Controllable Vanillin Hydrodeoxygenation over Co Catalysts: The Mediation of Products

Abstract

Vanillin is one of the most representative lignin depolymerization products and is widely employed as a substrate in thermocatalytic hydrodeoxygenation (HDO) systems. Controllable synthesis of different products from vanillin HDO is significant because of the diverse applications of these compounds. This work aimed to realize controllable production of three high-value lignin-derived products rather than pursuing a single high-yield product. Herein, a series of surfactant-modified cobalt catalysts were synthesized for selective vanillin HDO. By tuning NaOH dosage during catalyst preparation, the product distribution could be flexibly regulated to achieve high yields of 2-methoxy-4-methylphenol (p-cresol, abbreviated MMP), 4-methylcyclohexanol (4-MCYL), or 50.3% of p-cresol. Multiple characterizations revealed that different Co crystal phases dominated the product’s selectivity and distribution. The surfactant adsorbed on the catalyst surface played a key role in orienting the reaction by promoting the vertical adsorption configuration of the vanillin. Cobalt oxide species (CoOx), combined with abundant oxygen vacancies (Ov), acted as Lewis acidic sites to adsorb and activate vanillin molecules, triggering the HDO process. The Co catalysts exhibited excellent catalytic stability over five consecutive cycles and good applicability for HDO of various lignin-derived compounds. The product-tunable strategy demonstrated in this work provides new insights into rationally designing heterogeneous catalysts for converting biomass platform molecules into high-value chemicals.