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.

Na-W-Mn/SiO2 catalysts with different sodium contents (wt%) were prepared and used for the oxidative coupling of methane (OCM). The catab, sts were characterized bv XPS and XRD. It was found that the catalysts with sodium contents between 0.39wt% and 2.34wt% exhibited good catalytic performances and the crystalline phases of the manganese oxides which lhvoured the reaction were formed. Owing to the addition of Na to the WO4-Mn/SiO2 catalyst, W and Mn moved towards the surface. These resuks suggested that the sodium is an essential active component for a high CH4 conversion and a high C2H4 selectivity.

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.

A series of cobalt-based catalysts with different supports have been prepared using impregnation method, and characterized by X-ray diffraction (XRD), laser Raman (LR), and infrared spectroscopy (IR). The catalytic activities for methane combustion were assessed in a micro-reactor. The ZrO2 and Al2O3 supports are themselves active in methane combustion, and ZrO2 supported cobalt catalyst was found to have the highest activity amongst the TiO2, Al2O3, MgO supported catalysts and bulk Co3O4. The Co content has a marked effect on the activity of the ZrO2 supported catalyst with 1.0 and 15 wt.% of Co having the lowest light-off temperature in methane combustion. In the MgO supported catalyst, Co oxide was highly dispersed over the MgOsupport surface or enters the lattice ofMgOto form a solid solution, whose activity for methane combustion is reasonable. The zirconia supported cobalt catalysts are very active and stable when calcination or reaction temperature is no more than 900◦C. Calcining the catalysts at temperatures above 900℃ for more than 1h decreases the catalyst activity. The deactivation of the catalyst probably results from the decrease of the surface area.

Investigation on molybdenum carbide catalyst, its oxide precursor and its modifiers was performed using temperature programmed surface reaction (TPSR) technique, BET surface specific area and X-ray diffraction (XRD) measurement. The carbide catalyst and its modifiers were evaluated using microreactor apparatus. The evaluation result showed that the addition of nickel promoted the POM to syngas, the addition of copper exhibited weaker promotion at the initial stage, but it turned unfavorable to the POM to syngas hereafter. As for potassium doped catalyst, it was unfavorable to the POM. According to the characterizations, the effect of added metals on the carburization, especially under the condition of POM, was elucidated.