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.     

Effect of yttrium addition on water-gas shift reaction over CuO/CeO2 catalysts

This paper presented a study on the role of yttrium addition to CuO/CeO2 catalyst for water-gas shift reaction. A single-step co-precipitation method was used for preparation of a series of yttrium doped CuO/CeO2 catalysts with yttrium content in the range of 0-5wt.%. Properties of the obtained samples were characterized and analyzed by X-ray diffraction (XRD), Raman spectroscopy, H2-TPR, cyclic voltammetry (CV) and the BET method. The results revealed that catalytic activity was increased with the yttrium content at first, but then decreased with the further increase of yttrium content. Herein, CuO/CeO2 catalyst doped with 2wt.% of yttrium showed the highest catalytic activity (CO conversion reaches 93.4% at 250℃) and thermal stability for WGS reaction. The catalytic activity was correlated with the surface area, the area of peak y of H2-TPR profile (I.e., the reduction of surface copper oxide (crystalline forms) interacted with surface oxygen vacancies on ceria), and the area of peak C2 and A1 (Cu0→Cu2+ in cyclic voltammetry process), respectively. Besides, Raman spectra provided evidences for a synergistic Cu-Ovacancy interaction, and it was indicated that doping yttrium may facilitate the formation of oxygen vacancies on ceria.     

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.     

Effects of CeO2 on structure and properties of Ni-Mn-K/bauxite catalysts for water-gas shift reaction

Multiple-metal catalysts (Ni-Mn-Ce-K/bauxite) for Water-Gas Shift (WGS) reaction were prepared by impregnation, and the catalytic structure and properties were investigated by N2 physical, XRD, H2-TPR, and CO-TPD. The results indicated that the addition of 7.5% CeO2 improved the activity of the WGS reaction obviously, and also increased the specific surface area and pore volume of the catalysts. The addition of CeO2 decreases the reduction temperature, enhanced the adsorption and activation of H2O, and improved the adsorption content of CO. Besides, active sites were not changed and the number of active sites on catalysts did not increase obviously.     

Effects of CeO2 on structure and properties of Ni-Mn-K/bauxite catalysts for water-gas shift reaction

Multiple-metal catalysts （Ni-Mn-Ce-K/bauxite） for Water-Gas Shift （WGS） reaction were prepared by impregnation, and the catalytic structure and properties were investigated by N2 physical, XRD, H2-TPR, and CO-TPD. The results indicated that the addition of 7.5% CeO2 improved the activity of the WGS reaction obviously, and also increased the specific surface area and pore volume of the catalysts. The addition of CeO2 decreases the reduction temperature, enhanced the adsorption and activation of H2O2, and improved the adsorption content of CO. Besides, active sites were not changed and the number of active sites on catalysts did not increase obviously.     

Reverse water gas shift reaction over Co-precipitated Ni-CeO2 catalysts

The Ni-CeO2 catalysts with different Ni contents were prepared by a co-precipitation method and used for Reverse Water Gas Shift （RWGS） reaction. 2wt.%Ni-CeO2 showed excellent catalytic performance in terms of activity, selectivity, and stability for RWGS reaction. Characterizations of the catalyst samples were conducted by XRD and TPR. The results indicated that, in Ni-CeO2 catalysts, there were three kinds of nickel, nickel ions in ceria lattice, highly dispersed NiO and bulk NiO. Oxygen vacancies were formed in CeO2 lattice due to the incorporation of Ni^2＋ ions into ceria lattice. Oxygen vacancies formed in ceria lattice and highly dispersed Ni were key active components for RWGS, and bulk Ni was key active component for methanation of CO2.     

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.     

