Visible-light deep reduction of low concentration CO2 over composite catalyst Ru/CoAl-LDH and the performance enhancement mechanism

DAI Jun; JIA Fengting; YANG Juan; FENG Zhixiang; WANG Dazhao; LENG Chongchong

doi:10.13225/j.cnki.jccs.2024.1194

Abstract：Under the dual-carbon goal,the resource utilization of CO2 driven by clean and renewable solar energy has be-come an important research topic.However,the previous reports have mostly used high-purity CO2 as the research object,while the CO2 concentration in the flue gas emitted by coal-fired power plants is only 3％-15％.To avoid the high-energy CO2 enrichment process,photocatalytic directional conversion of low concentration CO2 into high-valued fuels or chemic-als has important scientific significance for energy saving,emission reduction and its resource utilization.Cobalt-alumin-um layered double hydroxide(CoAl-LDH)was firstly prepared by coprecipitation-hydrothermal method and visible-light catalysts Ru/CoAl-LDH were constructed by loading ruthenium nanoparticles onto the surface of CoAl-LDH via surface impregnation coupled with hydrogen heat treatment.The unique surface composition and structural characteristics of Ru/CoAl-LDH composites are conductive to implement deep photoreduction of low concentration CO2 using H2O as the hydrogen source.Structural composition and micro-morphology of the composite catalysts Ru/CoAl-LDH were determ-ined by X-ray diffraction,transmission electron microscopy,X-ray photoelectron spectroscopy and ultraviolet-visible dif-fuse reflection spectroscopy.The results indicate that the loaded Ru species is zero valence state of metal Ru.Loading Ru has no effect on the nano-lamellar morphology of CoAl-LDH,but can significantly improve the photoresponse perform-ance of composite catalysts.By using Ru/CoAl-LDH as photocatalysts,H2O as electron donor and hydrogen source,and 10％CO2/N2 mixture as simulated flue gas,the effect of Ru loading amount on the productivity of CO2 reduction products and the selectivity of deep reduction products were investigated under visible light irradiation.1.6％Ru/CoAl-LDH exhib-ited the optimal CO2 photoreduction performance.After 3 hours of visible light irradiation,the productivity and selectiv-ity of deep reduction product methane reached 452.4 μmol/g and 86.3％,which were 10.4 and 3.3 times of single CoAl-LDH,respectively.Meanwhile,the performance enhancement mechanism on deep photoreduction of low concentration CO2 was explored by using CO2 adsorption isotherms,in-situ XPS,transient photocurrent and impedance spectroscopy.The—OH groups on the surface of CoAl-LDH facilitate selective adsorption of composite catalysts for low concentration CO2.Excellent H2O oxidation performance of CoAl-LDH can provide sufficient in-situ hydrogen source for deep photore-duction of CO2,without the use of H2 having explosive risk.As the photoelectron acceptor,the loaded Ru can not only en-hance the separation and migration efficiency of photogenerated charges,but also implement multi-electron reduction as active reductive sites of CO2.Therefore,the synergistic effect of CoAl-LDH and cocatalyst Ru is the primary reason for the improvement of low concentration CO2 deep photoreduction performance.The composite catalysts Ru/CoAl-LDH realize the effective coupling of visible-light water oxidation and low concentration CO2 deep reduction,providing import-ant theoretical guidance for the construction of essentially safe and low-energy consumptive CO2 conversion system.It also provides a new idea for the resource utilization of CO2 from coal flue gas.