Influence of initial reactants in propene ammoxidation on the isomerization activity of complex Mo-containing oxide catalysts

Surface reduction of complex Mo-containing oxide catalysts by the initial reactant in propene ammoxidation increases its activity in isomerization of butene-1 to butene-2. Isomerization and conversion of ammonia, propene and their mixtures are suggested to take place on the same active centers of the catalyst.

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Mo- -1 -2. , , .

     

Selective oxidation and ammoxidation of isobutene over mixed oxides of tin and antimony

The oxidation and ammoxidation of isobutene were studied over mixed oxides SnO₂/Sb₂O₄ as catalysts, in a pulse reactor between 598 and 698 K. From the point of view of methacrylonitrile production the catalysts of compositions SnSb=4–51 behaved most appropriately at the optimum reaction temperature of 673 K. Below this temperature the production of methacrolein was preferred, even in the presence of ammonia, whereas at higher temperatures total oxidation prevailed.

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SnO₂/Sb₂O₄, 598 698 . SnSb=4–51 , 673 . , , .

     

Selective catalytic oxidation of NO over iron and manganese oxides supported on mesoporous silica

The selective catalytic oxidation （SCO） of NO was studied on a catalyst consisting of iron-manganese oxide supported on mesoporous silica （MPS） with different Mn/Fe ratios. Effects of the amount of manganese and iron, oxygen, and calcination temperature on NO conversion were also investigated. It was found that the Mn-Fe/MPS catalyst with a Mn/Fe molar ratio of 1 showed the highest activity at the calcination temperature of 400 °C. The results showed that over this catalyst, NO conversion reached 70% under the condition of 280 °C and a space velocity of 5000 h-1. SO2 and H2O had no adverse impact on the reaction activity when the SCO reaction temperature was above 240 °C. In addition, the SCO activity was suppressed gradually in the presence of SO2 and H2O below 240 °C, and such an effect was reversible after heating treatment.     

Transient response study of the participation of adsorbed forms of ammonia in propene ammoxidation

On the basis of transient response studies, it is suggested that ammonia on the surface of a Mo–Si–Bi–P oxide catalyst forms a compound that is stable at the reaction temperature and whose reaction with propene yields acrylonitrile.

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, Mo–Si–Bi–P , .

     

Oxidation of propene over various doped tungsten oxides

The oxidation of propene was studied on several tungsten oxides which contained small amounts of Ti, Ta, Nb and Sn. Only the Sn-containing specimen was found to be selective in the conversion of propene to acrolein. The catalytic results are correlated with crystal structures determined by electron microscopy.

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, Ti, Ta, Nb Sn. , , Sn, . , .

     

Alumina and silica oxides as catalysts for the oxidation of benzoins to benzils under solvent-free conditions

Alumina or silica gel are used as catalysts for a solvent-free oxidation of benzoins to the corresponding benzils. These catalysts are easily recovered after completion of the reactions, which are carried out either by heating in a sand bath or using microwave irradiation. Comparison of the results obtained with both catalysts indicates that all the reactants examined were oxidized faster on alumina than on silica under these conditions.     

Methanol oxidation on semiconducting oxides

Correlations between reaction rates and selectivities vs. Egap (eV) of the semiconducting oxides Co₃O₄, CuO, NiO, Cr₂O₃, -Fe₂O₃, TiO₂ and MoO₃ were obtained for the catalytic air oxidation of methanol at 573 K. Higher and lower selectivities to formaldehyde for Egap>2 n-type, and Egap >2 p-type semiconducting oxides, are observed, respectively.     

Using DFT in search for support effects during methanol oxidation on supported molybdenum oxides

The oxidation of methanol on supported molybdenum oxides was studied using DFT. Starting from a cluster model for a mono-oxo and di-oxo molybdenum oxide on a SiO(2) support, the reaction energies and rates for the oxidation of methanol were computed and interpreted with chemical reaction indices. This pointed out that the apparent barrier was significantly lower on the mono-oxide model, favoring it over the di-oxo species. Accordingly, we assumed similar behavior on Al(2)O(3), TiO(2) and ZrO(2) supports, so that we could compare characteristics over different supports. The obtained reaction energies and rates followed the experimental turn-over frequency (TOF) sequence.     

