SnO_2-based solid solutions for CH_4 deep oxidation: Quantifying the lattice capacity of SnO_2 using an X-ray diffraction extrapolation method

A series of SnO2‐based catalysts modified by Mn, Zr, Ti and Pb oxides with a Sn/M （M=Mn, Zr, Ti and Pb） molar ratio of 9/1 were prepared by a co‐precipitation method and used for CH4 and CO oxidation. The Mn3＋, Zr4＋, Ti4＋and Pb4＋cations are incorporated into the lattice of tetragonal rutile SnO2 to form a solid solution structure. As a consequence, the surface area and thermal stability of the catalysts are improved. Moreover, the oxygen species of the modified catalysts become easier to be reduced. Therefore, the oxidation activity over the catalysts was improved, except for the one modified by Pb oxide. Manganese oxide demonstrates the best promotional effects for SnO2. Using an X‐ray diffraction extrapolation method, the lattice capacity of SnO2 for Mn2O3 was 0.135 g Mn2O3/g SnO2, which indicates that to form stable solid solution, only 21%Sn4＋cations in the lattice can be maximally replaced by Mn3＋. If the amount of Mn3＋cations is over the capacity, Mn2O3 will be formed, which is not favorable for the activity of the catalysts. The Sn rich samples with only Sn‐Mn solid solution phase show higher activity than the ones with excess Mn2O3 species.

Preparation and Characterization of CeO_2-ZrO_2 Solid Solution Ultrafine Particles Using Reversed Microemulsion

Ce0.6Zr0.4O2 solid solution ultrafine particle was prepared in the cyclohexane/water/OP-10/n-hexanol reversed microemulsion. The quasi-ternary phase diagram investigations showed that the system has narrow W/O type microemulison region, so it is the proper system to prepare Ce0.6Zr0.4O2 solid solution ultrafine particle. Some physical-chemical techniques such as TG/DTA, XRD, BET, and HRTEM are used to characterize the resultant powders. The results show that the fluorite cubic Ce0.6Zr0.4O2 solid solution is obtained at 400 ℃. The surface area is （146.7 m^2·g^-1）, which is higher than the surface area for sol-gel prepared sample （59.5m^2·g^-1）. HRTEM images indicated that the Ce0.6Zr0.4O2 solid solution ultrafine particle is well-crystallized, narrow size distribution, less agglomeration, within mean size of 5 -7 nm.

Investigation of lattice capacity effect on Cu2+-doped SnO2 solid solution catalysts to promote reaction performance toward NOx-SCR with NH3

To understand the effect of the doping amount of Cu^2+ on the structure and reactivity of SnO2 in NOx-SCR with NH3, a series of Sn-Cu-O binary oxide catalysts with different Sn/Cu ratios have been prepared and thoroughly characterized. Using the XRD extrapolation method, the SnO2 lattice capacity for Cu^2+ cations is determined at 0.10 g Cu O per g of SnO2, equaling a Sn/Cu molar ratio of 84/16. Therefore, in a tetragonal rutile SnO2 lattice, only a maximum of 16% of the Sn4+ cations can be replaced by Cu^2+ to form a stable solid solution structure. If the Cu content is higher, Cu O will form on the catalyst surface, which has a negative effect on the reaction performance. For samples in a pure solid solution phase, the number of surface defects increase with increasing Cu content until it reaches the lattice capacity, as confirmed by Raman spectroscopy. As a result, the amounts of both active oxygen species and acidic sites on the surface, which critically determine the reaction performance, also increase and reach the maximum level for the catalyst with a Cu content close to the lattice capacity. A distinct lattice capacity threshold effect on the structure and reactivity of Sn-Cu binary oxide catalysts has been observed. A Sn-Cu catalyst with the best reaction performance can be obtained by doping the SnO2 matrix with the lattice capacity amount of Cu^2+.

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.

