Selective Oxidation of Propane by Lattice Oxygen of Vanadium-Phosphorous Oxide in a Pulse Reactor

Selective oxidation of propane by lattice oxygen of vanadium-phosphorus oxide (VPO) catalysts was investigated with a pulse reactor in which the oxidation of propane and the re-oxidation of catalyst were implemented alternately in the presence of water vapor. The principal products are acrylic acid (AA),acetic acid (HAc), and carbon oxides. In addition, small amounts of C1 and C2 hydrocarbons were also found, molar ratio of AA to HAc is 1.4-2.2. The active oxygen species are those adsorbed on catalyst surface firmly and/or bound to catalyst lattice, i.e. lattice oxygen; the selective oxidation of propane on VPO catalysts can be carried out in a circulating fluidized bed (CFB) riser reactor. For propane oxidation over VPO catalysts, the effects of reaction temperature in a pulse reactor were found almost the same as in a steady-state flow reactor. That is, as the reaction temperature increases, propane conversion and the amount of C1 C2 hydrocarbons in the product increase steadily, while selectivity to acrylic acid and to acetic acid increase prior to 350℃ then begin to drop at temperatures higher than 350℃, and yields of acrylic acid and of acetic acid attained maximum at about 400℃. The maximum yields of acrylic acid and of acetic acid for a single-pass are 7.50% and 4.59% respectively, with 38.2% propane conversion. When theamount of propane pulsed decreases or the amount of catalyst loaded increases, the conversion increases but the selectivity decreases. Increasing the flow rate of carrier gases causes the conversion pass through a minimum but selectivity and yields pass through a maximum. In a fixed bed reactor, it is hard to obtainhigh selectivity at a high reaction conversion due to the further degradation of acrylic acid and acetic acid even though propane was oxidized by the lattice oxygen. The catalytic performance can be improved inthe presence of excess propane. Propylene can be oxidized by lattice oxygen of VPO catalyst at 250℃, nevertheless, selectivity to AA and to HAc are even lower, much more acetic acid was produced (molar ratio of AA to HAc is 0.19:1-0.83:1) though the oxidation products are the same as from propane.     

BiMo 基复合氧化物催化剂晶格氧性质与丙烷选择氧化性能

研究了不同组成、结构的BiMo基复合氧化物催化剂的丙烷选择氧化至丙烯醛的性能.X射线衍射(XRD)、X光电子能谱(XPS)、原位傅里叶变换激光拉曼光谱(FT-LRS)、电子顺磁共振(ESR)等多种表征结果表明,BiMo基复合氧化物催化剂上丙烷经由中间物丙烯选择氧化至丙烯醛,催化剂的晶格氧为选择性活性氧物种.丙烷直接氧化下丙烷至丙烯醛的选择性和收率与催化剂的Mo=O物种的氧化-还原性质密切关联,而Mo=O物种的性质又取决于Mo离子的配位环境,Mo=O物种的选择性转化丙烷经由丙烯至丙烯醛活性随畸变MoO6八面体、共顶点八面体、共边八面体、MoO4四面体配位环境递增.组成、结构优化调变的催化剂上丙烷选择氧化至丙烯醛选择性和收率可达45%和13.5%,催化剂中具有选择氧化活性的晶格氧物种数可达258 μmol/g.     

Preparation and characterization of nano-sized Pt-Ru/C catalysts and their superior catalytic activities for methanol and ethanol oxidation

Carbon-supported PtRu nanoparticles (Ru/Pt: 0.25) were prepared by three different methods; simultaneous reduction of PtCl(4) and RuCl(3) (catalyst I) and changing the reduction order of PtCl(4) and RuCl(3) (catalysts II and III) to enhance the performance of the anodic catalysts for methanol and ethanol oxidation. Structure, microstructure and surface characterizations of all the catalysts were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results of the XRD analysis showed that all catalysts had a face-centered cubic (fcc) structure with different and smaller lattice parameters than that of pure platinum, showing that the Ru incorporates into the Pt fcc structure by different ratios in all the catalysts. The typical particle sizes of all catalysts were in the range of 2-3 nm. The most active and stable catalyst for methanol and ethanol oxidation is catalyst III, in which a large amount (more than 90%) of PtRu alloy formation was observed. It has been found that this catalyst is about 8.0 and 33.4 times more active at ～0.60 V towards the methanol and ethanol oxidation reactions, respectively, compared to the commercial Pt catalyst.     