Catalytic oxidation and ammoxidation of propylene. Modelling studies on well-defined molybdenum complexes

Molybdenum (VI)-allyloxo and -allylamido complexes possessing ancillary oxo and imido ligands have been synthesised and their subsequent decomposition studied in the perspective of modelling the postulated surface intermediates of the catalytic oxidation and ammoxidation of propylene. In solution and under mild conditions, these complexes undergo two types of reactions corresponding effectively to certain elemental steps of the heterogeneous processes, i.e. oxidative dehydrogenation of the allyl groups and allyl migration to oxo and imido functions. The mechanisms and the relative rates of these reactions are compared with that proposed for the surface catalytic chemistry. The possibility of alternate reaction pathways is discussed such as for CN bond formation and the involvement of an allylideneamine intermediate in the catalytic cycle.     

Selective oxidation and ammoxidation of ethane over ion-exchanged Co-MCM-49 zeolites

Summary Ion-exchanged Co-Na-MCM-49 and Co-H-MCM-49 zeolites are active catalysts for the selective oxidation and ammoxidation of ethane. The presence of ammonia in the feeds can considerably improve the selectivity and yield of the sum of ethylene and acetonitrile.     

Partial oxidation of propene on oxygen-covered Au(111)

Partial oxidation of propene is promoted by Au following deposition of atomic oxygen (0.3 ML) via O3 decomposition on Au(111) at 200 K. Several partial oxidation products--acrolein, acrylic acid, and carbon suboxide (O=C=C=C=O)-are produced in competition with combustion to CO2 and H2O. Acrolein is the primary partial oxidation product, and it is further oxidized to the other products by excess oxygen. We propose that acrolein is derived from allyloxy intermediate that is formed via insertion of oxygen into the allylic C-H bond. While no propene epoxide formation is detected from oxidation of C3H6, a small amount of epoxidation is observed during reaction of C3D6 and CD3CH=CH2. These results are strong indications that small changes in the energy required for allylic C-H activation, in this case due to a kinetic isotope effect, may dramatically change the selectivity; thus, small modifications of the properties of oxygen on Au may lead to the more desirable epoxidation process. Our results are discussed in the context of the origin of activity of Au-based catalysts.     

Photocatalytic oxidation of propylene with molecular oxygen over highly dispersed titanium, vanadium, and chromium oxides on silica

Photocatalytic oxidation of propylene with molecular oxygen at room temperature was investigated over various silica-supported metal oxides with low loading. The photocatalytic active site is assumed to be the isolated tetrahedrally coordinated metal oxides in the ligand-to-metal charge-transferred state, such as (Mdelta- -OLdelta+). Photocatalytic epoxidation of propylene into propylene oxide was promoted over silica-supported V and Ti oxides at steady state. Over silica-supported Cr oxide, the propylene oxide formation rate was remarkably decreased with the time course in the reaction. The oxidation state and the coordination environment of the supported Ti, V, and Cr oxide species were determined by diffuse reflectance UV-vis spectroscopy (DRS) and electron spin resonance (ESR). During the photocatalytic oxidation, the oxidation state of the Ti4+ species was not varied. On the other hand, the V5+ species was partially reduced to V4+ and the Cr6+ species was successively reduced to Cr5+ and Cr3+. An isotopic tracer study of the C3H6-18O2 reaction suggests the difference of the active oxygen species between TiO2/SiO2 and V2O5/SiO2. The active oxygen species on TiO2/SiO2 is derived from molecular oxygen. On the other hand, the photogenerated products on V2O5/SiO2 incorporate the lattice oxygen of the surface metal oxide species. It is suggested that the kinds of terminal ligand (hydroxyl or oxo) of the tetrahedrally coordinated metal oxides on silica decide the active oxygen species in the photocatalytic oxidation. A photoinduced hole center on the monohydroxyl (SiO)3Ti-OH species activates molecular oxygen that reacts with propylene. In the case of the monooxo (SiO)3V=O and dioxo (SiO)2Cr=O2 species, the photoactivated lattice oxygen (OL-) directly reacts with propylene.     

