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.

Properties of TiO_2-SiO_2 Mixed Oxides and Photocatalytic Oxidation of Heptane and Sulfur Dioxide

A series of TiO 2-XSiO 2[X denotes the molar fraction(%) of silica in the mixed oxides] with different \{n(Ti)\}/n(Si) ratios was prepared with ammonia water as a hydrolysis catalyst. The photocatalysts prepared were characterized by XRD, thermal analysis, FTIR, UV-Vis and SPS. The characterization results of FTIR and UV-Vis spectra show that Ti atoms were gradually changed from octahedral coordination to tetrahedral coordination with the addition of silica, which is not beneficial for obtaining strong Brnsted acidity and higher photocatalytic activity. The photocatalytic activity experiments, which were conducted by using heptane(or SO 2) as the model reactant, showed that TiO 2-SiO 2 containing a suitable amount of silica can exhibit much higher photocatalytic activity than pure TiO 2. The enhanced photocatalytic activity can be attributed to three following factors: (1) smaller crystalline size; (2) higher thermal stability; (3) the new strong Brnsted acidity.

Comparative structural and electrochemical properties of mixed P2/O′3-layered sodium nickel manganese oxide prepared by sol-gel and electrospinning methods:Effect of Na-excess content

The effect of Na-excess content in the precursor on the structural and electrochemical performances of sodium nickel manganese oxide(NNMO)prepared by sol-gel and electrospinning methods is investigated in this paper.X-ray diffraction results of the prepared NNMO without adding Na-excess content indicate sodium loss,while the mixed phase of P2/O′3-type layered NNMO presented after adding Na-excess content.Compared with the sol-gel method,the secondary phase of NiO is more suppressed by using the electrospinning method,which is further confirmed by field emission scanning electron microscope images.N_(2) adsorption-desorption isotherms show no remarkably difference in specific surface areas between different preparation methods and Na-excess contents.The analysis of X-ray absorption near edge structure indicates that the oxidation states of Ni and Mn are+2 and+4,respectively.For the electrochemical properties,superior electrochemical performance is observed in the NNMO electrode with a low Na-excess content of 5wt%.The highest specific capacitance is 36.07 F·g^(-1)at0.1 A·g^(-1)in the NNMO electrode prepared by using the sol-gel method.By contrast,the NNMO electrode prepared using the electrospinning method with decreased Na-excess content shows excellent cycling stability of 100%after charge-discharge measurements for 300 cycles.Therefore,controlling the Na excess in the precursor together with the preparation method is important for improving the electrochemical performance of Na-based electrode materials in supercapacitors.

Highly Dispersed Pd Nanoparticles Supported on Zr-Doped MgAl Mixed Metal Oxides for 2-Ethylanthraquinone Hydrogenation

In this study,Pd-Mg(Al)-LDH/γ-Al2O3 and Pd-Mg(Al)Zr-LDH/γ-Al2O3 precursors were synthesized by impregnating Na2PdCl4 on Mg(Al)-LDH/γ-Al2O3 and Mg(Al)Zr-LDH/γ-Al2O3,and then the precursors were calcinated and reduced to obtain Pd-Mg(Al)-MMO/γ-Al2O3 and Pd-Mg(Al)Zr-MMO/γ-Al2O3 catalysts.Compared with Pd/γ-Al2O3 catalyst,the hydrogenation efficiency of Pd-Mg(Al)-MMO/γ-Al2O3 and Pd-Mg(Al)Zr-MMO/γ-Al2O3 increased by 15.7%and 24.0%,respectively.Moreover,the stability of Pd-Mg(Al)Zr-MMO/γ-Al2O3 catalyst was also higher than that of Pd/γ-Al2O3.After four runs,the hydrogenation efficiency of Pd/γ-Al2O3 decreased from 12.1 to 10.0 g/L,while that of Pd-Mg(Al)Zr-MMO/γ-Al2O3 decreased from 15.0 to 14.3 g/L.The active aquinones selectivities of all catalysts were almost 99%.The structures of the catalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),N2 adsorption–desorption,inductively coupled plasma-atomic emission spectrometry(ICP-AES),CO chemisorption analysis,transmission electron microscopy(TEM),temperature-programmed reduction with hydrogen(H2-TPR),and X-ray photoelectron spectroscopy(XPS).The results indicate that the improved catalytic performance is attributed to the stronger interaction between Pd and Mg(Al)Zr-MMO/γ-Al2O3,smaller Pd particle size and higher Pd dispersion.This work develops an effective method to synthesize highly dispersed Pd nanoparticles based on the layered double hydroxides(LDHs)precursor.

