Ammoxidation of C2 hydrocarbons over Mo–zeolite catalysts prepared by solid-state ion exchange: Nature of molybdenum species

• The solid-state exchange of MoCl3 into MFI, BEA, and MOR zeolites is efficient.
• The intensity of dominant XRD peak enlightened the agglomeration state of MoO3.
• The elucidation of Mo species in zeolites is possible by measuring band gap energy.
• Mo contributes in the global acidity with MOR zeolite, having small apertures.

Successful introduction of molybdenum (from MoCl3) into zeolites of different topologies was carried out using solid-state ion exchange. MOR like support extended the formation of Mo oxides due to its particular aperture/channel-shapes. However, BEA and MFI (ZSM-5) zeolites structures loaded small aggregates of Mo oxide. Exchanging MoCl3 with NH4+–BEA, H+–ZSM-5 (Si/Al = 15) and NH4+–ZSM-5 (Si/Al = 26) led to the consumption of Brönsted acid sites and silanol groups, while the lack of exchange sites in NH4+–MOR generated Mo–OH as revealed by DRIFTS and TPD of NH3. Polymeric Mo and MoO3 occupied the bulk of BEA and MOR issued solids. Nevertheless, NH4+–ZSM-5 (Si/Al = 26) support triggered the formation of dimeric species. For H+–ZSM-5 (Si/Al = 15) solid, monomeric species migrated throughout the channels of H+–ZSM-5, which condensed easily to form rather polymeric species. Small oxide crystallites and Mo moieties that weakly interact with NH4+–BEA and NH4+–ZSM-5 (Si/Al = 26) were easily reduced under hydrogen, while the negatively charged H+–ZSM-5 (Si/Al = 15) framework inhibited the reducibility.

Figure optionsDownload as PowerPoint slide