DFT Study of Methanol Adsorption on Defect-Free CeO2 Low-Index Surfaces

Methanol decomposition is a promising method for hydrogen production. However, the performance of current catalysts for this process is not sufficient for commercial applications. In this work, methanol adsorption on the CeO₂ low-index surfaces is studied by density functional theory (DFT). The results show that methanol always dissociates spontaneously on the (100) surface, whereas dissociation on the (110) surface is site-selective; dissociation does not occur at all on the (111) surface, where only weak physisorption is found. The results confirm that surfaces with higher energies are more catalytically active. Analysis of the surface geometries shows that the dominant factors for the dissociation of methanol are the degree of undercoordination and the charges of the surface ions. The adsorption energy of each methanol molecule decreases with increasing coverage and there is a transition threshold between dissociative and associative adsorption. The present work indicates that a strategy to design catalysts with high activity is to maximize exposure of surfaces on which the ions have a high degree of undercoordination and a strong tendency to donate/accept electrons. The results demonstrate the importance of appropriately selecting and controlling exposed facets and particle morphology for optimizing catalyst performance.     

La2O3对CuO/CeO2水煤气变换反应催化剂微观结构及催化性能的影响（英文）

以La2O3为助剂,采用共沉淀法制备了具有良好催化活性和热稳定性的CuO/CeO2-La2O3水煤气变换反应催化剂,其中,当La2O3含量为2wt%时,催化剂的催化性能最为优异.同时运用X射线衍射、N2吸附-脱附、Raman光谱、程序升温还原等手段,研究了不同含量的La2O3对CuO/CeO2催化剂微观结构及催化性能的影响.结果表明,La2O3助剂进入了载体CeO2的晶格并对CuO/CeO2催化剂的微观结构和催化性能产生了直接影响,适量La2O3的添加可以抑制CuO和CeO2晶格的长大、增强CuO与CeO2间的相互作用、提高催化剂的比表面积、促进CeO2载体中生成更多的氧空位,CuO/CeO2催化剂的催化活性和热稳定性也明显改善.     

A Highly Reactive and Sinter-Resistant Catalytic System Based on Platinum Nanoparticles Embedded in the Inner Surfaces of CeO(2) Hollow Fibers

Ceria (CeO(2) ) hollow fibers with Pt nanoparticles (Pt?NPs) embedded in their inner surfaces were prepared by sequentially depositing Pt?NPs and CeO(2) sheaths on electrospun fibers of polystyrene, followed by calcination in air at 400?°C. Despite a relatively low Pt loading in this system, the turnover frequency for CO oxidation was 2-3 orders of magnitude higher than those of other systems, and the reactivity was also stable up to 700?°C.     

Fe2O3掺杂Ce0.8Nd0.2O1.9固体电解质的结构与导电性能

采用溶胶-凝胶法合成SiO2含量小于50×10-6的Ce0.8Nd0.2O1.9(NDC)陶瓷粉体,并将少量Fe2O3加入到NDC体系中,讨论Fe2O3的掺杂对其微观结构及电性能的影响。通过X射线衍射(XRD)等手段对氧化物进行结构表征,交流阻抗谱(AC)测试电性能。研究表明,Fe2O3的掺杂显著提高NDC陶瓷材料的致密度;相比于NDC而言,加入Fe2O3后材料的晶界电导率提高约12倍,总电导率提高约6倍。     

Oxidative coupling of methane over （Na2WO4＋Mn or Ce）/SiO2 catalysts： In situ measurement of electrical conductivity

The effects of manganese oxide or ceria promoters on the performance of Na2WO4/SiO2 catalysts for oxidative coupling of methane (OCM) are reported. The OCM reaction was performed in a continuous-flow microreactor at 800 ℃, atmospheric pressure and under GHSV = 13200 ml gC-1at h-1. Catalysts were characterized by in situ conductivity measurement, FT-IR spectroscopy, XRD, SEM and temperature programmed reduction analysis. Manganese oxide promoted Na2WO4/SiO2 is considered as one of the active and selective ca...     

