Comparative Study of CuO Species on CuO/Al2O3, CuO/CeO-Al2O3 andCuO/La2O-Al2O3 Catalysts for CO Oxidation

CuO/Al2O3, CuO/CeO2-Al2O3, and CuO/La2O3-Al2O3 (denoted as Cu/Al, Cu/CeAl, and Cu/LaAl) catalysts were prepared by an impregnation method. CuO species and CuO/Al2O3 thermal solid-solid interaction were characterized by in situ XRD, Raman spectroscopy and H2-TPR techniques. For the Cu/Al catalyst, a CuAl2O4 phase exists between the CuO and Al2O3 layer and the CuO phase exists on the surface in both highly dispersed and bulk forms. For the Cu/CeAl catalyst, there is highly dispersed and bulk CuO on the surface, but most of the CuO has transferred into the internal layer of CeO2 as bulk CuO and CuAl2O4. For the Cu/LaAl catalyst, only bulk CuO is present on the surface of the catalyst and no CuAl2O4 is formed. The catalytic activity order for CO oxidation is Cu/CeAl>Cu/Al>Cu/LaAl. The highly dispersed CuO on the catalyst surface may be the active phase for CO oxidation. The results show that the addition of CeO2 not only promotes both the transference of CuO and the formation of CuAl2O4 but also favors the CO oxidation due to the association of highly dispersed CuO with CeO2, while La2O3 hinders the transference of CuO and the formation of CuAl2O4.     

不同方法制备的CeO2载体对CuO/CeO2催化剂水煤气变换活性和稳定性的影响

分别采用沉淀法(A),水热法(B)和柠檬酸溶胶-凝胶法(C)制备了三种CeO2材料,并以其为载体采用沉积-沉淀法制备了CuO/CeO2催化剂.运用N2物理吸附、粉末X射线衍射(PXRD)、原位粉末X射线衍射(in situ PXRD)、氢气-程序升温还原(H2-TPR)和循环伏安法(CV)等技术对其进行了表征,考察了不同方法制备的CeO2载体对CuO/CeO2水煤气变换(WGS)催化剂的结构、氧化-还原性能、催化活性和稳定性的影响.结果表明,它们的催化活性和稳定性顺序都是CuO/CeO2-A＞CuO/CeO2-B＞CuO/CeO2-C.联系表征结果,CuO/CeO2催化剂的活性与催化剂中CuO的颗粒度、CuO的微观应力和中等大小且与二氧化铈相互作用的CuO的数量等有关,而这些因素很大程度上受CeO2载体本身的热稳定性的影响.根据CV中扫描次数的增加,Cu2+←→Cu0氧化还原峰面积减小,推断CuO/CeO2催化剂在一定条件下氧化还原是不可逆的,这可能是其在反应气氛下经受温度循环之后活性降低的原因.     

CeO2对CuO／Al2O3分散状态及催化性能的影响

用色谱－液反流动法技术,考察了ＣｕＯ催化剂对ＣＯ的性及添加ＣｅＯ２对催化活性的影响,并运用ＸＲＤ,ＴＰＲ和ＸＰＳ技术,研究了催化剂的物相结构和还原牧场 生。实验结果表明,ＣｅＯ２的添加增加了ＣｕＯ的分散性,使ＣｕＯ的特征衍射峰消失,从而改善了催化剂的氧化活性。     

不同方法制备的CeO2载体对CuO/CeO2催化剂水煤气变换活性和稳定性的影响

分别采用沉淀法(A), 水热法(B)和柠檬酸溶胶-凝胶法(C)制备了三种CeO2材料, 并以其为载体采用沉积-沉淀法制备了CuO/CeO2催化剂. 运用N2物理吸附、粉末X射线衍射(PXRD)、原位粉末X射线衍射(in situ PXRD)、氢气-程序升温还原(H2-TPR)和循环伏安法(CV)等技术对其进行了表征, 考察了不同方法制备的CeO2载体对CuO/CeO2水煤气变换(WGS)催化剂的结构、氧化-还原性能、催化活性和稳定性的影响. 结果表明, 它们的催化活性和稳定性顺序都是CuO/CeO2-A>CuO/CeO2-B>CuO/CeO2-C. 联系表征结果, CuO/CeO2催化剂的活性与催化剂中CuO的颗粒度、CuO的微观应力和中等大小且与二氧化铈相互作用的CuO的数量等有关, 而这些因素很大程度上受CeO2载体本身的热稳定性的影响. 根据CV中扫描次数的增加, Cu2+←→Cu0氧化还原峰面积减小, 推断CuO/CeO2催化剂在一定条件下氧化还原是不可逆的, 这可能是其在反应气氛下经受温度循环之后活性降低的原因.     

