Reactivity of Silica-Supported Hafnium Tris-neopentyl with Dihydrogen: Formation and Characterization of Silica Surface Hafnium Hydrides and Alkyl Hydride

Highly Selective and Efficient Perdeuteration of n-Pentane via H/D Exchange Catalyzed by a Silica-Supported Hafnium-Iridium Bimetallic Complex

A Surface OrganoMetallic Chemistry (SOMC) approach is used to prepare a novel hafnium-iridium catalyst immobilized on silica, HfIr/SiO2, featuring well-defined [≡SiOHf(CH2 tBu)2(μ-H)3IrCp*] surface sites. Unlike the monometallic analogous materials Hf/SiO2 and Ir/SiO2, which promote n-pentane deuterogenolysis through C-C bond scission, we demonstrate that under the same experimental conditions (1 bar D2, 250 °C, 3 h, 0.5 mol %), the heterobimetallic catalyst HfIr/SiO2 is highly efficient and selective for the perdeuteration of alkanes with D2, exemplified on n-pentane, without substantial deuterogenolysis (<2 % at 95 % conversion). Furthermore this HfIr/SiO2 catalyst is robust and can be re-used several times without evidence of decomposition. This represents substantial advance in catalytic H/D isotope exchange (HIE) reactions of C(sp3)-H bonds.

Lewis Acid Strength of Interfacial Metal Sites Drives CH3 OH Selectivity and Formation Rates on Cu-Based CO2 Hydrogenation Catalysts

CH₃ OH formation rates in CO₂ hydrogenation on Cu-based catalysts sensitively depend on the nature of the support and the presence of promoters. In this context, Cu nanoparticles supported on tailored supports (highly dispersed M on SiO₂ ; M=Ti, Zr, Hf, Nb, Ta) were prepared via surface organometallic chemistry, and their catalytic performance was systematically investigated for CO₂ hydrogenation to CH₃ OH. The presence of Lewis acid sites enhances CH₃ OH formation rate, likely originating from stabilization of formate and methoxy surface intermediates at the periphery of Cu nanoparticles, as evidenced by metrics of Lewis acid strength and detection of surface intermediates. The stabilization of surface intermediates depends on the strength of Lewis acid M sites, described by pyridine adsorption enthalpies and ¹³ C chemical shifts of -OCH₃ coordinated to M; these chemical shifts are demonstrated here to be a molecular descriptor for Lewis acid strength and reactivity in CO₂ hydrogenation.

Surface organometallic chemistry in heterogeneous catalysis

Surface organometallic chemistry has been reviewed with a special focus on environmentally relevant transformations (C–H activation, CO₂conversion, oxidation).