高分散隔离活性位催化剂中过渡金属离子结构对丙烷选择氧化反应性能的影响

考察了碱金属K修饰的SiO2负载极低含量过渡金属的高分散隔离活性位系列催化剂(K-M/SiO2(n(K)∶n(M)∶n(Si)=10∶1∶1000),M=V,Cr,Mn,Fe,Co,Ni,Cu,Zn)的丙烷选择氧化催化性能,并运用UV-Raman和CO2-TPD等方法,对该系列催化剂进行了结构和物化性能表征,探讨了催化剂的表面离子结构与催化反应性能之间的关系。 发现钾修饰的SiO2负载过渡金属高分散隔离活性位催化剂上过渡金属离子的组态结构,对丙烷选择氧化反应性能有重要影响。相对稳定的全充满或无d电子的表面离子结构有利于选择氧化反应进行,而存在多种价态的相对不稳定的离子结构有利于深度氧化的进行。 这一离子结构与丙烷选择氧化催化性能的关系与前期乙烷选择氧化规律相似,进一步说明在高分散隔离活性位催化剂中,过渡金属离子的电子组态结构是影响低碳烷烃选择氧化反应性能的最重要因素。     

不同RuO2含量对RuO2-Fe2O3催化剂氨选择性催化氧化性能的影响

采用溶胶-凝胶法（sol-gel）制备了一系列具有不同RuO₂含量的RuO₂-Fe₂O₃催化剂,并将其应用于氨选择性催化氧化（NH₃-SCO）研究中。结果表明,所有RuO₂-Fe₂O₃催化剂都表现出较好的低温活性,且RuO₂含量对催化剂的NH₃催化氧化活性影响显著。此外,利用BET、XRD、H₂-TPR和DRIFTS等表征手段研究了催化剂的物理化学性质和催化活性之间的关系。结果表明,RuO₂的加入增大了催化剂的比表面积。RuO₂与Fe₂O₃之间存在的协同效应提高了催化剂的氧化还原能力,从而提高了催化剂的氨氧化活性。同时,RuO₂含量对催化剂表面酸性影响很大,且催化剂表面主要存在Lewis酸性位点。     

Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen

The selective oxidation of propylene with O₂ to propylene oxide and acrolein is of great interest and importance. We report the crystal‐plane‐controlled selectivity of uniform capping‐ligand‐free Cu₂O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O₂: Cu₂O octahedra exposing {111} crystal planes are most selective for acrolein; Cu₂O cubes exposing {100} crystal planes are most selective for CO₂; Cu₂O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One‐coordinated Cu on Cu₂O(111), three‐coordinated O on Cu₂O(110), and two‐coordinated O on Cu₂O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO₂, respectively. These results reveal that crystal‐plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level.     

Cooperative Catalysis for Selective Alcohol Oxidation with Molecular Oxygen

The activation of dioxygen for selective oxidation of organic molecules is a major catalytic challenge. Inspired by the activity of nitrogen‐doped carbons in electrocatalytic oxygen reduction, we combined such a carbon with metal‐oxide catalysts to yield cooperative catalysts. These simple materials boost the catalytic oxidation of several alcohols, using molecular oxygen at atmospheric pressure and low temperature (80 °C). Cobalt and copper oxide demonstrate the highest activities. The high activity and selectivity of these catalysts arises from the cooperative action of their components, as proven by various control experiments and spectroscopic techniques. We propose that the reaction should not be viewed as occurring at an ‘active site’, but rather at an ‘active doughnut’–the volume surrounding the base of a carbon‐supported metal‐oxide particle.     

Characterizations and Catalytic Properties of Transition Metal Ions Incorporated in Mesoporous Materials

