Conversion of Kraft lignin to phenol monomers and liquid fuel over trimetallic catalyst W-Ni-Mo/sepiolite under supercritical ethanol

Abstract

Highly efficient conversion of lignin to value-added liquid fuel or phenol monomers has attracted widespread attentions. The W-Ni-Mo/SEP trimetallic catalyst was firstly prepared and used for lignin catalytic depolymerization (LCD) under supercritical ethanol, which significantly ameliorated the problem of complex product compositions and poor cycle-stability in Mo/SEP. Characterization results confirmed that doping W and Ni metals led to the transformation of metallic oxide phases, and then increased oxygen vacancies (OV), enhanced the metal-support interaction, and lowered acid site content. The experimental results revealed that W-Ni-Mo/SEP yielded 39.56% of lignin oil (LO) with 32.37 MJ/kg of HHV at 280 °C for 4 h. The selectivity to guaiacol and ethoxyphenol monomer was remarkably increased as compare with Mo/SEP. Furthermore, the W-Ni-Mo/SEP catalyst exhibited unique cycle stability and produced LO even increased to 41.41% after five LCD cycles. The possible reaction paths of lignin converted to guaiacol and ethoxyphenol over W-Ni-Mo/SEP were proposed. Brønsted-acid site promoted the self-activation of ethanol to form aliphatic products. The higher OV preferentially adsorbed phenol-intermediates containing dual oxygens and activated direct dealkylation to obtain guaiacol. The lower Lewis-acid site promoted the demethylation of methoxy in side-chains of phenol-intermediates and then interacted with free ethyl groups to form ethoxyphenol.