Ga(iii)-alkyl and alkoxide model compounds demonstrate XANES edge energy shifts similar to those in Ga dehydrogenation catalysts without a change in Ga oxidation state.
Alkyl-zinc and zinc oxide-type sites were synthesized via atomic layer deposition on highsurface-area silica using an integrated atomic layer deposition-catalysis instrument (I-ALD-CAT). One-cycle ALD experiments using diethylzinc (DEZ) afforded Zn/SiO 2 systems that provided key insights into the reactivity and stability of Zn sites as a function of dispersion at the submonolayer level. The I-ALD-CAT tool design allowed for systematic comparison of the reactivity of different grafted zinc sites. Open-shell 16-electron, tricoordinate ethyl zinc-silica sites exhibit higher activity in propane hydrogenation-dehydrogenation compared to 18-electron, tetracoordinate zinc oxide-type centers. Silica surface saturation with Zn(II) sites (~75% of a monolayer) results in facile zinc agglomeration and catalyst deactivation under reaction conditions. Reduced DEZ dosing coupled with thermal substrate pretreatment techniques (e.g., dehydration under vacuum) resulted in increased Zn dispersion and produced Zn/SiO 2 catalysts with improved activity and stability under propylene hydrogenation (200°C) and propane dehydrogenation (550°C) conditions.
The development of on-purpose 1,3-butadiene (BDE) technologies remains an active area in catalysis research, because of the importance of BDE in industrial polymer production. Here, we report on a nonoxidative dehydrogenation catalyst for the production of BDE prepared by atomically precise installation of platinum sites on a Zn-modified SiO 2 support via atomic layer deposition (ALD). In situ reduction X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), CO chemisorption, and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) imaging of activated PtZn/SiO 2 , revealed the formation of a uniform, well-distributed subnanometer-to nanometer-sized PtZn (1.2 ± 0.3 nm) alloy as the active catalytic species.
A structurally unique class of hydrocarbon-soluble, ancillary-ligand-free, tetrametallic Co(I) and Ni(I) clusters is reported. The highly unsaturated complexes are supported by simple, sterically bulky phosphoranimide ligands, one per metal. The electron-rich nitrogen centers are strongly bridging but sterically limited to bimetallic interactions. The hydrocarbon-soluble clusters consist of four coplanar metal centers, mutually bridged by single nitrogen atoms. Each metal center is monovalent, rigorously linear, and two-coordinate. The clusters are in essence two-dimensional atomic-scale "molecular squares," a structural motif adapted from supramolecular chemistry. Both clusters exhibit high solution-phase magnetic susceptibility at room temperature, suggesting the potential for applications in molecular electronics. Designed to be catalyst precursors, both clusters exhibit high activity for catalytic hydrogenation of unsaturated hydrocarbons at low pressure and temperature.
Well-defined organoplatinum(IV) sites were grafted on a Zn(II)-modified SiO support via surface organometallic chemistry in toluene at room temperature. Solid-state spectroscopies including XAS, DRIFTS, DRUV-vis, and solid-state (SS) NMR enhanced by dynamic nuclear polarization (DNP), as well as TPR-H and TEM techniques revealed highly dispersed (methylcyclopentadienyl)methylplatinum(IV) sites on the surface ((MeCp)PtMe/Zn/SiO, 1). In addition, computational modeling suggests that the surface reaction of (MeCp)PtMe with Zn(II)-modified SiO support is thermodynamically favorable (Δ G = -12.4 kcal/mol), likely due to the increased acidity of the hydroxyl group, as indicated by NH-TPD and DNP-enhanced O{H} SSNMR. In situ DRIFTS and XAS hydrogenation experiments reveal the probable formation of a surface Pt(IV)-H upon hydrogenolysis of Pt-Me groups. The heterogenized organoplatinum(IV)-hydride sites catalyze the selective partial hydrogenation of 1,3-butadiene to butenes (up to 95%) and the reduction of nitrobenzene derivatives to anilines (up to 99%) with excellent tolerance of reduction-sensitive functional groups (olefin, carbonyl, nitrile, halogens) under mild reaction conditions.
A synergistic effect has been uncovered between ppm levels of Pd and Ni embedded within iron nanoparticles that leads to selective catalytic reductions of nitro-containing aromatics in water.
A well-defined, isolated, single-site organovanadium(iii) catalyst on SiO [(SiO)V(Mes)(THF)] was synthesized via surface organometallic chemistry, and fully characterized using a combination of analytical and spectroscopic techniques (EA, ICP, H NMR, TGA-MS, EPR, XPS, DR-UV/Vis, UV-Raman, DRIFTS, XAS). The catalyst exhibits unprecedented reactivity in liquid- and gas-phase alkene/alkyne hydrogenation. Kinetic poisoning experiments revealed that 100% of the V sites are active for hydrogenation.
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