Mesoporous materials typified by MCM-41 possess well-ordered mesoporous channels with controllable pore sizes from 2-30 nm, and are expected as desirable materials for catalysis.However, silicious mesoporous materials generally do not have sufficient intrinsic catalytic activities.Thus many studies have focused on introducing catalytically active sites. It is expected that different synthetic methods would result in different coordination structures of metal cations introduced in MCM-41, and thus different catalytic properties in catalytic reactions. The author's group has used two methods, i.e., direct hydrothermal synthesis (DHT) and template-ion exchange (TIE), for the syntheses of V-, Fe-, and Cr-MCM-41 and applied them as catalysts to selective oxidations of hydrocarbons. This paper highlights the characterizations of the coordination structures of these metal cations introduced into MCM-41 by the DHT and the TIE methods, and the structural-property relationships of these metal ion-containing MCM-41 materials in selective oxidation reactions.MCM-41 was prepared by hydrothermal synthesis using hexadecyltrimethylammonium bromide and sodium silicate as the sources of template and silicon, respectively. In the DHT method, metal cations were directly added into the synthesis gel before hydrothermal synthesis, while the exchanging of metal ions in ethanolic solutions with the template cations contained in the uncalcined MCM-41 was performed in the TIE method. XRD and N2-adsorption measurements showed that the mesoporous regularity was not destroyed with both synthetic methods for all the metal ion-containing MCM-41 with appropriate contents of metal cations.For V-MCM-41, the characterizations with mainly EXAFS suggested that V5+ cations were in tetrahedral coordination and mainly incorporated inside the framework of MCM-41 to substitute Si4+in the samples by the DHT method. Tetrahedrally coordinated Vanadyl species were also obtained by the TIE method, but the VO4 was dispersed on the wall surface of MCM-41. The V-MCM-41-DHT showed higher selectivity in the partial oxidations of C3H8 and i-C4H10 to alkenes and acrolein and methacrolein, but the V-MCM-41-TIE exhibited better catalytic activities in the partial oxidation of CH4 to HCHO and the oxidative dehydrogenation of C2H6.For Fe-MCM-41, EXAFS studies indicated that the DHT method also resulted in Fe3+ cations incorporated inside the framework of MCM-41 if iron content was lower than ca. 1 wt%. However,aggregated iron oxides with iron in octahedral coordination were mainly observed in the calcined Fe-MCM-41 by the TIE method. In the partial oxidation of CH4 to HCHO with O2 and the epoxidation of styrene with H2O2, the Fe-MCM-41 by the DHT method exhibits remarkably higher catalytic performances than that by the TIE method.Chromium could not be incorporated inside the framework of MCM-41 to substitute Si4+, and both synthetic methods led to surface chromate species. However, the DHT method resulted in only monochromate species on the wall surface of MCM-41 while polychromate species existed over the sample by the TIE method as indicated by the UV-Raman spectroscopic studies. The two types of Cr-MCM-41 exhibited distinctly different catalytic behaviors in the partial oxidation of CH4 with O2.The Cr-MCM-41-DHT was remarkably more selective towards HCHO formation.     

Quantum chemical treatment of active sites in zeolites

A short review on the quantum chemical study of the Bronsted and Lewis acid sites (BAS and LAS) is presented. Various factors that strongly influence the power of BAS in zeolites are considered. Different possible ways of LAS formation in zeolites are dicussed. The probable mechanism of selective oxidation in FeHZSM-5 is considered and the resulting active site structure is calculatedab initio. The initial step of hydrogen peroxide activation in Ti-silicalite is studied and the scale of the energy of structural deformation to proceed during the reaction is evaluated.     

Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons

The size of the active phase is one of the most important factors in determining the catalytic behaviour of a heterogeneous catalyst. This Feature Article focuses on the size effects in two types of reactions, i.e., the metal nanoparticle-catalysed dehydrogenation of alcohols and the metal oxide nanocluster-catalysed selective oxidation of hydrocarbons (including the selective oxidation of methane and ethane and the epoxidation of propylene). For Pd or Au nanoparticle-catalysed oxidative or non-oxidative dehydrogenation of alcohols, the size of metal nanoparticles mainly controls the catalytic activity by affecting the activation of reactants (either alcohol or O(2)). The size of oxidic molybdenum species loaded on SBA-15 determines not only the activity but also the selectivity of oxygenates in the selective oxidation of ethane; highly dispersed molybdenum species are suitable for acetaldehyde formation, while molybdenum oxide nanoparticles exhibit higher formaldehyde selectivity. Cu(II) and Fe(III) isolated on mesoporous silica are highly efficient for the selective oxidation of methane to formaldehyde, while the corresponding oxide clusters mainly catalyse the complete oxidation of methane. The lattice oxygen in iron or copper oxide clusters is responsible for the complete oxidation, while the isolated Cu(I) or Fe(II) generated during the reaction can activate molecular oxygen forming active oxygen species for the selective oxidation of methane. Highly dispersed Cu(I) and Fe(II) species also function for the epoxidation of propylene by O(2) and N(2)O, respectively. Alkali metal ions work as promoters for the epoxidation of propylene by enhancing the dispersion of copper or iron species and weakening the acidity.     

