CeO_2/CuO catalysts using different template agent for preferential CO oxidation in H_2-rich stream

The CeO_2/CuO catalysts using different template agent(F68 L64, F127 and P123) were synthesized by the simple template and impregnation method. They were characterized by FESEM, XRD, N2 physisorption and H2-TPR techniques. It is found that the CeO_2/CuO catalysts are double pore distribution, and CeO_2 can enter into the gap of CuO supports and form the contact interface of copper and cerium. Among the asprepared catalysts, the CeO_2/CuO-F127 catalyst displays better activity at lower temperature and the CeO_2/CuO-P123 catalyst presents higher activity at higher temperature. The CeO_2/CuO-P123 catalyst has the smallest crystallite sizes of CuO and CeO_2 as well as the largest size of cubes, which may improve the interaction of copper and cerium and enhance the performance of CO oxidation.     

Influence of preparation method on performance of Ni-CeO2 catalysts for reverse water-gas shift reaction

This study investigated 1 wt.% Ni-CeO₂ catalysts that were prepared using co-precipitation, deposition-precipitation, and impregnation methods for the reverse water-gas shift (RWGS) reaction. Characterizations of the catalyst samples were conducted by Brumauer-Emmett-Teller (BET), atomic absorption spectrophotometer (AAS), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and temperature programmed reduction (TPR). The results showed that the Ni-CeO₂ catalyst prepared using the co-precipitation method exhibited the best catalytic performance. In the Ni-CeO₂ catalyst prepared using co-precipitation method, a combination of highly dispersed NiO and abundant oxygen vacancies was assumed to play a crucial role in determining the catalytic activity and selectivity of the RWGS reaction.     

Catalytic performance of Zr-doped CuO-CeO_2 oxides for CO selective oxidation in H_2-rich stream

Zr-doped CuO-CeO_2 catalysts for CO selective oxidation were designed and prepared by the hydrothermal method and coprecipitation. The experimental samples were characterized by means of N_2 adsorption-desorption isotherms, powder X-ray diffraction, temperature-programmed reduction and Xray photoelectron spectroscopy. It is observed that the catalyst prepared by hydrothermal method exhibits larger specific surface area, smaller crystalline size and higher dispersion of active components compared with those of the catalyst obtained by coprecipitation. Meanwhile, redox properties of copper oxide are improved significantly and highly dispersed copper species providing CO oxidation sites are present on the surface. Furthermore, adsorptive centers of CO and active oxygen species increase on the copper-ceria interfaces. The Zr-doped CuO-CeO_2 catalyst prepared by hydrothermal method possesses superior catalytic activity and selectivity for selective oxidation of CO at low temperature compared with those of the sample prepared by coprecipitation. The temperature corresponding to 50% CO conversion is only 73 ℃ and the temperature span of total CO conversion is expanded from 120 to 160 ℃.     

Study on Surface and Bulk Properties of Ce-5 % Lanthanum Alloy

The surface and bulk properties of Ce-5% La were studied with X-ray photoelectron spectroscopy (XPS)and X-ray diffraction (XRD), respectively.The XRD analysis shows that cerium in bulk is in γ-phase, and its lattice parameter is 0.516 nm.And we also find Ce2O3 in the bulk from the XRD figure but no existence of metal lanthanum because of its small quantity.The XPS analysis shows that there are always oxides existing in the surface.The O1s peak always exists at the binding energy of 530.3 eV, which may be attributed to Ce2O3 and La2O3, but no evidence was found for the existence of CeO2.It is concluded that there is a thick layer of Ce2O3 on the sample surface.And the Ce3d peak show multi-split in the figure, in which there are two peaks in each region, 3d5/2 and 3d3/2, and the binding energy of these peaks are 882.86, 887.70 eV for 3d5/2, and 901.44, 905.93 eV for 3d3/2.The special phenomena can be attributed to the changes of 4f electronic configuration, and the cerium in the sample exhibits properties similar to Ce2O3.But the influence of the addition of lanthanum to cerium is not visible, and further investigations are expected.     

