Unsaturated Penta-Coordinated Mo5c5+ Sites Enabled Low-Temperature Oxidation of C-H Bonds in Ethers.

Selective oxidation of C-H bonds under mild conditions is one of the most important and challenging issues in utilization of energy-related molecules. Molybdenum oxide nanostructures containing Mo5+ species are effective for these reactions, but the accurate identification of the structure of active Mo5+ species and the catalytic mechanism remain unclear. Herein, unsaturated penta-coordinated Mo5c5+ with a high fraction in MoOx fabricated by the hydrothermal method were identified as the active sites for low-temperature oxidation of dimethyl ether (DME) by the deep correlation of characterizations, density functional theory calculations, and activity results, giving a methyl formate selectivity of 96.3% and DME conversion of 12.5% at unreported 110 °C. Low-temperature electron spin resonance (ESR) and quasi in situ X-ray photoelectron spectra (XPS) with the designed experiments confirm that the Mo5c5+ species can be formed in situ. Molybdenum located at the pentachronic site is preferable to significantly promote the oxidation of the C-H bond in CH3O* at lower temperatures.

Introduction of TiO2 enhancing the catalytic performance of Ti(SO4)2/SiO2 for dimethyl ether oxidation.

The introduction of a small amount of TiO2 changes the surface properties of the SiO2 material, which further significantly affects the dispersion state of Ti(SO4)2. The differences in acidity and redox caused by the distribution of Ti(SO4)2 are closely related to the catalyst performance for dimethyl ether (DME) oxidation. In particular, the calcination temperature could adjust the surface hydroxyl content of TiO2/SiO2, which determines the dispersion of Ti(SO4)2 components, resulting in distinct acid sites and Ti valence. The most number of weak acid sites and the highest proportion of Ti3+/Ti4+ in the Ti(SO4)2/TS-400 °C catalyst remarkably promote the formation of dimethoxymethane (DMM) from 14.4% to 82.6%, compared to the Ti(SO4)2/SiO2 catalyst.

Highly efficient acrylic acid production from formaldehyde and acetic acid over the NASICON-type catalyst.

The condensation of formaldehyde and acetic acid to acrylic acid (AA) is considered as one of the important routes for the clean and high value utilization of coal-based methanol derivatives. Herein, we successfully synthesized environment-friendly NASICON catalysts using Ti(SO4)2 as the titanium source. With guaranteed high selectivity (∼78%), the space time yield of AA + MA (methyl acrylate) can be up to 123.9 µmol g-1 min-1, far higher than the results reported previously. Based on the characterizations, it is demonstrated that the modulation of the acidic and basic properties (including distribution, ratio of B/L, etc.) led by the specific elemental and hybrid TiP2O7 phase plays crucial roles in catalyst supremacy.

Selective oxidation conversion of methanol/dimethyl ether.

As important platform compounds, methanol and dimethyl ether (DME) are vital bridges between the coal chemical, petrochemical and fine chemical industries. At present, the synthesis of methanol/DME has been industrialized, and the production capacity is much larger than the market demand. Therefore, the conversion of methanol/DME into more valuable chemicals is an important and significant topic. The synthesis of high value-added oxygenated chemicals and diesel oil additives from methanol/DME by an oxidation method has attracted substantial attention due to it being green and environmentally friendly and having good atom economy. In this feature article, we have summarized the recent advances in the synthesis of formaldehyde, methyl formate, dimethoxymethane, and polyoxymethylene dimethyl ethers, from the selective oxidation of methanol/DME, and further discussed the adsorption and activation of reactant molecules, selective cleavage of C-O, C-H or O-H bonds in methanol/DME molecules and the C-O chain growth in the target products. In the end, major challenges and future prospects are proposed from the viewpoint of catalyst design and application. It is expected that this feature article will provide theoretical guidance for the activation and cleavage of C-O, C-H, or O-H bonds in other small molecules of alcohol/ether as well as low-carbon alkanes, so as to synthesize high value-added chemicals.

Biomass-Based Carbon-Supported Sulfate Catalyst for Efficient Synthesis of Dimethoxymethane from Direct Oxidation of Dimethyl Ether.

The synthesis of dimethoxymethane (DMM) from direct oxidation of dimethyl ether (DME) is a green and competitive route with good atomic economy and low carbon emission and is also an urgent need. In this work, biomass-based carbon-supported sulfate catalysts were designed and prepared for the efficient synthesis of DMM from DME oxidation. The prepared carbon support from cellulose displayed much larger specific surface area and a developed microporous structure, which effectively benefited a high dispersion of sulfate components, leading to mainly weak acid sites and more oxygen functional groups on the catalyst surface. The Ti(SO4)2/PC-H2SO4 catalyst exhibits excellent performance for DME oxidation with DMM1-2 selectivity up to 96.7%, and DMM selectivity reaches 89.1%, notably higher than that of previously reported results. The distinctive surface structure and chemical properties of the carbon support have important impacts on the dispersion state of sulfate species, affecting the acidic and redox properties of the catalysts.

Oxidative coupling of methane over Mo-Sn catalysts.

A novel Mo-Sn catalyst for the oxidative coupling of methane was designed using a hydrothermal method. At 650 °C, the conversion of methane was 8.6% and the selectivity of the C2 hydrocarbons reached as high as 98.1% over the Mo1Sn3 catalyst, with a CO2 selectivity of only 0.8%. We demonstrated that the deep oxidation of methane to CO2 was further inhibited due to the synergistic effects of moderately strong basic sites and reactive oxygen species on the catalyst surface.