**4.2. Hydrogenation in general**

Hydrogenation is one of the depolymerisation strategies of lignin which utilise hydrogen as a reductant to yield aromatic products with lower oxygen content and higher stability than other strategies (c.f. **Figure 6**) [47]. This process operates in mild condition affording highvalue fine chemicals. However, it is extremely difficult to selectively yield products towards aromatic such as C=C, linear C=C, C=O, C=C, etc. due to the nature of catalysts and reaction conditions. In this process, the selection of the suitable catalysts is the critical parameter to ensure the desired products can be achieved.

**Figure 6.** Summary of lignin conversion process (note: the abscissa represents the typical temperature range of the lignin conversion processes). Reprinted with permission Ref. [47]. Copyright (2015) American Chemical Society.