CuO-CeO2/Al2O3/FeCrAl monolithic catalysts prepared by in situ combustion synthesis method for preferential oxidation of carbon monoxide

This work described in situ combustion synthesis method for depositing CuO-CeO2 on the FeCrAl honeycomb supports.The in-fluence of the solution concentration and the role of the additive were studied and analyzed by scanning electron microscopy (SEM),X-ray diffractometer (XRD),and temperature programmed reduction (TPR) techniques.The results showed that 200 g/L of the active solution was the most appropriate concentration for preparing the monolithic catalysts,and the additives of praseodymium and lanthanum...     

Effect of preparation method on MnOx-CeO2 catalysts for NO oxidation

The NO oxidation reaction was studied over MnO_x-CeO₂ catalysts prepared by co-precipitation, impregnation and mechanical mixing method, respectively. It was found that the co-precipitation was the most active and a 60% NO conversion was achieved at 250 °C. X-ray diffraction (XRD), Brumauer-Emmett (BET), H₂-temperature programmed reduction (H₂-TPR) and oxygen storage capacity (OSC) techniques were employed to characterize the physical and chemical properties of the catalysts. XRD results showed that amorphous MnO_x or Mn-O-Ce solid solution existed in co-precipitation and impregnation prepared sample, while crystalline MnO_x was found in mechanical mixing catalyst. A larger surface area was observed on co-precipitation prepared catalyst compared to those prepared by impregnation and mechanical mixing. The strong interaction between MnO_x and CeO₂ enhanced the reducibility of the oxides and increased the amount of Mn⁴⁺ and activated oxygen, which are favorable for NO oxidation to NO₂.     

Construction of mesoporous ceria-supported gold catalysts with rich oxygen vacancies for efficient CO oxidation

Bearing unique redox nature and high oxygen storage capacity, ceria (CeO₂) has always been a promising CO oxidation catalyst support for gold (Au) catalysts and the like. Herein, a series of Au–CeO₂–P (P stands for pH value) samples was prepared by a co-precipitation method with the assistance of an alkaline environment and amino groups functionalized ordered mesoporous polymer (OMP-NH₂). Afterward, all samples described above were characterized that the Au–CeO₂–P catalysts are made of Au–Ce–O solid solution and Au nanoparticles (NPs) supported on CeO₂. It turns out that OMP-NH₂ is not just a simple sacrificial template for mesoporous structure, but also plays an important role as an amino source, explaining the presence of rich oxygen vacancies. Due to the concentration of oxygen vacancies in Au–Ce–O solid solution is the key factor for the oxygen mobility of CO oxidation, the catalytic results also demonstrate that the catalytic activity of Au–CeO₂–P catalysts is related to the concentration of their oxygen vacancies. Moreover, Au–CeO₂-9.6 with a highest concentration of oxygen vacancies (as high as 13.98%) in Au–CeO₂–P catalysts exhibits the best catalytic activity (complete conversion at 10 °C).     

Influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 for NO reduction by CO

In order to investigate the influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 catalyst for NO reduction by CO,two series of catalysts(xCuyMn/Ce and xCu/yMn/Ce) were prepared by co-impregnation and stepwise-impregnation methods,and characterized by means of X-ray diffraction(XRD),Raman spectra,H2-temperature programmed reduction(H2-TPR),in situ diffuse reflectance infrared Fourier transform spectra(in situ DRIFTS) techniques.Furthermore,the catalytic performances of these catalysts were evaluated by NO+CO model reaction.The obtained results indicated that:(1) The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method,which was beneficial to the improvement of the reduction behavior;(2) The excellent reduction behavior was conducive to the formation of low valence state copper species(Cu+/Cu0) and more oxygen vacancies(especially the surface synergetic oxygen vacancies(SSOV,Cu+-□-Mn(4–x)+)) during the reaction process,which were beneficial to the adsorption of CO species and the dissociation of NO species,respectively,and further promoted the enhancement of the catalytic performance.Finally,in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods,a possible reaction mechanism(schematic diagram) was tentatively proposed.     

