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.

Synthesis and highly efficient photocatalytic activity of mixed oxides derived from ZnNiAl layered double hydroxides

ZnO/NiO/ZnAl2O4 mixed-metal oxides were successfully synthesized through a hydrotalcite-like precursor route, in which appropriate amounts of metal salts solutions were mixed to obtain a new series of ZnNiAl layered double hydroxides（LDHs） as precursors, followed by calcination under different temperatures. The as-obtained samples were characterized by SEM, HRTEM, TEM, XRD, BET, TG-DTA, and UV-Vis spectra techniques. The photocatalytic activities of the samples were evaluated by degradation of methyl orange（MO） under the simulated sunlight irradiation. The effects of Zn/Ni/Al mole ratio and calcination temperature on the composition, morphology and photocatalytic activity of the samples were investigated in detail. The results indicated that compared with ZnNiAl-LDHs, the mixed-metal oxide showed superior photocatalytic performance for the degradation of MO. A maximum of 97.3% photocatalytic decoloration rate within 60 min was achieved from the LDH with the Zn/Ni/Al mole ratio of 2：1：1 and the calcination temperature of 500 ℃, which much exceeded that of Degussa P25 under the same conditions. The possible mechanism of photocatalytic degradation over ZnO/NiO/ZnAl2O4 was discussed.

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.

Effect of Manganese Doping on Oxygen Storage Capacity of Ceria-Zirconia Mixed Oxides

CeO2-ZrO2-MnOx mixed oxide series were prepared by sol-gel method. CO pulse and CO-O2 cycle measurements were carried out to examine the oxygen storage complete capacity （OSCC） and dynamic oxygen storage capacity （OSC） of the samples. The doping method brought about strong interactions between manganese oxide and ceria, both in the bulk and on the surface. Only a small part of Mn cations are incorporated into the ceria lattice to form solid solutions and the remaining are left on the surface as finely dispersed Mn3O4. The OSC behaviors of the materials are influenced by the doping amount of Mn and the solubility of Mn in the CeO2 lattice. The OSC is more easily affected by available contents of oxygen storage components when the measurement frequency is low. Comparatively, the concentration of lattice defects, which affects the mobility of bulk oxygen, is the determining factor under high frequency.

Catalytic performance for methane combustion of supported Mn-Ce mixed oxides

A series of supported Mn-Ce mixed oxide catalysts were prepared by the impregnation method and used for the oxidation of methane. The catalysts were characterized by N2 adsorption （BET）, X-ray diffraction （XRD）, laser Raman spectrum （LRS）, and temperature programmed reduction （TPR） techniques. The XRD and LRS results confirmed the high dispersion of active components or formation of solid solution between manganese and cerium oxides in the bulk and on the surface of mixed oxide catalysts. The reducibility was remarkably promoted by the stronger synergistic interaction between the two oxides from H2-TPR measurements. As expected, all the experimental mixed oxide catalysts showed excellent activity for methane combustion at low temperature. Especially, for the catalyst with Mn-Ce ratio 3：7, methane conversion reached 92% at a temperature as low as 470 ℃.

Co–Cr–O mixed oxides for low–temperature total oxidation of propane: Structural effects, kinetics, and spectroscopic investigation

A series of Co–Cr–O mixed oxides with different Co/Cr molar ratios are synthesized and tested for the total oxidation of propane.The reaction behaviors are closely related to the structural features of the mixed oxides.The catalyst with a Co/Cr molar ratio of 1:2(1 Co2 Cr)and a spinel structure has the best activity(with a reaction rate of 1.38μmol g^–1 s^–1 at 250℃),which is attributed to the synergistic roles of its high surface acidity and good low-temperature reducibility,as evidenced by the temperature-programmed desorption of ammonia,reduction of hydrogen,and surface reaction of propane.Kinetic study shows that the reaction orders of propane and oxygen on the 1 Co2 Cr catalyst(0.58±0.03 and 0.34±0.05,respectively)are lower than those on the 2 Co1 Cr catalyst(0.77±0.02 and 0.98±0.16,respectively)and 1 Co5 Cr(0.66±0.05 and 1.30±0.11,respectively),indicating that the coverages of propane and oxygen on 1 Co2 Cr are higher than those on the other catalysts due to its higher surface acidity and higher reducibility.In addition,in-situ diffuse reflectance infrared spectroscopic investigation reveals that the main surface species on 1 Co2 Cr during the reaction are polydentate carbonate species,which accumulate on the surface at low temperatures(<250℃)but decompose at relatively high temperatures.

