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To investigate the role of vanadium oxide supported on mesoporous silica (VOx/m-SiO2) catalysts in methane oxidation to formaldehyde, various catalysts were prepared. The type of m-SiO2 (SBA-15 and MCF-17), vanadium loading (1, 3, and 5%), and preparation method (wet impregnation; WI and dry impregnation; DI) were changed to produce VOx/m-SiO2 with different vanadium species. Because of the larger surface area and pore size, a higher dispersion of vanadium loading, 1% VOx/MCF-17(DI), showed the highest conversion (20.2%) in methane oxidation at 600 °C. Various characterizations revealed that DI was a better method to produce isolated tetrahedral monovanadate species in VOx/m-SiO2 catalysts than WI. As the vanadium loading was decreased from 5 to 1%, the methane conversion was further increased due to the higher degree of dispersion of monomeric VO4 generated in the catalysts with low vanadium loading. The combined results demonstrate that the dispersion of vanadium and the isolated monomeric VO4 phase increased when the vanadium catalyst was loaded on MCF-17 and prepared by the DI method. [ABSTRACT FROM AUTHOR]

The formation of methanol directly from methane and steam was observed over Cu ion-exchanged mordenite. Furthermore, the continuous production of methanol was achieved by co-feeding methane and steam over Cumordenite. The methanol production rate was comparable to that reported in the stepwise process in which activation, methane reaction, and extraction of methanol were carried out separately. [ABSTRACT FROM AUTHOR]

Ni/SiC and Ni/SiO2 catalysts prepared by both wet impregnation (WI) and deposition-precipitation (DP) methods were compared for CO and CO2 methanation. The prepared catalysts were characterized using N2 physisorption, temperature-programmed reduction with H2 (H2-TPR), H2 chemisorption, pulsed CO2 chemisorption, temperature-programmed desorption of CO2 (CO2-TPD), transmission electron microscopy, and X-ray diffraction. H2-TPR analysis revealed that the catalysts prepared by DP exhibit stronger interaction between the nickel oxides and support than those prepared by WI. The former catalysts exhibit higher Ni dispersions than the latter. The catalytic activities for both reactions over Ni/SiC and Ni/SiO2 catalysts prepared by WI increase on increasing the Ni content from 10 to 20 wt%. The Ni/SiC catalyst prepared by DP shows higher catalytic activity for CO and CO2 methanation than that of the Ni/SiC catalyst prepared by WI. Furthermore, it exhibits the highest catalytic activity for CO methanation among the tested catalysts. The high Ni dispersion achieved by the DP method and the high thermal conductivity enabled by SiC are beneficial for both CO and CO2 methanation. [ABSTRACT FROM AUTHOR]

RF plasma excitation of methane has been studied in an effort to optimize the reaction conditions for a selective partial oxidation of methane. The reaction products of RF-excited methane are C2 hydrocarbons such as ethane and acetylene when O2 is not used. The introduction of a few percent of O2, however, is found to switch the selectivity in favor of CO while CO2 formation is suppressed down to a level below a few percent. Interestingly, in the low O2 ratio regime (0-0.6), the selectivity between CO and C2 hydrocarbons is observed to vary systematically in response to the detailed reaction conditions, including flow rate, pressure and applied RF power, which are explained by the competition between coupling and partial oxidation reactions. Variation in the density and the residence time of the active species in the plasma is suggested to determine the overall reaction pathways. The present results suggest a possibility of a selective production of the partial oxidation products of methane such as CO with a high selectivity and a high conversion efficiency using controlled RF plasma from methane and O2. [ABSTRACT FROM AUTHOR]

The effect of Pt particle size on propane combustion was investigated over Pt/ZSM-5 catalysts. The particle size of Pt was controlled by adjusting the SiO 2/Al 2O 3 ratio in H-ZSM-5, a cation in ZSM-5, and an aging temperature. Several techniques such as inductively coupled plasma-atomic emission spectroscopy, N 2 physisorption, CO chemisorption, C 3H 8 chemisorption, solid-state 27Al magic-angle spinning nuclear magnetic resonance spectroscopy, transmission electron microscopy, and infrared spectroscopy after CO chemisorption were used to characterize the catalyst. Among Pt catalysts supported on H-ZSM-5 with different SiO 2/Al 2O 3 molar ratios, Pt/H-ZSM-5 (SiO 2/Al 2O 3 = 150) having small Pt particles and large external surface area showed the highest specific reaction rate for propane combustion. The specific reaction rate decreased with an increase in the Pt particle size in Pt/H-ZSM-5 (SiO 2/Al 2O 3 = 23) catalysts with different Pt particle sizes. Although Pt/Na-ZSM-5 catalysts had larger Pt particles than Pt/H-ZSM-5 catalysts, the former showed a lower apparent activation energy for propane combustion than the latter. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

MnOx supported on γ-Al2O3, TiO2, Y-ZrO2 and SiO2 was prepared by an impregnation and a deposition-precipitation method, and their catalytic activities for the low-temperature selective catalytic reduction (SCR) of NOx with NH33 in the presence of excess O2 were examined. The catalytic activity of the catalysts prepared by a deposition-precipitation method was higher than that of catalysts prepared by an impregnation method. The activity follows in the order: MnOx/TiO2 ≈ MnOx/γ-Al2O3 > MnOx/SiO2 > MnOx/Y-ZrO2. Supported MnOx catalysts prepared by a deposition-precipitation method appeared to have an amorphous manganese oxide phase and those prepared by an impregnation method exhibited a crystalline MnO2 phase, respectively. The addition of SO2 with H2O in the feeding gas slightly deactivates the SCR activity of MnOx/TiO2 catalysts. [ABSTRACT FROM AUTHOR]