溶胶-凝胶法制备Fe2(MoO4)3超微粒子催化剂

以硝酸铁和钼酸铵为原料，采用溶胶－凝胶法和微波加热技术制备了F 2(MoO4)3超微子催化剂，使用DTA－TG，IR，XRD以及BET比表面测试等手段，考察了制备条件对复合氧化物超微粒子形成、晶相和比表面积的影响。同时测试了该样品对甲苯选择性氧化制苯甲醛的催化性能。结果表明：制备Fe2(MoO4)2超微粒子的适宜条件为：初始溶液pH=1.0,mol柠檬酸：mol(铁＋钼）＝0．4。在此条件下制得的干凝胶，经微波加热处理后粒子的比表面积为36.4m^2/g，粒径约为35nm。在由甲苯气相选择氧化制苯甲醛的反应中表现出较高的催化活性。     

Co-Ce-O超细微粒催化剂的结构与催化性能

应用ＴＥＭ、ＸＲＤ、ＸＰＳ、ＢＥＴ表面积测试和微型催化反应装置研究了Ｃｏ－Ｃｅ－Ｏ复合氧化物超细微粒催化剂结构及其４－甲基苯酚（ＰＭＰ）选择氧化制４－羟基苯甲醛（ＰＨＢ）的催化性能,结果表明Ｃｏ－Ｃｅ－Ｏ复合氧化物超细微粒催化剂的选择氧化催化活性与催化剂粒子大小、组成和结构密切相关,在Ｃｏ／（Ｃｏ＋Ｃｅ）原子比为０．３３时选择氧化催化活性达极大值,Ｃｏ－Ｃｅ－Ｏ复合氧化物超细微粒催化剂优良的选择氧化催化活性不仅仅是因为其粒子较小、比表面积较大,而且还因为高分散粒催化剂优良的选择氧化催化活性不仅仅是因为其粒子较小、比表面积较大、而且还因为高分散的Ｃｏ、Ｃｅ组份发生了相互作用,催化剂具有较主贩表面吸附态氧物浓度,经高温（〉５００℃）处理,Ｃｏ－Ｃｅ－Ｏ复合氧化物超细微粒发生烧结、比表面积减小且Ｃｏ－Ｃｅ相互作用遭到     

2,2,6,6-四甲基哌啶氧自由基/Ca(ClO)2催化氧化甲基葡糖苷制备葡醛酸

采用2,2,6,6-四甲基哌啶氧自由基/Ca(ClO)2体系选择氧化甲基葡萄糖苷(简称甲苷)合成了葡萄糖甲苷酸盐,再用硫酸酸解葡萄糖甲苷酸盐,得到葡萄糖醛酸和副产物硫酸钙。考察了氧化工艺条件对葡萄糖醛酸收率的影响;用pH计监控反应过程,反应中间体和终产物用UV和HPLC检测。结果表明,该体系对甲苷伯羟基的氧化具有较好的催化活性和反应选择性,葡萄糖醛酸收率达到92%,且金属离子易于去除。和传统的淀粉HNO3氧化法工艺相比,该方法具有资源节约、环境友好的特点。     

过渡金属型汽车尾气净化催化材料的制备及性能研究

采用固定床反应装置,模拟汽车尾气的组成成分,以CO/NH3为探针反应,分别研究了活性成分负载量及焙烧温度等因素对过渡金属氧化物催化材料MnOx/γ-Al2O3和Mn-Ce-O(x)/γ-Al2O3的催化活性的影响,并考察了该催化剂的抗硫化中毒性能和抗老化性能。在该研究条件下,氧化物负载量在0.12(质量分数),焙烧温度在700℃左右时,催化剂对NO-CO体系中CO的氧化率在85%以上。将催化剂在3.0%的SO2/空气气氛中强制中毒后,其对CO/NO体系中CO的催化转化率明显下降,但抗老化实验表明,该催化剂经900℃下,12%水蒸汽老化 60 h后,对CO的催化活性不仅没有下降,反而略有升高,说明该催化剂具有良好的抗老化性能和高温活性。     

