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 degrees C. 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 degrees C 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 degrees C in 3 min with an apparent rate constant k(app) of 2.3 x 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 H-2/Ar at 300 degrees C for 30 min, the highest activity is achieved in case of 0.5Pt1.5Ag/CeO2 catalyst characterized by 94% 4-NP conversion at 23 degrees C in 3 min with the kapp of 1.6 x 10(-2) s(-1) and the kMe of 152,100 s(-1) mol(-1).