Effect of Ceria on Structure and Thermostability of Copper-Iron-Oxide Catalyst

The solid structures and thermostabilities of Cu-Fe-O and Cu-Fe-Ce-O supported on alumina were studied by XRD, ESR, Mossbauer and TPR techniques. The studies indicate that there are Fe2CuO4, CuO and alpha-Fe2O3 phases in Cu-Fe-O with the granula of less than 13 nm. With the catalyst pretreatment temperature rising, the crystallite of Fe2CuO4 in the catalysts grows up and that of CuO disappears gradually. The presence of Ce leads to the increase of Cu2+ concentration, inhibits the crystal growth of CuO and Fe2CuO4 in the catalyst except that of Fe2O3, and eliminates the difference for reductive reaction of oxygen in Fe-O and Cu-O. At 800 degrees C, the crystal growth of Fe2O3 in Cu-Fe-Ce-O is slower than that in Cu-Fe-O, i.e., CeO2 in Cu-Fe-Ce-O inhibits the growth of Fe2O3 phase effectively, and enhances the thermostability of catalysts so as to avoid the sintering of active elements in catalysts. CeO2 promotes the reducibility of catalysts at lower temperature.

Roles of Ceria on Base Metal Oxide Catalysts——NO+CO Reaction

A microreactor system was used to study the catalytic reaction of NO+CO→1/2 N_2+CO_2 over Cu,Fe, Mn,Cr,and Ce oxides supported on alumina,and the effect of adding Ce in supported Cu-M-O(M=Mn,Fe and Cr) catalysts on their catalytic activities for the topic reaction and the concentration of N_2O produced.It was found that the catalytic activity order of the single-element oxide is:CuO>Fe_2O_3≈Cr_2O_3> MnO_2>CeO_2>NiO.Cu-Mn-O is more active than CuO,and Cu-Fe-O is more active than Cu-Mn-O and Cu-Cr-O for NO+CO reaction.This study shows that the addition of Ce in supported Cu-M-O can promote their catalytic activities Jot the topic reaction,which makes the reaction of 2NO+CO→N_2O+CO_2 fast,and N_2O is an intermediate compound produced during NO+CO reaction.

Oxidation of Carbon Monoxide over Cu/CeO_2 Catalysts Prepared by SMAI

Supported Cu catalysts for low-temperature CO oxidation were prepared by solvated metal atom impregnation (SMAI). X-ray photoelectron spectroscopy (XPS) investigations indicated that the copper in all the samples was in a metallic state. XRD measurements showed that the mean diameters of Cu particles prepared by SMAI were small. Catalytical tests showed that the SMAI catalyst had high CO oxidation activity.

Homogeneous Oxidative Coupling Catalysts： Reactivity of [（Pyr）nCuX]4O2 with Carbon Dioxide to Generate New Active Initiators [（Pyr）nCuX]4（CO3）2 （n = 1 or 2, X = Cl, Br or I, Pyr = Pyrrolidine）

This paper represents the interaction of well characterized Lewis base [（Pyr）nCuX]4O2, n = 1 or 2, X = Cl, Br or I, Pyr = pyrrolidine with CO2 as a Lewis acid to produce new series of oxidative coupling and catechol oxidase initiators [（Pyr）nCuX]4（CO3）2. These carbonato derivatives are isolated as stable solids. They are easily soluble in aprotic solvents as CH2Cl2 or PhNO2. Cryoscopic measurements support tetranuclear core structure for all of them. Infrared spectra show differences from their oxo analogous in the carbonato domains but those differences did not distinguish between tridentate bridging carbonato and bidentate one. Rate of oxidation of 2,6-dimethylphenol （DMP） by [（Pyr）CuCl]4（CO3）2, supports coordination number six for Cu（Ⅱ） centers in [（Pyr）CuCl]4（CO3）2. In order to fulfill coordination number six, for n = 1, carbonate will act as tridentate while for n = 2, it will act as bidentate, as shown in Scheme 4. Near infrared spectra indicate a [（3 halo） Cu（Ⅱ） charge transfer] for [（Pyr）nCuX]4（CO3）2, n = 1 or 2, X = Cl or Br. Low molecular absorptivities of the maxima at 825 nm and 730 nm for [（Pyr）nCuI]4（CO3）2, n = 1 or 2 with a minimum of high molecular absorptivities at 600 nm, comparing to X= CI or Br analogous, support a step structure for [（Pyr）,Cul]4（CO3）2, as shown in Scheme 5. Cyclic voltammograms for [（Pyr）nCuX]4（CO3）2; n = 1 or 2, X = CI or Br, are irreversible in characters.

