Combustion Preparation Of Ni-based Catalysts And Their Catalytic Performance For Slurry Methanation

Natural gas is one of important clean and high-efficient utilization of coals. Methanationtechnology is the core. As a strong exothermic reaction, methanation produces high adiabatictemperature rise. However, industrial fixed bed reactor which has poor heat transmission andis easy to cause sintering. In slurry bed reactor, catalysts scatter in inert liquid-phase mediumevenly and methanation reaction heat could be eliminated timely, thus avoid catalyst sinteringcaused by local overheating. However, temperature in slurry bed reactor is relative low,high-activity and high-stability catalyst for slurry bed reactor methanation will be the researchkey.Combustion method shows characteristic, such as short preparation process, easyoperation, little device investment. The products shows large specific surface area and littleparticle size. In addition, a wide variety of inorganic materials can be prepared, and theresearch on this method is increased. In this paper, Ni-based catalyst was prepared bycombustion method (solution combustion method and impregnation combustion method).Structure and surface properties of Ni-based catalyst were studied through various moderncharacterization means. Catalytic performance of the prepared Ni-based catalyst in COmethanation in the slurry bed reactor was investigated. Main research contents are included asfollow: (1) Ni-Al2O3catalysts are prepared by impregnation combustion method. Catalysts withdifferent Ni content has been prepared by impregnation combustion method. With theincreasing of Ni content, the amount of metallic Ni in reduced catalysts increases, however,the specific surface area of catalysts decreases, Ni particle size increases, and the Nidispersion decreases. As a result, the metal Ni surface area increases and then keeps constant.Catalysts with Ni content above25%shows optimize catalytic performance. Catalysts are alsoprepared by different fuels. Catalyst prepared by urea as fuel shows the best Ni dispersion,largest metal Ni surface area, and has optimize methanation catalytic performance. However,the structure and property of catalysts prepared by glycine and glycol as fuel are close to thatof catalyst prepared by urea, and the metal Ni surface area is less then the latter a little, andtheir catalytic performance are also close. It can be indicated that the microstructure ofcatalysts mainly influenced by the strcture of support. However, there is less effect of fuel onthe structure.(2) The deactivation of Ni-Al2O3catalyst in slurry bed reactor are analyzed. After reactedfor450h under280℃, the CO conversion of catalyst drops from92%to69%. The resultsshow that no Ni loses or aggregates, but amorphous carbon appears, the catalyst surface ispartly occupied, and the metal Ni surface area decreases, resulting the decreasing of catalyticactivity. Reacted catalyst is heated for4h in400℃air to eliminate carbon deposit, structuralproperties and activity of the catalyst recover, and the CO conversion reaches99%of that offresh catalyst.(3) Ni-Al2O3catalysts are prepared by solution combustion method. The precursor ofsupport, such as aluminium nitrate, zirconyl nitrate, lanthanum nitrate and cerium nitrate,influences combustion process. When using aluminium nitrate as the precursor, thecombustion is mild and keeps a long time, the catalysts has large specific surface area andmetal Ni surface area, small Ni particle size and well dispersion, as a result has good activityin CO methanation reaction. The catalytic performance of catalysts follows the order asNi-Al2O3> Ni-ZrO2> Ni-La2O3> Ni-CeO2. Catalysts are also prepared by different fuels.The catalyst prepared by urea as the fuel has larger specific surface area, more dispersed NiO,smaller Ni particle size and larger metal Ni surface area. However, catalysts prepared byglycine or glycol have less surface area, more free NiO, larger Ni particle size and less meta lNi surface area. The catalytic performance of catalysts prepared by different fuels follows theorder of urea> glycine> glycol. The catalysts prepared by different method are compared.The catalyst prepared by solution combustion method has better Ni dispersion, larger metal Ni surface area and better catalytic activity for slurry methanation; the catalyst prepared byimpregnation combustion method has less Ni dispersion and worse catalytic activity thancatalyst above; the catalysts prepared by solution combustion method and impregnationcombustion method have better catalytic performance than catalyst prepared by impregnationmethod.