Conversion of fly-ash into pristine ZSM-5 and its application for methane dehydroaromatization reaction

Abstract

Increasing Fly-Ash (FA) residues as a by-product in pulp/paper industries requires efficient routes for green and economical ash management. Converting FA into zeolite shows great potential for its efficient utilization. In this work, FA received from Indian paper mills was converted into pristine ZSM-5, support in methane dehydroaromatization (MDA). Following acid leaching, Fe and Al content were reduced to make ash residue, a precursor for ZSM-5 synthesis. Synthesized FA-derived ZSM-5 consisted of a highly crystalline structure (91 %) and high BET surface area (468 m2/g) comparable to commercial ZSM-5. Synthesized ZSM-5 (FA) possessed micropores/mesopores, with comparatively smaller particle size as confirmed by pore size distribution analysis/N2-sorption isotherms and SEM analysis. NH3-TPD study confirmed the acidity content (1.16 mmol/gcat) over ZSM-5 (FA) and was found to be compatible with that of commercial ZSM-5 (1.58 mmol/gcat). Further, the activity of ZSM-5 (FA) with 5 wt% Mo loading was evaluated towards MDA reaction and compared its activity with conventional Mo/HZSM-5. Higher activity was achieved with 5Mo/HZSM-5 (FA-derived) exhibiting a higher benzene production rate than the 5Mo/HZSM-5 due to effective textural properties and suitable acidity, which provides sites for dispersion of MoOx species in case of Mo/ZSM-5 (FA) thereby conferring improved activity.