Biomass is the only renewable resources on the earth that can be converted to liquid fuels and chemicals to replace fossil resources. Recently, the catalytic conversion of biomass to platform molecules has attracted more and more attentions from the researchers worldwide. γ-Valerolactone (GVL) is regarded as a platform molecule that has extensive application potential, similar to levulinic acid (LA). Up to now, various of catalysts and reaction systems were developed and applied to the selective reduction of biomass-derived LA to GVL, and the hydrogenation of LA can be driven by various hydrogen sources, including molecule H₂, formic acid (FA), syngas and alcohols. In this review, the catalytic hydrogenation routes and recent research progress for the reduction of LA are systematically summarized in view of the diversity of hydrogen sources. The future research trends of the selective reduction of LA to GVL are suggested.

Contents
1 Introduction
2 Catalytic hydrogenation mechanism of LA to GVL
3 Production of GVL using external molecule H₂ as a hydrogen source
3.1 Heterogeneous catalytic systems
3.2 Homogeneous catalytic systems
4 Production of GVL using FA as a hydrogen source
5 Production of GVL using syngas as a hydrogen source
6 Production of GVL using alcohols as a hydrogen donor
7 Conclusion and outlook