Ce_xTi_(1-x)O_2 Mixed Oxides Supported CuO Catalyst for NO Reduction by CO

Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effects of CuO on NO+CO reaction were investigated, and the structure and reductive properties of various CuO/Ce x Ti 1- x O 2 were characterized by the methodologies of BET, TPR and XRD. The results show that different Ce/Ti mole ratios and calcination temperatures induce changes of structure and reductive properties of the Ce x Ti 1- x O 2 mixed oxides. When x =0.1～0.5, amorphous CeTi 2O 6 phase mainly forms at 650 ℃ compared to the formation of CeTi 2O 6 which crystallizes at 800 ℃. When x >0.6, some TiO 2 enters the CeO 2 lattice and a CeO 2 TiO 2 solid solution is formed. The activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 650 ℃ is largely affected by the x values, which is the highest when x =0.3, 0.4 and 0.9. The NO conversion reaches 70% at a reaction temperature of 150 ℃. By comparison, the x values have little effect on the activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 800 ℃ . There are strong interactions between CuO and CeTi 2O 6, i.e., formation of the CeTi 2O 6 phase shifts the CuO reduction peak temperature from 380 to 200 ℃, and CuO, in turn, shifts the CeTi 2O 6 reduction peak temperature from 600 to 300 ℃.

Electrical Conductivity of Sintered Chromia Mixed with TiO_2,CuO and Mn-Oxides

The electrical conductivity of sintered Cr2O3 mixed with 2% and 5% （in molar fraction） TiO2 or CuO was investigated in the temperature range 500-900℃ in air and in At/4 vol. pct H2 atmospheres. The effect of different Mn-oxides on the electrical conductivity of Cr2O3 was also studied under the same conditions. From the conductivity measurements it is established that additions of TiO2 change the defect structure of Cr2O3 and the effect of TiO2 on the electrical conductivity is controlled by TiO2 concentration as well as temperature and O2 partial pressure of the surrounding atmosphere. The conductivity of Cr2O3 increased in air and decreased in the At/H2 atmosphere by CuO additions. The effect of CuO was discussed with possible changes in the defect concentration in Cr2O3. Mixing of Cr2O3 with different Mn-oxides at the same Mn to metal atom fraction decreased the conductivity in air and in Ar/H2 atmospheres. No clear correlation between the spinel fraction and the changes in conductivity could be found.

Effect of Calcination Temperature on Structure and O_2 Desorption Properties of Ce_xPr_(1-x)O_(2-δ) Mixed Oxides

A series of CexPr1-xO2-δ (x=0, 0.5, 0.9, 1.0) mixed oxide calcined at different temperatures were synthesized by sol-gel method and characterized by Raman, XRD and O2-TPD techniques. When x=0.9, only a cubic phase CeO2 is observed. When x=0.5, the compound was combined by Pr6O11 and CeO2 mixed oxides. For CexPr1-xO2-δ (x=0.5, 0.9)samples 465 cm-1 Raman peak is attributed to the Raman active F2g mode of CeO2. The broad peak at about 570 cm-1 can be linked to lattice defects resulting in oxygen vacancies. The crystallite size of the samples increased as increasing the calcined temperature. But the increased value of Ce0.9Pr0.1O2-δ and Ce0.5Pr0.5O2-δ is smaller than single CeO2 and Pr6O11 obviously. It reveals that the insertion of Pr atom into the ceria lattice could enhance the sintering resistance and thermal stability of the mixed oxides. Calcination temperatures had great effect on the peak intensity for CeO2 but less effect on Ce0.8Pr0.2O2-δ in Raman spectra, and it may be caused by the colors transformation of the mixed oxides. The result of O2-TPD experiment indicates that the formation of solid solution has elevation the stabilization and thermal stability of the mixed oxides.

Preparation of Mesoporous Ce_(0.5)Zr_(0.5)O_2 Mixed Oxide by Hydrothermal Templating Method

Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis temperature and the molar ratio of PEG-4000/（[ Ce] ＋ [ Zr] ）, on specific surface area were investigated. The products were characterized by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements, respectively. The results showed that synthesis temperature and the molar ratio of PEG-4000/（[ Ce] ＋ [ Zr] ） had great influence on specific surface area. Under the optimum synthesis conditions, the prepared Ce0.5Zr0.5O2 mixed oxide presented cubic fluorite-type structure and possessed high surface area of 148.6 m2·g^-1 with wormlike pores.

