Photoreduction of low concentrations of CO2 into methane in self-assembled palladium/porous organic cages nanocomposites

Self-assembled catalyst has the excellent selectivity and activity at low concentrations of CO2. [Display omitted] •The self-assembled catalyst of CC3/Pd is synthesized.•Catalyst has the excellent selectivity and activity at low concentrations of CO2.•The size effect of Pd nanoparticles has been systematically studied.•The mechanism of catalyst photoreduction CO2 to CH4 is studied. Porous heterogeneous photocatalysts containing both CO2 adsorption and catalytically active sites can be might beneficial to achieve photoreduction of low concentrations of CO2 to methane. Here, we show a self-assembled catalyst by combining catalytically-active Pd nanoparticles and porous organic cages for the CO2-to-CH4 photoreduction reaction in the presence a molecular photosensitizer and a sacrificial reagent. The Pd nanoparticles is vital for the high CH4 selectivity (over 97%) for the CO2 photoreduction reaction, but they suffer from the low catalytic activity. When these Pd nanoparticles are equipped with an underneath support of porous organic cages, it dramatically boosts the catalytic activity with a high production rate of 78.5 μmol g-1h−1, while the CH4 selectivity is up to ∼ 98% (electron basis). Importantly, when the photoreduction is performed under low concentration of CO2 (10% concentration), over 98% of CH4 selectivity and nearly 50% of the catalytic activity for the Pd-based catalysts retains.