Ce_2Mo_3O_(12)超微粒子的制备及催化性能

以硝酸铈和钼酸铵为原料 ,采用溶胶 -凝胶法和微波加热技术制备了Ce2 Mo3 O12 超微粒子催化剂 ,使用DTA -TG ,IR ,XRD以及BET比表面测试等表征手段 ,考察了制备条件对复合氧化物超微粒子形成 ,晶相和比表面积的影响 .同时 ,测试了该样品对甲苯选择性氧化制苯甲醛反应的催化性能 .结果表明 :制备Ce2 Mo3 O12 超微粒子的适宜条件为 :初始溶液pH =1.0 ,柠檬酸 / (铈 +钼 )摩尔比等于 0 .4 ,在此条件下制得的干凝胶 ,经微波加热处理后 ,粒子的比表面积为 35 .8m2 /g ,粒径约为 4 0nm .在由甲苯气相选择氧化制苯甲醛的反应中表现出较好的催化活性     

Selective oxidation of propane to acrylic acid over mixed metal oxide catalysts

The effects of metal atomic ratio, water content, oxygen content, and calcination temperature on the catalytic performances of MoVTeNbO mixed oxide catalyst system for the selective oxidation of propane to acrylic acid have been investigated and discussed. Among the catalysts studied, it was found that the MoVTeNbO catalyst calcined at a temperature of 600 ℃ showed the best performance in terms of propane conversion and selectivity for acrylic acid under an atmosphere of nitrogen. An effective MoVTeNbO oxide catalyst for propane selective oxidation to acrylic acid was obtained with a combination of a preferred metal atomic ratio （Mo1V0.31Te0.23Nb0.12）. The optimum reaction condition for the selective oxidation of propane was the molar ratio of C3H8 ：O2 ： H2O ： N2 = 4.4： 12.8 ： 15.3 ： 36.9. Under such conditions, the conversion of propane and the maximum yield of acrylic acid reached about 50% and 21%, respectively.     

Conductive 2D Metal-organic Framework (Co,NiCo, Ni) Nanosheets for Enhanced Non-enzymatic Detection of Urea

2D metal-organic framework (MOF) has potential applications in electrocatalysis owing to fast mass transfer, charge transfer and large specific surface area. Here, we had prepared three conductive 2D MOF based on Ni, NiCo and Co in a simple and rapid way. The 2D nanostructure of MOF was confirmed by SEM and TEM. The chemical composition was studied by XRD, Raman and XPS spectrum. The electrochemical oxidation and detection was investigated through cyclic voltammetry and current-time method. Their sensing performance for urea was determined by varying oxidation potentials and metal sites. The non-enzymatic Ni-, NiCo- and Co-MOF sensors had good catalytic activity for urea. Compared with NiCo- and Co-MOF, Ni-MOF had a wider linear range (0.5–832.5 μM), high sensitivity (1960 μA mM⁻¹ cm⁻²), low detection limit (0.471 μM), and fast response time. The sensors had well repeatability, reproducibility, and selectivity to specific interfering species. Furthermore, Ni- and NiCo-MOF modified electrode was also applied to detection of milk samples. The results showed that the recovery was satisfactory, which further confirmed the effectiveness of non-enzyme sensor. In general, the highly-sensitive 2D Ni- and NiCo-MOF modified electrode has great potential as nonenzymatic urea sensors for real samples detection in hydrogen energy, clinical diagnostics, and environmental protection, et al.     

Selective oxidation of ethylbenzene by dioxygen in the presence of complexes of nickel and cobalt with macrocyclic polyethers

The oxidation of alkylarenes by dioxygen in the presence of complexes of nickel and cobalt with macrocyclic ethers 18-crown-6 and 15-crown-5 was studied. The conditions for selective catalytic oxidation of ethylbenzene to α-phenylethyl hydroperoxide were determined. The kinetics of the accumulation of all oxidation products was studied. The order of the formation of the products at different stages of chain oxidation was determined. The activity of the complexes at the elementary stages of the chain oxidation of ethylbenzene is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 689–693, April. 1997.     