MOLECULAR BEAM STUDIES ON OXIDATION OF CO ON Pd WITH DIFFERENT MIXED RATIOS OF P_(CO) TO P_(O2) ~*

Here some steady-state experiments on oxidation of CO on Pd were performed on a molecular beam apparatus. It is found that the characteristics of the rate of CO_2 formation r versus substrate temperature T are dependent on the ratio P=P_(CO)/P_(O2) in the mixed beam. These characteristics are related to the complicated interactions of co-adsorbed CO and O particles on Pd surface.

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.

纳米复合材料Ag/TiO_2-ZrO_2的制备及其微波增强光催化降解甲基橙

采用EO20PO70EO20(P123)作模板剂,通过溶胶-凝胶-程序升温溶剂热一步法,并经萃取处理制备了具有光催化活性的纳米复合材料Ag/TiO2-ZrO2.用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、N2吸附-脱附测定和扫描电子显微镜配合X射线能量色谱仪(SEM-EDS)等测试手段对其组成、结构及形貌等进行了表征.结果表明,复合材料Ag/TiO2-ZrO2中Ag以单质形式存在,材料具有双孔结构,颗粒分布较均匀,结构也较规整,平均孔径约为3.6和9.0nm.通过微波增强光催化降解染料甲基橙的实验,对复合材料Ag/TiO2-ZrO2的光催化活性进行了探究.实验结果表明,微波辅助光催化效果优于紫外辐射,并且萃取后的合成产物Ag/TiO2-ZrO2在90min内对甲基橙的降解率可达81.5%,其活性高于市售P25以及TiO2-ZrO2.

TiO_2-ZrO_2的表征及其异丙醇催化转化性能

用共沉淀法制备了TiO2-ZrO2复合氧化物.采用N2吸附、XRD、TEM、NH3和CO2吸附量热、NH3吸附红外对TiO2-ZrO2体系的结构及酸碱性等进行了表征.结果表明:与单纯的氧化物相比,形成的复合氧化物为无定形物相,有介孔结构,表面积明显提高,可达218m2·g-1;初始吸附热差别不大,但具有更多的表面B酸位;随着TiO2掺入量的增大,复合氧化物表面碱位减少.异丙醇催化转化,在无氧条件下,ZrO2、TiO2和TiO2-ZrO2复合氧化物上丙烯的选择性大于90%,说明这些氧化物具有强的表面酸性;在有氧条件下,ZrO2和TiO2丙酮的选择性达到70%～85%,主要体现为氧化还原性;而在复合氧化物上丙烯选择性增大到70%左右,丙酮的选择性下降为30%左右,表明生成的复合氧化物表面上的氧化还原性削弱,酸性增强.

B_2O_3/TiO_2-ZrO_2催化剂上环己酮肟的气相Beckmann重排反应

用共沉淀法制备了TiO2 ZrO2 复合氧化物载体。BET、DTA、XRD表征结果表明 ,该复合载体具有较大的比表面积和较好的热稳定性。对于环己酮肟气相Beckmann重排反应制己内酰胺 ,用复合载体制备的B2 O3 /TiO2 ZrO2 催化剂 ,比分别以TiO2 、ZrO2 为载体所制备的B2 O3 /TiO2 和B2 O3 /ZrO2 催化剂具有更高的活性和选择性。实验结果表明 ,催化剂表面中等强度的酸位是环己酮肟气相Beckmann重排反应的有效活性中心。

固体酸催化剂S_2O_8^(2-)/TiO_2-ZrO_2合成马来酸二辛酯

The preparation of peroxodisulfated zirconia titania(PSZT) solid super acid has been investigated as function of molar ratio of Ti to Zr, impregnation time, calcination time and temperature in esterification of maleic anhydride with n octanol. The highest yield of dioctyl maleate was 98 2% at the optimum reaction conditions.

TiO_2-ZrO_2复合薄膜的制备和摩擦学性能

以ZrOCl2@8H2O和TiCl4为原料,用溶胶-凝胶法制备了高取向的TiO2-ZrO2复合薄膜,研究了复合薄膜的组成结构、表面形貌和摩擦学性能结果表明,该复合薄膜均匀致密、具有四方ZrO2结构;复合薄膜具有良好的减摩抗磨性能.在0.5 N低负荷下,复合薄膜与AISI 52100钢和Si3N4对磨时的摩擦系数为0.14～0.20,耐磨寿命大于5000次.TiO2-ZrO2复合薄膜可用作特殊工况条件下的减摩抗磨保护性涂层.