Effects of supports and combined process on hydrogen purification over nickel supported catalysts

Hydrogen purification must be done to meet the different purposes of hydrogen utilization.In the present work,it is confirmed that the catalyst Ni/CeO_2 has the highest activity for total methanation(Total MET) of CO and CO_2,and is thus most suitable for hydrogen purification for ammonia synthesis.While,the catalyst Ni/ZrO_2 appears the best one for selective methanation of CO(CO-SMET) in the H_2-rich gas to produce clean fuel for proton exchange membrane fuel cell(PEMFC).In spite of this,the catalyst Ni/ZrO_2 without adding chlorine ions as promoter is not yet capable of removing the CO in the reformate gas to below 10 ppm in a wide reaction temperature range by the way of CO-SMET.Adding chlorine ions as promoter is indeed not favorable for practical application due to its gradual loss in the catalytic reaction as proved in our previous work.Therefore,a step to decrease CO_2 concentration(called as de-CO_2 step) is suggested to be set prior to the CO-SMET step in this work.It is proved that such combination of de-CO_2 step and CO-SMET step is efficient to achieve a deep removal of CO to below 10 ppm with a high selectivity more than 50% in a wide reaction temperature range of 220—280℃over the catalyst Ni/ZrO_2 without adding chlorine ions as promoter.The combined process has potential for practical application,at least in the large-scale power plant of PEMFC.     

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 N_2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H_2-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 CeO_2 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 Cu~(2+)and W~(6+)before and after the reaction,but the introduction of tungsten oxide(WO_3)significantly changes the metal-support interaction(transfer the CuO_x clusters to Cu-[O_x]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.     

Copper-ceria sheets catalysts: Effect of copper species on catalytic activity in CO oxidation reaction

Copper-ceria sheets catalysts with different loadings of copper(2 wt.%, 5 wt.% and 10 wt.%) supported on ceria nanosheets were synthesized via a depositioneprecipitation(DP) method. The prepared catalysts were systematically characterized with various structural and textural detections including X-ray diffraction(XRD), Raman spectra, transmission electron microscopy(TEM), X-ray absorption fine structure(XAFS), and temperature-programmed reduction by hydrogen(H_2-TPR), and tested for the CO oxidation reaction. Notably, the sample containing 5 wt.% of Cu exhibited the best catalytic performance as a result of the highest number of active CuO species on the catalyst surface. Further increase of copper content strongly affects the dispersion of copper and thus leads to the formation of less active bulk CuO phase, which was verified by XRD and H_2-TPR analysis. Moreover, on the basis of in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS) results, the surface Cu~+ species, which are derived from the reduction of Cu~(2+), are likely to play a crucial role in the catalyzing CO oxidation.Consequently, the superior catalytic performance of the copper-ceria sheets is mainly attributed to the highly dispersed CuO_x cluster rather than Cu-[O_x]-Ce structure, while the bulk CuO phase is adverse to the catalytic activity of CO oxidation.     

Effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts for oxidation of toluene

A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized.The experimental results show that 0.71 wt%Na+can inhibit active growth,generate more active small crystal grains,and promote improvement of the catalytic activity by the grain boundary segregation block mechanism,and the catalyst with 0.71 wt%of Na shows toluene conversion of 90 vol%at 250℃.Over 0.71 wt%of Na+content will neutralize the acid centre of the catalyst,lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.     

