A rationale for the development of thermally stable nanostructured CeO_2-ZrO_2-containing mixed oxides

CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for practical application since temperatures up to 1273 K are easily experienced by these materials under real working conditions. In the present paper, we investigated how hydrothermal treatments applied to cakes of doped and undoped ZrO2-rich CeO2-ZrO2 precursors might improve the thermal stability of the final CeO2-ZrO2 solid solution. A rationale was developed that allowed to correlate the morphology of the hydrothermaUy treated cake with the thermal stability at 1273 K of the final product, which did not depend on the composition of the mixed oxides.

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-ZrO_2-La_2O_3-Al_2O_3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles （NGVs） operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction （XRD） and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperatnre-programmed reduction （H2-TPR） and oxygen storage capacity （OSC） measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.

Preferential Oxidation of Carbon Monoxide in Excess Hydrogen over Au/Co_3O_4-CeO_2 Catalysts

Au/Co3O4-CeO2 mixed-oxide catalysts were shown tion of CO in hydrogen-rich mixture. Activity was markedly experimentally to be highly active and selective for the oxidainfluenced by the composition of the support, aging temperature and Au-loading temperature. It provided that single-step removal of CO from hydrogen-rich stream both in the absence and presence of CO2 and H2O to a PEMFC tolerant level. It was found that catalytic activity is greatly affected by adding CO2 in the mixture and increased by farther adding H2O. It recants H2O has the effect to rise catalytic activity. Moreover, it shows better stability with reaction time for the preferential CO oxidation.

Preparation of M2O3-CeO2(M=La,Fe,and Al) Compoundoxide Catalyst and Its Degradation Performance

As one of the most active rare earths,CeO2 has caused extensive concern due to its multifunctional properties.CeO2-based compound oxide of M2O3-CeO2(M=La,Fe,and Al)were prepared by coprecipitation and impregnation methods.The photocatalytic performance of the samples for the degradation methylene blue was studied under UV and visible light irradiation.The effects of constituents on the properties of the CeO2-based catalysts were investigated by XRD,TEM,BET,and UV-Vis spectrophotometer.The highest degradation of methylene blue under 230W UV light was almost 100%at 50 min by La2O3/Fe2O3-CeO2/γ-Al2O3 catalyst and 99.42%at 50 min by Fe2O3-CeO2/γ-Al2O3 catalyst.The methylene blue removal efficiency under indoor natural light reaches 93.81%by La2O3/Fe2O3-CeO2/γ-Al2O3 catalyst and 92.34%by Fe2O3-CeO2/γ-Al2O3 catalyst at 50 min.The order of catalytic degradation activity is La2O3/Fe2O3-CeO2/γ-Al2O3>Fe2O3-CeO2/γ-Al2O3>La2O3-CeO2/γ-Al2O3>Al2O3,owing to their structural features.The doping of La^3+or Fe3+onto CeO2/γ-Al2O produced much more oxygen vacancies under light irradiation and reduced the energy laps of CeO2 with value of 2.86 ev,which improved the photocatalytic redox performance of the composite oxide.

Morphology and crystal-plane effects of Zr-doped CeO2 nanocrystals on the epoxidation of styrene with tert-butylhydroperoxide as the oxidant

The morphology effect of Zr-doped CeOwas studied in terms of their activities in the selective oxidation of styrene to styrene oxide using tert-butyl hydroperoxide as the oxidant. In the present work, Zrdoped CeOnanorods exhibited the highest catalytic performance（yield of styrene oxide and TOF value）followed by nanoparticles and nanocubes. For the Zr-doped CeOnanorods, the apparent activation energy is 56.3 k J/mol, which is much lower than the values of catalysts supported on nanoparticles and nanocubes（73.3 and 93.4 k J/mol）. The high resolution transmission electron microscopy results indicated that（100） and（110） crystal planes are predominantly exposed for Zr-doped CeOnanorods while（100）and（111） for nanocubes,（111） for nanoparticles. The remarkably increased catalytic activity of the Zrdoped CeOnanorods is mainly attributed to the higher percentage of Cespecies and more oxygen vacancies, which are associated with their exposed（100） and（110） crystal planes. Furthermore, recycling studies proved that the heterogeneous Zr-doped CeOnanorods did not lose its initial high catalytic activity after five successive recycles.

Catalytic Performance of CeO_2/ZnO Nanocatalysts on the Oxidative Coupling of Methane with Carbon Dioxide and their Fractal Features

CeO2/ZnO nanocatalysts were prepared from the coupling route of homogeneous precipita-tion with microemulsion and the impregnation method. The catalytic performance of these two kinds of catalysts on the oxidative coupling of methane with carbon dioxide was tested and compared; the frac-tal behavior of the nanocatalysts was analyzed using fractal theory. The CeO2/ZnO nanocatalysts had much higher activity than the catalysts prepared by impregnation method. There was no regular relation-ship between the average size of CeO2/ZnO nanocatalysts and their catalytic performance; however, the conversion of methane increased with the increase of the fractal dimension of CeO2/ZnO nanocatalysts.

