Driven by the rising environmental concerns linked to massive exploitation of fossil resources and the resulting increase of CO2 emissions the development of the lignocellulosic biorefinery for the conversion of biomass into energy, chemicals, and materials, is playing a critical role in the transition toward a more circular, sustainable economy. The foremost objective of any biorefinery is to obtain valuable products from its carbohydrate fraction (cellulose and hemicellulose), and also make efficient use of the lignin for the production of aromatic chemicals. Besides, bio-oils obtained from the thermochemical processes like pyrolysis and hydrothermal liquefaction of biomass can be a prominent source of high-value chemicals. However, its upgradation is required to reduce its high oxygen content for its uncomplicated transportation, storage and further processing. In this view, the present work aims at studying heterogeneous catalytic processes, namely reductive catalytic fractionation (RCF), and hydrodeoxygenation (HDO) for the upgradation of biomass, biomass-derived oxygenates, and bio-oils. Firstly, RCF is studied for the separation of lignin from the biomass in its stable and useful form. The activity of carbon supported Pt-, Pd-, Ni-, and Ru-catalysts, and the effect of reaction conditions on the degree of lignin separation and product selectivity is studied. As a next step, effects of catalyst support (carbon, alumina, silica and zeolite) on the Ru-catalysed RCF are evaluated. Secondly, HDO of single and binary mixtures of bio-oil oxygenates is studied using a set of carbon supported Pt-, Pd-, and Ru-catalysts and zeolite Y supported Pt catalysts. In the HDO of binary mixtures of oxygenates, the effects of acid, ketone, and aldehyde functional groups on the HDO of guaiacol (a major bio-oil oxygenate) is evaluated. Further, the optimum catalyst is being studied for the HDO of bio-oil obtained from the biomass pyrolysis. In summary, this work is focused on understanding the role of various catalysts and effects of reaction parameters on the valorization of biomass and bio-oils.