Nano Ni / Zro <sub> 2 </ Sub> Catalyst For Methane Steam Reforming Reaction

With the crud oil resource become more and more short the development of natural gas has attracted researchers' much attention in the world. The steam reforming of methane is a major process for producing Hydrogen rich syngas in industry. It has become a new hotspot to develop an efficient catalytic process for producing highly pure hydrogen gas from steam reforming of methane owing to the development of hydrogen fuel cell. Ni based catalysts have been mostly used in the steam reforming of methane in industry. In order to decrease the carbon deposit on the surface of Ni catalyst, a high H2O/CH4 ratio has been usually adopted. Furthermore, high reaction temperatures are required for the steam reforming of methane because it is a highly endothermic reaction. Therefore, highly thermo-stable and carbon deposit-resisting catalysts are desired in the steam reforming of methane. The selection of a suitable support may be an effective way for improving the thermo-stability and carbon deposit-resisting ability of the based catalysts.Nanoscale particles have shown great advantages as catalysts in many catalytic reactions. ZrO2 possesses both acidic and basic properties and shows a relatively high thermo-stability in catalytic reactions. Recently, Ni/ZrO2 has been widely investigated as a support in the carbon dioxide reforming of CH4 to syngas and showed a higher carbon deposit-resisting ability. In this paper we have investigated the performance of Ni/ZrO2 catalyst in the steam reforming of methane. The influences of preparation conditions and reaction conditions of the catalyst on the catalytic performance of Ni/ZrO2 were studied.It was found that Ni/ZrO2 is more active for the steam reforming of methane than CN-32 and 85% CH4 conversion and 70% CO selectivity were obtained at the reaction conditions of 650℃, H2O:CH4:N2=2:1:2.67 and GHSV=1.98×104 h-1, The stability of Ni/ZrO2 was also examined under the reaction conditions of 650℃, H2O:CH4 =1.5:1 and 5.1×104 mL/g-cat.h for 30 hours. Although the tested times (30 hours) was not enough for check the stability of the catalyst, both CH4 conversion andCO selectivity did not decrease and kept constant during the tested period.The effects of preparation conditions on the performance of the catalyst were investigated. The crystal structures of the catalysts were determined by X-ray diffraction (XRD). The BET surface areas and the distribution of pore volumes were measured by nitrogen adsorption. The particle sizes were measured by transmission electron microscope (TEM). The results showed that the specific surface area of ZrO2 decreased evidently and its crystal size increased in some sort with the increase of calcination temperature. Influence of calcination temperatures of the support ZrO2 on the catalytic performance showed the catalyst calcined at 650℃ with a little higher CH4 conversion and no evident influence on CO selectivity. The effect of the reduction temperatures of Ni/ZrO2 catalyst on the catalytic performance was also examined in the reduction temperature range of 450-750℃. Under the reaction temperature of 650 ℃, the catalyst reduced at 550℃ exhibited a higher CH4 conversion than at other reduction temperatures. But no influence was found on CO selectivity when changing the reduction temperature of Ni/ZrO2 catalyst. The Ni content of Ni/ZrO2 catalyst with 10w% would be proper for steam reforming of methane. The catalyst prepared by a wet impregnation method exhibited a higher CH4 conversion than that prepared by mixing particles Ni or NiO with ZrO2.The effects of reaction conditions on the catalytic performance were measured. With the increase of temperatures the conversion of methane increased and researched 100% at 800℃. CO selectivity also increased monotonously with the increase of temperatures from 650℃ to 800℃ . The conversion of methane increased monotonously with the increase of H2O/CH4 ratios. When the H2O/CH4 ratio was over 3.5, the conversion of methane kept constant. The selectivity of CO decreased with the increase of H2O...