Selective oxidation of propylene to acrolein by silica-supported bismuth molybdate catalysts

Silica-supported bismuth molybdate catalysts have been prepared by impregnation, structurally characterized and examined as improved catalysts for the selective oxidation of propylene to acrolein. Catalysts with a wide range of loadings (from 10 to 90 wt%) of beta bismuth molybdate (??-Bi₂Mo₂O₉) were studied to provide a better understanding about the distribution of active sites, and to elucidate the role of lattice oxygen in the reaction. The catalyst containing 50 wt% of beta bismuth molybdate on SiO₂ was found to possess good distribution of active sites and sufficiently high lattice oxygen, which resulted in an extraordinary increase of the catalytic activity.     

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.     

Thermochemistry and Reactivity of Lattice Oxygen in V–Sb Oxide Catalysts for the Oxidative Dehydrogenation of Light Paraffins

Differential scanning calorimetry is used to study in situthe properties of strongly bound (lattice) oxygen in vanadium-containing supported catalysts for the oxidative dehydrogenation of paraffins C₂–C₄. Evidence is found that the process occurs via a stepwise redox mechanism with the participation of lattice oxygen from the catalyst. When the supported component is modified by an antimony additive, the amount of reactive oxygen increases and redox processes accelerate. Simultaneously, the rate of coke formation decreases. Additional modification by Bi and Ba leads to a further increase in the amount of reactive oxygen. In all cases, oxygen bound to vanadium atoms is responsible for the redox properties of the systems. The observed effects are analyzed from the standpoint of the ratio between different forms of active oxygen.     

Effect of pretreatment methods on the performance of Cu-Zr-Ce-O catalyst for CO selective oxidation

The Cu-Zr-Ce-O catalysts prepared using the coprecipitation method exhibited better catalytic performance for CO selective oxidation. The Cu-Zr-Ce-O catalysts pretreated with different methods were studied by CO-TPR and XPS techniques. The results showed that the Cu-Zr-Ce-O catalyst pretreated with oxygen exhibited the best catalytic performance and had the widest operating temperature window, with CO conversion above 99% from 160 to 200 ℃. The O2 pretreatment caused an enrichment of the oxygen storaged on the Cu active species and promoted the conversion of adsorbed oxygen into surface lattice oxygen. It also improved the amount of Cu＋/Cu^2＋ ionic pair, and then facilitated the formation of CuO active species on the catalyst for selective CO oxidation.     

Iron-catalyzed propylene epoxidation by nitrous oxide: studies on the effects of alkali metal salts

SBA-15-supported iron catalysts with and without alkali metal salt modifications were studied for propylene oxidation by nitrous oxide. The reaction route could be dramatically changed from allylic oxidation to epoxidation by modification of the FeOx/SBA-15 catalyst with alkali metal salts. The KCl-1 wt % FeOx/SBA-15 (K/Fe = 5) catalyst exhibited the best catalytic performances for propylene epoxidation, over which ca. 50% propylene oxide selectivity could be gained at a 10% propylene conversion at 648 K. Characterizations with diffuse reflectance UV-Vis, XANES, and Raman spectroscopic techniques revealed that the modification with KCl increased the dispersion of the iron species and changed the local coordination of iron into a tetrahedral configuration on the inner surface of SBA-15. This tetrahedrally coordinated iron site, which was probably stabilized by potassium ions, was proposed to account for the epoxidation of propylene by nitrous oxide. At the same time, the reactivity of lattice oxygen was inhibited, and the acidity of the FeOx/SBA-15 was eliminated. These changes should also contribute to the increase in the selectivity to propylene oxide. The counteranions in the alkali metal salts exerted a significant influence on the catalytic behaviors probably via an electronic effect.     

改性Ag/α-Al_2O_3催化丙烯气相环氧化反应

制备了以分子氧为氧化剂,对丙烯气相环氧化具有较好催化性能的改性负载银催化剂,并利用氧气程序升温脱附(O2-TPD)技术研究了氧在其表面上的脱附行为.实验结果表明:Ag/α-Al2O3催化剂只能使丙烯完全氧化成二氧化碳和水;当该催化剂用K2O改性后,可获得少量的环氧丙烷;Y2O3改性的Ag/α-Al2O3催化剂,可获得极少量的丙醛和丙酮;将0.1%(w)Y2O3添加到Ag-K2O/α-Al2O3后,可以显著提高催化剂的丙烯环氧化性能.在0.1MPa、245℃、20%C3H6/8%O2/72%N2和气体空速2000h-1的反应条件下,通过20%(w)Ag-0.1%Y2O3-0.1%K2O/α-Al2O3催化剂时,丙烯转化率为4.0%,环氧丙烷的选择性为46.8%.O2-TPD研究表明,少量的Y2O3、K2O或Y2O3-K2O作为助剂添加到20%Ag/α-Al2O3催化剂中时,减少了高温区与丙烯完全氧化有关的吸附氧物种的量,低温区余下的吸附氧物种量不变,有利于丙烯环氧化反应,提高了环氧丙烷的选择性.     

