*5.2.5 Hydrogenolysis*

Hydrogenolysis is a reaction that breaks ether bonds in lignin at high temperature and hydrogen in the presence of a catalyst. For example, in the presence of Ni, lignin is converted into aromatics compounds such as dihydroconiferyl alcohol, dihydroxysinapyl alcohol, guaiacol, and 4-propylsyringol. In hydrogenolysis, the selective reaction on specific bonds of the lignin towards valuable chemicals, identification and separation of the specific product from the complex mixture of aromatics is a challenging task [26].
