扫帚状氧化铈制备及其对Pt基阳极催化剂催化性能的影响

采用水热合成法,合成了比表面积为175 m²·g^-1,孔径在2~4nm范围内的扫帚状CeO₂。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO₂/RGO催化剂,探究扫帚状CeO₂的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪（XRD）、扫描电镜（SEM）、N₂吸附-脱附、X射线光电子能谱（XPS）对所制备的CeO₂及催化剂进行表征。利用电化学工作站对催化剂进行电化学性能测试。结果表明,催化剂中CeO₂保持原有扫帚状,Pt纳米粒子均匀分布于石墨烯载体表面;当m_RGO∶m_CeO2=1∶2时,添加了扫帚状CeO₂的Pt-CeO₂/RGO催化剂的电催化性能最优,电化学活性表面积为102.83 m²·g^-1,对乙醇氧化的峰值电流密度为757.17 A·g^-1,1 000 s的稳态电流密度为108.17 A·g^-1,对乙醇催化氧化反应的电荷转移电阻最小,活化能最低。     

扫帚状氧化铈制备及其对Pt基阳极催化剂催化性能的影响

采用水热合成法,合成了比表面积为175 m~2·g~(-1),孔径在2~4nm范围内的扫帚状CeO_2。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO_2/RGO催化剂,探究扫帚状CeO_2的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪(XRD)、扫描电镜(SEM)、N_2吸附-脱附、X射线光电子能谱(XPS)对所制备的CeO_2及催化剂进行表征。利用电化学工作站对催化剂进行电化学性能测试。结果表明,催化剂中CeO_2保持原有扫帚状,Pt纳米粒子均匀分布于石墨烯载体表面;当m_(RGO)∶m_(CeO2)=1∶2时,添加了扫帚状CeO_2的Pt-CeO_2/RGO催化剂的电催化性能最优,电化学活性表面积为102.83 m~2·g~(-1),对乙醇氧化的峰值电流密度为757.17A·g~(-1),1 000 s的稳态电流密度为108.17 A·g~(-1),对乙醇催化氧化反应的电荷转移电阻最小,活化能最低。     

Single-Atom Rh on High-Index CeO2 Facet for Highly Enhanced Catalytic CO Oxidation

Reducible oxide-supported noble metal nanoparticles exhibit high activity in catalyzing many important oxidation reactions. However, atom migration under harsh reaction conditions leads to deactivation of the catalyst. Meanwhile, single-atom catalysts demonstrate enhanced stability, but often suffer from poor catalytic activity owing to the ionized surface states. In this work, we simultaneously address the poor activity and stability issues by synthesizing highly active and durable rhodium (Rh) single-atom catalysts through a “wrap-bake-peel” process. The pre-coated SiO₂ layer during synthesis of catalyst plays a crucial role in not only protecting CeO₂ support against sintering, but also donating electron to weaken the Ce−O bond, producing highly loaded Rh single atoms on the CeO₂ support exposed with high-index {210} facets. Benefiting from the unique electronic structure of CeO₂ {210} facets, more oxygen vacancies are generated along with the deposition of more electropositive Rh single atoms, leading to remarkably improved catalytic performance in CO oxidation.     

Construction of Cu-Ce interface for boosting toluene oxidation: Study of Cu-Ce interaction and intermediates identified by in situ DRIFTS

A facile hydrothermal method was applied to gain stably and highly efficient CuO-CeO₂ (denoted as Cu1Ce2) catalyst for toluene oxidation. The changes of surface and inter properties on Cu1Ce2 were investigated comparing with pure CeO₂ and pure CuO. The formation of Cu-Ce interface promotes the electron transfer between Cu and Ce through Cu²⁺ + Ce³⁺ ↔ Cu⁺ + Ce⁴⁺ and leads to high redox properties and mobility of oxygen species. Thus, the Cu1Ce2 catalyst makes up the shortcoming of CeO₂ and CuO and achieved high catalytic performance with T₅₀ = 234 °C and T₉₉ = 250 °C (the temperature at which 50% and 90% C₇H₈ conversion is obtained, respectively) for toluene oxidation. Different reaction steps and intermediates for toluene oxidation over Cu1Ce2, CeO₂ and CuO were detected by in situ DRIFTS, the fast benzyl species conversion and preferential transformation of benzoates into carbonates through C=C breaking over Cu1Ce2 should accelerate the reaction.     

Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking

Ni‐CeO₂ is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO₂ at temperatures as low as 300 K, generating CH_x and CO_x species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO_2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CH_x or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.     