Insights into facet-dependent reactivity of CuO–CeO2 nanocubes and nanorods as catalysts for CO oxidation reaction

Copper–ceria(Cu O–CeO2) catalysts have been known to be very effective for the oxidation of CO, and their chemical behavior has been extensively studied during the last decades. However, the effect of different CeO2 crystal surfaces on the catalytic activity of Cu O–CeO2 for the oxidation of CO is still unclear and should be further elucidated. In this study, we deposited 1 wt% Cu on mostly {100}-exposed CeO2 nanocubes(1 Cu Ce NC) and mostly {110}-exposed CeO2 nanorods(1 Cu Ce NR), respectively. Both 1 Cu Ce NC and 1 Cu Ce NR have been used as catalysts for the oxidation of CO and achieved 100% and 50% CO conversion at 130 ℃, respectively. The differences in the catalytic activity of 1 Cu Ce NC and 1 Cu Ce NR were analyzed using temperature-programmed reduction of H2 and temperature-programmed desorption of CO techniques. The results confirmed the excellent reducibility of the 1 Cu Ce NC catalyst, which was attributed to the weak interactions between Cu and the CeO2 support. Moreover, in situ diffuse reflectance infrared Fourier-transform spectroscopy studies indicated that the {100} planes of 1 Cu Ce NC facilitated the generation of active Cu(I) sites, which resulted in the formation of highly reactive Cu(I)-CO species during the oxidation of CO. Both the excellent redox properties and effective CO adsorption capacity of the 1 Cu Ce NC catalyst increased its catalytic reactivity.

Low-temperature CO oxidation over CuO-CeO_2/SiO_2 catalysts:Effect of CeO_2 content and carrier porosity

The effects of CeO2 contents and silica carrier porosity with their pore diameters ranging from 5.2 nm to 12.5 nm of CuO-CeO2/SiO2 cata-lysts in CO oxidation were investigated.The catalysts were characterized by N2 adsorption/desorption at low temperature,X-ray diffraction （XRD）,temperature-programmed reduction by H2 （H2-TPR）,oxygen temperature programmed desorption （O2-TPD） and X-ray photoelectron spectroscopy （XPS）.The results suggested that,the ceria content and the porosity of SiO2 carrier possessed great impacts on the structures and catalytic performances of CuO-CeO2/SiO2 catalysts.When appropriate content of CeO2 （Ce content 8 wt%） was added,the catalytic activity was greatly enhanced.In the catalyst supported on silica carrier with larger pore diameter,higher dispersion of CuO was observed,better agglomeration-resistant capacity was displayed and more lattice oxygen could be found,thus the CuO-CeO2 supported on Si-1 showed higher catalytic activity for low-temperature CO oxidation.

Gas-phase epoxidation of propylene by molecular oxygen over Ag-Cu-Cl/BaCO_3 catalyst:Effects of Cu and Cl loadings

