Co-immobilization of a Rh Catalyst and a Keggin Polyoxometalate in the UiO-67 Zr-Based MetalOrganic Framework: In Depth Structural Characterization and Photocatalytic Properties for CO2 Reduction [component]

The Keggin-type polyoxometalate (POM) PW12O40 3-and the catalytic complex Cp*Rh(bpydc)Cl2 (bpydc = 2,2'bipyridine-5,5'-dicarboxylic acid) were co-immobilized in the Zr(IV) based metal organic framework UiO-67. The POM is encapsulated within the cavities of the MOF by in situ synthesis and then, the Rh catalytic complex is introduced by postsynthetic linker exchange. Infrared and Raman spectroscopies, 31 P and 13 C MAS NMR, N2 adsorption isotherms and X-ray diffraction indicate the structural
more » ... e the structural integrity of all components (POM, Rh-complex and MOF) within the composite of interest (PW12,Cp*Rh)@UiO-67. DFT calculations identified two possible locations of the POM in the octahedral cavities of the MOF: one at the center of a UiO-67 pore with the Cp*Rh complex pointing towards an empty pore and one off-centered with the Cp*Rh pointing towards the POM. 31 P-1 H heteronuclear (HETCOR) experiments ascertained the two environments of the POM, equally distributed, with the POM in interaction either with the Cp* fragment or with the organic linker. In addition, Pair Distribution function (PDF) were collected on the POM@MOF composite and provided key evidence of the structural integrity of the POM once immobilized into the MOF. The photocatalytic activity of the (PW12,Cp*Rh)@UiO-67 composite for CO2 reduction into formate and hydrogen were evaluated. The formate production was doubled when compared with that observed with the POM-free Cp*Rh@UiO-67 catalyst and reached TONs as high as 175 when prepared as thin films, showing the beneficial influence of the POM. Finally, the stability of the composite was assessed by means of recyclability tests. The combination of XRD, IR, ICP and PDF experiments were essential in confirming the integrity of the POM, the catalyst and the MOF after catalysis. ASSOCIATED CONTENT Experimental and computational details. This material is available free of charge via the Internet at
doi:10.1021/jacs.0c02425.s001 fatcat:jxmhhee655cw5icqhh4wgsjs3m