Investigation On Carbon Dioxide Reforming Of Methane Over Nickel Modified Tungsten Carbide Catalysts

Dry reforming of methane with carbon dioxide (DRM) uses greenhouse gas CO2 and CH4 as the feed stock, which is a potential method to utilize the greenhouse gases in the atmosphere. The syngas produced has a H2-to-CO ratio of 1, and the mixture can serve as the feedstock for a variety of downstream processes, such as F-T synthesis and oxo-synthesis. In addition, it is also considered as a mean of converting solar and atomic energy into chemical energy, which is easier to store and transport. Although the reforming has economic, environmental and scientific advantages, it still has not been industrialized, which mainly due to the high cost of precious metal and serious carbon deposition on nickel-based catalysts.In this paper, tungsten carbides and nickel modified tungsten carbide catalysts were prepared and their catalytic performances were investigated for dry reforming. The modified catalysts have been characterized in terms of XRD, CH4-TPSR and CO2-TPO measurements. Associated the results of characterized and the performance of the catalyst, the following results were achieved:(1). α-WC and β-W2C catalysts were prepared from precursor WO3 and temperature programmed carbonization method and characterized by XRD analysis. The results of CH4-TPSR, CO2-TPO and XRD measurements illustrated that α-WC has higher thermal stability and oxidation resistance than β-W2C.(2). NiWOx and Ni-WCx were prepared by co-precipitation method and temperature-programmed carbonization method respectively. The effect of added nickel on carburized temperature of the carbide was studied. We also investigated the impact of different Ni/W ratio, reaction temperature on the catalytic activity and stability of Ni-WCx catalysts. The results show that Ni-WCx catalysts show excellent catalytic activity and stability under a large range of Ni/W molar ratio. The characterized results of SEM, CH4-TPSR and CO2-TPO suggested that with the increase of the Ni/W molar ratios, the CO2 was easily activated in the dry reforming, which leaded the deactivation of the catalysts by oxidation.(3). The method of introducing active metal nickel on carbides was studied, including deposition-precipitation method and co-precipitation method. Form of catalysts prepared via deposition-precipitation method was metal Ni, while the latter was mainly Ni17W3 alloy. Comparing with the two catalysts, CH4 dissociation of the former was faster and activation of CO2 was lower, leading to the deactivation of catalysts. For the latter, nickel was stabilized in the form of Ni17W3 alloy, which made the catalyst excellent activity and stability in the dry reforming.