Preparative aspects of supported Ni2P catalysts for reductive upgrading of technical lignin to aromatics

Supported Ni2P was evaluated as a hydrodeoxygenation (HDO) catalyst in the reductive upgrading of a soda lignin in supercritical ethanol by a hydrotalcite-derived mixed Cu-Mg-Al oxide (CuMgAlOx) catalyst. Various Ni2P catalysts were prepared by different approaches on silica, γ-alumina and a siliceous amorphous silica-alumina (ASA) supports. Calcined NiO/SiO2 precursors were impregnated with phosphate, phosphite and hypophosphite followed by reduction. With γ-alumina, the desired Ni2P could not be obtained, presumably due to the reaction of the P-source with alumina. NiO on ASA could be converted to Ni2P by addition of phosphite, preferably at a P/Ni ratio of 1. Low P/Ni ratio avoids blockage of the pores by P-oxide species remaining after reduction. By further comparison to a sol–gel prepared NiO/SiO2 and co-impregnated silica, it was established that the most active Ni2P catalyst was obtained by impregnation of NiO/SiO2 with phosphate at P/Ni = 1 and reduction at 620 °C. In combination with CuMgAlOx, more than half of soda lignin can be converted to aromatics monomers with a relatively high degree of deoxygenation and limited degree of ring hydrogenation. The co-catalyst system is more active than the separate catalysts.