固体超强酸SO_4^(2-)/TiO_2-ZrO_2催化合成己二酸二丁酯

研究了SO_4^(2-)/TiO_2-ZrO_2型催化剂的制备及其催化合成己二酸二丁酯反应。考察了催化剂焙烧温度、原料配比、反应时间及催化剂用量等因素对酯化反应的影响,较佳反应条件为:催化剂焙烧温度500℃,催化剂用量5%(以己二酸质量为基准),n(己二酸):n(正丁醇)=1:2．5,正丁醇为带水剂、在回流温度下反应4 h,酯化率可达99．35%。结果表明,SO_4^(2-)/TiO_2-ZrO_2在产物颜色、出水率和催化剂回收等方面明显优于对甲苯磺酸、浓硫酸催化剂。

固体酸SO_4^(2-)/TiO_2-ZrO_2催化制备乙酰丙酸的研究

以蔗糖为原料,固体SO42-/TiO2-ZrO2为催化剂,以水为溶剂制备乙酰丙酸。研究了浸渍用硫酸浓度和催化剂焙烧温度对催化剂活性的影响,并探讨了不同反应条件及催化剂重复使用次数对乙酰丙酸得率的影响。用XRD和NH3-TPD对使用前后的催化剂的结构和酸性进行了表征。实验结果表明,1.0 mol/L硫酸浓度浸渍,550℃焙烧3 h的催化剂活性较强。在催化剂投加量为1.0 g,反应温度为190℃的条件下反应1 h,乙酰丙酸摩尔得率高达50.0%。回收的SO42-/TiO2-ZrO2催化剂焙烧后在多次重复使用过程中仍然表现出较好的催化活性。

TiO2-ZrO2复合氧化物的制备与表征

采用共沉淀法制备了TiO2-ZrO2复合氧化物和单一的TiO2、ZrO2粉体,不同温度下煅烧后得到样品。用N2吸附、X-射线衍射仪、热重-差示扫描量热法对样品进行了表征。考察了单一组分与复合氧化物结构性能的差别以及煅烧温度对复合氧化物性能的影响。结果表明:550℃煅烧2h后,单一TiO2、ZrO2分别是结晶良好的锐钛矿和单斜相(含少量四方相),而TiO2-ZrO2复合氧化物依然是无定型结构且具有较大的比表面积(190.15m2/g)。600℃煅烧后TiO2-ZrO2复合氧化物中出现了ZrTiO4晶型。随煅烧温度的升高,复合氧化物的比表面积出现了明显的下降(190.15～19.16m2/g)。DSC-TG曲线给出了TiO2、ZrO2以及TiO2-ZrO2的相转变温度,分别为440.2℃、445.7℃、713.5℃。

制备方法对B_2O_3/TiO_2-ZrO_2催化环己酮肟制己内酰胺的影响

考察了载体TiO2 ZrO2 的制备方法对B2 O3 /TiO2 ZrO2 催化环己酮肟气相Beckmann重排制己内酰胺反应性能的影响。孔径分布和NH3 TPD的测定结果表明 ,以共沉淀法制备的TiO2 ZrO2 为载体所制备的催化剂具有较适宜的孔径分布和酸性 ,从而对环己酮肟气相Beckmann重排反应制己内酰胺表现出最高的催化活性和选择性。实验结果还表明 ,TiO2 ZrO2 比其它二元复合氧化物更适宜于作为环己酮肟气相Beckmann重排反应B2 O3催化剂的载体。

堇青石蜂窝陶瓷负载CuO/CeO_2-ZrO_2/TiO_2催化氧化含酚废水的性能研究

选取球状堇青石蜂窝陶瓷作为催化剂基体,制备了堇青石蜂窝陶瓷负载CuO/CeO2-ZrO2/TiO2催化剂,采用XRD、BET等方法对其进行了结构表征,测定了其催化湿式氧化含酚废水的活性及抗压强度、脱落率、Cu2+溶出浓度等性能指标。结果表明,CuO/CeO2-ZrO2/TiO2堇青石蜂窝陶瓷催化剂在反应温度180℃、压力5Mpa、搅拌速率为600r/min时,催化湿式氧化反应200minCOD去除率可达92.7%;球状堇青石蜂窝陶瓷CuO/CeO2-ZrO2/TiO2催化剂具有强度高、易装填、易更换、脱落率低特点,Cu2+溶出浓度低于环保排放标准,适合工业化处理含酚废水。