Removal of Carbon Monoxide from Hydrogen-rich Fuels over CeO₂-promoted Pt/Al₂O₃

A comparative study of catalytic CO oxidation and selective CO oxidation over Pt/Al2O3 and CeO2-promoted Pt/Al2O3 catalysts has been investigated for the removal of a trace amount of CO from the reformed gas. The catalysts were prepared by sol gel and incipient wetness impregnation. CO oxidation and selective CO oxidation were carried out with a 5%Pt/Al2O3 and a 5%Pt/15%CeO2/Al2O3. The presence of 15%CeO2 inthe 5%Pt/Al2O3 dramatically improves the activities to CO oxidation and selective CO oxidation at low temperature (0℃). FTIR results indicate that CO could react with lattice oxygen from ceria and release CO2 as a product. Low space velocity would obtain high CO conversion at low temperatures while high space velocity would obtain high CO conversion at high temperatures. The results also show that a 5%Pt/15%CeO2/Al2O3 can completely oxidize 1% CO at180℃with selectivity of 52% and space velocity of70,000 cm3·g-1·h-1. Under the realistic gas feed with 1%O2, this catalyst is very stable and retains its activity and selectivity at180℃during 72 h.

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.

Preparation of Au/CeO_2 catalyst and its catalytic performance for HCHO oxidation

Aqueous precipitation and deposition-precipitation method were used to prepare CeO2 supports and Au/CeO2 catalysts, respectively. The effect of preparation condition of support on the catalyst activity was investigated. The catalytic combustion of HCHO was considered as the probe reaction for comparing the catalyst activity. The BET, X-ray diffraction, X-ray photoelectron spectroscopy （XPS）, and reduction （TPR） were carried out to analyze the influence factor on the catalysts activity. The results showed that the addition of dispersant and use of microwave in the support preparation procedure could be beneficial for enhancing the interaction of supports and gold species and thus improved the catalytic activity. The total conversion temperature for HCHO was 146 ℃ over AC400. With the modification during supports preparation process, the catalytic activity increased with total conversion temperature decreasing to 98 ℃. The results of XPS indicated that Au^0 and Au^＋1 species coexisted in these catalysts and the activity of catalyst correlated with Au^＋1/Au^0 ratio. Temperature-programmed reduction results demonstrated that the reduction peak appeared between 100-170 ℃ with the inducing of gold. The dependence of activity on the reduction peak temperature implied that ionic gold was catalytic activity component for HCHO oxidation.

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 ℃.

Catalytic Partial Oxidation of Methane over Ni/CeO_2-ZrO_2-Al_2O_3

Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.

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.

Effect of Cu Loading to Catalytic Selective CO Oxidation of CuO/CeO₂–Co₃O₄

This work studied CuO/CeO2-Co3O4 with wt% Ce:Co ratio 95:5 for selective CO oxidation with effect of? wt% Cu loading. The catalysts were prepared by co-precipitation. Characterizations of catalysts were carried out by XRD and BET techniques. The results showed a good dispersion of CuO for 5 wt% Cu loading catalysts and showed high specific surface area of catalyst. For selective CO oxidation, both 5CuO and 30CuO catalysts could remove completely CO in the presence of excess hydrogen at 423 K and 20CuO could eliminate CO completely at 443 K. Moreover, considering the selectivity to CO oxidation, the 5CuO catalyst has shown the highest selectivity of 85% while the 30CuO catalyst obtains the selectivity of 65% at the reaction temperature of 423 K.

CuO/CeO_2催化剂的催化氧化性能及其表征

用CO流动反应法 ,程序升温还原 (TPR) ,光电子能谱 (XPS)和X射线衍射Rietveld分析等技术研究了CuO ,CeO2 及CuO/CeO2 各组分催化剂。结果表明 :单组分的CuO和CeO2 对CO的氧化活性较低 ,但CuO与CeO2 形成复合氧化物后 ,其CO氧化活性明显提高 ,这可能与铜物种在CeO2 表面的价态 (Cu2 + 和Cu+ ) ,分散状态和还原性能有关。CuO在CeO2 上的负载量对铜物种在CeO2 表面形成的价态 (Cu2 + 和Cu+ )至关重要 ,CuO的负载量为 1 0 %时 ,XPS检测不到Cu2p3/2 (eV)结合能 ;当CuO的负载量为 5 0 %时 ,CuO主要以Cu2 + 和Cu+ 形式存在 ,而负载量大于 5 0 %时 ,CuO则以Cu2 + 形式存在。由于形成了CuO/CeO2 复合氧化物 ,使离子半径小于Ce4 + 的CuO进入了CeO2 晶格 ;当CuO的负载量达到 5 0 %时 ,CuO的晶粒尺寸值为最小 ( 6 1nm) ,而晶格畸变值为最大 ( 2 86× 10 - 3) ,此时 。