Nanostructured Cu(x)Ce1-xO2-y mixed oxide catalysts: characterization and WGS activity tests

Cu(x)Ce(1-x)O(2-y) mixed oxide catalysts were prepared by different preparation procedures: co-precipitation, the sol-gel peroxide route, and the sol-gel citric acid-assisted route. The resulting solids were investigated by means of XRD, BET, H(2) and CO temperature-programmed reduction (TPR), oxidation (TPO) and desorption (TPD) analyses, and N(2)O pulse selective reaction. It was confirmed that H(2) (CO) consumed for complete reduction of well-dispersed and bulk-like CuO phases to Cu(0), reduction of surface ceria and H(2) (CO) adsorption on the catalyst surface contribute to the total H(2) (CO) consumption. Among catalysts examined, the Cu(0.15)Ce(0.85)O(2-y) mixed oxide sample prepared by means of co-precipitation method exhibits the highest activity and stability for water-gas shift (WGS) pulse reaction in the range of employed operating conditions. WGS activity of copper-ceria mixed oxide catalysts is determined by the extent of surface ceria reduction and dispersion of copper species.     

氧化铈气凝胶担载氧化铜催化剂的TPR研究

 采用程序升温还原研究了氧化铈气凝胶担载氧化铜催化剂的还原行为,并与其对一氧化碳氧化反应的催化活性进行了关联．发现此类催化剂中存在两种类型的氧化铜,即体相氧化铜和分散于载体表面的氧化铜,且后者中的部分氧化铜还原后易被氧化．随着此易被氧化的铜含量的增加,催化剂对一氧化碳氧化反应的催化活性升高,表明此种类型的铜为催化剂的活性组分．     

CuO／CeO2和CuO／Al2O3催化剂的催化性能

本文以ＣＯ氧化为模式反应考察了ＣｅＯ２和Ａｌ２Ｏ３负载氧化铜催化剂的氧化活性，运用ＸＲＤ和ＴＰＲ技术研究了催化剂的还原性能和物相结构，结果表明：载体性质对负载ＣｕＯ催化剂的ＣＯ氧化活性有很大影响，ＣｕＯ／ＣｅＯ２催化剂活性明显高于ＣｕＯ／Ａｌ２Ｏ３催化剂．催化剂的还原特性随载体不同而不同．同时发现，热处理对催化剂铜物种的存在形式，晶粒大小、还原特性及其催化活性有明显影响，ＣｕＯ／Ａｌ２Ｏ３催化剂活性下降的主要因素是生成了活性较低的ＣｕＡｌ２Ｏ４相，而ＣｕＯ／ＣｅＯ２催化剂活性下降是由于ＣｕＯ和ＣｅＯ２发生烧结，晶粒变大     

Preferential oxidation of CO in excess H2 over CeO2/CuO catalyst:Effect of calcination temperature

Different from the classical configuration CuO/CeO2 catalyst,the inverse configuration CeO2 /CuO catalyst (atomic ratio of Ce/Cu=10/100) was prepared by impregnation method.Five calcination temperatures were selected to investigate the interaction between CeO2 and CuO support.It is found that as calcination temperature increased from 500 to 900 C,sintering of CeO2 particles on the support occurred together with the diffusion of a portion of Ce 4+ ions into CuO crystals,forming solid solution.Formation of interface complex Ce-O-Cu was suggested by TPR measurements.The catalyst calcined at 700 C gives the highest activity for preferential oxidation of CO in excess H2 stream.     