Improved sulfur-resistant ability on CO oxidation of Pd/Ce0.75Zr0.25O2 over Pd/CeO2-TiO2 and Pd/CeO2

The influence of sulfation on Pd/Ce0.75Zr0.25O2, Pd/Ce O2-Ti O2 and Pd/Ce O2 was investigated. Physical structure and chemical properties of different catalysts were characterized by N2 adsorption, X-ray diffraction(XRD), CO chemisorption, X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR) and X-ray fluorescence(XRF). After 10 h SO2 sulfation, it was found that the decrement on CO oxidation catalytic activity was limited on Pd/Ce0.75Zr0.25O2 compared to Pd/Ce O2-Ti O2 and Pd/Ce O2. It demonstrated that Pd/Ce0.75Zr0.25O2 was more sulfur resistant compared to the other two catalysts. After sulfur exposure, catalyst texture was not much influenced as shown by N2 adsorption and XRD, and surface Pd atoms were poisoned indicated by CO chemisorption results. Pd/Ce0.75Zr0.25O2 and Pd/Ce O2-Ti O2 exhibited less sulfur accumulation compared to Pd/Ce O2 in the sulfation process. Furthermore, XPS results clarified that surface sulfur amount, especially surface sulfates amount on the sulfated catalysts was more crucial for the deactivation in sulfur containing environment.     

Support interaction of Pt/CeO_2 and Pt/SiC catalysts prepared by nano platinum colloid deposition for CO oxidation

The interaction between Pt and its various supports can regulate the intrinsic electronic structure of Pt particles and their catalytic performance.Herein,Pt/CeO_2 and Pt/SiC catalysts were successfully prepared via a facile Pt colloidal particle deposition method,and their catalytic performance in CO oxidation was investigated.XRD,TEM,XPS and H_2-TPR were used to identify the states of Pt particles on the support surface,as well as their effect on the performance of the catalysts.Formation of the Pt-O-Ce interaction is one of the factors controlling catalyst activity.Under the oxidative treatment at low temperature,the Pt-O-Ce interaction plays an important role in improving the catalytic activity.After calcining at high temperature,enhanced Pt-O-Ce interaction results in the absence of metallic Pt~0 on the support surface,as evidenced by the appearance of Pt~(2+) species.It is consistent with the XPS data of Pt/CeO_2,and is the main reason behind the deactivation of the catalyst.By contrast,either no interaction is formed between Pt and SiC or Pt nanoparticles remain in the metallic Pt~0 state on the SiC surface even after aging at 800℃in an oxidizing atmosphere.Thus,the Pt/SiC shows better thermal stability than Pt/CeO_2.The interaction between Pt and the active support may be concluded to be essential for CO oxidation at low temperature,but strong interactions may induce serious deactivation of catalytic activity.     

Copper-cerium oxides supported on carbon nanomaterial for preferential oxidation of carbon monoxide

The CuxO-Ce O2/Fe@CNSs, CuxO-Ce O2/MWCNTs-Co and CuxO-Ce O2/MWCNTs-Ni catalysts were prepared by the impregnation method and characterized by transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, H2-temperature programmed reduction and N2 adsorption-desorption techniques. It was found that the Fe nanoparticles were encapsulated into the multi-layered carbon nanospheres(CNSs). However, the multi-wall carbon nanotubes(MWCNTS) were generated on the Co/Al2O3 and Ni/Al2O3 precursor. The addition of carbon nanomaterial as supports could improve structural properties and low-temperature activity of the Cu O-Ce O2 catalyst, and save the used amount of metal catalysts in the temperature range with high selectivity for CO oxidation. The copper-cerium oxides supported on carbon nanomaterial had good resistence to H2 O and CO2.     

Activity and deactivation behavior of Au/LaMnO3 catalysts for CO oxidation

Perovskite oxide LaMnO3 was prepared by sol-gel method and the nanosize Au/LaMnO3 catalyst was prepared by deposition-precipitation(DP) method in the paper.Characterization of the catalyst sample was made by X-ray diffractometer(XRD),atom absorption spectra(AAS) and X-ray photoelectron spectroscopy(XPS) instrumental methods.The activity,long-term stability and the reasons for deactivation of the gold catalyst in CO oxidation were investigated.The experiment results demonstrated that the Au/LaMnO3 catalyst e...     

