. After eight circles of reuse, the conversion of p-CNB and the selectivity of p-CAN is still as high as 98.18 and 99.97 %, respectively, indicating the good stability of 0.01 %Pd-0.5 %Au/TiO2. Through twenty times scale-up preparation or after sixty days of storage, our catalysts still maintain excellent catalytic performance in p-CNB reduction, demonstrating the promising prospects of 0.01 %Pd-0.5 %Au/TiO2 for industrial applications. This work offers a facile method to design bimetallic noble metal catalysts with excellent catalytic activities and good reusability, and clarifies their potential applications in industry.