碱金属助剂对 Au-Pt/CeO2 催化剂催化水煤气变换反应活性的影响

 制备了碱金属 M (M = Na, K, Rb 和 Cs) 掺杂的 Au-Pt/CeO2 催化剂, 考察了其催化水煤气变换反应的活性, 并采用 X 射线衍射、H2 程序升温还原、紫外-可见漫反射光谱和 X 射线光电子能谱技术研究了 K 助剂对 Au-Pt/CeO2 催化剂结构和表面性质的影响. 结果表明, 添加少量电负性较低的 K 虽然使 Pt 的还原变得困难, 但有利于 Au 金属态的稳定, 并使催化剂表面 Ce3+ 富集而产生氧空位, 显著提高了 Au-Pt/CeO2 催化剂活性. 当 K 负载量为 0.025%, 反应温度 250 oC 时, CO 转化率可达 95%.     

低水碳摩尔比条件下液化石油气高效预重整的Ni/CeO2/Al2O3 催化剂

 采用硝酸镍和硝酸铈水溶液共浸渍薄水铝石制备了 Ni/CeO2/Al2O3 催化剂, 并将其用于低水碳摩尔比条件下商用液化石油气 (LPG) 预重整反应. 考察了 Ni 含量和反应温度对催化剂性能的影响. 结果表明, 在 300~400 oC 和水碳摩尔比为 1.0 的条件下, 该催化剂具有很高的催化 LPG 预重整反应活性. 15%Ni/CeO2/Al2O3 催化剂在 350 oC, 3 000 ml/(g•h) 和水碳摩尔比 1.0 的条件下, 反应 105 h 后 LPG 转化率和产气组成均保持不变, 表现出较高的稳定性. 反应后催化剂表面没有明显的积炭.     

氧化铈纳米粒子光催化降解亚甲基蓝的动力学和机理

 CeO2 nanocrystals were synthesized by a simple precipitation method and calcination at 600 °C. (NH4)2Ce(NO3)6 and ammonia were used as precursors. The CeO2 nanoparticles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and N2 adsorption. The photodegradation of methylene blue catalyzed by CeO2 nanoparticles was studied under UV and sunlight irradiation. The highest degradation was obtained with 1.0 g/L CeO2 at pH 11 within 125 min. The pseudo first order rate constants of dye bleaching were calculated as 16.2x10-3 and 15.7x10-3 min-1 under UV and sunlight irradiation, respectively. The effect of iso-PrOH, iodide ion, and H2O2 was studied to predict the pathway of dye degradation. The obtained results indicate the effect of photogenerated holes in the degradation mechanism of the dye. Also, the photocatalytic activity of the prepared photocatalyst was studied in the presence of several negative ions.     

Pt-CeO2/C催化剂对甲醇氧化的电催化活性

将CeO2溶胶与Pt/C催化剂机械混合制备了Pt-CeO2/C催化剂,研究了酸性条件下Pt-CeO2/C催化剂对甲醇氧化的电催化活性。结果表明,与Pt/C催化剂相比,Pt-CeO2/C催化剂对甲醇展现出更好的催化活性。XRD和TEM测试结果表明,Pt-CeO2/C催化剂中Pt与CeO2的平均粒径均为3~4 nm。对CeO2含量不同的Pt-CeO2/C催化剂在CH3OH-H2SO4中进行循环伏安测试发现,Pt-CeO2/C催化剂对甲醇氧化的电催化活性较高,其中Pt与CeO2质量比为1∶1时,催化剂的催化活性最高,对甲醇氧化的峰电流密度达到0.112 A/cm2。     

Effect of CeO2 preparation method and Cu loading on CuO/CeO2 catalysts for methane combustion

CeO2 was synthesized by sol-gel, hydrothermal, nitrate thermal decomposition methods, respectively, and used as support to prepare CuO/CeO2 catalysts. According to characterization and reaction results, preparation method of CeO2 had a great influence on the physicochemical properties and activities of CuO/CeO2 catalysts. CuO with high dispersion and strong interaction with CeO2 was highly active in methane combustion, while CuO particles less associated with CeO2 showed less activity. The CuO catalyst supported on CeO2 which was prepared via nitrate thermal decomposition method showed the largest area, the smallest particle size, the highest dispersion of copper species and strong support metal interactions. Therefore, it presented the highest redox ability and activity for methane combustion. Activities of the catalysts with different copper content kept increasing until 5% Cu loading and from then on kept constant. Moreover, methane conversion decreased as methane space velocities increased on CuO/CeO2 catalyst. Addition of CO2 to the feed did not produce a significant effect on the catalytic activity, but the presence of H2O provoked a remarkable decrease on the activity of CuO/CeO2 catalyst.