Nickel nano-particles confined in ZSM-5 framework as an efficient catalyst for selective hydrodeoxygenation of lignin-derived monomers

The present study offers an efficient, economical, non-noble metal based catalytic process for the selective HDO of lignin-derived compounds. HDO of major lignin constituting monomers like vanillin, syringaldehyde, guaiacol, and cresol were studied over Ni(2.5)@ZSM-5 catalysts. Complete conversion of vanillin and syringaldehyde was achieved with >99% selectivity towards creosol and 4-methylsyringol respectively, while the reactions with guaiacol and cresol did not show any conversion. The catalyst is highly selective towards the conversion of the aldehydic group to methyl group. Potential of the catalyst to be used at more realistic conditions was ascertained by evaluating the catalyst with simulated feed prepared by mixing lignin monomers and impurities like S, Na, and K. The catalyst showed excellent results with simulated feed similar to the pure model compounds. Various characterization techniques like XRD, FTIR, NH3-TPD, H2-TPR, UV-DRS, TEM, TGA, etc. were employed to understand the physico-chemical properties of the catalytic material. The nature and location of Ni species in the catalyst were determined as well as the most plausible active center for the HDO reaction was identified. The study revealed that active metal and acid site in close proximity exhibits a synergistic effect which leads to superior catalytic activity. Effect of support acidity was studied in more detail by evaluating the catalysts with variable acidity. The meritorious properties of the catalyst like exceptionally high selectivity, good stability, tolerance for impurities, excellent recyclability as well as economical catalyst formulation make it suitable to be used for the processing of real feeds at realistic conditions.