Ag‐Cu‐Cl/BaCO3 catalysts with different Cl and Cu loadings, prepared by the reduction deposition impregnation method, were investigated for gas‐phase epoxidation of propylene by molecular oxygen and characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy and O2 temperatureprogrammed desorption. Ag‐Cu‐Cl/BaCO3 catalyst with 0.036 wt% Cu and 0.060 wt% Cl exhibitedthe highest catalytic performance for gas‐phase epoxidation of propylene by molecular oxygen. Apropylene oxide selectivity of 83.7% and propylene conversion of 1.2% were achieved under thereaction conditions of 20% C3H6‐10% O2‐70% N2, 200 °C, 0.1 MPa and 3000 h?1. Increasing the Clloading allowed Ag to ensemble easier, whereas changing the Cu loading showed little effect on Agcrystallite size. The appropriate Cl loading of Ag‐Cu‐Cl/BaCO3 catalyst can reduce the dissociationadsorption of oxygen to atomic oxygen species leading to the combustion of propylene to CO2, whichbenefits epoxidation of propylene by molecular oxygen. Excessive Cl loading of Ag‐Cu‐Cl/BaCO3catalyst decreases propylene conversion and propylene oxide selectivity remarkably because of Clpoisoning. The appropriate Cu loading of Ag‐Cu‐Cl/BaCO3 catalyst is efficient for the epoxidation ofpropylene by molecular oxygen, and an excess Cu loading decreases propylene oxide selectivitybecause the aggregation of Cu species increases the exposed surfaces of Ag nanoparticles, whichwas shown by slight increases in atomic oxygen species adsorbed. The appropriate loadings of Cu and Cl of Ag‐Cu‐Cl/BaCO3 catalyst are important to strike the balance between molecular oxygen and atomic oxygen species to create a favorable epoxidation of propylene by molecular oxygen.

Preparation of Cerium Doped Cu/MIL-53(A1) Catalyst and Its Catalytic Activity in CO Oxidation Reaction

Metal-organic framework（MOF） material MIL-53（A1） with high thermal stability was prepared by a solvothermal method,serving as a support material of cerium doped copper catalyst（Ce-Cu）/MIL-53（A1） material for CO oxidation with high catalytic activity.The catalytic performance between the（CuCe）/MIL-53（A1） and the Cu/MIL-53（A1） catalytic material was compared to understand the catalytic behavior of the catalysts.The catalysts were characterized by thermogravimetric-differential scanning calorimetry（TGDSC）,N2 adsorption- desorption,X-ray diffraction（XRD）,and transmission electron microscopy（TEM）.The characterization results showed that MIL-53（A1） had good stability and high surface areas,the（Ce-Cu）nanoparticles on the MIL-53（A1） support was uniform.Therefore,the heterogeneous catalytic composite materials（Ce-Cu）/MIL-53（A1） catalyst exhibited much higher activity than that of the Cu/MIL- 53（A1） catalyst in CO oxidation test,with 100%conversion at 80 ℃.The results reveal that（Cu-Ce）/MIL-53（A1） is the suitable candidate for achieving low temperature and higher activity CO oxidation catalyst of MOFs.

Synthesis of Mesoporous Silica-zirconia Supported Phosphotungstic Acid and Its Catalytic Performance for Oxidative Desulfurization of Fuel

Mesoporous silica-zirconia supported phosphotungstic acid was synthesized by evaporation induced self-assembly method and used as oxidative desulfurization catalysts. The structural properties of as-prepared catalysts were characterized using various analytical techniques including X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and nitrogen adsorption desorption. The experimental results showed that HPW was highly dispersed on mesoporous framework. The surface acidity of catalysts was analyzed by FTIR measurement of adsorbed pyridine.The surface Lewis acidity was improved with increasing the content of zirconium in the samples. The mesoporous composites were used as catalysts with H2O2 as oxidant for oxidative desulfurization of model fuel. The catalytic activity results showed that the surface Lewis acid sites acted as selective adsorption active sites for dibenzothiophene, which facilitated the sulfur removal from model fuel in the presence of arene. A slight decrease in activity of the recovered catalyst used in the proceeding rounds indicated the reusability of the catalyst.

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga_2O_3 nanowires which was synthesized on nickel oxide particle.But indeed,recent researches about synthesis of β-Ga_2O_3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst.In this work,Gallium oxide(β-Ga_2O_3)nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700-1000℃ using the iron,nickel,copper,cobalt and zinc oxide as a catalyst,respectively.The β-Ga_2O_3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850,900 and 950℃ in all the catalysts.But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst.As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods,and its diameter increased.From these results,we could be proposed that the growth mechanism of β-Ga_2O_3 nanowires was changed with synthesis temperature of nanowires.Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM,FE-SEM,EDX and XRD.