氧化铈对氧化锰表面氧脱附与恢复性能的影响

采用TPD-MS技术研究了Mn-Ce-O体系催化剂的表面氧脱附(供出)和恢复性能,并以甲醇氧化反应为探针考察了催化剂在不同气氛下的氧化活性。结果表明,氧化铈的存在并不影响氧化锰O₂-TPD特征峰的位置,但氧化锰表面的吸附氧数量明显增加,氧化锰表面吸附氧的恢复能力随氧化铈含量的增加而增大。催化剂对甲醇的氧化活性与其表面吸附氧数量有很好的对应关系。催化剂表面氧恢复能力越大,对甲醇的氧化活性受气相氧影响越小。     

高比表面介孔MoVTeNbO催化剂的制备及其催化性能

采用水热法添加模板剂十六烷基三甲基溴化铵(CTAB)和配合剂柠檬酸(CA)制备了Mo VTe Nb O系列催化剂,并将其应用于丙烯一步氧化制备丙烯酸的反应.结果表明,CA的添加量对催化剂的形貌、孔结构、比表面积及催化性能具有明显的影响.当n(CA)/n(Mo)=0.36时,Mo VTe Nb O催化剂为介孔纳米催化剂,其平均孔径为4.9 nm,具有较高的比表面积(37.8 m2/g)和较小的催化剂晶粒(粒径范围为10~16 nm),与常规水热法制备的催化剂相比,Mo VTe Nb O介孔纳米催化剂的晶粒变小、催化性能得到了显著提高,丙烯一步氧化制丙烯酸的转化率可由53.9%提高至71.2%,丙烯酸收率可提高到45.8%.     

多组分Mo-Bi-Fe-O催化剂上丙烯氨氧化研究进展

综述了多组分Mo_Bi_Fe_O催化剂上丙烯氨氧化研究进展 ,包括反应机理、催化剂设计、晶格氧迁移、活性位模型与协同效应四个方面     

Preparation of Al2O3-supported nano-Cu2O catalysts for the oxidative treatment of industrial wastewater

Cuprous oxide (Cu₂O) nanoparticles supported on Al₂O₃ prepared using two different methods (hereafter referred to as catalyst I and II, respectively) were characterized by XRD and TEM. The catalytic activities of catalyst I and II during the treatment of industrial wastewater were then investigated. Specifically, the progress of the catalytic oxidation of industrial wastewater was observed by monitoring the time-dependent change in the chemical oxygen demand (COD) of industrial wastewater when the catalysts were applied. The results indicated that the catalytic activity of catalyst II was greater than that of catalyst I. Furthermore, under optimal conditions the COD removal efficiency was 94.59%. Finally, the mechanism by which the oxidative degradation of the industrial wastewater occurred could be explained based on a hydroxyl radical mechanism.     

STUDY ON THE MOBILITY AND REACTIVITY OF OXYGEN OF CERIA-BASED OCM CATALYSTS BY TEMPERATUREPROGRAMMED PULSE REACTION(TPPR)

IntroductionThisprojectwassupportedbytheNationalNaturalScienceFoundationofChina.Becausemostofthecatalystsforoxidativecouplingofmethane(OCM)arecompositechides,thereactivitiesofdifferentkindsofoxygenspeciesareeXtensivelystudied.Generally,agoodOCMcatalystsho…     

CO2氧化丙烷脱氢MoO3-V2O5/SiO2催化剂研究

采用表面改性和等体积浸渍法制备了MoO3-V2O5／SiO2复合氧化物，采用TPR、IR、TPD和微反技术表征了催化剂对CO2和C3H8的吸附性能和CO2部分氧化丙烷脱氢的反应性能．结果表明：随MoO3加入量的增加，V=O还原温度降低，晶格氧更易活化．CO2和丙烷的活化温度降低，丙烷转化率增高，丙烯选择性下降．V=O中晶格氧的活化是CO2氧化丙烷制丙烯反应的关键．     

