Jian Li1,3, Hongliang Huang  1,3, Wenjuan Xue1,3, Kang Sun2,3, Xiaohui Song1 , Chunrui Wu1 , Lei Nie  1 ,  Yang Li1 , Chengyuan Liu2 , Yang Pan2 , Hai-Long Jiang  2 ✉, Donghai Mei  1 ✉ and Chongli Zhong  1 ✉ 

    Solar-light-driven reduction of CO2-to-CH4 is a complex process involving multiple elementary reactions and various by-products.  Achieving high CH4 activity and selectivity therefore remain a significant challenge. Here we show a bioinspired photocatalyst  with flexible dual-metal-site pairs (DMSPs), which exhibit dynamic self-adaptive behaviour to fit mutative C1 intermediates,  achieving CO2-to-CH4 photoreduction. The Cu and Ni DMSPs in their respective single-site forms under flexible microenvironment are incorporated into a metal-organic framework (MOF) to afford MOF-808-CuNi. This dramatically boosts CH4 selectivity up to 99.4% (electron basis) and 97.5% (product basis), and results in a high production rate of 158.7 μmol g−1  h−1  with  a sacrificial reagent. Density functional theory calculations reveal that the flexible self-adaptive DMSPs can stabilize various  C1 intermediates in multistep elementary reactions, leading to highly selective CO2-to-CH4 process. This work demonstrates  that efficient and selective heterogeneous catalytic processes can be achieved by stabilizing reaction intermediates via the  self-adaptive DMSP mechanism.

    Photocatalytic CO2 reduction measurements. Here, 25mg of photocatalyst powder  and 50mg (molar concentration 1.3mM) of [Ru(bpy)3]Cl2•6H2O were mixed in  a 50-ml solution containing 30ml of acetonitrile, 10ml of TEOA and 10ml of  H2O in a 250-ml quartz reaction cell. The CO2 (purity >99.999%) was purged into  this reaction cell for 0.5h to eliminate the dissolved oxygen. Before illumination,  the reactor was installed to CEL-SPH2N system (Beijing China Education  Au-light Co., Ltd) equipped with a 300-W Xe lamp with the 420-nm cutoff filter  (420nm<λ<760nm). On degassing,the system was filled with CO2 (purity  >99.999%) to 1 atm. For photocatalytic CO and HCOOH reduction measurements,  10ml of CO (99.999%) or 1ml of liquid HCOOH was injected into photocatalytic  system. Subsequently, the Ar as the packed gas was purged into the system to  reach atmospheric pressure. Gas chromatography (Agilent 7890B) was applied to  analysed gaseous products by the detectors of a thermal conductivity detector and  a flame ionization detector using Ar as the carrier gas. The HCOOH in the liquid  phase was analysed using ion chromatography (Thermo ICS-5000). The possible  alcohol products were detected by a liquid chromatogram (Waterse 2695), and no  related signals could be observed. The catalytic results were repeated three times  with three batches of catalysts to give more reliable data. Gas chromatography– mass spectrometry (Bruker solanX 70 FT-MS) was applied to analyse the isotope  labelled products using 13CO2 as the feed gas. The light intensity data were  measured using a PM100D optical power meter (Thorlabs) equipped with a  S425C detector (Supplementary Table 9). The heterogeneity test was performed by  removing the catalyst from the reaction medium at 6h by centrifugation49.

Download:Nature Catalysis 2021, 4, 719–729 MOF-808-CuNi CO2RR.pdf