CuPd Mixed-Metal HKUST-1 as a Catalyst for Aerobic Alcohol Oxidation

Metal-organic frameworks (MOFs) featuring isolated coordinatively unsaturated metal sites (CUS) have enormous potential as single-site catalysts. In particular, mixed-metal MOFs may exhibit unique catalytic properties compared to their monometallic counterparts. Herein, we report a thorough fundamental study on the mixed-metal CuPd-HKUST-1 ([Cu_3-xPd_x(BTC)₂]_n; BTC = 1,3,5-benzenetricarboxylate) including the two-step synthesis, characterization, and catalytic performance evaluation. The combined results from a multitechnique approach provide solid evidence that the chemical properties of HKUST-1 can be tuned via successful incorporation of Pd-CUS into the framework, leading to the formation of new Cu-Pd and/or Pd-Pd dimers. The introduction of Pd occurs exclusively at the metal nodes in a controlled manner while retaining the structural integrity. The incorporated Pd ions have an oxidation state of +2, whereas no PdO or metallic Pd nanoparticles embedded inside MOFs are detected. These mixed-metal CuPd-MOFs exhibit superior catalytic activity and selectivity for the aerobic oxidation of benzyl alcohol to benzaldehyde, and the doped Pd²⁺-CUS species are identified as isolated single-active sites.