Influence of preparation methods on the physicochemical properties and catalytic performance of MnO_x-CeO_2 catalysts for NH_3-SCR at low temperature

This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation,hydrothermal treatment, co‐precipitation, and a sol‐gel technique, were used to synthesizeMnOx‐CeO2 catalysts. The catalysts were characterized in detail, and an NH3‐SCR model reaction waschosen to evaluate the catalytic performance. The results showed that the preparation methodsaffected the catalytic performance in the order: hydrothermal treatment > sol‐gel > co‐precipitation> impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content,oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sitesand acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalystformed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalyticperformance, and good H2O resistance in NH3‐SCR reaction. This was attributed to incorporationof Mnn+ into the CeO2 lattice to form a uniform ceria‐based solid solution (containing Mn‐O‐Cestructures). Strengthening of the electronic interactions between MnOx and CeO2, driven by thehigh‐temperature and high‐pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment‐friendly route to synthesizing low‐temperature denitrification (deNOx) catalysts.

Preparation, Characterization of CuO/CeO_2 and Cu/CeO_2 Catalysts and Their Applications in Low-Temperature CO Oxidation

CeO2 was synthesized via sol-gel process and used as supporter to prepare CuO/CeO2, Cu/CeO2 catalysts by impregnation method. The catalytic properties and characterization of CeO2, CuO/CeO2 and Cu/CeO2 catalysts were examined by means of a microreactor-GC system, HRTEM, XRD, TPR and XPS techniques. The results show that CuO has not catalytic activity and the activity of CeO2 is quite low for CO oxidation. However, the catalytic activity of CuO/CeO2 and Cu/ CeO2 catalysts increases significantly. Furthermore, the activity of CuO/CeO2 is higher than that of Cu/CeO2 catalysts.

Identification of relevant active sites and a mechanism study for reverse water gas shift reaction over Pt/CeO_2 catalysts

Reverse water gas shift (RWGS) reaction can serve as a pivotal stage in the CO2 conversion processes, which is vital for the utilization of CO2. In this study, RWGS reaction was performed over Pt/CeO2 catalysts at the temperature range of 200-500 degrees C under ambient pressure. Compared with pure CeO2, Pt/CeO2 catalysts exhibited superior RWGS activity at lower reaction temperature. Meanwhile, the calculated TOF and E-a values are approximately the same over these Pt/CeO2 catalysts pretreated under various calcination conditions, indicating that the RWGS reaction is not affected by the morphologies of anchored Pt nanoparticles or the primary crystallinity of CeO2. TPR and XPS results indicated that the incorporation of Pt promoted the reducibility of CeO2 support and remarkably increased the content of Ce 3 + sites on the catalyst surface. Furthermore, the CO TPSR-MS signal under the condition of pure CO2 flow over Pt/CeO 2 catalyst is far lower than that under the condition of adsorbed CO2 with H-2 -assisted flow, revealing that CO2 molecules adsorbed on Ce3+ active sites have difficult in generating CO directly. Meanwhile, the adsorbed CO2 with the assistance of H-2 can form formate species easily over Ce3+ active sites and then decompose into Ce3+-CO species for CO production, which was identified by in-situ FTIR. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

Preparation and characterization of Fe_2O_3-CeO_2-TiO_2/γ-Al_2O_3 catalyst for degradation dye wastewater

In order to develop a catalyst with high activity for catalytic wet oxidation （CWO） process at room temperature and atmospheric pressure, Fe2O3-CeO2-TiO2/γ-Al2O3 catalyst was prepared by consecutive impregnation method and the prepared parameters were optimized. The structure of the catalyst was characterized by BET, XRF, SEM and XPS technologies, and the actual wastewater was used to investigate the catalytic activity of Fe2O3-CeO2-TiO2/γ-Al2O3 in CWO process. The experimental results showed that the prepared catalyst exhibited good catalytic activity when the doping amount of Ti was 1.0 wt% （the weight ratio of Ti to carriers）, and the middle product, Fe2O3-CeO2-TiO2/γ-Al2O3, was calcined in 450℃ for 2 h. The CWO experiment for treating actual dye wastewater indicated that the COD, color and TOC of actual wastewater were decreased by 62.23%, 50.12% and 41.26% in 3 h, respectively, and the ratio of BOD5/COD was increased from 0.19 to 0.30.

