Effects of rare-earth (Nd, Er and Y) doping on catalytic performance of HZSM-5 zeolite catalysts for methyl mercaptan (CH3SH) decomposition

Abstract

A series of HZSM-5 zeolite catalysts modified with various rare earth metals (Nd, Er and Y) was prepared and used for CH3SH catalytic decomposition test. The results revealed that addition of rare earth metals significantly improved activity and stability of the HZSM-5 zeolite catalysts, and Nd-modified catalyst exhibited the best performance. Several characterization studies were undertaken to correlate structural and surface properties of the obtained catalysts with their catalytic performance. It was found that acid-base properties of the catalysts were closely related to the catalytic performance. The NH3-TPD and CO2-TPD analysis showed that the concentration of strong acid sites of the HZSM-5 catalysts decreased after rare earth metals addition, while the concentration of basic sites of the catalysts increased. The decrease in the amount of strong acid sites suppressed the formation of coke on the catalysts. The catalysts with increased amount of basic sites displayed better adsorption ability to CH3SH. The UV–vis, 27Al NMR and XRD analysis indicated that the existence of an empty f orbit Nd3+ caused the increase of non-framework aluminium species amount, which leaded to the decrease of the strong acid sites amount. In addition, the optimal loading amount of Nd was investigated and 13wt%Nd/HZSM-5 catalyst showed no obvious deactivation during 60h test. The spent Nd/HZSM-5 catalyst can be successfully regenerated, showing that Nd/HZSM-5 was an efficient catalyst for CH3SH elimination.