草酸盐热分解法制备CeO_2负载CuO催化剂用于CO优先氧化反应

采用草酸盐热分解-浸渍法制备了一系列不同CuO负载量的CuO/CeO_2催化剂,并将其用于CO优先氧化(PROX)研究.当CuO负载量为10%时催化剂活性最高,具有温区最宽且温度最低的CO完全转化窗口(96~160℃),并且当反应温度低于131℃时,产物中CO2选择性始终保持100%.研究结果表明,当负载少量CuO时,Cu~(2+)离子会进入CeO_2晶格形成固溶体;进一步提高CuO负载量会导致CuO在CeO_2表面聚集.对于CuO/CeO_2催化剂,形成Cu-Ce固溶体会在催化剂表面生成大量的表面氧空位和Ce3+;Ce3+则与Cu~(2+)作用产生更多的表面Cu~+,而Cu~+是CO PROX的活性中心,因此表面Ce3+含量的提高和Cu-Ce之间相互作用的增强是活性提高的主要原因.与普通沉淀-浸渍法制备的CuO/CeO_2催化剂相比,草酸盐热分解-浸渍法制备的催化剂更有利于Cu-Ce固溶体的形成,从而具有更多的表面Ce3+和更强的表面Cu-Ce相互作用,因此具有更高的CO优先氧化活性.     

CO Selective Oxidation in Hydrogen-Rich Gas over Copper-Series Catalysts

The performances of CO selective oxidation in hydrogen-rich gas over four catalytic systems of CuO/ZrO2, CuO/MnO2, CuO/CoO and CuO/CeO2 were compared. The reducibility of these catalysts and the effect of CuO and CeO2 molar ratio of CuO/CeO2 catalysts on the activity of selective CO oxidation are investigated by XRD and TPR methods. The results show that the catalysts with the exception of CuO/ZrO2 have the interactions between CuO and CoO, CeO2 or MnO2, which result in a decrease in the reduction temperature. Among the catalysts studied, CuO/ZrO2 catalyst shows the lowest catalytic activity while CuO/CeO2 catalyst exhibits the best catalytic performance. The CuO(10%)/CeO2 catalyst attains the highest CO conversion and selectivity at 140 and 160℃. The addition of 9% H2O in the reactant feed decreases the activity of CuO/CeO2 catalyst but increases its CO selectivity.     

CuO/TiO2的制备及对NO＋CO反应性能的研究

以三种不同的TiO2为载体，负载6%CuO，在色谱-微反装置上考察了三种Cu6-Ti催化剂对NO＋CO反应的活性。结果表明，由于制备方法不同，活性差别很大，三者活性顺序依次为：Cu6-Ti(T)> Cu6-Ti(S)> Cu6-Ti(nm)，TiO2的比表面积及晶型对活性的影响不明显。H2-TPR结果表明，Cu6-Ti在整个TPR过程中出现了3或4个还原峰，表明有多种CuO物种存在。不同预处理Cu6-Ti的TPR显示，在反应中Cu物种可能以多种价态同时存在。NO-TPD结果亦证明，Cu6-Ti对NO＋CO的反应活性与NO在催化剂表面的解离难易密切相关，而与NO的吸附量关系不大。     

Thermodynamic, electronic and structural properties of Cu/CeO2 surfaces and interfaces from first-principles DFT+U calculations

The thermodynamic, structural and electronic properties of Cu-CeO(2) (ceria) surfaces and interfaces are investigated by means of density functional theory (DFT+U) calculations. We focus on model systems consisting of Cu atoms (i) supported by stoichiometric and reduced CeO(2) (111) surfaces, (ii) dispersed as substitutional solid solution at the same surface, as well as on (iii) the extended Cu(111)/CeO(2)(111) interface. Extensive charge reorganization at the metal-oxide contact is predicted for ceria-supported Cu adatoms and nanoparticles, leading to Cu oxidation, ceria reduction, and interfacial Ce(3+) ions. The calculated thermodynamics predict that Cu adatoms on stoichiometric surfaces are more stable than on O vacancies of reduced surfaces at all temperatures and pressures relevant for catalytic applications, even in extremely reducing chemical environments. This suggests that supported Cu nanoparticles do not nucleate at surface O vacancies of the oxide, at variance with many other metal/ceria systems. In oxidizing conditions, the solid solutions are shown to be more stable than the supported systems. Substitutional Cu ions form characteristic CuO(4) units. These promote an easy and reversible O release without the reduction of Ce ions. The study of the extended CeO(2)(111)/Cu(111) interface predicts the full reduction of the interfacial ceria trilayer. Cu nanoparticles supported by ceria are proposed to lie above a subsurface layer of Ce(3+) ions that extends up to the perimeter of the metal-oxide interface.     