Ceria modified three-dimensionally ordered macro-porous Pt/TiO2 catalysts for water-gas shift reaction

Three-dimensionally ordered macro-porous(3DOM) TiO2 and ceria-modified 3DOM TiO2 supported platinum catalysts were pre-pared with template and impregnation methods, and the resultant samples were characterized by scanning electron microscopy(SEM), X-ray dif-fractometer(XRD), high-resolution transmission electron microscopy(HRTEM) and texture programmed reduction(TPR) techniques. The catalytic performances over the platinum-based catalysts were investigated for water-gas shift (WGS) reaction in a wide temperature range macro-porous catalyst, owing to the macro-porous structure favoring mass uansfer. Addition of ceria into 3DOM Pt/TiO2 led to improvement of catalytic activity. TPR and HRTEM results showed that the interaction existed between ceria and titanium oxide and addition of ceria promoted the reducibility of platinum oxide and TiO2 on the interface of platinum and TiO2 particles, which contributed to high activity of the ceria modi-fied catalysts. The results indicated that ceria-modified 3DOM Pt/TiO2 was a promising candidate of fuel cell oriented WGS catalyst.     

Structure-activity relationship in water-gas shift reaction over gold catalysts supported on Y-doped ceria

The utilization of pure hydrogen as an energy source in fuel cells gave rise to renewed interest in developing active and stable water-gas shift catalysts. Gold catalysts have proven to be very efficient for water-gas shift reaction at low temperature. The aim of the present study was to investigate the effect of:(i) different preparation methods(impregnation and coprecipitation) to obtain a modified ceria support,and(ii) the amount of Y_2 O_3(1.0 wt%, 2.5 wt%, 5.0 wt% and 7.5 wt%) as dopant on the water-gas shift activity of Au/CeO_2 catalysts. An extended characterization by means of S_(BET), XRD, HRTEM/HAADF, FTIR,H_2-TPR and CO-TPR measurements in combination with careful evaluation of the catalyst behavior allowed to shed light on the parameters governing the water-gas shift activity. The catalysts show very high activity(90% CO conversion) in the temperature range 180-220 ℃,with a slightly better performance of the gold catalysts on supports prepared by impregnation. The decreased activity with increasing Y_2 O_3 concentration is related to the hindering of oxygen mobility due to ordering of surface oxygen vacancies in vicinity of segregated Y~(3+). The effect of catalyst pre-treatments and the stability of the best performing samples were examined as well.     

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.     

Zirconia modified monolithic macroporous Pt/CeO2/Al2O3 catalyst used for water-gas shift reaction

Monolithic macroporous Pt/CeO2/Al2O3 and zirconia modified Pt/CeO2/Al2O3 catalysts were prepared by using concentrated emulsions synthesis route. The catalytic performances over the platinum-based catalysts were investigated by water-gas shift (WGS) reaction in a wide temperature range (180-300 oC). The samples were characterized with thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and temperature programmed reducti...     

Effects of ZrO2 Content on Structure and Performance of Cu/CeO2-ZrO2 Catalysts for Water-Gas Shift Reaction

Water-gas shift(WGS)is a critical step in fuelprocessors for preli minary COclean-up and additionalhydrogen generation prior to the CO clean-up stage,which opened up new potential applications for WGScatalysts.Recently several formulations of noble-met-al…     

Luminescent properties of Eu~(3+) doped Gd_2WO_6 and Gd_2(WO_4)_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in dif...     

NiO-Ce0.5Zr0.5O2 catalysts prepared by citric acid method for steam reforming of ethanol

NiO-Ce0.5Zr0.5O2catalysts were prepared by citrate method and used for hydrogen production from steam reforming of ethanol (SRE). The effect of nickel content and space velocity on the catalytic performance was investigated. The prepared catalysts were character-ized with XRD and thermal analysis techniques. 20%NiO-Ce0.5Zr0.5O2 catalyst was very active and selective for hydrogen production via SRE, in which ethanol conversion of 100% could be obtained with feed component of 20% (H2O+EtOH) and 80% N2, water/ethanol of 3/1 in molar ratio at 350 ℃. Also, the catalyst showed good stability for anti-sintering and carbon-resistance. The XRD illuminated that both NiO and Ce0.5Zr0.5O2 crystal sizes were very small in NiO-Ce0.5Zr0.5O2 catalyst, and Ce0.5Zr0.5O2 solid solution was formed.     

