Abstract:

CeO₂ nanoparticles(W-CeO₂), CeO₂ nanosheets(S-CeO₂), CeO₂ nanorods(B-CeO₂) and CeO₂ nano-octahedra(O-CeO₂) were firstly prepared by hydrothermal method, and then CuO/CeO₂ catalysts with fixed copper mass fraction were obtained by impregnation method. The catalysts were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy (Raman), automated adsorption analyzer (BET), H₂ programmed temperature rise reduction (H₂-TPR), N₂O titration and other characterization techniques, and their catalytic performance was assessed in a fixed bed quartz tube reactor with controlled temperature and pressure. The effects of the CuO/CeO₂ catalyst morphology on the methanol production by CO₂ hydrogenation were investigated. The catalytic activity of the CuO/CeO₂ catalysts showed a strong dependence on their morphology, and the factors of the exposed crystalline surface, specific surface area, surface basic sites and surface oxygen defects of the catalysts all affected the CO₂ conversion, methanol selectivity and the yield. Among them, the order of the activity of the preferentially exposed crystalline surfaces of CeO₂ with different morphologies is S-CeO₂({100}+{110})>W-CeO₂{100}>B-CeO₂{111}≈ O-CeO₂{111}). The higher the activity of the exposed crystalline surfaces, the more oxygen defects on the catalyst surface, and the stronger the CuO/CeO₂ interactions, the better the catalytic activity. Regarding CuO/S-CeO₂, it had the most basic sites on the surface with a specific surface area of 88.8m²/g and copper dispersion of 19.2%, giving the best catalytic activity of CO₂ conversion 6.56%, methanol selectivity 96.3% and yield 0.063g/(g_cat·h). The activity evaluation tests showed the conversion rates of the catalysts were in the order of S-CeO₂>B-CeO₂>W-CeO₂>O-CeO₂, which indicates that the CeO₂ morphology could determine the physical and chemical properties and the catalytic activity of the CuO/CeO₂ catalysts.

Key words: CeO₂ morphology, catalyst, carbon dioxide, hydrogenation, methanol

摘要：

采用水热法制备CeO₂纳米颗粒（W-CeO₂）、CeO₂纳米片（S-CeO₂）、CeO₂纳米棒（B-CeO₂）及CeO₂纳米八面体（O-CeO₂），用浸渍法负载相同质量分数的铜形成CuO/CeO₂催化剂。通过扫描电镜（SEM）、高分辨透射电子显微镜（TEM）、X射线衍射（XRD）、拉曼光谱（Raman）、自动吸附分析仪（BET）、H₂程序升温还原（H₂-TPR）、N₂O滴定等表征技术对催化剂进行表征，并在可控温控压的固定床石英管反应器中对催化剂的催化性能进行评价。研究了不同形貌CuO/CeO₂催化剂对CO₂加氢制备甲醇的影响；结果表明，CuO/CeO₂催化剂的催化活性存在明显的形貌依赖性，催化剂的暴露晶面、比表面积、表面碱性位点、表面氧缺陷的差异均会对CO₂转化率、甲醇选择性和产率产生影响。其中，不同形貌CeO₂优先暴露晶面的活性顺序为S-CeO₂（{100}+{110}）>W-CeO₂{100}>B-CeO₂{111}≈O-CeO₂{111}，暴露晶面活性越高，催化剂表面氧缺陷越多，CuO-CeO₂间相互作用越强，则催化活性越好。当为CuO/S-CeO₂时，催化剂表面中碱性位点最多，催化剂比表面积为88.8m²/g，铜分散度为19.2%，CO₂转化率为6.56%，甲醇选择性和收率为96.3%和0.063g/(g_cat·h)，催化活性最好，由活性评价试验得转化率由高到低依次为S-CeO₂>B-CeO₂>W-CeO₂>O-CeO₂，可知CeO₂形貌差异会决定CuO/CeO₂催化剂的物化性能和催化活性，从而提升对不同形貌CuO/CeO₂催化剂催化CO₂加氢制甲醇的基础认识。

关键词: CeO₂形貌, 催化剂, 二氧化碳, 加氢, 甲醇