CO Selective Oxidation in Hydrogen-Rich Gas over Copper-Series Catalysts

The performances of CO selective oxidation in hydrogen-rich gas over four catalytic systems of CuO/ZrO2, CuO/MnO2, CuO/CoO and CuO/CeO2 were compared. The reducibility of these catalysts and the effect of CuO and CeO2 molar ratio of CuO/CeO2 catalysts on the activity of selective CO oxidation are investigated by XRD and TPR methods. The results show that the catalysts with the exception of CuO/ZrO2 have the interactions between CuO and CoO, CeO2 or MnO2, which result in a decrease in the reduction temperature. Among the catalysts studied, CuO/ZrO2 catalyst shows the lowest catalytic activity while CuO/CeO2 catalyst exhibits the best catalytic performance. The CuO(10%)/CeO2 catalyst attains the highest CO conversion and selectivity at 140 and 160℃. The addition of 9% H2O in the reactant feed decreases the activity of CuO/CeO2 catalyst but increases its CO selectivity.     

Selective oxidation of ethylbenzene by dioxygen. The effect of chelate center on catalysis by bicyclic nickel complexes

The effect of the nature of the chelate center in Ni^II complexes on their catalytic activity in the selective oxidation of ethylbenzene by dioxygen to α-phenylethyl hydroperoxide in the presence of nickel bis(acetylacetonate) (chelate center Ni(O,O)₂) and nickel bis(enaminoacetonate) (chelate center Ni(O,NH)₂) was studied. The efficiency of selective oxidation of ethylbenzene increases substantially in the presence of the chelate with the Ni(O,NH)₂ active center as a catalyst, which is mainly due to the transformation of the catalyst into more active species during the oxidation process. The mechanism of transformation of nickel bis(enaminoacetonate) under the action of dioxygen was suggested. The sequence of formation of the reaction products at different stages of the catalytic process was determined. The activity of the nickel complex with the Ni(O,NH)₂ chelate center and the products of its transformation in the elementary stages of chain oxidation of ethylbenzene is discussed. Translated fromIzvestiya Akedemii Nauk. Seriya Khimicheskaya, No. 1, pp. 55–60, January, 1999.     

Selective Oxidation of Isobutane over NH4CsFePVMoAs Heteropolycompound Catalysts

A series of NH4Cs1.5Fe0.08HxPVMo11AsαOy heteropolycompound catalysts for the selective oxidation of isobutane, having Keggin structure, were synthesized by using co-precipitation method. The catalysts were characterized by FT-IR, H2-TPR, TG-DTA, SEM and XRD. Effects of the As content,reaction time, reaction temperature and molar ratio of isobutane to oxygen in feedstock on the activity and selectivity of the catalyst were investigated. The activation energy of the catalysts was measured by kinetics researches. Results showed the introduction of Cs^ into the catalysts shortened the stable period of them and enhanced their catalytic activity for the selective oxidation of isobutane. The highest conversion of isobutane and the total selectivity to liquid products were 18.6% and 81.2%, respectively,which were obtained at 380 *(3 with a space velocity of 975h^-1 over the NH4Cs1.5Fe0.08HxPVMo11 As0.3Oy heteropolycompound catalyst. It is confirmed that completely oxidized products were controlled well.     

Relationship between sulfur dioxide oxidation and selective catalytic NO reduction by ammonia on V2O5?TiO2 catalysts doped with WO3 and Nb2O5

The performance of V₂O₅–TiO₂ catalysts doped by WO₃ and Nb₂O₅ in sulfur dioxide oxidation, and in selective catalytic reduction (SCR) of NO by ammonia has been studied. Addition of tungsten and niobium oxides was found to suppresses sulfur dioxide oxidation thus increasing the catalysts resistance to SO₂ poisoning and their activity in SCR.     

焙烧温度对Au/Fe2O3选择性氧化富氢气体中CO催化性能的影响

甲醇重整在线制氢作为质子交换膜燃料电池的燃料成为当前研究的热点。受重整反应动力学及热力学的限制，使得甲醇重整气(富氢气体)中除含有大量的氢气外还含有少量的CO，CO极易吸附在燃料电池阳极催化剂表面，使电池性能下降，因而必须去除重整气中的CO，选择性氧化脱除富氢气