Surface Basic Site Effect on Boron-Promoted Platinum Catalysts for Dry Reforming of Methane

Platinum has been shown to be an active catalyst for the dry reforming of methane (DRM), which converts CO2 and CH4 into 2CO and 2H2 (synthesis gases) that can further be processed to produce valuable chemical feedstocks. Catalytic activity is often improved by the addition of promoter atoms, which are typically transition metals or noble metals, such as PtNi and PtSn. Recently, boron has shown to be an effective and low-cost catalyst promoter. Pt/B/SiO2 catalysts were prepared for DRM catalysis and compared with Pt/SiO2 catalysts without boron promotion. Both catalysts had similar surface concentrations of platinum, but the catalytic activity at 750 °C after 14 h for boron-containing catalyst was very high, resulting in nearly 100% CO2 conversion and a H2/CO ratio close to unity, compared to 12% CO2 conversion and H2/CO of 0.35 for boron-free Pt/SiO2. The catalysts were investigated with X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and CO2 temperature-programmed desorption (CO2-TPD) to identify the deactivating factors. It was determined that neither platinum nanoparticle sintering nor coking was a significant factor in catalyst deactivation; instead, boron had an effect on the reactive surface groups on the SiO2 support. These surface groups, such as hydroxyls and surface basic sites, enhance the adsorption of CO2 and potentially stabilize intermediate carbonate species, resulting in a high CO2 conversion for boron-promoted platinum catalysts

Supported Single-Site Ti(IV) on a Metal–Organic Framework for the Hydroboration of Carbonyl Compounds

A stable and structurally well-defined titanium alkoxide catalyst supported on a metal–organic-framework (MOF) of UiO-67 topology (<b>ANL1-Ti­(O</b>^{<b><i>i</i></b>}<b>Pr)</b>_<b>2</b>) was synthesized and fully characterized by a variety of analytical and spectroscopic techniques, including BET, TGA, PXRD, XAS, DRIFT, SEM, and DFT computations. The Ti-functionalized MOF was demonstrated active for the catalytic hydroboration of a wide range of aldehydes and ketones with HBpin as the boron source. Compared to traditional homogeneous and supported hydroboration catalysts, <b>ANL1-Ti­(O</b>^{<b><i>i</i></b>}<b>Pr)</b>_<b>2</b> is completely recyclable and reusable, making it a promising hydroboration catalyst alternative for green and sustainable chemical synthesis. In addition, <b>ANL1-Ti­(O</b>^{<b><i>i</i></b>}<b>Pr)</b>_<b>2</b> catalyst exhibits remarkable hydroboration selectivity toward aldehydes vs ketone in competitive study. DFT calculations suggest that the catalytic hydroboration proceeds via a (1) hydride transfer between the active Ti-hydride species and a carbonyl moiety (rate-determining step) and (2) alkoxide transfer (intramolecular σ-bond metathesis) to generate the borate ester product

Supported Platinum Nanoparticles Catalyzed Carbon–Carbon Bond Cleavage of Polyolefins: Role of the Oxide Support Acidity

Supported platinum nanoparticle catalysts are known to convert polyolefins to high-quality liquid hydrocarbons using hydrogen under relatively mild conditions. To date, few studies using platinum grafted onto various metal oxide (MxOy) supports have been undertaken to understand the role of the acidity of the oxide support in the carbon–carbon bond cleavage of polyethylene under consistent catalytic conditions. Specifically, two Pt/MxOy catalysts (MxOy = SrTiO3 and SiO2–Al2O3; Al = 3.0 wt %, target Pt loading 2 wt % Pt ∼1.5 nm), under identical catalytic polyethylene hydrogenolysis conditions (T = 300 °C, P(H2) = 170 psi, t = 24 h; Mw = ∼3,800 g/mol, Mn = ∼1,100 g/mol, Đ = 3.45, Nbranch/100C = 1.0), yielded a narrow distribution of hydrocarbons with molecular weights in the range of lubricants (Mw = Mn Đ = 1.5). While Pt/SrTiO3 formed saturated hydrocarbons with negligible branching, Pt/SiO2–Al2O3 formed partially unsaturated hydrocarbons (<1 mol % alkenes and ∼4 mol % alkyl aromatics) with increased branch density (Nbranch/100C = 5.5). Further investigations suggest evidence for a competitive hydrocracking mechanism occurring alongside hydrogenolysis, stemming from the increased acidity of Pt/SiO2–Al2O3 compared to Pt/SrTiO3. Additionally, the products of these polymer deconstruction reactions were found to be independent of the polyethylene feedstock, allowing the potential to upcycle polyethylenes with various properties into a value-added product