The development of more effective alkane dehydrogenation catalysts is a key technological challenge for the production of olefins from shale gas, an abundant source of light hydrocarbons. Surface organometallic chemistry provides an original approach to generate nanometric Ga-Pt bimetallic particles supported on partially dehydroxylated silica containing gallium single-sites, which displays high activity, selectivity, and stability in propane dehydrogenation. This catalyst was prepared via sequential grafting of a platinum precursor onto silica possessing site-isolated gallium sites followed by H reduction. Monitoring generation of the reduced species, GaPt/SiO, via in situ X-ray absorption spectroscopy reveals formation of a Ga Pt (0.5< x < 0.9) alloy with a fraction of gallium remaining as isolated sites. This bimetallic material exhibits catalytic performance that far surpasses each of the individual components and other reported Ga-Pt based catalysts; this is attributed to the highly dispersed Ga Pt alloyed structure on a support with low Brønsted acidity containing gallium single-sites.

Many industrial catalysts contain isolated metal sites on the surface of oxide supports. Although such catalysts have been used in a broad range of processes for more than 40 years, there is often a very limited understanding about the structure of the catalytically active sites. This Review discusses how surface organometallic chemistry (SOMC) engineers surface sites with well-defined structures and provides insight into the nature of the active sites of industrial catalysts; the Review focuses in particular on olefin production and conversion processes.

Since its early days, olefin metathesis has been in the focus of scientific discussions and technology development. While heterogeneous olefin metathesis catalysts based on supported group 6 metal oxides have...

Molybdenum-based molecular alkylidyne complexes of the type [MesC≡Mo{OC(CH)(CF)}] (MoF, x = 0; MoF, x = 1; MoF, x = 2; MoF, x = 3; Mes = 2,4,6-trimethylphenyl) and their silica-supported analogues are prepared and characterized at the molecular level, in particular by solid-state NMR, and their alkyne metathesis catalytic activity is evaluated. The C NMR chemical shift of the alkylidyne carbon increases with increasing number of fluorine atoms on the alkoxide ligands for both molecular and supported catalysts but with more shielded values for the supported complexes. The activity of these catalysts increases in the order MoF < MoF < MoF before sharply decreasing for MoF, with a similar effect for the supported systems (MoF ≈ MoF < MoF < MoF). This is consistent with the different kinetic behavior (zeroth order in alkyne for MoF derivatives instead of first order for the others) and the isolation of stable metallacyclobutadiene intermediates of MoF for both molecular and supported species. Detailed solid-state NMR analysis of molecular and silica-supported metal alkylidyne catalysts coupled with DFT/ZORA calculations rationalize the NMR spectroscopic signatures and discernible activity trends at the frontier orbital level: (1) increasing the number of fluorine atoms lowers the energy of the π*(M≡C) orbital, explaining the more deshielded chemical shift values; it also leads to an increased electrophilicity and higher reactivity for catalysts up to MoF, prior to a sharp decrease in reactivity for MoF due to the formation of stable metallacyclobutadiene intermediates; (2) the silica-supported catalysts are less active than their molecular analogues because they are less electrophilic and dynamic, as revealed by their C NMR chemical shift tensors.