Characterization of CuO supported on tetragonal ZrO2 catalysts for N2O decomposition to N2

A series of tetragonal zirconia-supported CuO oxide catalysts with various CuO loadings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), ultraviolet and visible diffuse reflectance spectroscopy (UV/vis-DRS), and temperature-programmed reduction (TPR) measurements. The results indicate that the dispersion capacity of copper oxide on this support is approximately 8.6 Cu(2+) ions/nm(2) ZrO(2). The state of the resulting supported copper species depends on the CuO loading. At CuO loadings below the dispersion capacity, only highly dispersed copper ion species are present on the surface of t-ZrO(2). In particular, isolated Cu ions are the predominant species at low loadings. In contrast, pair Cu ions become the most abundant species at loadings near the dispersion capacity. It has been proposed that these dispersed CuO (isolated and paired Cu ions) have a symmetric 5-fold-oxygen-coordination symmetry (C(3)(v) symmetry) and can be described as distorted octahedra with a missing corner or a trigonal bipyramids. Finally, at CuO loadings above the dispersion capacity the formation of crystalline CuO is observed. TPR results reveal that the dispersed Cu ion species have a different reducibility from CuO crystallites, presumably due to strong interactions between these species and the t-ZrO(2) support. The catalytic activity of these CuO/t-ZrO(2) catalysts for the decomposition of N(2)O can also be directly correlated to CuO dispersion, with paired Cu ions being the most active species for this reaction.     

K-MnO／y-A1203和Cu／SiO2催化剂应用于苯甲酸甲酯连续加氢合成无氯苯甲醇

以K—MnO／F—Al2O3和Cu／SiO2为催化剂，利用固定床串联反应器实现了苯甲酸甲酯连续加氢合成无氯苯甲醇反应过程．K-MnO/y-Al2O3和Cu／SiO2催化剂对于苯甲酸甲酯连续加氢合成苯甲醇具有良好的加氢活性，反应转化率可达89．2％，苯甲醇的选择性为84．1％．在苯甲酸甲酯加氢连续步骤中的氢醛比得到提高，有效地抑制了副产物甲苯的生成．XRD，SEM和TPR表征结果表明：采用吸附沉淀法制备的Cu／SiO2-C15．2催化剂，氧化铜在载体上具有良好的分散性能，并且易于还原，表现出最佳的苯甲醛加氢活性．     

Monolithic macroporous catalysts--a new route for miniaturization of water-gas shift reactor

Monolithic macroporous Pt/CeO2/Al2O3 catalysts were prepared using concentrated emulsions synthesis route, and the obtained samples were characterized with SEM, TG, TEM, XRD and TPR techniques. These monolithic catalysts were applied to water gas shift (WGS) reaction in reformed gases. The SEM and TEM results indicated that the monoliths possessed macroporosity, and that the platinum particles homogeneously dispersed on the supports with the particle size in the range of 1−2 nm. The reducibility of the catalysts was characterized by TPR method, and it was shown that the monolithic PtOx/CeO2/Al2O3 exhibited the similar reducibility property to that of the particle PtOx/CeO2 reported in literatures. The CO conversion over the monolithic catalysts is higher than that over micro-reactor catalysts for WGS reaction in the reformed gases conditions, indicating that the monolithic macroporous catalysts is a potential new route for miniaturization of WGS reactor.     