Roles of Oxygen Vacancies of CeO2 and Mn-Doped CeO2 with the Same Morphology in Benzene Catalytic Oxidation

Mn-doped CeO₂ and CeO₂ with the same morphology (nanofiber and nanocube) have been synthesized through hydrothermal method. When applied to benzene oxidation, the catalytic performance of Mn-doped CeO₂ is better than that of CeO₂, due to the difference of the concentration of O vacancy. Compared to CeO₂ with the same morphology, more oxygen vacancies were generated on the surface of Mn-doped CeO₂, due to the replacement of Ce ion with Mn ion. The lattice replacement has been analyzed through XRD, Raman, electron energy loss spectroscopy and electron paramagnetic resonance technology. The formation energies of oxygen vacancy on the different exposed crystal planes such as (110) and (100) for Mn-doped CeO₂ were calculated by the density functional theory (DFT). The results show that the oxygen vacancy is easier to be formed on the (110) plane. Other factors influencing catalytic behavior have also been investigated, indicating that the surface oxygen vacancy plays a crucial role in catalytic reaction.     

Adsorption and migration growth of the Ce,O, and F adatoms on the CeO2 (111) surface: A density functional theory study

In order to investigate the microscopic behavior of the crystal surface growth of the fluorinated cerium dioxide polishing powder, the adsorption and migration of the Ce, O, and F atoms on the CeO₂ (111) surface were studied by using density functional theory with Hubbard correction +U. The adsorption energies of three single atoms at five high-symmetry sites and the migration activation energies along the migration pathway on the CeO₂ (111) surface were calculated. Results show that the most stable adsorption sites of the Ce, O, and F atoms were the O_h, Ce_bri, and Ce_t sites, respectively. The Ce atom migrated from the O_h to the O_t site. The O atom migrated from the Ce_bri to the O_bri site. The F atom migrated from the Ce_t to the O_h site. The migration activation energies of the Ce, O, and F atoms along the migration pathways were 1.526, 0.597, and 0.263 eV, respectively. The F adatom does not change the spatial configuration of the Ce and the O atoms. When the O vacancy occurs on the CeO₂ (111) surface, the F adatom can make up for the O vacancy defect.     

The Claus Reaction: VI. The Reaction Mechanism over a Sn–Mo Oxide Catalyst

Based on the comparison of reactant conversions in pulses on the stationary surface of the catalyst, the Claus reaction is found to occur via a stepwise mechanism. The nature of interaction of the SO₂ and H₂S molecules with the catalyst surface was studied by FTIR and UV–VIS spectroscopy and the reactivity of the adsorbed species was studied in situ. The intermediate adsorbed reactant species are determined. A scheme of the reaction mechanism over the Sn–Mo oxide catalyst is discussed.     

Effect of promoters on the catalytic performance of Ni/Al2O3 catalyst for partial oxidation of methane to syngas

The effect of promoters such as Ce, La and Ca on catalytic performance of Ni catalyst was measured in a continuous fixed bed reactor. The effect of promoters on Ni/a-Al₂O₃ catalyst is more significant than on Ni/g-Al₂O₃ catalyst. Ce was proved to be the best promoter among the three promoters tested and the optimum loading of Ce was 1%. The catalyst was characterized by TG, XPS, TPR and XRD techniques. TPR results showed that Ce can improve the reducibility of the Ni/Al₂O₃ catalyst. XRD results indicated that Ce was highly dispersed when its loading was low, but at higher loading it was crystallized into bulk CeO₂, thus, decreased the catalytic activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Understanding the Solvent Effect on the Catalytic Oxidation of 1,4‐Butanediol in Methanol over Au/TiO2 Catalyst: NMR Diffusion and Relaxation Studies

The effect of water on the catalytic oxidation of 1,4‐butanediol in methanol over Au/TiO₂ has been investigated by catalytic reaction studies and NMR diffusion and relaxation studies. The addition of water to the dry catalytic system led to a decrease of both conversion and selectivity towards dimethyl succinate. Pulsed‐field gradient (PFG)‐NMR spectroscopy was used to assess the effect of water addition on the effective self‐diffusivity of the reactant within the catalyst. NMR relaxation studies were also carried out to probe the strength of surface interaction of the reactant in the absence and presence of water. PFG‐NMR studies revealed that the addition of water to the initial system, although increasing the dilution of the system, leads to a significant decrease of effective diffusion rate of the reactant within the catalyst. From T₁ and T₂ relaxation measurements it was possible to infer the strength of surface interaction of the reactant with the catalyst surface. The addition of water was found to inhibit the adsorption of the reactant over the catalyst surface, with the T₁/T₂ ratio of 1,4‐butanediol decreasing significantly when water was added. The results overall suggest that both the decrease of diffusion rate and adsorption strength of the reactant within the catalyst, due to water addition, limits the access of reactant molecules to the catalytic sites, which results in a decrease of reaction rate and conversion.     