Co,K-Supported Hexagonal Mesoporous Silicas for Catalytic Oxidation of 4-t-Butyltoluene

Co,K-Supported hexagonal mesoporous silicas（HMS） have been prepared by incipient wetness impregnation with cobalt acetate tetrahydrate and potassium acetate as metal precursors, and ethylene glycol as impregnation solvent. The products have been characterized via powder X-ray diffraction, N2 adsorption-desorption isotherms and diffuse reflectance UV-Vis spectroscopy. The divalent cobalt with a tetrahedral oxygen coordination exists mainly in the calcined samples. The catalytic properties have been tested for the oxidation of 4-t-butyltoluene with dioxygen in liquid phase at mild conditions. The products offered good catalytic activities in the oxidation reactions. Co-K-HMS catalyst with loading 4% Co and 2% K（mass fraction） affords a higher yield（22.4%） of 4-t-butylbenzaldehyde at a conversion of 28.3% under the reaction conditions. Adding a proper amount of potassium in Co-HMS results in an improvement catalytic activity and stability.

Catalytic perfomance of rhodium chalcogen halides and rhodium chalcogenides over silica supports in methane oxidative carbonylation

The gas phase methane oxidative carbonylation was studied in the presence of molecular oxygen over silica materials including their mechanical mixtures with rhodium chalcogen chlorides obtained in non-aqueous inorganic media. The formation of Rh4SCl7, Rh4S9Cl2, Rh4SesCl3 and Rh3Se3Cl solids was confirmed by elemental analysis, IR absorption spectroscopy, XPS and X-ray diffraction. Silica, vanadium-, and molybdenum-containing mesoporous molecular sieves have been used as supports. It was found that productivity of oxygenates （methanol, methyl acetate and acetic acid） depends mainly on the method of the catalyst preparation and the type of the support.

A Density Functional Study for the Reaction Mechanism of CO Oxidation on the Copper Cluster

We have studied the reaction mechanism of CO oxidation on the Cu13 cluster via density functional theory. There are two main reaction pathways to be considered： Eley-Rideal（ER） and Langmuir-Hinshelwood（LH） mechanisms, respectively. According to these two main reaction mechanisms, we have obtained five reaction pathways for the first CO oxidation（denoted as RER1,RER2, RLH1, RLH2 and RLH3, respectively）： RER1 is COgas ＋ O2（ads） → O（ads） ＋ CO2（gas）; RER2 is COgas ＋ O2（ads） → CO3（ads） → O（ads） ＋ CO2（gas）; RLH1 refers to CO（ads） ＋ O2（ads） → O（ads） ＋ CO2（gas）; RLH2 refers to CO（ads） ＋ O2（ads） → OOCO（ads） → O（ads） ＋ CO2（gas） and RLH3 refers to O2（ads） ＋ CO（ads）→ O（ads） ＋ O（ads） ＋ CO（ads） → O（ads） ＋ CO2（gas）. These pathways have low energy barriers and are strongly exothermic, suggesting the Cu13 cluster is very favorable catalyst for the first CO oxidation. However, there are higher energy barriers of 99. 8 and 45.4 kJ/mol in the process of producing and decomposing intermediates along the RLH2 and RER2, indicating that RER1, RLH1 and RLH3 are superior pathways with lower energy barriers, especially the RER1 channel. Thereafter, the second CO is more prone to react with the remaining oxygen atom on Cu13 along the ER channel in comparison with the LH pathway, in which the moderate barrier is 70.0 kJ/mol and it is exothermic by 59.6 kJ/mol. Furthermore, the interaction between the absorbate and cluster is analyzed by electronic analysis to gain insights into high activity of the copper cluster.

