Catalysis Today, Vol.339, 148-158, 2020
The influence of Pt loading and dispersion on the NOx storage and reduction performance of Pt/K2CO3/Co1Mg2Al1Ox catalysts
For NOx storage and reduction (NSR) catalysts, Pt is necessary for the NO oxidation during the lean stage and the NOx reduction during the rich stage. However, due to its high price, synthesis of NSR catalysts with low Pt loading is highly demanded. In this contribution, Pt/K2CO3/Co1Mg2Al1Ox as NSR catalysts with low Pt loadings (0.15, 0.33 and 0.59 wt%) were prepared via co-precipitation and incipient wetness impregnation methods. The optimal of K2CO3 loading was determined to be 15 wt% for both samples. The influence of Pt particle size and Pt dispersion on the NOx storage capacity and the NSR cycling performance of Pt/K2CO3/Co1Mg2Al1Ox were then systematically and comparatively investigated. It was demonstrated that the samples prepared by CP method can result in higher isothermal NOx storage capacity, and higher NOx removal rate and better cycle stability during lean-rich cycling tests. By increasing the Pt loading or extending the rich period duration, the overall NOx removal rate can be promoted and became more stable. No matter what method was used for loading Pt, the N-2 selectivity of all catalysts was higher than 95%. The results also indicated the samples prepared by CP method were more resistant to the effects of SO2, CO2 and H2O. CO-pulse and HR-TEM analyses confirmed that the 0.59 Pt/Co1Mg2Al1Ox (CP) possesses smaller Pt particle size (1.30-1.32 nm) and higher Pt dispersion (65.41%), while the values for 0.59 Pt/Co1Mg2Al1Ox (IWI) was 2.66-2.71 nm and 31.90%, respectively. All results indicated that the CP method, which can effectively improve Pt dispersion and reduce the Pt particle size, is superior to the traditional IWI for the preparation of highly efficient low Pt loading NSR catalysts.