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The running out of oil reserves and the concern for our environment promote the search for clean energy. The large reserve of natural gas and the recent discovery of methane hydrate suggest that methane is an important source of energy in the near future. 1 Methane is the most inert hydrocarbon, and its conversion into liquid fuels and value-added chemicals is a challenge in modern catalysis. 2 Since the report of nonoxidative methane dehydroaromatization (MDA) over Mo/ZSM-5 catalyst, 3 much work has been conducted for the modification of Mo/HZSM-5 and Mo/HMCM-22 catalysts. 4À8 The addition of the oxide of Zn, Ga, Ni, and Re would result in better performance. It was considered that Mo 2 C was the major active component for the nonoxidative MDA reaction. For example, Chouhary et al. 9 found that Zn-based/ZSM-5 catalysts showed good catalytic activities in such a reaction. Using 13 C-labeled methane, Stepanov et al 10,11 studied the mechanism of CH 4 / C 3 H 6 MDA over Zn-modified H-BEA zeolites in isotopetracing experiments. Their results suggested that the methane dissociated on ZnO species was incorporated in the aromatic rings formed from C 3 H 6 , generating methyl-substituted benzene derivatives through a ring-expansion/contraction mechanism. It was reported by Xiong et al. 12 that the addition of a proper amount of Zn 2+ or Li + would result in the elimination of most of the surface strong Bronsted acid sites. At the same time, there was the generation of a kind of new medium-to-strong acid sites that are catalytically active for MDA reactions, and the formation of coke was alleviated to a great extent because of the absence of strong Brjnsted acid sites. Recently, Fang et al. 13 reported that through the loading of Zn onto HZSM-5, the aromatization of dimethyl ether was enhanced. At 360 °C, the total yields of aromatics and C 8 aromatics (66.2 and 39.0%) over 2%Zn/HZSM-5 were significantly higher than those (50.0 and 28.6%) over HZSM-5. In addition, Xuan et al. 14 reported the nonoxidative aromatization of methane/propane (mole ratio 5:1) over a Zn/HZSM-5 catalyst and obtained propane conversion of 93.93% and aromatic selectivity of 80.29%, but they did not conduct discussion on CH 4 conversion. To the best of our knowledge, the direct conversion of methane over a Zn/ZSM-5 catalyst has not been previously reported. Herein we report the performance of Zn/ZSM-5, ZnGa/ZSM-5, and Zn(or Ga)-Mo/ZSM-5 catalysts in MDA reaction under the conditions of atmospheric pressure as well as supersonic jet expansion (SJE). The physical properties of the catalysts were

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The formation mechanism of polycyclic aromatic hydrocarbon (PAH) molecules in interstellar and circumstellar environments is not well understood although the presence of these molecules is widely accepted. In this paper, addition and aromatization reactions of acetylene over astrophysically relevant nesosilicate particles are reported. Gas-phase PAHs produced from exposure of acetylene gas to crystalline silicates using pulsed supersonic jet expansion (SJE) conditions were detected by time-of-flight mass spectrometry (TOF-MS). The PAHs produced were further confirmed in a separate experiment using a continuous flow fixed-bed reactor in which acetylene was introduced at atmospheric pressure. The gas-phase effluent and solutions of the carbonaceous compounds deposited on the nesosilicate particles were analyzed using gas chromatography-mass spectrometry (GC-MS). A mechanism for PAH formation is proposed in which the Mg 2+ ions in the nesosilicate particles act as Lewis acid sites for the acetylene reactions. Our studies indicate that the formation of PAHs in mixed-chemistry astrophysical environments could arise from acetylene interacting with olivine nano-particles. These nesosilicate particles are capable of providing catalytic centres for adsorption and activation of acetylene molecules that are present in the circumstellar environments of mass-losing carbon stars. The structure and physical properties of the particles were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and high-resolution transmission electron microscopy (HRTEM) techniques.

A series of La 2 O 3 -V 2 O 5 /MCM-41 catalysts with high specific surface area were prepared by means of incipient wetness impregnation for the dehydrogenation of ethylbenzene to styrene using CO 2 as oxidant. At 600°C, the conversion of ethylbenzene and selectivity to styrene over 10La15V/MCM-41 after an on-stream time of 4 h was about 86.5 and 91.0%, respectively. The properties of the catalysts before and after the reaction were characterized using techniques such as X-ray diffraction, specific surface area, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and oxidation. The high catalytic activity and stability of 10La15V/MCM-41 during dehydrogenation of ethylbenzene is attributed to an optimized La/V atomic ratio. The accumulation of amorphous carbon species on the external surface of La 2 O 3 -V 2 O 5 /MCM-41 is the cause for catalyst deactivation.

Catalytic conversion reactions of acetylene on a solid SiC grain surface lead to the formation of polycyclic aromatic hydrocarbons (PAHs) and are expected to mimic chemical processes in certain astrophysical environments. Gas-phase PAHs and intermediates were detected in situ using time-of-flight mass spectrometry, and their formation was confirmed using GC-MS in a separate experiment by flowing acetylene gas through a fixed-bed reactor. Activation of acetylene correlated closely with the dangling bonds on the SiC surface which interact with and break the C-C π bond. The addition of acetylene to the resulting radical site forms a surface ring structure which desorbs from the surface. The results of HRTEM and TG indicate that soot and graphene formation on the SiC surface depends strongly on reaction temperature. We propose that PAHs as seen through the 'UIR' emission bands can be formed through decomposition of a graphene-like material, formed on the surface of SiC grains in carbon-rich circumstellar envelopes.