Enhancement of catalytic performance and resistance to carbonaceous deposit of lanthanum (La) doped HZSM-5 catalysts for decomposition of methyl mercaptan

A series of rare earth elements (La, Ce, Pr, Nd, Sm, Y and Er) modified HZSM-5 catalysts were prepared and evaluated their catalytic performance for CH3SH decomposition. XRD, N-2 adsorption-desorption, FT-IR, CO2-TPD and NH3-TPD were conducted to analyze the relationships between catalytic behaviors and their structural characteristics. It indicated that addition of rare earth metal could significantly improve activity and stability of HZSM-5 catalyst for CH3SH decomposition, and the best one was La(13)/HZSM-5 sample. CH3SH can be completely converted over La(13)/HZSM-5 at 450 degrees C compared to parent HZSM-5 at 600 degrees C. The optimal La(13)/HZSM-5 catalyst exhibited excellent stability without significant deactivation even after 80h time-on-stream test, while parent HZSM-5 was rapidly deactivated within 20 h under same reaction conditions. The excellent performance of La(13)/HZSM-5 can be attributed to its tunable acid-base properties, which not only promote adsorption and activation of CH3SH molecule but also effectively inhibit the formation of coke deposit. In addition, spent La(13)/HZSM-5 catalyst can be easily regenerated and no significant deactivation was observed during regeneration process.