Highly Efficient Oxidation of Ethyl Lactate to Ethyl Pyruvate Catalyzed by TS-1 Under Mild Conditions

Enhanced anisole hydroxylation over a hierarchical micro/mesoporous TS-1 catalyst

Micro/mesoporous DTS-1 showed enhanced catalytic activity for anisole hydroxylation showing 54% conversion with 55% selectivity towards p-methoxyphenol.

Screening of Adsorbent/Catalyst Composite Monoliths for Carbon Capture-Utilization and Ethylene Production

Combining CO₂ adsorption and utilization in oxidative dehydrogenation of ethane (ODHE) into a single bed is an exciting way of converting a harmful greenhouse gas into marketable commodity chemicals while reducing energy requirements from two-bed processes. However, novel materials should be developed for this purpose because most adsorbents are incapable of capturing CO₂ at the temperatures required for ODHE reactions. Some progress has been made in this area; however, previously reported dual-functional materials (DFMs) have always been powdered-state composites and no efforts have been made toward forming these materials into practical contactors. In this study, we report the first-generation of structured DFM adsorbent/catalyst monoliths for combined CO₂ capture and ODHE utilization. Specifically, we formulated M-CaO/ZSM-5 monoliths (M = In, Ce, Cr, or Mo oxides) by 3D-printing inks with CaCO₃ (CaO precursor), insoluble metal oxides, and ZSM-5. The physiochemical properties of the monoliths were vigorously characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ physisorption, elemental mapping, pyridine Fourier transform infrared spectroscopy (Py-FTIR), H₂-temperature-programmed reduction (H₂-TPR), and NH₃-temperature-programmed desorption (NH₃-TPD). Their performances for combined CO₂ adsorption at 600 °C and ODHE reaction at 700 °C under 25 mL/min of 7% C₂H₆ were then investigated. The combined adsorption/catalysis experiments revealed the best performance in Cr-CaO/ZSM-5, which achieved 56% CO₂ conversion, 91.2% C₂H₄ selectivity, and 33.8% C₂H₄ yield. This exceptional performance, which was improved from powdered-state DFMs, was attributed to the high acidity and numerous oxidation states of the Cr₂O₃ dopant which were verified by NH₃-TPD and H₂-TPR. Overall, this study reports the first-ever proof-of-concept for 3D-printed DFM adsorbent/catalyst materials and furthers the area of CO₂ capture and ODHE utilization by providing a simple pathway to structure these composites.

Structure-Reactivity Effects of Biomass-based Hydroxyacids for Sustainable Electrochemical Hydrogen Production

Biomass electro-oxidation is a promising approach for the sustainable generation of H₂ by electrolysis with simultaneous synthesis of value-added chemicals. In this work, the electro-oxidation of two structurally different organic hydroxyacids, lactic acid and gluconic acid, was studied comparatively to understand how the chemical structure of the hydroxyacid affects the electrochemical reactivity under various conditions. It was concluded that hydroxyacids such as gluconic acid, with a considerable density of C-OH groups, are highly reactive and promising for the sustainable generation of H₂ by electrolysis at low potentials and high conversion rates (less than -0.15 V vs. Hg/HgO at 400 mA cm^-2 ) but with low selectivity to specific final products. In contrast, the lower reactivity of lactic acid did not enable H₂ generation at very high conversion rates (<100 mA cm^-2 ), but the reaction was significantly more selective (64 % to pyruvic acid). This work shows the potential of biomass-based organic hydroxyacids for sustainable generation of H₂ and highlights the importance of the chemical structure on the reactivity and selectivity of the electro-oxidation reactions.

Reversing Titanium Oligomer Formation towards High-Efficiency and Green Synthesis of Titanium-Containing Molecular Sieves

Green and efficient synthesis of titanium-containing molecular sieves is limited by the quantity of environmentally unfriendly additives and complicated synthesis procedures required. Oligomerization of Ti monomers into anatase TiO₂ is the typical outcome of such procedures because of a mismatch between hydrolysis rates of Si and Ti precursors. We report a simple and generic additive-free route for the synthesis of Ti-containing molecular sieves (MFI, MEL, and BEA). This approach successfully reverses the formation of Ti oligomers to match hydrolysis rates of Ti and Si species with the assistance of hydroxyl free radicals generated in situ from ultraviolet irradiation. Moreover, fantastic catalytic performance for propene epoxidation with H₂ and O₂ was observed. Compared with the conventional hydrothermal method, this approach opens up new opportunities for high-efficiency, environmentally benign, and facile production of pure titanium-containing molecular sieves.

The synthesis of pure and uniform nanosized TS-1 crystals with a high titanium content and a high space–time yield

Concentrated basic MFI building unit species played a key role in the crystal synthesis of uniform nanosized anatase-free titanium-rich TS-1.

