Catalytic conversion of NO assisted by plasma over Mn-Ce/ZSM5-multi-walled carbon nanotubes composites: Investigation of acidity, activity and stability of catalyst in the synergic system

摘要

Mn-Ce/ZSM5-MWCNTs (MWCNTs, multi-walled carbon nanotubes) catalysts were synthesized via an impregnation method to study NO conversion and sulfur resistance with the assistance of plasma. The reaction proceeded excellently at ambient temperature by using bimetallic manganese-cerium as active component, exhibited superior nitric oxide removal efficiency (around 90%) and turnover frequency at relatively low input energy; XRD, BET, TPD, XPS and in-situ FTIR investigations showed that the highly oxidizing environment, interaction of physicochemical structure, improvement of both Lewis and Bronsted acid sites as well as acceleration of the Eley-Rideal (E-R) mechanism were responsible for this catalyst enhancement. The comparison of characterizations over fresh and spent Mn-Ce catalyst along with mechanistic analysis revealed that valence variation of Mn and Ce cations not only provide oxygen vacancies, but more importantly, directly affect the formation and consumption of Lewis acid sites in whole reaction process. Subsequently, an increased number of Lewis acid sites coordinate NH3 molecules with Mn and Ce atoms, then contribute to ammonia adsorption and rob electrons directly from gaseous NO or nitrate anions as following Eley-Rideal pathway. At last, oxidizing radicals (O, O-3) and cerium modification inhibit further speciation of ammonium and manganese sulfates species on the catalyst surface, thereby promoting low temperature catalytic activity and sulfur durability.