Mauß, J. M.; Leiting, S.; Fare?s, C.; Scott, A. G.; Peredkov, S.; DeBeer, S.; Weidenthaler, C.; Schüth, F.: A Heterogenized Molecular Catalyst for the Gas-Phase Cyclotrimerization of Acetylene to Benzene. Journal of the American Chemical Society 147 (2025), p. 42088–42099
10.1021/jacs.5c16274
Open Access Version
Abstract:
Facilitating the cyclotrimerization of acetylene to benzene in the gas-phase on the surface of solid catalysts has captivated researchers, both theoretically and experimentally, for several decades. Coupled with acetylene production from renewable feedstocks, this reaction offers a promising pathway for the direct, low-temperature synthesis of renewable benzene. Recognizing the physical limitations of typical solid catalysts, which adsorb benzene too strongly, this study investigates various high-valent early transition metal chlorides─potent molecular cyclotrimerization catalysts─as solid catalysts in this gas-phase conversion. Alongside catalytic assessment under industrially relevant conditions, various analytical techniques such as 93Nb solid-state NMR spectroscopy, X-ray emission spectroscopy, and quasi in situ X-ray photoelectron spectroscopy were applied to reveal that the catalytic functioning proceeds through the in situ formation of catalytically active reduced species as reported for a homogeneous reaction environment. Investigating deactivation phenomena, various catalyst precursors and reaction conditions led to the design of an immobilized molecular catalyst via chemical grafting, dispersion, and spatial isolation of active catalytic species on a mesoporous silica gel support. The resulting NbClx–silica gel catalyst exhibits an average benzene selectivity of up to 70% at an acetylene conversion level between 30% and 70% and a lifetime at ≥90% acetylene conversion of up to 8.5 h under industrially relevant conditions (10 vol % C2H2, 3 bar, 180 °C), outperforming previously reported solid catalysts by orders of magnitude.