Synthesis of mesoporous cerium-zirconium mixed oxides by hydrothermal templating method

Mesoporous cerium-zirconium mixed oxides were prepared by hydrothermal method using cetyl trimethyl ammonium bromide (CTAB) as template. The effects of amount of template, pH value of solution and hydrothermal temperature on mesostructure of samples were systematically investigated. The final products were characterized by XRD, TEM, FT-IR, and BET. The results indicate that all the cerium-zirconium mixed oxides present a meso-structure. At molar ratio of n(CTAB)/n((Ce)+(Zr))= 0.15, pH value of 9, and hydrothermal temperature of 120 ℃, the samples obtained possess a specific surface area of 207.9 m2/g with pore diameter of 3.70 nm and pore volume of 0.19 cm3/g.

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.

Effects of co-precipitation temperature on structure and properties of La and Y doped cerium zirconium mixed oxides

Due to the oxygen storage and release properties,cerium zirconium mixed oxides are recognized as the key material in automotive three-way catalysts.To reveal the effects of co-precipitation temperature on structure,physical and chemical properties of multi-doped cerium zirconium mixed oxides,a series of La and Y doped cerium zirconium mixed oxides(CZLYs)were synthesized via a co-precipitation method,and the physical and chemical properties of CZLYs were systemically characterized by XRD,N_(2) adsorption−desorption,TEM,XPS,oxygen storage capacity(OSC)and hydrogen temperature programmed reduction(H_(2)-TPR).The results show that co-precipitation temperature is an important parameter to influence the crystal size,oxygen storage capacity and thermal stability of CZLYs.When the co-precipitation temperature was 60℃,the best redox properties and thermal stability of CZLYs were obtained.After thermal treatment at 1100℃for 10 h,the specific surface area and oxygen storage capacity of the corresponding aged sample were 15.42 m^(2)/g and 497.7μmol/g,respectively.In addition,a mechanism was proposed to reveal the effects of co-precipitation temperature on the structure and properties of CZLYs.

Preparation of Well Dispersed and Ultra-Fine Ce(Zr)O_2 Mixed Oxide by Mechanochemical Processing

Ultra-fine CeO_2-ZrO_2 mixed oxide was successfully synthesized by wet-solid phase mechanochemical processing, Ce_2(CO_3)_3·8H_2O, ZrOCl_2·xH_2O and ammonia were used as reactants. It is found that the crystalline Ce_2(CO_3)_3·8H_2O and ZrOCl_2·xH_2O are changed to amorphous cerium and zirconium hydroxide precursor after milling with ammonia, and Ce_(0.15)Zr_(0.85)O_2 mixed oxide with pure tetragonal phase structure and medium particle size(D_(50))less than 1μm is formed by calcining precursor over 673 K. The XRD patterns indicate that the crystal unite size increases with rising calcining temperature due to crystal growth. However, the particle size and BET surface area of the Ce(Zr)O_2 mixed oxide decreases with rising calcining temperature, which may be attributed to the contract of particles and the vanish of holes inside grains.

Preparation and characterization of Cu-Ce-La mixed oxide as water-gas shift catalyst for fuel cells application

Cu-Ce-La mixed oxides were prepared by three precipitation methods （coprecipitation, homogeneous precipitation, and deposition precipitation） with variable precipitators and characterized using X-ray diffraction, BET, temperature-programmed reduction, and catalytic reaction for the water-gas shift. The Cu-Ce-La mixed oxide prepared by coprecipitation method with NaOH as precipitator presented the highest activity and thermal stability. Copper ion substituted quadrevalent ceria entered CeO2 （111） framework was in favor of activity and thermal stability of catalyst. The crystallinity of fresh catalysts increased with the reduction process. La^3＋ or Ce^4＋ substituted copper ion entered the CeO2 framework during reduction process. The coexistence of surface copper oxide （crystalline） and pure bulk crystalline copper oxide both contributed to the high activity and thermal stability of Cu-Ce-La mixes oxide catalyst.