钙钛矿型La1+X/2Sr1-x/2Co1-xCuxO3催化CO氧化活性与表征

The catalytic activity and the reactive properties of perovskite-type oxides catalysts La(1+x/2)Sr(1-x/2)Co1-xCuxO3 for CO oxidation reaction were investigated. Results showed that the catalytic activity for CO oxidation reached to a maximum when x＝0.4. The temperature for complete CO oxidation under atmospheric and experimental conditions was 168℃. According to the stoicheometry of catalyst, all catalysts were oxygen defect compounds. The active oxygen species on this catalyst was the adsorbed oxygen which was adsorbed on the surface lattice oxygen defect. It was also found that Co4+ existed in the catalysts and the sufrace active oxygen species was caused by the Co4+. It was concluded that CO oxidation reaction on this catalyst was carried out by the valence change between Co3+ and Co4+ which was adjusted by the adsorbed oxygen.     

STUDY ON THE OXIDATIVE COUPLING OF METHANE III.CATALYTIC PERFORMANCE OF TiO2-BASED CATALYSTS STUDIED BY CO2-TPD AND TPR-TPO

The effects of surface acidity-basicity and surface oxidation reduction property of Li-La-Mn/TiO2 (I) and Li-La-Mn-W/TiO2 (II) catalysts on oxidative coupling of methane were studied by CO2-temperature programmed desorption (CO2-TPD) and temperature programmed reduction temperature programmed oxidation (TPR-TPO). The results show that there exist strong basic sites on catalysts I and II, but the quantity of these sites on catalyst II is more than that on catalyst I. Besides, the strength of basics site on catalyst II is stronger than that on catalyst I. The surface of catalyst II is easier to reduce and re-oxidize than that of catalyst I. The surface of catalyst II is easier to reduce and re-oxidize than of catalyst I, and the extent of reduction and reoxidation of catalyst II is more intensive than catalyst I, which results in a lowing of the reaction temperature and enhances the activity and C2 hydrocarbon yield as well as gas hourly space velocity(GHSV). Catalyst II is excellent for the oxidative coupling of methane (OCM).     

Cu离子A位掺杂对LaSrCoO4复合氧化物氧化性能的影响

采用聚丙烯酰胺法制备了La1-xCuxSrCoO4(x=0.2-0.8)复合氧化物,考察了Cu离子掺杂量(x)对CO及C3H8氧化反应活性的影响,并运用XRD、IR、TPR和TPD等多种手段对复合氧化物催化剂进行了表征。结果表明,催化剂活性随x的变化而变化,Cu部分取代A位La能提高LaSrCoO4催化剂的CO及C3H8氧化反应活性,当x=0.4时La1-xCuxSrCoO4催化剂的晶格氧和Co3 含量较多,晶格氧的活动性较高,催化活性最佳。     

Iron-catalysed propylene epoxidation by nitrous oxide: dramatic shift of allylic oxidation to epoxidation by the modification with alkali metal salts

A dramatic shift of allylic oxidation to epoxidation has been observed during the oxidation of propylene by N(2)O when the FeO(x)/SBA-15 catalyst is modified with alkali metal salts, and the roles of alkali metal salts are to suppress the reactivity of lattice oxygen and to induce an iron coordination structure effective for epoxidation with N(2)O.     

丙烯环氧化制环氧丙烷Fe-Al-P-O催化剂的研究

用溶胶-凝胶法制得了Fe-Al-P-O催化剂，采用IR、XRD、TEM、BET、TPR和微反等技术研究了催化剂的物化性质和反应性能。实验结果表明，Fe1/2-Al1/2-PO4由10 nm左右 FePO4和AlPO4微晶组合而成，其晶格氧的活泼性大于单纯FePO4，AlPO4在Fe1/2-Al1/2-PO4中起到分散FePO4微晶的作用；Fe1/2-Al1/2-PO4的反应性能与原料气组成密切相关，丙烯与O2的选择氧化产物主要是丙烯醛，原料气中加入H2后，反应产物以环氧丙烷为主，同时还有部分丙烯醛，原料气中引入水蒸气后，可进一步增加环氧丙烷的选择性及减少丙烯醛的产率；在0.1 MPa、200 ℃、C3H6/O2/H2/H2O/N2=1∶1∶1∶1∶6（mol比）和空速1 200 h－1条件下，丙烯的转化率为8.9％，环氧丙烷的选择性为81.0％。