Luminescent properties of Eu~（3＋） doped Gd_2WO_6 and Gd_2（WO_4）_3 nanophosphors prepared via co-precipitation method

Eu3+ doped Gd2WO6 and Gd2(WO4)3 nanophosphors with different concentrations were prepared via a co-precipitation method. The structure and morphology of the nanocrystal samples were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), respectively. The emission spectra and excitation spectra of samples were measured. J-O parameters and quantum efficiencies of Eu3+ 5D0 energy level were calculated, and the concentration quenching of Eu3+ luminescence in different matrixes were studied. The results indicated that effective Eu3+:5D0-7F2 red luminescence could be achieved while excited by 395 nm near-UV light and 465 nm blue light in Gd2WO6 host, which was similar to the familiar Gd2(WO4)3:Eu. Therefore, the Gd2WO6:Eu red phosphors might have a potential application for white LED.     

Effect of BaO on Catalytic Activity of Pt-Rh TWC

The effect of BaO doping to the Pt-Rh catalysts on its three-way catalytic activity and water-gas transfer was investigated. The results show that the light-off temperatures of hydrocarbon and carbon monoxide and nitrogen oxides have little difference in the fresh catalysts. But after the hydrothermal-aged 5 h at 1000 ℃, the catalysts containing CeO2-ZrO2-BaO has lower light-off temperature and better catalytic activity than the catalysts containing BaO and CeO2-ZrO2,     

Effect of Sm on Gas-Sensing Properties of SnO2 with Different Oxygen Vacancy Concentrations

In recent years, chemical modification ofsuffice has been widely used to improve gas.sensing property of SnOZ ...,..[1]. There aremany researches on chemical surface modification by rare earth .l....t,[2'3]. The deviationof oxygen from stoichiometric can be adjustedby process conditions, especially the temperature and atmosphere during SnOZ-- x preparation. The x value in SnOZ -- x presents the concentration of oxygen vacancy in SnO2. Theoxygen vacancy can form the donor level andaffect t…     

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...     

Photoluminescent properties of Sr2SiO4:Eu3+ and Sr2SiO4:Eu2+ phosphors prepared by solid-state reaction method

Eu2+ and (or) Eu3+ doped Sr2SiO4 phosphors particles were synthesized by a conventional solid-state reaction technique, and their structural and optical properties were investigated. The X-ray diffraction (XRD) results showed that the obtained phosphors were composed of orthorhombic α'-Sr2SiO4 and monoclinic β-Sr2SiO4 phase. When excited under 256 nm, Sr2SiO4:Eu3+ phosphors showed intense emission in the red region. Sr2SiO4:Eu3+ phosphors exhibited white emissions (x=0.30, y=0.40, TC=6500 K) ranging from 425 to 650 nm when it was excited by near-ultraviolet (near-UV) light, indicating that Sr2SiO4:Eu2+ was a good light-conversion phosphor candidate for near-UV chip.     

Influence of ammonium sulfate on YAG nanopowders and Yb:YAG ceramics synthesized by a novel homogeneous co-precipitation method

Homogeneous and dispersed Y_3 Al_5 O_(12)(yttrium aluminum garnet,YAG) nanopowders were synthesized via a homogeneous co-precipitation method from the mixed solutions of yttrium nitrate,aluminum nitrate and a small amount of ammonium sulfate using hot urea as the precipitant.The method has the superiorities that co-precipitation of cations is ensured and continuous decomposition of the hot urea is achieved to obtain the narrow size distribution particles.The addition of small amount of ammonium sulfate surfactant,although has no influence on YAG garnet phase formation,has significant effect on dispersion,particles distribution and sinterability of the resultant YAG and Yb:YAG powders.Compared with the undoped sample,the green body of Yb:YAG doped with ammonium sulfate has higher total shrinkage,linear shrinkage rate and relative density through sintering at 1600 ℃.The resultant Yb:YAG powders can be sintered into transparent ceramics at 1700 ℃ through vacuum sintering.The influence of the sulfate ions on characteristics of the resultant powders was thoroughly studied.