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.

Structure and Catalytic Behavior of CuO-ZrO-CeO_2 Mixed Oxides

The effect of doping CuO on the structure and properties of zirconia ceria mixed oxide was studied. The results show that addition of CuO decreases the reduction temperature of ceria, and stabilizes the cubic structure of mixed oxides, and enhances catalytic activity of CuO ZrO CeO 2 mixed oxides for CO oxidation. Increasing ceria content in the mixed oxides can enhance the catalytic activity, but some impurities such as sulfate make catalytic activity falling. There is little effect of calcination temperature on catalytic activities, implying that these catalysts are effective with good thermal stability.

Selective Oxidation of Isobutene over CsFeCoBiMnMoO_x Mixed Oxide Catalyst

Mixed oxide catalyst Cs0.1Fe2Co6BiMnMo12Ox was prepared by the coprecipitation method. Selective oxidation of isobutene was carried out in a fixed-bed reactor over Cs0.1Fe2Co6BiMnMo12Ox. The results showed that the catalyst had high catalytic activity. Under the optimum reaction conditions (n(i-C4=):n(O2)=1:2-1:4, space velocity=180 h-1, T=360℃), the yields of methacrolein and methacrylic acid can reach 80% and 8%, respectively. The total yield of liquid products (methacrolein, methacrylic acid and acetic acid) can reach about 90%.

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 ℃.

Highly efficient base-free aerobic oxidation of alcohols over gold nanoparticles supported on ZnO-CuO mixed oxides

The design and preparation of suitable supports are of great importance for gold catalysts to attain excellent catalytic performance for alcohol oxidation.In this work,we found that ZnO-CuO mixed oxides supported gold catalysts showed much better catalytic activity for base-free aerobic oxidation of benzyl alcohol than Au/ZnO and Au/CuO catalysts,and among them Au/Zn0.7Cu0.3O displayed the best catalytic performance.In addition,the Au/Zn0.7Cu0.3O catalyst could selectively catalyze the aerobic oxidation of a wide range of alcohols to produce the corresponding carbonyl compounds with high yields under mild conditions without base.Further characterizations indicated that the outstanding catalytic performance of Au/Zn0.7Cu0.3O was correlated with the small size of Au nanoparticles(NPs),good low-temperature reducibility,high concentration of surface oxygen species,and collaborative interaction between Au NPs and mixed oxide.

A Novel Synthesis of Titania-silica Mixed Oxide with MesoporousStructure

Mixture formed from sonicating TiCl4 and Si(OEt)4 in the absence of water is used as precursor and hydrolyzed by using a long-chain organic ammonium bromide as a structure-directing agent. The product, titania-silica, is of mesoporous structure and characterized with SEM, FT-IR, BET, XRD and so on.

Electron Donating Property and Catalytic Activity ofPerovskite-type Mixed Oxides (ABO_3) Consisting of Rare Earth and 3d Transition Metals

The catalytic activity of Perovskite-type mixed oxides (LaCoO3, PrCoO3 and SmCoO3) for the reduction of cyclohexanone to cyclohexanol with 2-propanol (Meerwein-PonndorfVerley reduction) has been studied. The data have been correlated with the surface electron donor properties of these mixed oxides

Study on Catalysts with Rhodium Loading on Different Cerium-Zirconium Mixed Oxides

The catalysts with Rh loading on different cerium-zirconium mixed oxides were characterized by BET, H2-TPR and OSC. The effects of different cerium-zirconium mixed oxides on catalytic performance and thermal stability of Rh loaded catalyst were studied. The results show that: (1) Rh can enhance cerium-zirconium mixed oxides OSC and catalytic reaction rates; (2) cerium-zirconium mixed oxides with high Ce contents and low Zr contents are more favorable to the stability of catalysts. Moreover, the contents of CeO2 have important effect on catalysts characteristics, and the addition of some rare earth components, such as La, Pr and Nd also have some influences.