Influence of the ligand structure on SLP-catalysed hydroformylation of propene

Hydroformylation of propene was studied at 90–120°C and 3–10 atm. The catalyst was hydrido-(carbonyl)tris(triphenylphosphine)rhodium [H(CO)Rh(PPh₃)₃] supported on silica, in an excess of a liquid phosphine (P) ligand as solvent. The following series of ligands (P) was synthesized and studied in this application: CH₃(CH₂)_nPPh₂ (n = 3, 7, 17), (c – C₆H₁₁)_xPPh_3?x (x = 0, 1, 2) and also unsaturated allyl- and poly(butadienyl)-diphenylphosphines. The activity and regioselectivity of the catalysts are discussed in terms of the mobility and coordination ability of the ligands used. With the same electron density of the phosphorus atom, the activity of the catalysts increases with the mobility of the ligands. On the other hand, given the same mobility of the ligand, a lower electron density on phosphorus results in increased catalytic activity.     

纳米钒铬复合氧化物的溶剂热合成、表征及催化2,6-二氯甲苯氨氧化反应（英文）

甲基芳烃气相氨氧化反应制备对应的芳香腈被认为是丙烯氨氧化制备丙烯腈之后化工领域又一重大进展,芳香腈是重要的精细化学品,广泛应用于医药、农药、颜料、染料、橡胶、光电材料等领域.其中2,6-二氯甲苯氨氧化反应制备2,6-二氯苯腈是特别重要的反应,2,6-二氯苯腈工业上可用于制备高效除草剂、杀菌剂及各种特种工程塑料;然而相较于其它的甲基芳烃,2,6-二氯甲苯由于甲基邻位有两个较大位阻且较强吸电子的氯原子影响,甲基活性较低,较难发生氨氧化反应,原料转化率和产品收率均较低.本课题组一直致力于发展高活性和选择性的氨氧化催化剂以及有效的策略实现甲基芳烃高效转化为芳香腈,我们曾以硅胶负载的钒磷氧化物(VPO/SiO_2)和钒铬氧化物(VCrO/SiO_2)为催化剂,成功实现了2,6-二氯甲苯氨氧化反应制备2,6-二氯苯腈.钒铬复合氧化物(VCrO)具有广泛的应用,可用于多相催化、气体传感、能量储存等领域.VCrO通常通过高温固相反应制备,然而一般得到的是混合相,产品形态和颗粒大小也不能很好控制;当用于氧化或氨氧化反应时,需要较高的反应温度,原料也容易发生过度氧化,导致积碳及活性降低.我们以V_2O_5和CrO_3为原料,在醇或者醇水溶液中于180℃进行溶剂热反应制备了无定形的VCrO前驱体,然后将前驱体在不同温度下氮气气氛中煅烧,产品通过粉末X射线衍射、透射电镜和X射线光电子能谱等进行表征.当以甲醇或甲醇水溶液为溶剂热反应介质,并且前驱体700℃进行煅烧后,产品为纯的正交晶系CrVO4纳米晶相;当以甲醇为溶剂时,CrVO_4晶相的尺寸大约为500 nm;而改为甲醇水溶液为溶剂时,产品尺寸急剧减小到50 nm以下,而且通过改变甲醇和水的体积比分别为10:1,5:1,1:1和1:5时,CrVO_4纳米晶相的尺寸从50 nm逐渐减小到30,20和10 nm,能够进行有效调控.据我们所知,这是首次合成纯的CrVO_4纳米晶相.我们以该纳米CrVO4为催化剂催化2,6-二氯甲苯氨氧化反应制备2,6-二氯苯腈,在335℃的相对较低温度下反应,原料转化率为84%,产品收率为75%;进一步升高温度到390℃,原料转化率为99%,产品收率可达81%.在所有已报道的二元复合氧化物催化剂中,纳米CrVO_4显示了最高的催化活性,主要归功于它较小的粒子尺寸、较大的表面积和更多暴露的活性中心     

Influence of Pt and Pd on the catalytic activity of tungsten and molybdenum oxides in the deep oxidation of methane

It has been shown that the phases H_xMO₃ and MO_3−x (M = Mo, W), obtained by reduction of the oxides WO₃ and MoO₃ with hydrogen with supported Pt(Pd) (0.5 mass %), have higher catalytic activity in the deep oxidation of methane than the catalysts Pt/Al₂O₃ and Pd/Al₂O₃ with the same amount of supported metal. At temperatures above 700 K the activity of these catalysts decreases in consequence of the thermal decomposition of the phases H_xMO₃ and MO_3−x and they become similar in activity with Pt(Pd)/Al₂O₃. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 126–129, March–April, 2008.     

