不同方法制备的Ni/ZrO_2-CeO_2-Al_2O_3催化剂对CH_4-CO_2重整反应的催化性能

Performance of Ni/ZrO_2-CeO_2-Al_2O_3 Catalyst Prepared by Different Methods for Carbon Dioxide Reforming of Methane

采用水热合成法、溶胶凝胶法和共沉淀 负载法制备了相同NiO含量的Ni ZrO2 CeO2 Al2 O3催化剂 ,考察了它们在CH4 CO2 重整反应中的催化性能及稳定性 ,测定了积碳量 .用CO2 程序升温脱附方法测试了它们的CO2 吸附性能 ,用H2 程序升温脱附方法测试了表面Ni的分散度 .结果表明 ,随温度升高 ,CH4和CO2 转化率降低的顺序是 :溶胶凝胶法≈共沉淀 负载法 >水热合成法 ,并且反应产物中n(CO) n(H2 ) 比随温度升高而降低 .水热法和共沉淀 负载法制备的催化剂稳定性好 ,且前者的活性比后者高 ;溶胶凝胶法制得的催化剂活性较高 ,但易失活 .积碳量大小顺序是 :水热法 >溶胶凝胶法 >共沉淀 负载法 .与其他方法制备的催化剂相比 ,水热法制备的催化剂对CO2 的吸附量更大 ,而且积碳主要存在于载体上 。

Traditional Ni catalyst for the reaction of CO_2-CH_4 reforming to synthesis gas is easily deactivated owing to carbon deposit, so work searching for catalysts that are highly stable and active for this reaction has been intensively done. Ni/ZrO_2-CeO_2-Al_2O_3 catalyst, which was prepared by hydrothermal synthesis method (Ni-hydro) that is favorable for the interaction among compositions at high temperature and under high pressure, had good stability and high activity. In order to study its speciality, other kinds of catalysts with the same composition were prepared by sol-gel method (Ni-gel) and precipitation-loading method (Ni-load) respectively. Their activity and stability in CO_2-CH_4 reforming reaction were studied, and the amount of carbon deposits was measured. Their capability of adsorbing CO_2 was measured by CO_2 temperature programmed desorption. The results showed that the higher the Ni dispersion degree, the higher the initial activity of the catalyst, and the weaker its capability of adsorbing CO_2. The catalytic activity increases in the order of Ni-gel≈Ni-load<Ni-hydro, and n(CO)/n(H_2) in products decreases with the increase of reaction temperature. Stability tests showed that Ni-hydro and Ni-load are not deactivated, but the activity of the former is higher than that of the latter. The activity of Ni-gel catalyst is rather high, but it is deactivated easily. The amount of carbon deposits increases in the order of Ni-load<Ni-gel<Ni-hydro. The Ni-hydro catalyst has low Ni dispersion degree, and the amount of carbon deposits during CH_4 decomposition over this catalyst is less. CO_2 was mainly adsorbed on the support of the catalyst, thus the catalyst was more stable.