添加水蒸气对CH_4-CO_2重整催化剂Ni/CeO_2-ZrO_2-Al_2O_3中Ni组分结构影响的EXAFS研究

采用水热合成法制备了Ni/CeO2 -ZrO2 -Al2 O3催化剂。进行了添加和不添加水蒸气的CH4 -CO2 催化重整反应 ,测量了积碳量 ,并用EXAFS手段测试了催化剂Ni的K吸收边。结果表明 ,反应前后最近邻Ni-Ni配位距离无明显变化 ,而配位数却变化明显。无水蒸气反应后Ni-Ni配位数有较大幅度的减少 ;而添加了水蒸气 ,Ni-Ni配位数比反应前减少幅度小。水蒸气的添加能减少积碳量 ,稳定催化剂中Ni的结构 。

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.

水热法制备Ni/Zr_(0.4)Ce_(0.6)O_2-Al_2O_3催化剂上CH_4-CO_2重整反应研究:NiO含量的影响

采用水热合成法制备不同NiO含量的Ni Zr0 4 Ce0 6 O2 Al2 O3催化剂 ,使用X射线衍射 (XRD)和H2 的程序升温还原 (H2 TPR)对样品进行表征 ,研究了NiO的含量对催化剂结构和CH4 CO2 重整性能的影响。结构表征表明 ,少量Ni组分能在催化剂表面分散并进入CeO2 ZrO2 固熔体晶格间隙而被固熔体包裹 ,并使固熔体晶粒变小 ,促进了固熔体的低温还原 ,而过量的NiO暴露在外生成NiO颗粒。活性测试结果表明 ,NiO含量少的样品活性随反应进行有较高的增长。选择适当空速 ,能使CH4 CO2 以 1∶1反应。

High-pressure synthesis and properties of CeO_2-ZrO_2 solid solution

Using nanoparticles of CeO2 and ZrO2 prepared by the chemical precipitation method as starting materials, the single-phase cubic Ce0.5Zr0.5O2 solid solution (c-Ce0.5Z0.5O2) has been synthesized under 3.1 GPa at 1073 K for the first time. The structure of the c-Ce0.5Zr0.5O2 has not been changed before and after annealing at 773 K for 1 h. Only an unknown EPR signal (g =1.990) has been observed in the c-Ce0.5Zr0.5O2 and not varied after annealing at 773 K for 1 h, which exhibited that there exists no Ce3+ in the c-Ce0.5Zr0.5O2 and the Ce4+ has not been reduced into Ce3+ after annealing. The transport mechanism is ionic for the c-Ce0.5Zr0.5O2. The bulk conductivity (a =1.2×10-5 S/cm at 823 K, σ=2.1 ×10-3 S/cm at 1123 K) is the same as that of CeO2, but smaller than that of Y2O3-stabilized ZrO2. A marked curvature at T = 823 K has been observed in the Arrhenius plot of the bulk conductivity. The activation energy below 823 K is lower than that above 823 K, and the reason has been discussed.

铈锆固溶物载Pd催化剂的构造特征及其活性

以共沉淀法和滤纸作为模板剂的模板法制备铈锆固溶物 (Ce/Zr=1 )负载Pd催化剂 ,用XRD对其进行晶相分析 ,两种方法均形成立方萤石结构 .TPR实验揭示了滤纸模板法制备的铈锆固溶物高温老化催化剂更易被还原 .催化剂表面Pd的分散度和活性评价实验表明 ,催化剂表面贵金属的分散度在一定程度上决定催化剂的活性 ,载体物性影响Pd的分散度 ,滤纸模板法制备的铈锆固溶物负载Pd催化剂有较高的Pd分散度 ,表现出比共沉淀法制备的铈锆固溶物负载Pd催化剂好的三效活性 .

