Tungsten-dioxo single-site heterogeneous catalyst on carbon: synthesis, structure, and catalysis†

Abstract

This study investigates the application of a novel third-row metal, tungsten, to carbon-supported single-site metal-oxo heterogeneous catalysis. Tungsten is a green and earth-abundant metal, but an unexplored candidate in this role. The carbon (AC = activated carbon)-supported tungsten dioxo complex, AC/WO₂ was prepared via grafting of (DME)WO₂Cl₂ (DME = 1,2-dimethoxyethane) onto high-surface-area activated carbon. AC/WO₂ was fully characterized by ICP-OES, XPS, EXAFS, XANES, SMART-EM, and DFT. W 4d_7/2 XPS and W L_III-Edge XANES assign the oxidation state as W(vi), while EXAFS reveals two WO double and two W–O single bonds at distances of 1.73 and 1.92 Å, respectively. These data align well with DFT computational results, supporting the structure as Carbon(–μ-O–)₂M(O)₂. SMART-EM verifies that single W(vi) catalytic sites are bonded in an out-of-plane manner. The catalytic performance of air- and water-stable AC/WO₂ is compared to that of AC/MoO₂. AC/WO₂ is more active and selective than the molybdenum analog in mediating alcohol dehydration of various substrates, and is recyclable. Notably, AC/WO₂ is an effective and recyclable catalyst for primary aliphatic alcohol dehydration and forms no dehydrogenation side products in contrast to AC/MoO₂. However, AC/WO₂ is less effective in epoxidation and PET depolymerization. Overall, this work demonstrates the potential of carbon-supported third row metals for future studies.