CeO2-supported Pt–Ag bimetallic catalysts for 4-nitrophenol reduction

The present work is focused on designing of ceria-supported Pt–Ag bimetallic catalysts for 4-nitrophenol reduction with NaBH4. The series of ceria-supported monometallic (Pt or Ag) and bimetallic Pt-Ag catalysts are prepared by wetness impregnation followed by calcination in air at 500 °С. The bimetallic 2-xPtxAg/CeO2 samples with a total metal loading of 2.0 wt% and Pt:Ag mass ratios of 1.5:0.5, 1:1, and 0.5:1.5 show superior activity caused by the formation of bimetallic Pt–Ag species upon simultaneous reduction of highly dispersed interplaying PtOx and silver species. The Ag addition to Pt and the conditions of the bimetallic catalyst treatment ensure the fine-tuning of the metal–support interactions and enhance the catalyst activity. The optimal Pt:Ag ratio in the bimetallic Pt-Ag catalysts depends on the sample pretreatment affecting the composition and dispersion of the surface Pt–Ag species formed. For samples calcined in air at 500 °С for 2 h and reduced with NaBH4 in the reaction mixture, the highest activity is achieved for the 1Pt1Ag/CeO2 catalyst characterized by the complete 4-NP conversion at 23 °С in 3 min with an apparent rate constant kapp of 2.3 × 10−2 s−1 and a specific rate constant kMe of 223,500 s−1 mol−1. For the air-calcined samples pre-reduced in H2/Ar at 300 °С for 30 min, the highest activity is achieved in case of 0.5Pt1.5Ag/CeO2 catalyst characterized by 94% 4-NP conversion at 23 °С in 3 min with the kapp of 1.6 × 10−2 s−1 and the kMe of 152,100 s−1 mol−1.