Oxidation ofn-butane and propene on exhydrotalcite Mg, Al, Fe mixed oxides

Oxidative dehydrogenation ofn-butane and propene has been studied on six Mg−Al−Fe oxide catalysts prepared by thermal decomposition of layered double hydroxides with a hydrotalcite-like structure, possessing Mg²⁺ and Al³⁺ ions in the brucite-like layers, and hexacyanoferrate in the interlayers. In all cases, CO₂ and H₂O are formed, together with minor amounts of ethylene and methane. On the solids prepared from hexacyanoferrate(II), formation of benzene is also observed.     

Heterogeneous partial oxidation catalysis on metal oxides

This review paper presents an overview of heterogeneous selective ammoxidation and oxidative dehydrogenation (ODH) of light alkanes, particularly of ethane. The conversion of ethane to ethene is in great demand in the domestic and worldwide chemical industry. The review has been voluntarily restricted to metal oxide-type catalysts, as it is devoted to the special issue honouring Edmond Payen and is based on 30 years of experience and discussions with pioneering scientists in the field. The main key factors, designated by Grasselli as the “7 pillars”, have been emphasised: isolation of active sites, M–O bond strength, crystalline structure, redox features, phase cooperation, multifunctionality and the nature of the surface oxygen species. The main features and physical and chemical properties of solid catalysts for selective oxidation compared to total oxidation have also been emphasised. Several case studies have been presented to illustrate the concept and importance of the key factors of catalyst preparation and activation and of the catalytic atmosphere. Based on such analysis and recent discoveries and process developments perspective views are also given.     

The effect of metal oxides on the oxidation of polybutadiene

Carboxy-terminated polybutadiene (CTPB) was oxidised as a coating on various metal oxides by heating in air on a thermobalance. The oxidation was found to be free from diffusion control and was catalysed by certain of the oxides. The catalysis was shown to be independent of semiconductor type and to be associated with those oxides for which the width of the forbidden zone between the valence and conduction bands (U) is less than 1.9 eV. In general, low values of U result in high catalytic activity. It is proposed that catalysis occurs by a redox mechanism, viz. RO₂H + p → RO₂^. + H⁺, RO₂H + e → RO^. + OH^?.     

Immobilized metalloporphyrins on 3-aminopropyl-functionalized silica support as heterogeneous catalysts for selective oxidation of primary and secondary alcohols

Abstract  

Iron(III), manganese(III), and cobalt(II) complexes of meso-tetrakis(p-chlorophenyl)porphyrin (Fe(TClPP)X, Mn(TClPP)X, and Co(TClPP)X, X = Cl or OAc) were immobilized onto 3-aminopropyl-functionalized silica (SF-3-APTS). SF-3-APTS acts as both axial base and support for immobilization of these metalloporphyrins. The obtained heterogeneous catalysts were characterized by Fourier transform infrared (FT-IR), UV–Vis, and inductively coupled plasma (ICP) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and thermogravimetric analysis (TGA) techniques. Their catalytic activity as biomimetic catalysts was investigated for the selective oxidation of primary and secondary benzylic alcohols to the corresponding carbonyl compounds with t-butylhydroperoxide as oxidant. SF-3-APTS–Fe(TClPP)Cl demonstrated higher catalytic activity than SF-3-APTS–Mn(TClPP)Cl and SF-3-APTS–Co(TClPP)OAc. The presence of electron-withdrawing substituents on benzylic alcohols enhances the rate of catalytic oxidation. SF-3-APTS–Fe(TClPP)Cl could be reused at least four times without significant loss of its catalytic activity.