The adsorption of water on the surfaces of ultradispersed diamond UDD.powder obtained from explosive detonation and modified by treatment in different gases under high temperatures is investigated by FTIR method. It is found that UDD adsorbs atmospheric water quickly and in the IR region of OH stretching vibration of water, a broad asymmetric band envelope centered at 3412 cmy1 with shoulders at 3575 cmy1 and 3240 cmy1 appears soon after the sample pellets are exposed to air. The amounts and the initial rates of water of adsorption are different for UDD modified by different gases. Based on the experimental results three forms of adsorbed water are suggested. q1998 Elsevier Science B.V. All rights reserved.

Alumina-supported molybdenum carbide and its modifier with small amounts of nickel were evaluated and characterized. The evaluation results showed that a nickel-doped carbide catalyst exhibited a much higher conversion of methane and selectivity to CO and H2for the partial oxidation of methane (POM) to syngas. Also, the addition of a small amount of nickel resulted in significant improvement of catalysis stability. Characterization by temperature programmed surface reaction (TPSR) indicated that the addition of nickel promoted the carburization of molybdenum oxide. Especially under the conditions of the POM to syngas, this promotion resulted in more active phases being held. The nickel doped catalyst had small particles, larger specific area and greater ability to resist sintering. All these improved the catalytic stability. The other characterizations by XRD, XPS, SEM as well as BET surface area measurement also confirmed these promotions of nickel. In addition, the doped nickel made possible the increase of the intrinsic activity of catalytic centers over molybdenum carbide catalyst.

A series of M-W-Mn/SiO2 catalysts (M=Li, Na, K, Ba, Ca, Fe, Co, Ni, and Al) have been prepared and their catalytic performance for the oxidative coupling of methane (OCM) was evaluated in a continuous-flow microreactor. The structural properties of the catalysts have been studied using X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). In the trimetallic catalysts studied, there was evidence for WO4 tetrahedron on the surface in the Li-, Na-, and K-W-Mn/SiO2 catalysts, which is mainly present in the subsurface of the Ba-W-Mn/SiO2 catalyst. It appears that the WO4 has a strong interaction with the α-cristobalite support and is stabilized in the Na-and K-W-Mn/SiO2 catalysts. However, the WO4 species appear to be less stable in Li-or Ba-W-Mn/SiO2 catalysts, in which the support turns into quartz SiO2 or amorphous SiO2. The WO4 tetrahedron on the catalyst surface appears to play an essential role in achieving high CH4 conversion and high C2 hydrocarbon selectivity in the OCM reaction. Calculations suggest that the WO4 tetrahedron interacts with the CH4, giving suitable geometry and energy matching with CH4, and this may account for the high OCM activities.

The performance of supported and unsupported molybdenum carbide for the partial oxida-tion of methane (POM) to syngas was investigated. An evaluation of the catalysts indicates that bulk molybdenum carbide has a higher methane conversion during the initial stage but a lower selectivity to CO and H2/CO ratio in the products. The rapid deactivation of the catalyst is also a signi cant problem. However, the supported molybdenum carbide catalyst shows a much higher methane conversion, increased selectivity and signi cantly improved catalytic stability. The characterization by XRD and BET specic area measurements depict an improved dispersion of molybdenum carbide when using alumina as a carrier. The bulk or the supported molybdenum carbide exists in the -Mo2C phase, while it is transformed intomolybdenum dioxide postcatalysis which is an important cause of molybdenum carbide deactivation.

in a continuousflow microreactor. The Co content has a significant effect on the activity of the cobalt-magnesium oxide solid solution catalysts. The catalysts containing 5 and 10% Co have the lowest light-off temperature in methane combustion. In the preparation of cobalt-magnesium oxide solid solution catalysts, higher urea to metal ratio favors the formation of the catalysts with smaller crystal particles and leads to a better catalytic performance for methane combustion. Addition of lanthanum nitrate to the solution of Co and Mg nitrate depressed the formation of the cobaltmagnesium oxide solid solution and decreased the activity of the catalysts for methane combustion. The cobalt-magnesium oxide solid solution catalysts are very stable when the calcination or reaction temperature is no more than 900◦C. However, the catalytic activity decreases rapidly after high temperature (>1000℃) calcination, possibly due to sintering of the catalyst and thus decrease of the surface area.