Search

An efficient and long-term stable nano-sized N-H-ZSM-5 zeolite catalyst for the one-step aldol condensation reaction of formaldehyde and MAc to produce MA and AA is reported. Its total lifetime reaches up to 226 h by three regeneration runs.

We found that the excellent ORR performance of Ni doped CuXP2S6 (X = In, Bi and Cr) is related to spin selective charge transfer and spin flip, which are clearly observed and analyzed by first-principles calculation.

Efficient direct transformation of methane into value-added chemicals has great significance for long-term sustainability of fuels and chemicals, but remains a major challenge due to its high inertness. Reported here is that methane can be activated effectively via carbonylation with CO over Zn/HZSM-5 catalysts under mild conditions. The selectivity to aromatics alone reaches 80% among all hydrocarbon products at 823 K, whereas as high as 92% ethane selectivity is achieved at a lower temperature of 673 K. 13CO isotope labelling experiments demonstrate that approximately 50% of the carbon atoms in all the products originate from carbon monoxide, whereas another half of the carbons come from methane, indicating that the precursors of hydrocarbon products are acyl compounds and/or acetic acid formed by carbonylation of methane with carbon monoxide. This provides potential for transformation of methane into value-added chemicals under mild reaction conditions.

As Bronsted acid sites in different types of channels exhibit distinct catalytic behaviors in the dimethyl ether (DME) carbonylation reaction over acidic mordenite (H-MOR) zeolites (e.g. acid sites in 8-membered ring channels for carbonylation reaction, acid sites in 12-membered ring channels for methanol-to-hydrocarbons reactions), the identification and regulation of acid site distribution in mordenite zeolites are of great importance to improve the catalytic performance. In this work, we employ the selective ion-exchange method to identify and control the acid site distribution in mordenite zeolites, and the chemical properties of acid sites in different channels are investigated by NH3-TPD and CD3CN FT-IR. Additionally, the effect of selective ion-exchange on the catalytic performance of DME carbonylation reaction is also discussed. The selective ion-exchange is realized by using tetramethylammonium (TMA+) ions, which can selectively remove the counter ions in the 12-membered ring channels but are inaccessible to the counter ions in 8-membered ring channels due to the steric hindrance. The selective ion-exchange reveals that the relative amounts of acid sites in 12-membered ring channels and 8-membered ring channels are 68% and 32%, respectively. Interestingly, it is found that introducing TMA+ into H-MOR zeolites significantly improves the catalytic activity and stability in DME carbonylation reaction as a result of depressing the methanol-to-hydrocarbons reactions. The 3TMA-H-MOR catalyst shows high stability for 210 hours on stream. The present work opens a new avenue for designing carbonylation catalysts with excellent stability in DME carbonylation reaction.

Direct propane dehydrogenation (PDH) is an attractive technology for propylene production. We show here that propane conversion is significantly enhanced by the addition of ZnO to Cr2O3. Furthermore, its activity is strongly dependent on the Zn/Cr molar ratio and one with Zn/Cr = 0.3 gives the highest propane conversion and propylene selectivity among the studied ZnxCr catalysts (x denoting the molar ratio, 0–0.5). Characterization with X-ray diffraction, nitrogen physisorption, X-ray fluorescence spectroscopy, temperature-programmed reduction, temperature-programmed desorption, transmission electron microscopy, and X-ray photoelectron spectroscopy indicates that addition of zinc to Cr2O3 leads to formation of a spinel phase and reduction of the particle size, and hence forms more defect sites. The Arrhenius plots suggest that the apparent activation energy of the PDH reaction is significantly lowered over Zn0.3Cr.

Commercial precipitated iron catalysts suffer from severe fragmentation when applied in the Fischer–Tropsch to lower olefins reaction (FTO). Herein, sintered precipitated iron catalysts for FTO are prepared by varying the calcination temperature from 800 to 1400 °C to enhance their fragmentation-resistance ability. Compared with traditional precipitated iron catalysts, sintered precipitated iron catalysts require higher reduction temperatures to maintain high and stable activity and shift the production of hydrocarbons towards lower olefins. Spent sintered precipitated iron catalysts show bulk morphologies with less fragmentation than the fragmented and aggregated morphologies of spent traditional precipitated iron catalysts. The amount of coke inside the spent catalysts decreases from 41.8 to 12.5% as the calcination temperature increases from 500 to 1200 °C, and simultaneously, the chain length of soluble coke decreases from C32 to C21. The lower amount of coke and shorter chain length of soluble coke of the sintered precipitated iron catalysts come from the stronger mechanical strength-induced less space for coke accumulation during FTO, which further enhance the fragmentation-resistance ability of the catalysts.