Pt/Al_2O_3和Pt/CeO_2/Al_2O_3催化甲烷部分氧化制合成气反应

研究了Ｐｔ／Ａｌ２Ｏ３和Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３对甲烷部分氧化制合成气反应的催化活性，发现Ｐｔ／ＣｅＯ２／Ａｌ２Ｏ３显示了更高的甲烷转化率和合成气选择性．用Ｈ２－ＴＰＲ、Ｈ２－ＴＰＤ、ＳＥＭ－ＥＤＸ和ＸＲＤ等技术对催化剂进行了表征．ＣｅＯ２和Ｐｔ相互作用促进Ｐｔ在催化剂表面的分散，抑制Ｐｔ在催化剂表面的迁移；降低了催化剂的燃烧活性，提高了催化剂的部分氧化活性和选择性，可避免因催化剂床层局部温度过高而导致催化剂活性下降或失活，提高了催化剂的稳定性．同时，ＣｅＯ２通过促进水汽变换反应使反应体系迅速达到平衡，提高了催化剂对Ｈ２的选择性．

CuO/CeO_2和CuO/Al_2O_3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。

CeO_2对镍基金属陶瓷复合层组织和耐腐蚀性能的影响

利用 5kWCO2 激光器在 5Cr2 1Mn9Ni4N不锈钢基体表面成功熔覆了含不同CeO2 量的镍基金属陶瓷复合层。研究了稀土氧化物CeO2 对激光熔覆金属陶瓷复合层显微组织形态和耐腐蚀性能的影响 ,发现稀土氧化物CeO2 能加速碳化钨颗粒的溶解 ,促使钨与铬形成金属间化合物 ;激光熔覆镍基金属陶瓷复合层的耐硫酸腐蚀能力显著优于 1Cr18Ni9Ti不锈钢 ;且含 0 5 %CeO2 (质量分数 )的激光熔覆层的耐腐蚀能力比含 1 5 %CeO2 (质量分数 )和不含CeO2

CeO_2在Pd/γ-Al_2O_3催化剂中的助剂作用

用色谱微反流动法技术考察了富氧和贫氧条件下，添加ＣｅＯ２对Ｐｄ／γＡｌ２Ｏ３催化剂上ＣＯ氧化反应的影响，并运用ＴＰＲ、ＴＰＤＭＳ及ＳＥＭ等技术研究了ＣｅＯ２Ｐｄ／γＡｌ２Ｏ３催化剂．结果表明：ＣｅＯ２、Ｐｄ的共助作用使ＣｅＯ２Ｐｄ／γＡｌ２Ｏ３催化剂ＴＰＲ还原峰温向低温方向移动；ＣｅＯ２的存在使Ｐｄ／γＡｌ２Ｏ３催化剂表面的吸附氧容易脱出，从而改善了催化剂的氧化活性；ＣｅＯ２、Ｐｄ间的强相互作用使催化剂上Ｐｄ元素的分散程度增加．

MnO_x-CeO_2复合氧化物催化氧化柴油机NO性能研究

为了研究MnO_x-CeO_2复合氧化物催化氧化柴油机NO的性能,采用溶胶凝胶法制备了不同Mn/Ce摩尔比的xMn10Ce/γ-Al_2O_3(x=5,6,7,8)催化剂。利用X射线衍射(X-ray diffraction,XRD)、X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)和H_2程序升温还原(H_2temperature programmed reduction,H_2-TPR)技术分别对其物相结构、元素价态及还原性能进行了表征。结果表明:CeO_2晶粒尺寸随Mn含量增加而逐渐变大,同时添加适量的Mn也有利于提高催化剂中Mn^(4+)的数量,从而促进NO氧化;当x=6时,催化剂的氧化还原性能最好。最后,基于模拟气试验平台考察了不同Mn/Ce比对xMn10Ce/γ-Al_2O_3催化剂氧化NO性能的影响。结果表明:在350℃时,NO浓度达饱和所需时间和反应速率与Mn添加量呈非线性关系;在250~450℃范围内,6Mn10Ce/γ-Al_2O_3的NO氧化性能最好,其NO浓度在350℃时最先达到稳定,仅需4min,但在450℃时则延长至6min,这主要是受热力学平衡及随反应进行活性氧数量及氧空位逐渐饱和共同作用的结果。