Study On Selective Catalytic Reduction Of NO With Propylene Over Au-Pd Catalysts

Nano-gold catalysts have become potential application catalysts in the reaction of automobile exhaust elimination, due to their exceptionally high activities at low temperature and superior ability of resistance to oxidation. Recent years, NO reduction has been studied over monometallic gold catalysts. But the actual application is limited for their narrow temperature window and poor stability at high temperature. Bimetallic nano-gold catalysts exhibit excellent catalytic performance in many reactions due to their unique electronic and geometry properties. However, there were few researches that Au-based bimetallic catalysts were applied to the reaction of NO reduction so far. Therefore, we investigated the performance of selective catalytic reduction of NO with C3H6 over Au-Pd bimetallic catalysts and obtained some significant results as follows:1. A series of Au-Pd bimetallic catalysts with different Au/Pd ratios were prepared by deposition-precipitation method and their catalytic performance in C3H6-SCR of NO reaction was investigated under conditions of 0.2%NO/0.2%C3H6/4%O2/He reaction gas and 24,000 h-1 space velocity. The results demonstrated that Au0.9Pd1.1/Al2O3 catalyst showed better performance regarding the Au- and Pd-/Al2O3. For instance, the maximum NO conversion to N2 for Au0.9Pd0.1/Al2O3 catalyst almost reached 50% at 400℃ with 100% N2 selectivity, while for 1%Au/Al2O3 catalyst, the maximum NO conversion to N2 reached 42% at 450℃ and it only reached 37% at 400℃. Moreover, with the further increase of Pd content, the reaction temperature window would shift to lower temperature, and the conversion of NO to N2 had decreased slightly due to the formation of N2O by-product.2. Different conditions of catalyst preparation process and reaction gas have influenced the performance of C3H6-SCR of NO over Au-Pd bimetallic catalysts, such as preparation method, calcination atmosphere and temperature. It concluded that Au0.9Pd0.1/Al2O3 catalyst exhibited better catalytic performance if it was prepared by DP method and calcined at 400℃ in H2/Ar atmosphere. XRD, STEM-EDX and XPS characterizations indicated that nanoparticles (NPs) of metallic gold and palladium were highly dispersed on γ-Al2O3 support with a size of 2-4 nm, and there was strong interaction between Au and Pd. Also, it resulted that high-concentration oxygen had positive effect on the activity of C3H6-SCR of NO. High-concentration oxygen would promote C3H6 partial oxidation reaction and NO oxidation so that it can form some key reaction intermediates(CxHyOz) and activated species(NOy). Markedly, these intermediates and activated species could facilitate HC-SCR of NO reaction. At last, the stability of Au0.9Pd0.1/Al2O3 catalyst was investigated under conditions of 0.2%NO/0.2%C3H6/4%O2/He reaction gas and 24,000 h-1 space velocity. The NO conversion to N2 maintained stable during 30 h at 400℃, which implied that Au0.9Pd0.1/Al2O3 catalyst was tolerant to excess oxygen atmosphere and high temperature for a long time.3. Au-Pd/SSZ-13 catalysts with different Au/Pd ratios were prepared by impregnation method and their catalytic performance in C3H6-SCR of NO reaction was investigated. It resulted that Au0.25Pd0.25/SSZ-13 showed better performance than monometallic catalysts. The maximum NO conversion to N2 for Au0.25Pd0.25/SSZ-13 catalyst reached 78% at 300℃ with 82% N2 selectivity under conditions of 0.2%NO/0.2%C3H6/4%O2/He reaction gas and 24,000 h"1 space velocity.