Elucidating Metal Composition–Coking Relationships and Coke Formation Pathways of the Gas Phase Oxydehydration of Glycerol over Clay Mineral-Supported Mo-V-O Catalysts

Catalyst deactivation by carbon deposition remains a major obstacle in many important industrial processes, such as catalytic gas-phase oxydehydration of glycerol. Understanding the chemical nature and development of coke species during the time-on-stream (TOS) of the catalytic solids is therefore crucial for mitigating the extent of coking and in the design of regeneration process of the coked catalysts. In this study, multiple analytical techniques, including SEM, XRD, FTIR, Raman, GC-MS, XPS, and 13C solid-state MAS NMR were employed to gain insights into the coking behavior of acid-activated montmorillonite (HMMT) supported Mo-V oxide catalysts with modulated metal ratios, along with soluble and insoluble coke compositions and their evolution over time. Insoluble coke was comprised of polycyclic aromatic compounds with 5 or more fused-benzene rings containing different types of oxygen-bonded groups, such as −OCH3, −COOH, −CHO, and −OH. The major chemical constituents of soluble coke were mononuclear aromatic derivatives (i.e., xylenes, 2,4-di-tert-butylphenol, and 1-hydroxycyclohexyl phenyl ketone) and paraffinic hydrocarbons with 12-18 carbon atoms. The latter species is thought to have formed from linear oligoglycerols through deoxygenation. The insights presented in this study provides a deeper understanding of the coking process during gas-phase oxydehydration of glycerol and may aid in the design of more robust supported Mo-V-O catalysts with superior coke resistance.