Effect of Structure of CeOHCO3 Precursor of CeO2 on Its Catalytic Performance

Abstract

A modified hydrothermal process method based on using urea instead of water as the solvent was used to prepare CeOHCO 3 . Pure CeOHCO 3 with a single crystalline structure was produced by varying the experimental conditions. CeO 2 particles obtained from these CeOHCO 3 precursors were tested for CH 4 oxidation. The temperatures for 90% methane conversion were 604 and 647°C for CeO 2 catalysts obtained from hexagonal and orthorhombic CeOHCO 3 , respectively, indicating that the CeO 2 catalyst from hexagonal CeOHCO 3 (CeO 2 -A) was more active than that from the orthorhombic form (CeO 2 -D). The specific surface area and pore volume of CeO 2 -A were 45 m 2 /g and 0.35 cm 3 /g, respectively, which were higher than those of CeO 2 -D. H 2 -TPR showed a much lower reduction temperature and enhanced reducibility with CeO 2 -A. XPS and O 2 -TPD results demonstrated there were more oxygen vacancies on the surface of CeO 2 -A than on CeO 2 -D, which implied increased oxygen mobility. The CeOHCO 3 -structure dependent activity was investigated and found to originate from the morphologies of the CeOHCO 3 precursors. Hexagonal CeOHCO 3 had a rod-like shape while orthorhombic CeOHCO 3 had a sphere-like morphology. After calcination, the obtained CeO 2 had the morphology of the precursor. The difference in morphology gave CeO 2 catalysts with different texture, structure, reducibility, and thus catalytic activity. 采用一种快速、无模板、低成本的微波辅助水热法在 2 min 内制备了三维花状 Co 3 O 4 . 所用原料均是无机盐. 前驱体浓度和尿素的逐渐水解对 Co 3 O 4 形貌影响很大. 制得的花状 Co 3 O 4 比表面积大, 且暴露了 (110) 高活性指数面, 对 CO 氧化具有较高的催化活性. The properties and catalytic activity of CeO 2 are closely related to the structure of CeOHCO 3 precursor. CeO 2 nanorods derived from hexagonal CeOHCO 3 have high activity than those from orthorhombic CeOHCO 3 .