Effect of water vapor on the CO and CH_4 catalytic oxidation over CeO_2-MO_x (M=Cu, Mn, Fe, Co, and Ni) mixed oxide

CeO2-MOx (M=Cu, Mn, Fe, Co, and Ni) mixed oxide catalysts were prepared by a citric acid complexation-combustion method. CeO2-MOx solid solutions could be formed with M cations doping into CeO2 lattice, while NiO and Co3O4 phases were detected on the surface of CeO2-NiO and CeO2-Co3O4 by Raman spectroscopy. The presence of M in CeO2 could obviously promote its catalytic activity for CH4 catalytic combustion and CO oxidation. Among the prepared samples, CeO2-CuO exhibited the best performance for CO oxidatio...

Structures and oxygen storage capacities of CeO_2-ZrO_2-Al_2O_3 ternary oxides prepared by a green route:supercritical anti-solvent precipitation

CeO2-ZrO2-Al2O3 ternary oxides were successfully prepared by a green route of supercritical anti-solvent precipitation with supercritical CO2 as anti-solvent and methanol as solvent. The structures and oxygen storage capacities of these ternary oxides were characterized by XRD, Raman spectra and oxygen storage capacity measurements. It was found that Al3＋ and Zr4＋ inserted into CeO2 lattice, forming CeO2-ZrO2-Al2O3 solid solution. The concentration of aluminium isopropoxide in the solution affected the concentration of oxygen vacancy and the distortion of oxygen sublattice which were responsible for the oxygen storage capacity. The rapidest oxygen uptake/release rate and maximum total oxygen storage capacity （122.0 mmolO2/molCeO2） were obtained with the aluminitun isopropoxide concentration at 0.2 wt.% in the solution.

Catalytic Activity of Ceria-Zirconia Nanostructured Materials Prepared via Reversed Microemulsion Method

Single-phase homogeneous Ce1-x ZrxO2 solid versed microemulsion method. The structural properties solutions with various compositions were synthesized using the reand performance of Ce1- xZrxO2 were studied using XRD, BET, SEM, HRTEM, TPR and CO oxidation measurements. The results show that in the range of x = 0.4 - 0.5 and x = 0.6 - 1.0, the solid solutions posses the cubic and the tetragonal phase structure, respectively, Solids obtained by the reversed microemulsion method were more homogeneous on the whole range of composition, XRD investigations of the prepared materials did not show segregation of cerium or zirconium oxides, Highly uniform nanosize solid solution particles of ceria-zirconia with high specific area （146.7 m^2·g^-1） were attained under the conditions of this study. The TPR results and CO oxidation measurements indicate that the performance of the CeO2-ZrO2 mixed oxides is strongly related to the composition and structure of the oxides. Enhancement of the activity was found for the catalyst prepared by reversed microemulsion method as compared to the sample prepared by sol-gel method.

Activity and hydrothermal stability of CeO_2–ZrO_2–WO_3 for the selective catalytic reduction of NO_x with NH_3

A series of CeO2–ZrO2–WO3（CZW）catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction（SCR）of NO with NH3 over a wide temperature of 150–550℃.The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H2O.The fresh catalyst showed above 90% NOx conversion at 201–459℃,which is applicable to diesel exhaust NOx purification（200–440℃）.The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures（below 300℃）,while the activity was notably enhanced at high temperature（above 450℃）.The aged CZW catalyst（hydrothermal aging at 700℃ for 8 hr）showed almost 80% NOx conversion at 229–550℃,while the V2O5–WO3/TiO2 catalyst presented above 80% NOx conversion at 308–370℃.The effect of structural changes,acidity,and redox properties of CZW on the SCR activity was investigated.The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO2–ZrO2 solid solution,amorphous WO3 phase and optimal acidity.In addition,the formation of WO3 clusters increased in size as the hydrothermal aging temperature increased,resulting in the collapse of structure,which could further affect the acidity and redox properties.