Ce掺杂对碳纳米管负载Mn催化剂结构及SCR反应性能的影响

采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂,考察了Ce掺杂对Mn/MWCNTs催化剂上NH₃选择性催化还原(SCR)NO_x反应活性的影响.并运用透射电镜扫描、N₂吸附-脱附、程序升温还原、X射线光电子能谱、X射线衍射等手段,重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响.结果表明,Ce掺杂能显著提高催化剂的SCR活性,其活性增量随着Ce含量的增加先增大后减小;当Ce/Mn为0.6时,催化剂活性最佳.表征结果显示,Mn/MWCNTs中添加Ce后,金属氧化物在MWCNTs上的分散程度提高;催化剂的比表面积和孔体积增大,平均孔径减小;氧化能力提高;表面氧含量增加,Mn化合价升高;结晶度降低,Mn主要以无定形或微晶形式存在,Ce主要以CeO₂物相存在.     

Au/CeO2中强金属-载体相互作用的形貌效应

以Au/CeO₂为研究对象,通过构建不同形貌的CeO₂载体来研究强金属-载体相互作用（SMSI）的形貌效应。分别以纳米立方块和纳米棒作为载体,通过高分辨（扫描）透射电子显微、光电子能谱、氢程序升温还原等一系列表征方法揭示了CeO₂纳米立方块表面更易发生质量传输并形成CeO_2-x包覆层。此包覆层大幅抑制了催化剂对小分子气体的吸附能力,并减少了催化活性位点的暴露,对探针反应（丁二烯选择性催化加氢）的催化活性影响显著。以上研究结果表明CeO₂纳米立方块比CeO₂纳米棒更易构建SMSI体系。     

改性SCR催化剂对Hg0催化氧化性能的研究

采用一系列金属氧化物对商用SCR催化剂进行掺杂改性,筛选出最优Ce掺杂SCR催化剂,模拟实际烟气组分,考察了Ce改性催化剂对烟气中Hg⁰氧化的影响。实验结果表明,Ce掺杂比例适当可显著提高其催化活性,Ce最佳负载量为9%时,Hg⁰的催化氧化效率比未掺杂SCR催化剂提高近40%,BET和XRD也显示,CeO₂在催化剂表面分散程度较好,未出现聚集现象。烟气工况对Hg⁰的催化氧化具有重要影响,其中,烟气组分HCl显著促进了Ce改性催化剂对Hg⁰的氧化,在一定温度范围内,Hg⁰的氧化效率随着温度升高而增加,在最佳空速、温度和烟气组分浓度时,Hg⁰的催化氧化效率可达95.11%。此外,掺杂CeO₂之后SCR催化剂的脱硝性能并未受到影响。     

合成方法对Rh/CeO2-ZrO2-La2O3催化剂的结构、表面性能及DeNOx活性的影响

用沉积沉淀法合成两种不同系列的CeO2-ZrO2-La2O3混合氧化物(ZrO2和La2O3沉积CeO2粒子(标记为A-x)以及CeO2和La2O3沉积ZrO2粒子(标记为B-x)),并用作Rh催化剂的载体。XRD、拉曼、TPR、XPS和O2脉冲等表征结果显示出不同的沉积顺序将导致不同的结构和氧化还原性能,且B-x具有更高的氧迁移性、储氧能力和表面Ce浓度。当其负载Rh后,Rh/B-x催化剂具有更高的NO和CO转化率及N2选择性,且Ce的最佳含量为50at%。这可能归因于Rh负载于富铈表面形成更多有利于NO分解的表面Ce3+活性位。     

Surface Reconstruction of Ultrathin Palladium Nanosheets during Electrocatalytic CO2 Reduction

A surface reconstructing phenomenon is discovered on a defect-rich ultrathin Pd nanosheet catalyst for aqueous CO₂ electroreduction. The pristine nanosheets with dominant (111) facet sites are transformed into crumpled sheet-like structures prevalent in electrocatalytically active (100) sites. The reconstruction increases the density of active sites and reduces the CO binding strength on Pd surfaces, remarkably promoting the CO₂ reduction to CO. A high CO Faradaic efficiency of 93 % is achieved with a site-specific activity of 6.6 mA cm⁻² at a moderate overpotential of 590 mV on the reconstructed 50 nm Pd nanosheets. Experimental and theoretical studies suggest the CO intermediate as a key factor driving the structural transformation during CO₂ reduction. This study highlights the dynamic nature of defective metal nanosheets under reaction conditions and suggests new opportunities in surface engineering of 2D metal nanostructures to tune their electrocatalytic performance.     