Pt-CeO_2/SiO_2 catalyst for CO oxidation in humid air at ambient temperature

CO self-poisoning and slow surface kinetics pose major challenges to a CO oxidation catalyst that should work at ambient temperature.Furthermore,the presence of moisture would cause passivation of the catalyst A highly active ceria promoted Pt catalyst（4%Pt-12%CeO_2/SiO_2;conversion≥99%at low（ 500 ppm） and high（ 2500 ppm） CO concentrations was developed for CO oxidation at ambient temperature in humid air.Catalyst preparation variables such as Pt and CeO_2 loading,ceria deposition method,drying and calcination conditions for the ceria and Pt precursors were optimized experimentally.The activity was correlated with surface properties using CO/H_2 chemisorption,O_2-H_2 titration,X-ray diffraction and BET surface area analysis.The method of CeO_2 deposition had a significant impact on the catalytic activity.CeO_2 deposition by impregnation resulted in a catalyst that was three times more active than that prepared by deposition precipitation or CeO_2grafting.O_2-H_2 titration results revealed that the close association of ceria and Pt in the case of CeO_2deposition by impregnation resulted in higher activity.The catalyst support used was also crucial as a silica supported catalyst was five times more active than an alumina supported catalyst.The particle size and pore structure of the catalyst support were also crucial as the reaction was diffusion controlled.The drying and calcination conditions of the ceria and Pt precursors also played a crucial role in determining the catalytic activity.The Pt-CeO_2/SiO_2 catalysts with Pt 2.5 wt%and CeO_2 15 wt%were highly active（TOF 0.02 s^（-1）） and stable（conversion 99%after 15 h） at ambient conditions.

Au/CuO_x-TiO₂Catalysts for CO Oxidation at Low Temperature

A series of Au/CuOx-TiO2 with various Cu/Ti ratios were prepared. CuOx/TiO2 was prepared by incipient-wetness im- pregnation with aqueous solution of copper nitrate. Au catalysts were prepared by deposition-precipitation method at pH 7 and 338 K. The catalysts were characterized by inductively-coupled plasma-mass spectrometry, temperature pro- gramming reduction, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron mi- croscopy and X-ray photoelectron spectroscopy. The reaction was carried out in a fixed bed reactor with a feed con- taining 1% CO in air at WHSV of 120,000 mL/h·g. High gold dispersion and narrow size distribution was obtained. The addition of CuOx in Au/TiO2 enhanced the activity on CO oxidation significantly. CuOx was in amorphous state which could stabilize the Au nanoparticles. Cu was in Cu1+ state. Cu donated partial electrons to Au. The interactions among Au, Cu1+ and TiO2 account for the high catalytic activity for CO oxidation. The significant promotional effect of CuOx on CO oxidation at low temperature was demonstrated.

Synergistic degradation of phenols by bimetallic CuO-Co_3O_4@γ-Al_2O_3 catalyst in H_2O_2/HCO_3^- system

The development of new catalytic techniques for wastewater treatment has long attracted much attention from industrial and academic communities.However,because of catalyst leaching during degradation,catalysts can be short lived,and therefore expensive,and unsuitable for use in wastewater treatment.In this work,we developed a bimetallic CuO-Co3O4@γ-Al2O3 catalyst for phenol degradation with bicarbonate-activated H2O2.The weakly basic environment provided by the bicarbonate buffer greatly suppresses leaching of active Cu and Co metal ions from the catalyst.X-ray diffraction and X-ray photoelectron spectroscopy results showed interactions between Cu and Co ions in the CuO-Co3O4@γ-Al2O3 catalyst,and these improve the catalytic activity in phenol degradation.Mechanistic studies using different radical scavengers showed that superoxide and hydroxyl radicals both played significant roles in phenol degradation,whereas singlet oxygen was less important.

