Preparation, Characterization and Catalytic Testing over Bimetallic Pt-Pd/HZSM-5 Catalysts in NO Reduction by Propylene

Bi-functional and bi-metallic ZSM-5 catalysts with different noble metal mass ratios were prepared using the deposition-precipitation method and ionic exchange with NH4+. Systemic XRD, BET/BJH, STEM, and XPS spectroscopy investigations of the structural and electronic properties of these catalysts showed that 2⁓3-nm Pt and Pd metallic nanoparticles were highly dispersed over the ZSM-5 support, with strong interactions between Platinum and Palladium, and a good distribution of the acid sites on the surface of the catalysts which have been observed using the FTIR method by adsorption of pyridine. Considering optimized values of NO/C3H6 ratio=1 and GHSV= 22000 h^-1, some parameters, acidity, temperature, surface morphology, and catalytic activity performance of Pd-Pt/HZSM-5 zeolites were investigated in the selective catalytic reduction of NO by C3H6, Pd-Pt/HZSM-5 bi-functional catalysts exhibited improved catalytic properties relative to their monometallic counterparts. The results show that the active components are uniformly dispersed and distribute well in the micro-porous support. For the Pt0.6Pd0.4/HZSM-5 catalyst, the maximum conversion of NO to N2 approached 63% at 450 ºC with 100% N2 selectivity. By contrast, for the 1%Pt/HZSM-5 catalyst, the maximum NO conversion to N2 reached 52% at 450 ºC and only 42% for 1%Pt/HZSM-5. The Pt0.6Pd0.4/ZSM-5 catalyst also exhibited high durability and catalytic activity at high reaction temperatures.