Revealing the Active Species for Aerobic Alcohol Oxidation by Using Uniform Supported Palladium Catalysts

The active species in supported metal catalysts are elusive to identify, and large quantities of inert species can cause significant waste. Herein, using a stoichiometrically precise synthetic method, we prepare atomically dispersed palladium–cerium oxide (Pd₁/CeO₂) and hexapalladium cluster–cerium oxide (Pd₆/CeO₂), as confirmed by spherical‐aberration‐corrected transmission electron microscopy and X‐ray absorption fine structure spectroscopy. For aerobic alcohol oxidation, Pd₁/CeO₂ shows extremely high catalytic activity with a TOF of 6739 h^?1 and satisfactory selectivity (almost 100 % for benzaldehyde), while Pd₆/CeO₂ is inactive, indicating that the true active species are single Pd atoms. Theoretical simulations reveal that the bulkier Pd₆ clusters hinder the interactions between hydroxy groups and the CeO₂ surface, thus suppressing synergy of Pd‐Ce perimeter.     

高热稳定性的铈铝复合氧化物用于柴油机尾气中碳烟的消除

采用柠檬酸络合燃烧法制备了一系列铝铈复合氧化物(铝掺杂的氧化铈),并通过程序升温氧化反应在紧密接触的模式下研究了其催化氧化碳烟的活性.结果表明,氧化铝和氧化铈之间存在强烈的相互作用,部分铝可以进入氧化铈晶格形成铝铈固溶体,大部分铝以γ-Αl2O3形式存在.与纯氧化铈相比,铝铈复合氧化物具有较好的催化燃烧活性,这是由于γ-Αl2O3能作为"扩散阻碍"阻止氧化铈粒子之间的接触而增强其热稳定.晶格氧的活动性决定了铝铈复合氧化物的催化活性,当铝与铈的摩尔比为1:30时,复合氧化物的催化活性最高.     

Ni/CeO2-SiO2催化剂的制备、表征及其甲烷部分氧化制合成气性能

以硝酸亚铈（Ce（NO₃）₃·6H₂O）和正硅酸四乙酯（C₈H₂₀O₄Si）为前驱体,采用溶胶-凝胶法合成了系列具有大比表面积的xCeO₂-（1-x）SiO₂（x = 0,0.25,0.50,0.75,1）复合氧化物载体,然后浸渍活性组分Ni制得用于甲烷部分氧化制合成气的Ni催化剂。运用N₂物理吸附-脱附、X射线粉末衍射、扫描电镜、紫外-可见漫反射光谱、氢程序升温还原、氨程序升温脱附和热重等手段对所得催化剂的组织结构、还原性、表面酸性和积炭行为等进行了表征;同时考察了催化剂的组成、焙烧温度和反应时间等对催化剂在甲烷部分氧化制合成气中催化性能的影响。表征结果表明,该系列Ni/CeO₂-SiO₂催化剂具有大比表面积,CeO₂晶粒较小,NiO的分散性好且易被还原,表面酸性弱,不容易积炭。当Ce/Si摩尔比为1：1,活性组分Ni的质量分数为10%,焙烧温度为700℃时,所制备的Ni/CeO₂-SiO₂催化剂表现出较好的稳定性、最高的CH₄转化率（~84%）和对产物CO及H₂的选择性（>87%）。     

Controllable Synthesis of Nearly Monodisperse Spherical Aggregates of CeO2 Nanocrystals and Their Catalytic Activity for HCHO Oxidation

Herein, we report a facile surfactant‐assisted solvothermal synthetic method to prepare nearly monodisperse spherical CeO₂ nanocrystals. A good control of the size of CeO₂ nanocrystals in the range of 100–500 nm was achieved by simply varying the synthetic parameters such as reaction time, volume ratio of ethanol to water (R), molar ratio of PVP, and concentration of Ce(NO₃)₃?6 H₂O in solution. A possible mechanism for the growth of spherical CeO₂ nanocrystals is proposed. The obtained CeO₂ nanocrystals with a surface area of up to 47 m²g^?1 were then employed as a catalyst support. By loading Au‐Pd nanoparticles (about 3 wt. %) onto the CeO₂ support, an Au‐Pd/CeO₂ catalyst was prepared that exhibited high catalytic activity for HCHO oxidation. At the low temperature of 50 °C, the percentage of HCHO conversion was 100 %, suggesting potential applications in preferential oxidation and other catalytic reactions. These Au‐Pd/CeO₂ catalysts may also find applications in indoor formaldehyde decontamination and industrial catalysis. The facile solvothermal method can be extended to the preparation of other metal oxide nanocrystals and provides guidance for size‐ and morphology‐controlled synthesis.