The need for sustainable energy sources has intensified interest in biomass upgrading, where biomass-derived feedstocks are transformed into fuels and valuable chemicals. A major challenge in biomass upgrading is the development of highly active, selective, and stable catalysts for complex reactions. Traditional synthesis methods often result in heterogeneous catalysts with poor dispersion of active sites, limiting their efficiency. This thesis explores the use of Atomic Layer Deposition (ALD) as a precise technique for synthesizing catalysts with controlled composition and uniform structure, aimed at understanding correlation between structure and reactivity as well as improving catalyst performance in biomass upgrading applications.To investigate this, I studied a few biomass upgrading reactions by depositing metal oxides and metals on various support materials by ALD. The formation of uniform thin films or highly dispersed particles with ALD was confirmed by XRD, TEM, and FTIR. Catalytic performance was evaluated for biomass upgrading reactions in flow reactor and TPD system. Our results demonstrated that ALD was capable of producing catalysts with well-defined structure, thus enhanced selectivity and stability compared to those produced by conventional methods. This research highlights the effectiveness of ALD in producing single-site and highly dispersed catalysts that improve biomass upgrading efficiency. By enabling precise control over catalyst structure and composition, ALD presents a promising approach for advancing sustainable catalytic processes in renewable energy applications. Future work will explore further optimization of ALD conditions to enhance the scalability and economic feasibility of ALD-synthesized catalysts in industrial biomass conversion