Screening of MgO- and CeO_2-Based Catalysts for Carbon Dioxide Oxidative Coupling of Methane to C_(2+) Hydrocarbons

The catalyst screening tests for carbon dioxide oxidative coupling of methane (CO2-OCM) have been investigated over ternary and binary metal oxide catalysts. The catalysts are prepared by doping MgO- and CeO2-based solids with oxides from alkali (Li2O), alkaline earth (CaO), and transition metal groups (WO3 or MnO). The presence of the peroxide (O2-2) active sites on the Li2O2, revealed by Raman spectroscopy, may be the key factor in the enhanced performance of some of the Li2O/MgO catalysts. The high reducibility of the CeO2 catalyst, an important factor in the CO2-OCM catalyst activity, may be enhanced by the presence of manganese oxide species. The manganese oxide species increases oxygen mobility and oxygen vacancies in the CeO2 catalyst. Raman and Fourier Transform Infra Red (FT-IR) spectroscopies revealed the presence of lattice vibrations of metal-oxygen bondings and active sites in which the peaks corresponding to the bulk crystalline structures of Li2O, CaO, WO3 and MnO are detected. The performance of 5%MnO/15%CaO/CeO2 catalyst is the most potential among the CeO2-based catalysts, although lower than the 2%Li2O/MgO catalyst. The 2%Li2O/MgO catalyst showed the most promising C2+ hydrocarbons selectivity and yield at 98.0% and 5.7%, respectively.

CeO_2-Co_3O_4 Catalysts for CO Oxidation

CeO2-Co3O4 catalysts for low-temperature CO oxidation were prepared by a co-precipitation method. In combination with the characterization methods of N2 adsorption/desorption, XRD, temperature-programmed reduction （TPR）, and FT-IR, the influence of the cerium content on the catalytic performance of CeO2-Co3O4 was investigated. The results indicate that the prepared CeO2-Co3O4 catalysts exhibit a better activity than that of pure CeO2 or pure Co3O4. The catalyst with the Ce/Co atomic ratio 1 ： 16 exhibits the best activity, which converts 77% of CO at room temperature and completely oxidizes CO at 45 ℃.

Electronic and geometric structure of the copper-ceria interface on Cu/CeO2 catalysts

The atomic structure of the active sites in Cu/CeO2 catalysts is intimately associated with the copper-ceria interaction. Both the shape of ceria and the loading of copper affect the chemical bonding of copper species on ceria surfaces and the electronic and geometric character of the relevant interfaces. Nanostructured ceria, including particles(polyhedra), rods, and cubes, provides anchoring sites for the copper species. The atomic arrangements and chemical properties of the(111),(110) and(100) facets, preferentially exposed depending on the shape of ceria, govern the copper-ceria interactions and in turn determine their catalytic properties. Also, the metal loading significantly influences the dispersion of copper species on ceria with a specific shape, forming copper layers, clusters, and nanoparticles. Lower copper contents result in copper monolayers and/or bilayers while higher copper loadings lead to multi-layered clusters and faceted particles. The active sites are usually generated via interactions between the copper atoms in the metal species and the oxygen vacancies on ceria, which is closely linked to the number and density of surface oxygen vacancies dominated by the shape of ceria.

Methane reforming with CO_2 to syngas over CeO_2-promoted Ni/Al_2O_3-ZrO_2 catalysts prepared via a direct sol-gel process

CeO2-promoted Ni/Al2O3-ZrO2 （Ni/Al2O3-ZrO2-CeO2） catalysts were prepared by a direct sol-gel process with citric acid as gelling agent. The catalysts used for the methane reforming with CO2 was studied by infrared spectroscopy （IR）, thermal gravimetric analysis （TGA）, microscopic analysis, X-ray diffraction （XRD） and temperature-programmed reduction （TPR）. The catalytic performance for CO2 reforming of methane to synthesis gas was investigated in a continuous-flow micro-reactor under atmospheric pressure. TGA, IR, XRD and microscopic analysis show that the catalysts prepared by the direct sol-gel process consist of Ni particles with a nanostructure of around 5 nm and an amorphous-phase composite oxide support. There exists a chemical interaction between metallic Ni particles and supports, which makes metallic Ni well dispersed, highly active and stable. The addition of CeO2 effectively improves the dispersion and the stability of Ni particles of the prepared catalysts, and enhances the adsorption of CO2 on the surface of catalysts. The catalytic tests for methane reforming with CO2 to synthesis gas show that the Ni/Al2O3-ZrO2-CeO2 catalysts show excellent activity and stability compared with the Ni/Al2O3 catalyst. The excellent catalytic activity and stability of the Ni/Al2O3-ZrO2-CeO2 are attributed to the highly, uniformly and stably dispersed small metallic Ni particles, the high reducibility of the Ni oxides and the interaction between metallic Ni particles and the composite oxide supports.

