制备方法对Co-Pd/TiO_2催化剂催化CH_4-CO_2梯阶转化的影响

Effect of preparation method on the catalytic performance of Co-Pd/TiO_2 catalysts for the step-wise conversion of CH_4 and CO_2

以钴、钯为活性金属,分别采用浸渍法和溶胶-凝胶法制备了Co-Pd/TiO2催化剂,考察了不同制备方法制备的Co-Pd/TiO2催化剂对CH4-CO2梯阶转化直接合成C2含氧化合物的影响。利用XRD、XPS和N2-吸附-脱附对催化剂进行了表征。结果表明:两种方法制备的催化剂反应前与反应后表面织构都存在较大变化,且催化剂中均存在CoTiO3物种,这是活性金属Co与载体TiO2之间发生强相互作用,Co2+替代TiO2晶格中的Ti4+的结果;CoO和金属Pd可能是该反应的活性中心;反应前与反应后溶胶-凝胶法制备的催化剂的表面Co含量均低于浸渍法制备的催化剂,而表面Pd含量则均高于浸渍法制备的催化剂,且溶胶-凝胶法制备的催化剂各种产物的生成速率均高于浸渍法制备的催化剂,因此,与浸渍法制备的催化剂相比,溶胶-凝胶法制备的催化剂具有更好的催化活性。

Co-Pd/TiO2 catalysts are prepared by impregnation and sol-gel methods, separately. The effect of preparation methods on Co-Pd/TiO2 catalyst performance is investigated for the direct synthesis of C2 oxygenates from CH4 and CO2 by a step-wise reaction technology. The as-prepared catalysts are characterized by XRD,XPS and nitrogen adsorption-desorption. The results show that the surface property and texture of both impregnation catalyst and sol-gel catalyst have obvious changes after reaction. The existence of CoTiO3 species in all catalyst samples shows that there is a strong interaction between active metal Co and the carrier TiO2,and that Co2＋ can substitute Ti4＋ in the titania lattice. Co O and Pd may act as the active center for this reaction. For both fresh and used catalyst samples,surface Co contents of sol-gel catalyst samples are lower than those of impregnation catalyst samples, while surface Pd contents of sol-gel catalyst samples are higher than those of impregnation catalyst samples. For sol-gel catalyst samples,the formation rates of all products are higher than those of impregnation catalyst samples. Consequently, sol-gel catalyst performs a better catalytic activity compared with impregnation catalyst.