Unsupported CoMoS catalysts for isoeugenol hydrodeoxygenation: optimisation of synthesis parameters for catalyst performance

Hydrodeoxygenation of isoeugenol as a model compound for lignocellulosic biomass-derived oils has been studied in this work. A series of unsupported cobalt-doped molybdenum oxide and sulfide catalysts were prepared via hydrothermal precipitation to systematically study the effect of catalyst preparation conditions on catalyst properties and catalytic performance. The effects of the preparation temperature, excess sulfur, and pH and their combinations were studied using a design of experiments approach. The catalysts were characterized with ICP-OES, N₂ physisorption, XRD, XPS and SEM-EDS and screened for bio-oil model compound isoeugenol hydrodeoxygenation under relevant process conditions of 300 °C and 30 bar in a batch reactor. Co was observed as a sulfide, while molybdenum exhibited mixtures of the oxide and sulfide, with the former favored under preparation conditions with less sulfur. The catalyst performance testing revealed a higher activity and increased deoxygenation selectivity of the sulfide catalysts compared to those of the oxide catalysts. In addition to the chemical nature, the catalyst activity in the model reaction was increased by the high pore volume and surface area, which were promoted by a low pH at the start of the synthesis. The observed tendencies provide a basis for catalyst tailoring in hydrotreatment processes for biofuel and biochemical production from lignocellulosic biomass.