Converting carbon dioxide (CO2) to hydrocarbons that can be used as fuels is beneficial from both environmental and economic points of view. In this study, nanoparticles are designed to enhance the photoreduction of CO2 on a titanium dioxide (TiO2) catalyst. An increase in catalytic activity is reported when silver (Ag), platinum (Pt) or bimetallic Ag-Pt and core-shell Ag@silica (SiO2) nanoparticles are used with the TiO2 semiconductor catalyst. Nanoparticles with different elemental composition or geometrical structure facilitate successive photo-excitation steps-generation, transport, storage and interfacial transfer of electrons and holes. Results show that while the addition of either type of nanoparticles augments product formation rates, bimetallic co-catalysts improve product selectivity. When both bimetallic co-catalysts and Ag@SiO2 nanoparticles are used in combination, product yields are enhanced more than seven fold in comparison to native TiO2 and high selectivity for methane (CH4) is observed. When the bimetallic Ag-Pt co-catalysts are tuned, a selectivity of CH4 of approximately 80%, as compared to 20% with only TiO2, can be achieved.