Renewable energy, currently occupying an appreciable portion of global energy, plays a major role in reducing greenhouse gas emissions. Biomass resources, which are superior to other renewables in terms of flexible transportation and storage, are widely available. Renewable liquid fuels production is the central theme of biomass conversion due to the significant market demand in the transportation sector. Coproduction of high value-added chemicals in an integrated biorefinery is also important from an economic perspective. However, there are still significant challenges for developing efficient biomass conversion technologies that would produce cost-competitive fuels and chemicals. Conventional thermochemical processes including pyrolysis or gasification have been extensively studied but still suffer from various drawbacks such as energy-intensive, low carbon efficiency, and so on. In contrast, liquid-phase processes have not been explored as thoroughly but have the potential to achieve high efficiencies.In this dissertation, four different liquid-phase catalytic processes are investigated for the conversion of a variety of biomass feedstocks: First, carbohydrates were converted to lactic acid over a perovskite LaCoOx catalyst with the redox properties in hydrothermal media. Second, dairy manure was fractionated and transformed to ethyl lactate, aromatic esters, and ethyl fatty acid esters, etc. in supercritical ethanol with the Zr-SBA-15 Lewis acid catalyst. Third, the aqueous-phase hydrodeoxygenation of Grindelia biocrude was carried out on the bifunctional heterogeneous palladium on tungstated zirconia catalyst. Lastly, the novel biphasic tandem catalytic process (BiTCP) was used to convert mono- and diterpenoids to cycloalkanes, which are high-density jet fuel components, with the homogeneous trifluoroacetic acid and the hydrophobic carbon-supported palladium catalysts in aqueous and cyclohexane solutions, respectively. This novel process was able to convert fatty acids and triglycerides to renewable diesel efficiently. Remarkably high carbon efficiencies were obtained in the conversion of terpenoids and lipids to paraffinic hydrocarbons. For each liquid-phase catalytic process, the reaction mechanism was investigated to gain a fundamental understanding of the effects of catalyst properties and process conditions on the conversion of the different types of biomass feedstock. The recommendations for future research are included at the end of the dissertation
