In Situ Mass Spectrometric Analysis on Zeolite-Catalyzed Pyrolysis of Furanic Compounds: The Role of Reactive Intermediates

Reactive intermediates are essential for determining the reaction mechanism of biomass pyrolysis. However, these short-life compounds are rarely reported because they are difficult to probe and identify. Here, the catalytic pyrolysis of furanic compounds over HZSM-5 was investigated by combining a low-pressure reactor and an in situ synchrotron vacuum ultraviolet photoionization molecular beam mass spectrometer (SVUV-PI-MBMS). Important reactive intermediates (m/z < 200) can be detected and characterized by this in situ analysis method, which also allows studying the dynamics of volatile formation as a function of catalyst deactivation. Strikingly, formaldehyde and acetaldehyde as reactive intermediates in the upgrading of 5-methylfurfural (5-MFF) are mainly produced from its side-chain cracking on the external surface of the zeolite, while their conversion is highly related to the contribution of the Brønsted acid site inside the zeolite. It is also evidenced that reactive methylcyclopenadienes (MCPDs) are formed from various compounds (alkynes, furans and olefins) and can be further converted to methylbenzenes (MBs) via ring-expansion. Finally, more complete conversion pathways that contain reactive intermediates for zeolite-catalyzed pyrolysis of furanic compounds are proposed. The key roles of some reactive intermediates in promoting the deoxidation and aromatization of furans are also illustrated.