Catalytic Oxidative Properties and Characterization of CuO/CeO_2 Catalysts

The oxidative properties and characterization of CuO, CeO 2 and CuO/CeO 2 cata lysts were examined by means of a CO micro-reactor GC system, TPR, XPS and X-r ay diffraction Rietveld methods. The results show that either CuO or CeO 2 ac tivity is quite low for CO oxidation. However, when CuO and CeO 2 are mixed, the oxidative activity of the catalyst increases significantly, probably owing to the valency status of copper species (Cu 2+ and Cu+) on the CeO 2 surfa ce, the dispersion and reducibility. XPS surface analysis shows that CuO loading is very important in forming of either Cu 2+ or Cu+. Rietveld analysis s hows that some CuO, which has smaller ion radius than Ce 4+, enters the Ce O 2 lattice after CuO and CeO 2 are mixed. When the CuO loading reaches 5.0%, the size of CuO crystals is a minimum (6.1 nm) and the micro-strain value i s a maximum (2.86×10 -3), resulting in high surface energy and the best ac tivity for CO oxidation.

Effects of ZrO_2 Content on Structure and Performance of Cu/CeO_2-ZrO_2 Catalysts for Water-Gas Shift Reaction

Cu/CeO2-ZrO2 catalysts for water-gas shift （WGS） reaction were prepared with co-precipitation method, and the influence of ZrO2 content on the catalytic structure and properties was investigated by the techniques of N2 physical adsorption analysis, XRD and H2-TPR. The results indicate that the BET surface areas of the catalysts are increased in varying degrees due to the presence of ZrO2. With increasing ZrO2 content, the pore size distribution is centered on 1.9 nm. ZrO2 can efficiently restrain the growth of Cu crystal particles. The appropriate amount of ZrO2 in the Cu/CeO2 catalysts can help the catalyst keep better copper dispersion in the WGS reaction, which can lead to both higher catalytic activity and better thermal stability. When ZrO2 content is 10% （atom fraction）, Cu/CeO2-Zr02 catalyst reaches a CO conversion rate of 73.7% at the reaction temperature of 200℃.

Effect of Addition of Base on Ceria and Reactivity of CuO/CeO_2 Catalysts for Low-Temperature CO Oxidation

In this work, we have reported the influence of the addition of base （KOH） on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction （XRD）, high resolution transmission electron microscopy （HRTEM）, and temperatureprogrammed reduction by H2 （H2-TPR）. The catalytic properties of the CuO/CeO2 catalysts for lowtemperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.

CeO_2-TiO_2复合光催化剂的制备及日光催化研究

采用水热法,在温和的条件下制备了具有较高光催化活性的CeO2 TiO2复合光催化剂,在太阳光照射下以罗丹明B的光降解为模型反应研究了其光催化活性。结果表明,适量Ce的掺杂能有效提高TiO2的日光催化活性。用FT IR、TG DTA和XRD等进行了性能表征。

Catalytic reduction of SO_2 by CO over CeO_2-TiO_2 mixed oxides

The structure and catalytic desulfurization characteristics of CeO2-TiO2 mixed oxides were investigated by means ofX-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and catalytic activity tests. According to the results, a CeO2-TiO2solid solution is formed when the mole ratio of cerium to titanium n（Ce）：n（Ti） is 5：5 or greater, and the most suitable n（Ce）：n（Ti） isdetermined as 7：3, over which the conversion rate of SO2 and the yield of sulfur at 500℃ reach 93% and 99%, respectively.According to the activity testing curve, Ce0.7Ti0.3O2 （n（Ce）：n（Ti）=7：3） without any pretreatment can be gradually activated by reagentgas after about 10 min, and reaches a steady activation status 60 min later. The XPS results of Ce0.7Ti0.3O2 after different time ofSO2＋CO reaction show that CeO2 is the active component that offers the redox couple Ce4＋/Ce3＋ and the labile oxygen vacancies, andTiO2 only functions as a catalyst structure stabilizer during the catalytic reaction process. After 48 h of catalytic reaction at 500℃,Ce0.7Ti0.3O2 still maintains a stable structure without being vulcanized, demonstrating its good anti-sulfur poisoning performance.

