This lecture covers the catalytic processes involved in downstream fuel synthesis, such as methanation, gas cleaning, and methanol synthesis. It discusses the conversion of CO and H2 to CH4, the removal of CO for fuel cells, and the production of clean fuels from biomass and coal. Various catalytic reactions and processes, including the Sabatier, Fischer-Tropsch, and Haber-Bosch reactions, are explored. The lecture also delves into the application of catalysis for emission control and energy production, highlighting the importance of catalysts in fuel synthesis and gas upgrading.