Effect of tungsten oxide on ceria nanorods to support copper species as CO oxidation catalysts

In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at%and 3.2 at%)was introduced to the ceria nanorods via a deposition-precipitation(DP)approach,and copper species of ca.10 at%were sequentially anchored onto the modified ceria support by a similar DP route.The aim of the study was to investigate the effect of the amount of tungsten oxide(0,0.4 at%,2.0 at%,and 3.2 at%)modifier on the copper-ceria catalysts for CO oxidation reaction and shed light on the structure-activity relationship.By the aids of multiple characterization techniques including N2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H2-TPR)in combination with the catalytic performance for CO oxidation reaction,it is found that the copper-ceria samples maintain the crystal structure of the fluorite fcc CeO2 phase with the same nanorod-like morphology with the introduction of tungsten oxide,while the textural properties(the surface area,pore volume and pore size)of ceria support and copper-ceria catalysts are changed,and the oxidation states of copper and tungsten are kept the same as Cu2+and W6+before and after the reaction,but the introduction of tungsten oxide(WO3)significantly changes the metal-support interaction(transfer the CuOx clusters to Cu-[Ox]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.

A Novel Cu-Mo/ZSM-5 Catalyst for NO_x Catalytic Reduction with Ammonia

The Cu-Mo/ZSM-5 catalysts with different Cu/Mo ratios were prepared by wetimpregnation method, and their catalytic performance for selective catalytic reduction of NO_x wasstudied. The results showed that Cu-Mo/ZSM-5 is a very effective catalyst for NO_x catalyticreduction with ammonia, especially when Cu/Mo molar ratio is about 1.5. It not only exhibited theextremely high catalytic activity, but also showed good stability for O_2. The bulk phase structureof Cu-Mo/ZSM-5 catalysts was determined by XRD technique, and the results indicated that there is amaximum dispersion for Cu species when Cu/Mo molar ratio is 1.5, and an interaction between Cu andMo along with HZSM-5 may be present in Cu-Mo/ZSM-5, which may possibly result in a special structurefavorable for the catalytic reduction of NO_x over Cu-Mo/ZSM-5 catalyst.

Effect of doping rare earth oxide on performance of copper-manganese catalysts for water-gas shift reaction

Rare earth-doped copper-manganese mixed oxide catalysts were prepared by coprecipitation and mechanical mixing using copper sulfate, manganese sulfate, and rare-earth oxides REO （REO indicates La2O3, CeO2, Y2O3, or Pr6O11） as raw materials. The samples were characterized by X-ray diffraction （XRD）, temperature-programmed reduction （TPR）, temperature-programmed reduc-tion of oxidized surfaces （s-TPR）, and temperature-programmed desorption （TPD）. Catalytic activities were tested for a water-gas shift reaction. Doping rare earth oxides did not alter the crystal structure of the original copper-manganese mixed oxides but changed the interplanar spacing, adsorption performance and reaction performance. Doping with La2O3 enhanced the activity and stability of Cu-Mn mixed oxides because of high copper distribution and fine reduction. Doping with CeO2 and Y2O3 also decreased the reduc-tion temperatures of the samples to different degrees while improving the dispersion of Cu on the surface, thus, catalytic activity was better than that of undoped Cu-Mn sample. The Pr6O11-doped sample was difficult to reduce, the dispersion of surface coppers was lowered, resulting in poor activity.

Doping Effect of CuO on CeO_2 for CO Oxidation

Cu-Ce-O catalysts, prepared by the amorphous citrate precursor (ACP) method, wereinvestigated by ICP, XRD and ndcro-reactor techniques. At low copper content of Cu-Ce-Ocatalysts, fluorite structures formed at low calcining temperatures, and Cuo doped into the CeO2matrix; at high copper content, in addition to the fluorite structure, crystalline monoclinic phaseCuO formed as well at high calcining temperatures. There was no other phase formed even calcinedat 1000℃. The results show that only a little CuO dopes into the CeO2 matrix to form complexoxide, which promotes the catalytic activity of CO oxidation greatly. The optimum Cu-Ce-Ocatalyst is composed of 15% copper by Cu/(Ce+Cu) atomic ratio, and calcined at 700℃ for 4h. Thephase compositions include the crystalline CuO and the active complex oxide with fluoritestructure. The formulation of the active complex oxide is Cu0.06Ce0. 94O1.94.