溶胶-凝胶法制备玻璃表面CeO_2-TiO_2紫外吸收薄膜的研究

分别以Ce(NO3)3.6H2O和Ti(OC4H9)4为前驱体制备CeO2和TiO2溶胶,通过改变Ce/Ti摩尔比(0/10,1/9,2/8,3/7,4/6,5/5,6/4,7/3,8/2,9/1,10/0)得到一系列复合溶胶,采用提拉法在玻璃基片上制备了CeO2-TiO2紫外吸收膜层。利用紫外-可见光谱、XRD对各溶胶以及溶胶沉积的薄膜进行了表征;用SEM观察了镀3层膜和镀7层膜样品的新鲜断面,得到膜厚,借以验证计算所得数据的可用性。结果表明,溶胶的颜色产生变化与溶胶中Ti3+浓度有关;由于CeO2和TiO2相互作用,复合溶胶及其膜层的紫外线吸收能力分别强于纯的CeO2和纯的TiO2,吸收曲线向长波方向移动;膜层中CeO2晶体会使膜面雾化,膜层内的Ce/Ti固溶体或当晶体微小和呈非晶态时,均不影响膜面质量;当薄膜达到一定厚度的时候,紫外线几乎全部被阻隔;在临界厚度内,膜层越厚阻隔效果越好,且对可见光区域的透过率基本无影响,均在70%～80%。

磁控溅射法制备CeO_2-TiO_2紫外吸收薄膜

采用射频磁控溅射在玻璃基片上沉积具有紫外吸收CeO2-TiO2混和薄膜。通过制备一系列不同物质的量浓度比的，n（CeO2）：n（TiO2）靶材（1．0：0，0．90：0．10，0．80：020，0．70：0．30，0．60：0．40，0．50：0．50，0．40：0．60，0．30：0．70，0．20：0．80，0．10：0．90，0：1．0），研究其紫外吸收性能最佳的物质的量浓度比：TiO2加入CeO2后，改变CeO2的结晶状态并提高UV吸收．采用Raman和XPS表征薄膜的特性，物质的量浓度比值在n（CeO2）：n（TiO2）=0．5：0．5，0．6：0．4时，薄膜为非晶态，并具有高的紫外吸收（98％）和可见光透过率（70％-80％）；XDS分析表明薄膜存在（F^4＋，Ce^3＋和Ti^4＋。

Cu网负载CeO_2-TiO_2微纳米复合材料(CeO_2-TiO_2)/Cu的水热制备与性能

以Cu网为载体,Ti(OBu)4和Ce(NO3)3·6H2O为原料,Na3PO4·12H2O为矿化剂,采用一步水热法制备了多种不同形貌的Cu网负载CeO2-TiO2微纳米复合材料(CeO2-TiO2)/Cu.采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和紫外-可见漫反射分光光度计(UV-Vis DRS)对材料的形貌、结构及光吸收特性进行了表征,通过测试接触角表征了材料的浸润性.以20μmol/L亚甲基蓝(MB)溶液为目标降解物,测试了材料在可见光照射下的催化性能.结果表明,制备的TiO2为锐钛矿型,CeO2为方铈矿型;CeO2晶体比TiO2晶体更易负载于Cu网;改变制备过程中Ce(NO3)3·6H2O的用量、Na3PO4·12H2O浓度、水热反应时间及温度可实现(CeO2-TiO2)/Cu的形貌调控;(CeO2-TiO2)/Cu显示出超亲水性及可见光催化活性.