Effects of Seed Crystals on the Growth and Catalytic Performance of TS-1 Zeolite Membranes

Dense and good catalytic performance TS-1 zeolite membranes were rapidly prepared on porous mullite support by secondary hydrothermal synthesis. The properties of seed crystals were very important for the preparation of high-catalytic performance TS-1 zeolite membranes. Influences of seed crystals (Ti/Si ratios, size, morphology, and zeolites concentration of the seed suspension) on the growth and catalytic property of TS-1 zeolite membranes were investigated in details. High Ti/Si ratio, medium-size, and morphology of the seed crystals were critical for preparing the high-performance TS-1 zeolite membrane. Compared with the bi-layer TS-1 zeolite membrane (inner and outer of the mullite tube), the mono-layer TS-1 zeolite membrane had a better catalytic performance for Isopropanol IPA oxidation with H2O2. When the Ti/Si ratio, size, and morphology of the TS-1 zeolites were 0.030, 300 nm, ellipsoid, and the zeolites concentration of the seed suspension was 5%, the IPA conversion, and flux through the TS-1 zeolite membrane were 98.23% and 2.58 kg·m-2·h-1, respectively.

High-Performance Vapor-Phase Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate over SiO2 Supported PMoVNb Oxides

This paper describes the application of P-Mo-V-Nb/SiO2 catalysts for the selective oxidation of ethyl lactate (EL) to ethyl pyruvate (EP). The P-Mo-V-Nb/SiO2 catalysts exhibit superior performance for EP selectivity than the corresponding samples of binary V-Nb/SiO2 ternary P-Mo-V/SiO2 and P-Mo-Nb/SiO2 catalysts at same temperatures. The origin of high EP selectivity of the P-Mo-V-Nb/SiO2 catalysts is explored and attributed to the synergistic effect of P, Mo, V, and Nb mixed oxides presented on the surface of the catalyst. The highly dispersive sites separated active species under the action of phosphorus, suppressing over oxidation and improving the selectivity. The existence of MoO3 to provide higher oxidation for catalyst. The redox cycle of V and Nb oxides could be completed through electron transfer between lattice oxygen and metal cations. Moreover, the weak acidity of catalyst surface is favorable to avoid the decarboxylation reaction to target a high selectivity of EP. Therefore, the P-Mo-V-Nb/SiO2 catalyst obtained the maximum yield of 91.8% with a selectivity of 93.8% and a conversion of 99.0% simultaneously at 280 °C.

Nickel-Modified TS-1 Catalyzed the Ammoximation of Methyl Ethyl Ketone

In this paper, five kinds of transition metal-modified titanium silicalite-1 (M-TS-1) were prepared by an ultrasonic impregnation method. We studied their catalytic performances in the ammoximation of methyl ethyl ketone (MEK). The various M-TS-1 catalysts revealed distinct differences in their MEK ammoximation activity. The nickel-modified TS-1 (Ni-TS-1), especially 3 wt % Ni-TS-1, exhibited a satisfactory conversion of MEK (99%) associated with a high selectivity of methyl ethyl ketoxime (MEKO) (99.3%), which was 6% higher than that of TS-1 under the same conditions. Moreover, the catalyst showed excellent recyclability and the reactivity could be completely recovered after regeneration. The catalysts were characterized by Powder X-ray Diffraction (XRD), Fourier Transformed Infrared Spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), and so on. It was demonstrated that the skeleton structure of TS-1 was basically maintained and the electron environment of the Ti active site was changed after the nickel modification, which can optimize the adsorption capacity and the activation for H2O2. Meanwhile, the surface nickel species reduced the surface acidity of the catalyst, which provided an appropriate pH and inhibited the deep oxidation of oxime.

Catalytic Synthesis of 2,5-Furandicarboxylic Acid from Concentrated 2,5-Diformylfuran Mediated by N-hydroxyimides under Mild Conditions

Producing polyester monomer 2,5-furandicarboxylic acid (FDCA) from biomass as an alternative to fossil-derived terephthalic acid has drawn much attention from both academy and industry. In this work, an efficient FDCA synthesis was proposed from 10.6 wt % 2,5-diformylfuran (DFF) in acetic acid using a combined catalytic system of Co/Mn acetate and N-hydroxyimides. The intermediate product of 5-formyl-2-furandicarboxylic acid (FFCA) possesses the least reactive formyl group. N-hydroxysuccinimide was found to be superior to N-hydroxyphthalimide in catalyzing the oxidation of the formyl group in FFCA intermediate, affording a near 95 % yield of FDCA under mild conditions of 100 °C. Trace maleic anhydride was detected as by-product, which mainly came from the oxidative cleavage of DFF via furfural, furoic acid and 5-acetoxyl-2(5H)-furanone as intermediates.

Insight into the stereoselectivity of TS-1 in epoxidation ofcis/trans-2-hexene: a computational study

The mechanism of the stereoselectivity forcis/trans-2-hexene epoxidation in TS-1 zeolite was studied using density functional theory and the ONIOM scheme.

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).