Xiumin Huang

Stability Enhancement of H-Mordenite in Dimethyl Ether Carbonylation to Methyl Acetate by Pre-adsorption of Pyridine

The carbonylation of dimethyl ether to methyl acetate over H-mordenite (HMOR) and pyridine-modified HMOR was compared. The catalytic stability of HMOR was improved significantly by pyridine pre-adsorption, and a yield of methyl acetate ∼30% was still obtained after 48 h on stream at 473 K. In situ infrared spectroscopy and ammonia temperature-programmed desorption revealed that pyridine preferentially occupied the acidic sites in 12-membered ring pores but not the acidic sites in 8-membered ring pores. 129Xe NMR studies suggested that the channels of HMOR were blocked by coke in the reaction but those in the pyridine-modified HMOR were not. The acidic sites in the 12-membered ring pores were responsible for the deactivation of HMOR, and the reaction can be directed to occur mainly on the acidic sties in the 8-membered ring pores by the selective adsorption of pyridine in the 12-membered ring pores.

A highly efficient Cu/La2O3 catalyst for transfer dehydrogenation of primary aliphatic alcohols

La2O3-supported copper nanoparticles are sufficiently active for transfer dehydrogenation of primary aliphatic alcohols to aldehydes. When used for 1-octanol, the yield of 1-octanal can be as high as 63%. The catalyst is also highly effective for a wide variety of substrates, such as aromatic, aliphatic, and cyclic alcohols. The yield of the desired products approaches 100% and the turnover frequency is 86.5 h−1. The synergistic effect between the basicity of La2O3 and the hydrogen spillover of Cu particle contributes significantly to the extremely high activity of the Cu/La2O3 catalyst for transfer dehydrogenation of primary aliphatic alcohols.

Synthesis and Catalytic Performance of Manganese Oxide Octahedral Molecular Sieve Nanorods for Formaldehyde Oxidation at Low Temperature

Abstract Uniform manganese oxide octahedral molecular sieve (OMS-2) nanorods were synthesized by adding a small quantity of K 2 S 2 O 8 to the solution containing MnSO 4 ·H 2 O and KMnO 4 , and used for complete oxidation of formaldehyde. According to the results of N 2 adsorption and X-ray diffraction, the material is a manganese oxide octahedral molecular sieve with the cryptomelane type structure. TEM observation shows that the diameters of the nanorods range from 15 to 25 nm, and the lengths are 300–400 nm. Complete conversion of HCHO to CO 2 and H 2 O can be achieved at 353 K over OMS-2, and the same conversion is obtained at 373 K on the MnO x powder under the same conditions, which demonstrates that the catalytic activity is closely related to the morphology of the catalysts.

Coking on micrometer- and nanometer-sized mordenite during dimethyl ether carbonylation to methyl acetate

As compared to conventional micrometer-sized mordenite particles, nanometer-sized mordenrte gave a much higher activity and better stability in dimethyl ether carbonylation to methyl acetate by suppressing the deposition of hard coke. A structural analysis revealed that intra-crystalline diffusion limitation of the reactants and products to and from the active sites inside the channels was greatly decreased by reducing the zeolite size to the nanometer size.

A 13CO isotopic study on the CO promotion effect in methane dehydroaromatization reaction over a Mo/HMCM-49 catalyst

Abstract The promotion effect of CO in methane dehydroaromatization was investigated using 13 CO probe molecules. By alternative injection of 13 CO to the methane feed, the distribution of 13 C x C 6- x H 6 ( x = 0-3) products changed significantly, confirming the participation of 13 CO in the reaction network. The addition of 13 CO did not change the conversion of CH 4 but improved slightly the durability of the methane dehydroaromatization (MDA) reaction, which might be caused by the interaction of the dissociated oxygen species and the deposited carbon species. The ratio of 13 C x C 6- x H 6 ( x = 0-3) varied with the time on stream, which was determined by the competitive reactions of methane decomposition and 13 CO dissociation.

Transfer Dehydrogenation of 1-Octanol to 1-Octanal over Cu/MgO Catalyst: Effect of Cu Particle Size

Cu/MgO catalysts with different Cu particle sizes were prepared by a precipitation-deposition method and investigated for their activity in the transfer dehydrogenation of alcohols to carbonyl compounds. They were highly active for the conversion of primary aliphatic alcohols, e.g. 1-octanol. With increasing Cu particle size from 4.6 to 7.4 nm, the aldehyde yield decreased from 65% to 55%, which showed a size effect. The copper particle abstracted an a-hydrogen from the reactive alkoxide intermediate formed on the surface of MgO and simultaneously catalyzed the hydrogenation of styrene.

Facile Synthesis of Ag-Hollandite Nanofibers and Their Catalytic Activity for Ethanol Selective Oxidation

Abstract Ag-hollandite nanofibers were synthesized by refluxing a mixture of AgMnO4 and Mn(NO3)2 in nitrate acid solution at 373 K and used for ethanol selective oxidation. The X-ray diffraction pattern showed that the main crystalline phase was Ag-hollandite, but a small amount of pyrolusite was also formed. The N2 adsorption-desorption isotherms confirmed the presence of a microporous structure. Field emission scanning electron microscopy and transmission electron microscopy showed that the lengths of the nanofibers were 0.5–4.0 μm, and the diameters were 10–20 nm. The Ag-hollandite nanofibers gave a promising catalytic performance for ethanol selective oxidation to acetaldehyde, with an ethanol conversion of 82% and acetaldehyde selectivity of 95% at 503 K for 120 h time-on-stream.

Synthesis of mordenite nanosheets with shortened channel lengths and enhanced catalytic activity

Mordenite nanosheets of 20–40 nm thickness significantly shortened the lengths of parallel 12-member and 8-member ring channels and greatly facilitated the diffusion of molecules inside the micropores, and therefore remarkably enhanced the catalytic activity for the carbonylation of dimethyl ether.

Carbonylation of dimethyl ether over Co-HMOR

Incorporation of Co2+ into the framework of HMOR significantly enhanced the activity for the carbonylation of dimethyl ether to methyl acetate. About 68% of the Co2+ cations are located at site A in the 8-membered ring (8-MR) pores, while 32% of the metal cations are incorporated at site E of the 12-MR pores. Although the amount of the Bronsted acid sites in the 8-MR pores that are intrinsically active for DME carbonylation decreased considerably upon Co-doping, the conversion of DME increased remarkably, almost doubled. The promotional role of Co2+ in the 8-MR channels was to facilitate the adsorption/activation of both CO and DME molecules. Meanwhile, the Co2+ cations located in the 12-MR channels effectively suppressed coke deposition and thus improved the stability of the Co-HMOR catalyst.