.ni / Mgo-al <sub> 2 </ Sub> O <sub> 3 </ Sub> Preparation And Methane Reforming Reaction Behavior

For a long time, methane reforming to syngas, which is the first step for the indirect conversion of natural gas to liquid fuels or chemicals, has attracted much attention. In this thesis, targeted for the development of a highly active and stable catalyst for the tri-reforming of methane to synthesis gas under pressurized conditions, layed double hydroxides are used as a precursor to prepare the Ni-based catalyst. The catalysts were screened using CDR as a probe reaction, which can be quickly deactivated. Firstly, Ni/Mg-Al-LDO and Ni-Mg-Al-LDO with various contitution were synthesized with a co-precipitation method and incipient impregnation method, respectively. The influence of Mg/Al ratio, nickel loadings and preparation methods of the catalysts on the performance of CDR were quantitatively studied, and an active and stable catalyst of Ni-Mg-Al-LDO for the titled reaction was obtained. The textural, reductive properties and acid-base properties of the catalysts were characterized with XRD, H2-TPR, CO2-TPD and N2 adsorption/desorption methods. The properties of the carbonaceons materials deposited on the used catalysts investigated with TG-DTA. The catalytic performance was correlated with the characterization results of the catalysts. The best catalysts of Ni (20wt.%)-Mg-Al-LDO was evaluated for the tri-reforming of mathane, under various conditions. The main works and conclusions of this thesis are as follows:(1) Under the same reaction conditions of 750℃, CH4/CO2=1, GHSV=44000-53200 mL(CH4+CO2)-g cat.-1·h-1,P=l atm, conversions of CH4 and CO2 and H2 yield were strongly affected by Mg/Al ratios in the catalyst. Among the catalysts investigated, when Mg/Al ratio equals to 3/1 and Ni loading equals to 10%, the best CDR performance indexed by conversions of CO2 and CH4 was achieved. Increasing the Mg/Al ratio increases from 1/1 to 5/1, there existsed a maximum for conversion of CH4 and CO2, H2/CO, and H2 yield. For the catalysts with an optimal Mg/Al ratio of 3/1, the conversions of CH4 and CO2 and H2 yield increased monotonically with increasing the Ni loading from 10% to 25%.(2) Fixing Mg/Al=3/1, Ni-Mg-Al-LDO catalysts with various nickel contents synthesized with a co-precipitation method, were evaluated for CDR under the conditions of 750℃, CH4/CO2=1, GHSV=53200 mL(CH4+CO2)·g cat.-1·h-1, P=l atm. Results indicate that the BET surface area, pore volume and average pore distribution of the Ni-Mg-Al-LDO were much higher than those of the Ni/Mg-Al-LDO having the same composition. Moreover, in comparison with Ni/Mg-Al-LDO obviously higher conversion of CH4 and CO2 and H2 yield were obtained over Ni-Mg-Al-LDO. These results indicate that the content and introduction method of Ni are the most important factors to determine the CDR performance of LDO based catalysts. (3) Under the same operation condition, the activing and stability of Ni (20wt.%)-Mg-Al-LDO for the tri-reforming of methane were obviously higher than that for CDR. Syngas with H2/CO ratios of 1.0～4.5 was obtained by simply changing the feed composition of H2O, CO2 and O2. Based on the XRD and TG-DSCresults of the used catalysts, Ni crystal size and the amount of carbonaceous deposits over the catalysts were revealed to be the main factors to determine the activity and stability of the catalysts for tri-reforming of methane. Therefore, increasing the content of H2O or O2 is favorable to improve the activity and stability of the catalysts.