Mn incorporated RuO_(2) nanocrystals as an efficient and stable bifunctional electrocatalyst for oxygen evolution reaction and hydrogen evolution reaction in acid and alkaline

The development of efficient and stable bifunctional overall water-splitting is a crucial goal for clean and renewable energy,which is a challenging task.Herein,we report an Mn-incorporated RuO_(2)(MnRuO_(2))catalyst for highly efficient electrocatalytic oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)in acid and alkaline media.Benefiting from a more electrochemical active area with the incorporation of Mn,the Mn-RuO_(2)required an overpotential of 200 mV to attain a current density of 10 mA/cm^(2)for OER in acid.DFT result indicates that the doping of Mn into RuO_(2)can enhance the OER activity.An acidic overall water-splitting electrolyzer with good stability constructed by bifunctional Mn-RuO_(2)only requires a cell voltage of 1.50 V to afford 10 m A/cm^(2)and can operate stably for 50 h at50 mA/cm^(2),which is better than the state-of-the-art Ru-based catalyst.Additionally,the Mn-Ru O_(2)exhibits excellent HER and OER activity in alkaline media,and it shows superior activity and durability for overall water-splitting,only needing a cell voltage of 1.49 V to attain 10 m A/cm^(2).The present work provides an efficient approach to designing and constructing efficient Ru-based electrocatalysts for overall water-splitting.

三氧化二铝含量对Ni/Zr_(0.4)Ce_(0.6)O_2-Al_2O_3催化剂的CH_4-CO_2重整反应性能影响

采用水热合成法 ,制备了不同 Al2 O3含量的 Ni/ Zr0 .4Ce0 .6 O2 - Al2 O3催化剂 .采用 X-射线衍射 (XRD)和扩展 X光吸收精细结构 (EXAFS) ,对催化剂样品进行结构表征 ;考察了 Al2 O3的加入对催化剂结构和 CH4- CO2 重整反应活性的影响 .结构表征和活性测试表明 ,催化剂中存在的主要晶相是 Zr0 .4Ce0 .6 O2 . Al2 O3的加入 ,使催化剂颗粒度变小 ,镍的分散度提高 ,并使反应活性有明显改进 ;而过量 Al2 O3的加入 。

Ce-Zr固溶体的纯度及其在三效催化剂中的作用

采用溶胶 -凝胶法和有机溶剂分解法 ,制备了 Ce- Zr固溶体 .应用 XRD和 L RS谱测试 ,详细研究了经不同温度焙烧后固溶体的结构、晶相和热稳定性 ,并进行了储氧量、比表面积的测定和催化活性评价 .结果表明 ,XRD和 L RS相结合 ,可以较好地表征固溶体的结构和纯度 ;固溶体的纯度、晶相和储氧量与制备方法有直接关系 ,溶胶 -凝胶法能制得纯度高的萤石型富铈固溶体 ,并且储氧量高 ,但热稳定性较有机溶剂分解法制得的固溶体差 ;含富铈固溶体的三效催化剂老化后的催化活性明显高于含纯 Ce O2

Catalytic oxidation of CO on mesoporous codoped ceria catalysts:Insights into correlation of physicochemical property and catalytic activity

Codoping approach is an appealing strategy to further improve the catalytic activity of Ce-based catalysts.In the present study,Mn and/or Cu doped ceria solid solutions MnxCuyCe1-x-yO2,CuxCe1-xO2,MnxCe1-xO2 and pure CeO2 were prepared by CTAB-assisted hydrothermal method for CO oxidation.XRD,SEM,EDS,BET,Raman,H2-TPR,XPS and in situ DRIFTS techniques were carried out to study the physicochemical properties and to correlate them to the activity.The doped samples maintain the cubic fluorite structure of CeO2 with high crystallinity and small crystallite size,forming Ce-based solid solutions.The obtained catalysts have large mesoporous structure with average pore size of 10-14 nm.The doped transition metal enhances the oxygen vacancies and improves reducibility of the solids.The synergistic interaction of Mn and Cu codoping induces mo re oxygen vacancies,pro moting the increase of surface adsorbed oxygen and the transfer of bulk oxygen of catalyst,thereby enhancing the catalytic activity for CO oxidation.Besides,the decomposition rate of the carbonate species which is derived from in situ DRIFTS for each catalyst can provide a measure to evaluate its catalytic activity of CO oxidation.