Efficient depolymerization of Kraft lignin to liquid fuels over an amorphous titanium-zirconium mixed oxide supported partially reduced nickel-cobalt catalyst

Abstract

A series of non-precious metal/metal oxide nickel-cobalt catalysts was prepared for a highly efficient depolymerization of Kraft lignin (KL) into liquid fuels using amorphous TiZr-oxide (Ti1−yZryO2) as a carrier. The effects of Ni-NiOx, Co-CoOx, NiCo-NiCoOx, NiCoOx and NiCo catalysts supported on amorphous TiZr-oxide carrier on KL depolymerization were investigated. It was found that the NiCo-NiCoOx/Ti1−yZryO2 catalyst is optimal for converting KL to petroleum ether (PE)-soluble product (mainly composed of monomers and dimers) in an 80.2% high yield at 320 °C for 24 h, with excellent reusability and a low formation of char. Under these conditions, the higher heating value (HHV) increased from 25.11 to 33.89 MJ/kg. A meticulous study on NiCo-NiCoOx/Ti1−yZryO2 catalysts revealed that the synergistic effect among Lewis acid sites, basic sites and metal active sites played an important role in obtaining high yields of monomers and low rates of char formation during lignin conversion.