Supported bimetallic AuRh/γ-Al2O3 nanocatalyst for the selective catalytic reduction of NO by propylene

A new method entitled Ultrasound-assisted Membrane Reduction (UAMR) was developed to prepare highly dispersed monometallic Rh/γ-Al2O3 and bimetallic AuRh/γ-Al2O3 catalysts. In this process, the reductant (NaBH4) solution is infiltrated through ceramic membrane tubes to a flowing suspension mixture of noble metal precursors and γ-Al2O3, and then the noble metal ions were reduced and deposited on the γ-Al2O3 to form nanoparticles or clusters on the surface of the carrier. The smaller noble metal nanoparticles (∼5 nm) and higher activity for the selective catalytic reduction (SCR) of NO by propylene at low temperature were obtained over the catalysts prepared by the new method, compared to the catalysts prepared by conventional impregnation method. The AuRh/γ-Al2O3 catalyst with 0.33 wt% Au and 0.17 wt% Rh (MRh:MAu = 1:1) loading exhibited higher propylene and NO conversions but lower NO conversion to N2 than 0.5 wt% Rh/γ-Al2O3 catalyst, both of which were fabricated by the new preparation process. The stronger NO adsorption capability and formation of surface nitrates were validated over bimetallic AuRh/γ-Al2O3 catalysts in NO-TPD experiment. The synergistic effect of bimetallic system could improve the performance of SCR of NO and reduce the cost for platinum group metals based catalysts.