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

No abstract

Escherichia coli (strain K‐12, substrain MG1655) glycerol dehydrogenase (GldA) is required to catalyze the first step in fermentative glycerol metabolism. The protein was expressed and purified to homogeneity using a simple combination of heat‐shock and chromatographic methods. The high yield of the protein (∼250 mg per litre of culture) allows large‐scale production for potential industrial applications. Purified GldA exhibited a homogeneous tetrameric state (∼161 kDa) in solution and relatively high thermostability (Tm = 65.6°C). Sitting‐drop sparse‐matrix screens were used for protein crystallization. An optimized condition with ammonium sulfate (2 M) provided crystals suitable for diffraction, and a binary structure containing glycerol in the active site was solved at 2.8 Å resolution. Each GldA monomer consists of nine β‐strands, thirteen α‐helices, two 310‐helices and several loops organized into two domains, the N‐ and C‐terminal domains; the active site is located in a deep cleft between the two domains. The N‐terminal domain contains a classic Rossmann fold for NAD+ binding. The O1 and O2 atoms of glycerol serve as ligands for the tetrahedrally coordinated Zn2+ ion. The orientation of the glycerol within the active site is mainly stabilized by van der Waals and electrostatic interactions with the benzyl ring of Phe245. Computer modeling suggests that the glycerol molecule is sandwiched by the Zn2+ and NAD+ ions. Based on this, the mechanism for the relaxed substrate specificity of this enzyme is also discussed.

No abstract

The nature of magnetism in 10% Cu-doped ZrO2, TiO2, MgO, SiO2, and Al2O3 is investigated using superconducting quantum interference device magnetometry and electron magnetic resonance (EMR). The doping was done by the incipient wetness impregnation technique. X-ray diffraction studies showed the presence of some CuO notably in TiO2, SiO2, and Al2O3. However, EMR yielded typical Cu2+ spectra in all the samples, resulting from some doping. Magnetic field (H) and temperature (T) dependences of the magnetization (M) show only paramagnetism in these oxides in contrast to ferromagnetism with Tc=380K observed in Cu∕ZnO. Concentrations x of Cu2+ doped into the oxides are determined from the M vs T and M vs H data, showing Cu∕ZrO2 with the largest x and hence largest magnetization.