中温制备CeO_2-TiO_2复合氧化物及其结构研究

采用sol gel法在 70 0℃制备出氧化物陶瓷法 130 0℃才能获得的CeTi2 O6 复合氧化物。XRD结构分析表明 ,其晶体结构中存在 8%的Ce缺位 ,化学式为Ce0 .92 Ti2 O5.84 ,单斜晶系 ,空间群C 2 /m ,晶胞参数 :a =0 9811( 8)nm ,b =0 372 6( 3)nm ,c =0 6831( 6)nm ,β =118 84°。在 130 0℃焙烧该复合氧化物 ,晶系不变 ,缺位消失 ,化学式转变为正常的CeTi2 O6 ,晶胞参数 :a =0 9813( 3)nm ,b =0 375 2 ( 4)nm ,c =0 6883( 5 )nm ,β =119 0 5°。用sol gel法制备CeTi2 O6 复合氧化物先驱物 ,关键是要保证Ce及Ti原子在溶液 溶胶 凝胶 干凝胶整个过程中原子 (分子 )尺寸范围内的混合状态不被破坏。

Effect of yttrium addition on water-gas shift reaction over CuO/CeO_2 catalysts

This paper presented a study on the role of yttrium addition to CuO/CeO2 catalyst for water-gas shift reaction. A single-step co-precipitation method was used for preparation of a series of yttrium doped CuO/CeO2 catalysts with yttrium content in the range of 0-5wt.%. Properties of the obtained samples were characterized and analyzed by X-ray diffraction （XRD）, Raman spectroscopy, H2-TPR, cyclic voltammetry （CV） and the BET method. The results revealed that catalytic activity was increased with the yttrium content at first, but then decreased with the further increase of yttrium content. Herein, CuO/CeO2 catalyst doped with 2wt.% of yttrium showed the highest catalytic activity （CO conversion reaches 93.4% at 250 ℃） and thermal stability for WGS reaction. The catalytic activity was correlated with the surface area, the area of peak γ of H2-TPR profile （i.e., the reduction of surface copper oxide （crystalline forms） interacted with surface oxygen vacancies on ceria）, and the area of peak C2 and A1 （Cu^0→←Cu^2＋ in cyclic voltammetry process）, respectively. Besides, Raman spectra provided evidences for a synergistic Cu-Ovacancy interaction, and it was indicated that doping yttrium may facilitate the formation of oxygen vacancies on ceria.

BaO-CeO_2-TiO_2微波介质陶瓷的烧结特性及物相组成

采用TG-DTA、SEM、EDAX、XRD等测试手段研究了BaO-CeO_2-TiO_2微波介质陶瓷的烧结特性及物相组成.BaO-CeO_2-TiO_2的预烧温度和烧结温度分别为900～1100℃和1250～1300℃.结果表明:Ba_(6-3x)Ce_(8+2x)Ti_(18)O_(54)(x=0.8)在1300℃下烧结后形成了由A、B两相共存的体系,其中A、B两相的元素摩尔比分别为Ce:O=1.0:1.3,Ba:Ti:Ce:O=1.00:6.70:0.35:9.46.此时体系的介电常数为28.72,品质因数为最高值4862.13GHz.

CeO_2-TiO_2/Ti复合膜电极液膜光催化降解染料废水

采用溶胶-凝胶法制备了CeO_2-TiO_2/Ti复合膜电极,以该复合膜电极为阳极、Cu为阴极,组装高效低耗的斜置双极液膜光催化反应装置,以活性艳红X-3B(RBR)为目标污染物,在可见光激发下进行光催化降解,探讨了电极制备条件对CeO_2-TiO_2/Ti复合膜电极光催化性能的影响,考察了不同条件对RBR脱色率的影响,并初步探究了可见光光催化降解RBR的机制。结果表明:(1)最佳制备条件为CeO2、TiO2摩尔比(简写为n(Ce∶Ti))1∶10、煅烧温度400℃。线性伏安曲线和紫外—可见漫反射谱图分析表明,该制备条件下得到的CeO_2-TiO_2/Ti复合膜电极具有较明显的可见光响应。(2)在RBR初始质量浓度为20mg/L、RBR废水循环流量为5.10L/h、初始pH为2.0的最佳条件下,可见光光催化90min时,RBR脱色率可达80.8%。(3)RBR光催化降解过程中的紫外—可见分光光度谱图分析表明,CeO_2-TiO_2/Ti复合膜电极液膜光催化降解RBR主要是使其发色基团即偶氮键断裂,并由苯环生成小分子有机酸等中间产物,而不能使其矿化。