We designed and prepared nanocomposite catalysts containing nanosized or sub-nanometer-sized metals or metal oxides for the selective green catalytic reactions, including (1) selective oxidation of propylene by dioxygen to produce acrolein or propylene oxide, (2) selective oxidation of methane by dioxygen to produce methanol or Cn compounds, and (3) CO2 hydrogenation to produce methane or methanol. We applied multiple advanced techniques, including in-situ or operando spectroscopies, to study the catalytic reactions’ kinetics. We anticipated gaining more insights into the reaction mechanisms and the structure-activity relationships for these catalytic systems, which will improve the design of the catalyst further and over catalytic performance.