| Under the growing shortage of fossil fuel and environmental pollution, biomass, due to its low sulfur, low nitrogen, zero emissions of carbon dioxide, renewability, and environmental benefits, has been attracted as a potential alternative fuel resource. Biomass gasification for syngas is one of the most potential and promising technologies. However, this process is inevitably accompanied by the formation of tar that can corrode pipeline and harm human health. It is widely recognized that tar as a significant impediment to the use of biomass gasification systems must be removed with a variety of ways.Among the various methods to remove tars from producer gas, such as cyclone separation, dry gas cleaning, pyrolysis, steam reforming is commonly recognized as the best option that can convert tar into syngas efficiently. Nickel-based catalyst is the most suitable choice for its high activity and economic advantages. Improvement of the catalytic performance by changing supports and adding promoter has been become the research focusIn this paper, we studied the effect of MgO and CeO2 promotor on Ni/olivine catalyst using toluene as a model tar compound. At T=790℃, SV=782 h"1, S/C=3, the results show that MgO really have a significant impact on catalytic activity and resistance to carbon deposition for Ni/olivine catalyst.3%Ni-3%Mg/olivine and 3%Ni-1%Ce-3%Mg/olivine show the better activity with 80% and 96% yield of toluene conversion, respectively.When S/C is 5, the catalytic performance of Ni-Mg/olvine is decreased with the content of MgO. Various characterization techniques such as XRD, H2-TPR, XPS and TG were performed to investigate the relationship between MgO and the content of water in material. MgO promoter can improve the dispersion of active components and reduce the amount of carbon deposition and the degree of graphitization on the surface of nickel-based catalysts. The results shown above seem that MgO can hydrate with water on the catalyst surface, and the hydration of MgO further influence the oxidation of Ni metal particles leading to the activity less than that of Ni/olivine catalyst without MgO. Consequently, the promoter MgO can improve the catalytic performance of nickel-based catalysts, but, it is sensitive to water. The catalysts contained MgO are more suitable to use in low S/C condition.The experimental results shown catalysts 3%Ni-1%Ce-3%Mg/olivine modified by MgO and rare earth metal Ce simultaneously has the best catalystic performance. At S/C=3, The 3%Ni-1%Ce-3%Mg/olivine system showed about 96% toluene conversion and keep up the better activity in 450 minutes compared to that at S/C=5. Therefore, this catalyst and operating condition are more suitable for industrial application. |