Heavy metals in the environment. Part VI: Recovery of cobalt values from spent cobalt/manganese bromide oxidation catalysts

Cobalt is recovered from a series of spent cobalt/ manganese bromide oxidation catalysts containing 27–31% Co, 25–33% Mn, 0–14% Fe together with Cr, Cu and Ni. While ammoniacal leaching in the presence of reducing agents can be used to extract cobalt, the process has to be separately optimized for each sample. Leaching with 4 M HCl at 80°C for 4 hours, however, proved successful for all the catalysts. A method of successive neutralization is used for the separation of cobalt from the acid solutions. Addition of solid NaOH to pH 2 removes Fe and Cr as hydroxide, while addition of ammonia to pH 10 precipitates manganese oxide from an aerated solution leaving Co as a Co^III hexammine complex. Cobalt can be recovered from this solution by chemical or electrochemical processes. After crystallization the complex is converted to anhydrous cobalt chloride by heating it to 320°r to Co₂O₃ by roasting it in air at 500°C. Either of these materials may be readily converted into other cobalt chemicals. Alternatively, fluidized bed cell electrolysis of the Co^III. complex solution yields cobalt with purity > 99.5%.     

CuO-CeOe/AleO3/FeCrAl monolithic catalysts prepared by in situ combustion synthesis method for preferential oxidation of carbon monoxide

This work described in situ combustion synthesis method for depositing CuO-CeO2 on the FeCrAl honeycomb supports.The in-fluence of the solution concentration and the role of the additive were studied and analyzed by scanning electron microscopy (SEM),X-ray diffractometer (XRD),and temperature programmed reduction (TPR) techniques.The results showed that 200 g/L of the active solution was the most appropriate concentration for preparing the monolithic catalysts,and the additives of praseodymium and lanthanum improved the adhesion stability of the monolithic catalysts.The addition of Pr did not greatly affect the catalytic performance,but CO could not be totally converted into CO2 after the addition of La into the CuO-CeO2/Al2O3/FeCrAl catalysts.     

CO_2氢化催化剂的制备及性能研究

采用共沉淀-程序升温焙烧的方法制备Cu/Mn氧化物催化剂,考察元素组成对催化剂结构和性能的影响.通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、比表面积分析仪(BET)等对样品进行表征.结果表明,催化剂前驱体在程序升温焙烧过程中可形成Cu_(1.5)Mn_(1.5)O_4尖晶石相,该尖晶石相结构有利于Cu晶粒分散,防止Cu晶粒在反应过程中团聚和烧结.元素组成显著影响催化剂的前驱体结构和性能.当Cu占Cu、Mn总质量的40%时,催化剂前驱体中几乎全部的Cu都与Mn结合形成Cu_(1.5)Mn_(1.5)O_4尖晶石相,比表面积最大,催化活性最高,CO_2转化率最高达到16.3%.尖晶石相结构有利于催化剂活性提高.Cu/Mn氧化物催化剂更有助于促进逆水煤气变换(RWGS)反应.     

稀土改性镍催化剂对CO2甲烷化反应的影响

以稀土为助剂 ,金属镍为活性组份 ,研究了不同稀土对镍催化剂的改性作用 ,同时用活性比表面、H2 -TPD、CO2 - TPD及 XPS等方法对催化剂进行了表征。结果表明 ,稀土对镍催化剂的 CO2 甲烷化活性有明显的促进作用 ,其中以稀土 Sm的改善效果最好 ;海泡石和 Sm既能增大镍催化剂的活性比表面积 ,又能提高 H2 和 CO2 的吸附量 ,同时降低反应的活化能 ,增大镍上的电子云密度。