Cu⁰/Cu₂O Catalysts For Coupling Photo-Thermal Catalytic Reduction Of CO₂

Sustainable conversion of CO2-H2O to fuel and value-added chemicals using solar energy is one of the effective ways to realize carbon neutral.Here we report direct coupling of photocatalytic water splitting and thermocatalytic CO2 hydrogenation over a bifunctional catalyst by one-pot synthesis.It was found that the prepared Cu0/Cu2O catalyst shows better performance of photocatalytic water splitting,thermocatalytic CO2 hydrogenation and coupling photo-thermal catalytic conversion of CO2-H2O.This dissertation focuses on the following two aspects to explore the preparation of Cu0/Cn2O catalyst and its structure-function relationship for coupling photo-thermal catalytic conversion of CO2-H2O.(1)Cu0/Cu2O catalysts with a close contact Cu0/Cu2O interface and a controllable ratio of Cu0 to Cu2O can be synthesized by tuning the ratio of the reductant agent(N2H4)to Cu precursor.Compared with Cu,Cu2O and mechanically mixed Cu+Cu2O,the performances for photocatalytic water splitting,thermocatalytic CO2 hydrogenation and coupling photo-thermal catalytic conversion of CO2-H2O over Cu0/Cu2O catalysts are improved obviously.The activity of the prepared Cu0/Cu2O catalysts in photothermal catalytic conversion of CO2 and H2O is greatly influenced by the ratio of Cu0 to Cu2O and reaction temperature.Cu0/Cu2O-R2,a catalyst prepared with a N2H4 to Cu precursor ratio of 2:1,exhibited the highest activity,i.e.,13.2 μmol g-1h-1 CO and 2.6μmol g-1h-1 CH3OH at 383 K,which is much higher than those of Cu(3.5 μmol g-1h-1 CO)or Cu2O(4.0μmol g-1h-1 CO).Such enhanced performance is attributed to the formation of the interface between Cu0 and Cu2O,which is beneficial not only to photocatalysis,but also to thermocatalytic CO2 hydrogenation.This result illustrates that a bifunctional catalyst with mixed metal oxidation-states can be prepared by a onepot method and is efficient for improving the performance of direct coupling photothermal catalytic conversion of CO2 and H2O.(2)The Cu0/Cu2OR2 catalysts with controlled shapes from spherical to octahedral were synthesized by adjusting the amount of NaOH.The experimental results show that the activities of photo-thermal catalytic conversion of CO2-H2O over spherical Cu0/Cu2O-R2 catalyst are-4 times higher than those of octahedral one at 383 K.We postulate that the(111)crystal plane exposed by the octahedral Cu2O is positive charged,which is not conducive to the CO2-H2O reduction,while the spherical Cu2O catalyst exposes multiple crystal planes can form more effective Schottky contact sites than the octahedral catalyst,leading to more efficient separation and migration of photogenerated carriers,accelerating the surface reaction,and thus improve the performance of photo-thermal catalytic conversion of CO2-H2O.