Preparation of Pd-Pt/HZSM-5 catalysts and their catalytic performance for low-concentration methane combustion

Pd-Pt/HZSM-5 catalysts were prepared by impregnation method using Pt(NH3)4Cl2 and Pd(NO3)2•2H2O as precursor salts of Pt as well as Pd, and HZSM-5 molecular sieves as carriers. The Pd-Pt/HZSM-5 catalysts with different Si/Al ratios [n(SiO2)∶n(Al2O3)=38∶1, 200∶1, 800∶1], named as Pd-Pt/HZSM-5(38), Pd-Pt/HZSM-5(200) and Pd-Pt/HZSM-5(800), respectively, were characterized by XRD, SEM, TEM, Raman, XPS, CO2-TPD and NH3-TPD, and evaluated on their catalytic activity for low-concentration (0.5% volume fraction) methane combustion by a fixed bed reactor. The results showed that Pd-Pt/HZSM-5(38) exhibited the best catalytic performance with smaller Pd/Pt particle size (6.3 nm), the largest number of PdO crystals, active Pd/Pt species and acidic sites, the highest n(Pd0)∶n(Pd2+) and the highest Pt mass fraction (0.19%). Compared with those of Pd-Pt/HZSM-5(800) and Pd-Pt/HZSM-5(200), the ignition temperature (T10) of low-concentration methane combustion catalyzed by Pd-Pt/HZSM-5(38) decreased by 27.54 and 30.92 ℃, respectively, while the total conversion temperature (T90) was reduced by 3.38 and 17.51 ℃, respectively. Moreover, Pd-Pt/HZSM-5(38) could run stably at 360 ℃ for 150 h with no significant decrease in the activity, and the methane conversion rate was maintained above 99.6%. © 2024 Fine Chemicals. All rights reserved.