限域纳米空间制备高效HCl氧化CuO-CeO_2催化剂

利用KIT-6的有序介孔作为限域空间制备了一系列的介孔Cu O-Ce O2催化剂.借助XRD、BET、Raman、ESEM、TEM和H2-TPR等手段对催化剂进行表征,并考察其在HCl氧化反应中的催化性能.结果表明:铜含量35%时,Cu O物种高度分散在催化剂的表面或者进入Ce O2晶格,催化剂具有高比表面积(140 m2·g-1)和较小的晶粒尺寸,其中25Cu O-Ce O2催化剂具备最高的表面氧空位浓度和最优的低温氧化还原性能,并在HCl氧化反应中表现出最佳的催化活性,O2/HCl=6,370℃时转化率达到90%.反应动力学结果表明,25Cu O-Ce O2中更多的高分散的Cu O促进了HCl在催化剂表面的吸附和活化,更高浓度的氧空位增强了氧分子的吸附和活化.     

SBA-16负载金属氧化物催化剂合成、表征及催化CO氧化反应活性

将V2O5, CeO2和CuO分散到提取自稻米壳的SBA-16上,考察了其催化CO氧化反应活性,并采用X射线衍射、扫描电镜、透射电镜、程序升温还原和紫外漫反射光谱对所制催化剂进行了表征。结果表明,掺杂CuO的介孔氧化硅是一种有前景的催化剂,其CO转化率可达98%以上。     

Au/CeO2-TiO2表面物种在还原和CO氧化过程中的变化

采用溶胶-凝胶法制备了CeO2-TiO2载体, 再用沉积沉淀法制备了Au/CeO2-TiO2催化剂. 利用原位漫反射红外(FT-IR), 程序升温还原(TPR)、X射线衍射(XRD)、N2吸附-脱附方法考察了催化剂的结构和表面性能. 结果表明, CeO2的存在有效抑制TiO2晶粒的长大, 增加TiO2的比表面积和晶格应变, 从而增强了Au和载体中TiO2的相互作用, 使得催化剂表面的氧化能力显著增强. 结合原位CO吸附的FT-IR结果表明, 不同温度的还原预处理能有效改变催化剂表面氧物种的组成, 并对不同氧物种在CO低温氧化过程中的作用进行了分析.     

Characterization and reactivity of copper oxide catalysts supported on TiO2-ZrO2

A series of copper catalysts supported on TiO2-ZrO2 with copper loading varying from 1.0 to 21.6 wt % were prepared by a wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy, electron spin resonance (ESR), temperature programmed reduction (TPR), and Brunauer-Emmett-Teller specific surface area measurements. Copper dispersion and metal area were determined by N2O decomposition by the passivation method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings <16.8 wt % in the sample and as a crystalline CuO phase at higher Cu loadings. Copper dispersion increases with Cu loading up to 5.1 wt % and levels off at higher loadings. The XPS peak intensity ratios of Cu 2p(3/2)/Ti 2p(3/2) and Cu 2p(3/2)/Zr 3d(5/2) were compared with the copper dispersion calculated from N2O decomposition. ESR results suggest the presence of two types of copper species on the TiO2-ZrO2 support. TPR profiles reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and related to the dispersion of Cu on TiO2-ZrO2.     

Formation of colloidal CuO nanocrystallites and their spherical aggregation and reductive transformation to hollow Cu2O nanospheres

In this work, we demonstrate that cuprous oxide Cu(2)O nanospheres with hollow interiors can be fabricated from a reductive conversion of aggregated CuO nanocrystallites without using templates. A detailed process mechanism has been revealed: (i) formation of CuO nanocrystallites; (ii) spherical aggregation of primary CuO crystallites; (iii) reductive conversion of CuO to Cu(2)O; and (iv) crystal aging and hollowing of Cu(2)O nanospheres. In this template-free process, Ostwald ripening is operative in (iv) for controlling crystallite size in shell structures and thus for precisely tuning the optical band gap energy (E(g)) of resultant semiconductor nanostructures. For the first time, a wealth of colorful Cu(2)O hollow nanospheres (outer diameters in 100-200 nm), with variable E(g) in the range of 2.405-2.170 eV, has been fabricated via this novel chemical route. Considering their unique hollow structure and facile tuning in band gap energy, the prepared Cu(2)O hollow spheres can be potentially useful for harvesting solar energy in the visible range. Possibility of fabrication of Cu-Cu(2)O nanocomposites has also been discussed.