Lignin valorization by cobalt-catalyzed fractionation of lignocellulose to yield monophenolic compounds.

Herein, we present a catalytic reductive fractionation of lignocellulose using a heterogeneous cobalt catalyst and formic acid or formate as a hydrogen donor. The catalytic reductive fractionation of untreated birch wood yield monophenolic compounds in up to 34 wt% yield of total lignin, and this corresponds to 76% of the theoretical maximum yield. By model compound studies, we found that the main role of the cobalt catalyst is to stabilize reactive intermediates formed during the organosolv pulping by transfer hydrogenation and hydrogenolysis reactions. In addition to this, the cobalt catalyst is responsible for depolymerization reactions of fragments of lignin by transfer hydrogenolysis reactions targeting the β-O-4' bond. We were able to recycle the catalyst three times with only negligible decline in efficiency showing the robustness of this novel system.