Advancement in the understanding of biomolecular interactions has benefited from the development of surface imaging microscopy with high sensitivity and contrast. In this work, surface imaging microscopy with tunable penetration depth as short as 20 nm is proposed. By employing a hyperbolic metamaterial (HMM) composed of metal/dielectric multifilms, the deep subwavelength bulk plasmon polaritons (BPPs) are excited as the uniform and large area surface illumination source. Moreover, the penetration depth of the surface illumination structure could be continually tuned by changing the incidence angle of excitation light. In the experiments, a penetration depth of 25–38 nm in air is achieved at 532 nm by the HMM with Ag/SiO2 multilayers. Subsequently, a fluorescence pattern was imaged against another fluorescent background by this surface imaging microscopy, and the results indicate that distinct surface images with high contrast could indeed be obtained under BPP illumination with ultra-short penetration depth. This approach provides a promising avenue for tracking single-molecule and cell plasma membrane events.

A one-step aldol condensation reaction to produce MA and AA is a green and promising strategy. Here, the aldol condensation reaction was first conducted with DMM and MAc over different types of zeolite catalysts. The H-ZSM-35 zeolite demonstrates excellent catalytic performance with a DMM conversion of 100% and a MA + AA selectivity of up to 86.2% and superior regeneration ability, with great potential for industrial operation.

Acetic acid is one of the most important bulk commodity chemicals and is currently manufactured by methanol carbonylation reactions with rhodium or iridium organometallic complexes and halide-containing promoters named Monsanto or BP Cativa™ homogeneous processes, respectively. Developing a halide-free catalyst and a heterogeneous process for methanol carbonylation is of great importance and has recently attracted extensive research attention. Here, we report a green route for direct synthesis of acetic acid via vapor-phase carbonylation of methanol with a stable, selective, halide-free, and noble metal-free catalyst based on pyridine-modified H-mordenite zeolite. Methanol conversion and acetic acid selectivity can reach up to 100% and 95%, respectively. Only little deactivation is observed during the 145 hour reaction.

Phosphorous (P)-modified ordered mesoporous carbon CMK-3 was used as a catalyst for the direct dehydrogenation (DH) of propane to propylene without any auxiliary stream, and this catalyst exhibited better activity and selectivity than the pristine ordered mesoporous carbon. The prepared samples were characterized by N2 adsorption and desorption, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). After the introduction of P using an impregnation method, PO groups formed on the surface of the materials and substantially improved the activity and selectivity. The PO groups are believed to be electron donors for CO active centers, or independent active centers for catalytic DH of propane.

A series of Fe-modified mordenite zeolite samples were synthesized by a template-free method and employed in dimethyl ether (DME) carbonylation reaction for the production of methyl acetate (MAc). XRD, UV-Vis, and UV-Raman characterization studies proved that Fe atoms have been introduced into the mordenite zeolite framework by partial substitution of Al atoms, which led to evident changes of activity and MAc selectivity. With the increase of iron content (as metal) from 0.0 to 3.6 wt%, DME conversion first increased and then decreased. MAc selectivity and catalyst stability were enhanced for all Fe-modified samples. TG and GC-MS analysis of deactivated catalysts showed that the amount of coke retained in the catalysts decreased as the iron content of the zeolites increased. The enhancement effects were expounded in terms of the decrease of the acid strength and acid density in the 12MR channels of mordenite after introduction of Fe, resulting in the reduction of carbon deposition.

Schottky contacts, formed at metal/semiconductor interfaces, always have a large impact on the performance of field-effect transistors (FETs). Here, we report the experimental studies of Schottky contacts in two-dimensional (2D) transition metal dichalcogenide (TMDC) FET devices. We use scanning photocurrent microscopy (SPCM) to directly probe the spatial distribution of the in-plane lateral Schottky depletion regions at the metal/2D-TMDC interfaces. The laser incident position dependent and the gate voltage tunable polarity and magnitude of the short-circuit photocurrent reveal the existence of the in-plane Schottky depletion region laterally extending away from the metal contact edges along the channel. This lateral depletion region length is estimated to be around several microns and can be effectively tuned by the gate and drain-source biases. Our results solidify the importance of lateral Schottky depletion regions in the photoresponse of 2D TMDC optoelectronic devices.

A highly active Nafion-H catalyst is developed for vapour phase carbonylation of dimethoxymethane (DMM) to methyl methoxyacetate (MMAc) with a significant MMAc selectivity as high as 90%. The excellently catalytic performance is because of the unique structure and high acid strength of the Nafion-H catalyst.