Mononuclear metavanadate catalyses gas phase oxidation of methanol to formaldehyde employing dioxygen as the terminal oxidant

Multistage mass spectrometry experiments reveal a sequence of gas phase reactions for the oxidation of methanol to formaldehyde with a mononuclear oxo vanadate anion as the catalyst and dioxygen as the terminal oxidant.     

Oxidation of methanol to formaldehyde on supported vanadium oxide catalysts compared to gas phase molecules

The oxidation of methanol to formaldehyde on silica supported vanadium oxide is studied by density functional theory. For isolated vanadium oxide species silsesquioxane-type models are adopted. The first step is dissociative adsorption of methanol yielding CH3O(O=)V(O-)2 surface complexes. This makes the O=V(OCH3)3 molecule a suited model system. The rate-limiting oxidation step involves hydrogen transfer from the methoxy group to the vanadyl oxygen atom. The transition state is biradicaloid and needs to be treated by the broken-symmetry approach. The activation energies for O=V(OCH3)3 and the silsesquioxane surface model are 147 and 154 kJ/mol. In addition, the (O=V(OCH3)3)(2) dimer (a model for polymeric vanadium oxide species) and the O=V(OCH3)3(*+) radical cation are studied. For the latter the barrier is only 80 kJ/mol, indicating a strong effect of the charge on the energy profile of the reaction and questioning the significance of gas-phase cluster studies for understanding the activity of supported oxide catalysts.     

Catalytic behavior of a silica-supported polystannazane-copper complex for the oxidation of methanol to formaldehyde at mild reaction conditions

A very cheap catalyst, a silica-supported polystannazane-copper complex (abbreviated as SiO₂ Sn N Cu) was prepared by the reaction of the silica-supported polystannazane ligand with CuCl₂ in ethanol. The results showed that SiO₂ Sn N Cu can catalyze the oxidation of methanol to formaldehyde in high yield at mild conditions, i.e. at 40°C and 1 atm of oxygen. The catalyst could be recovered and could catalyze the reaction repeatedly.     

Iron-molybdate deactivation during methanol to formaldehyde oxidation: effect of water

Stoichiometric iron-molybdate has been prepared by coprecipitation and submitted to a long activity test to check the role of water in its deactivation behavior during methanol to formaldehyde oxidation. Water retards the reoxidation of the catalyst which is responsible for the acceleration of its deactivation.     

含硼杂原子Na-B-ZSM-5分子筛对甲醇脱氢制甲醛反应的催化性能

以白炭黑为硅源、硼酸为硼源、NaOH为碱源、四丙基溴化铵(TPABr)和1,6-己二胺(HMDA)混合模板剂,采用水热合成法制备含硼杂原子Na-B-ZSM-5分子筛,用XRD、SEM、FT-IR、UV-vis、11B MAS NMR、NH3-TPD等方法对其进行表征。在连续流动常压固定床反应器上评价Na-B-ZSM-5分子筛对甲醇脱氢制甲醛反应的催化性能,考察n(Si)/n(B)、n(Na2O)/n(SiO2)、晶化温度和晶化时间等制备参数以及反应温度和质量空速等工艺参数对催化性能的影响。结果表明,硼进入了分子筛的骨架结构中,存在与B酸中心有关的骨架四配位硼和与L酸中心有关的骨架三配位硼,Na-B-ZSM-5分子筛含有较多的弱酸位和少量的中强酸位。催化剂的最佳制备参数为n(Si)/n(B)比值为7.5、n(Na2O)/n(SiO2)比值为0.14、晶化温度170℃、晶化时间48 h。Na-B-ZSM-5(7.5)分子筛在反应温度550℃、质量空速1.85 h-1的反应条件下对甲醇的转化率为62.97%,甲醛的选择性为68.86%。     

Catalytic relevance of phase transformations accompanying the gas phase oxidation of ethanol on silica supported vanadia

Nonsteady state activity during the gas phase oxidation of ethanol in a simple flow reactor and its dependence on pretreatment and reaction conditions can be explained utilizing the previously presented model of possible surface vanadia phases on silica.

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Recovery of MoO3 from spent catalysts of partial oxidation of methanol to formaldehyde

An effect of an ammonia solution concentration, temperature, l: s ratio on a MoO₃ extraction process was revealed in studying ammonia leaching of molybdenum oxide from spent iron-molybdenum catalyst of oxidation of methanol to formaldehyde The data obtained allow to optimize the extraction process of MoO₃ from the spent Fe-Mo catalysts.     

Density functional theory study of the oxidation of methanol to formaldehyde on a hydrated vanadia cluster

Density functional theory was used to study the mechanism for the oxidation of methanol to formaldehyde. A vanadium oxide cluster O?V(OH)₃ has been utilized to represent the catalytic system under hydrated conditions, i.e., in the presence of V? OH hydroxyl groups. Two types of methoxy‐intermediates have been considered: a penta‐coordinate methoxy‐intermediate (OH)₄V(OCH₃) and a tetrahedral methoxy‐intermediate (OH)₂VO(OCH₃)(H₂O). The most plausible reaction pathway corresponds to the process involving first the formation of the tetrahedral methoxide, and a subsequent rate‐limiting step where hydrogen is transferred from the methoxy groups toward the oxygen atom of the vanadyl V?O site. The reaction mechanism is a typical two‐state reactivity process due to a change of the multiplicity (reactive singlet → product triplet) along the reaction coordinate accompanied by a reduction of the vanadium center from V^V (d⁰) to V^III (d²). Minimum energy crossing points were localized and possible spin inversion processes are discussed by means of the intrinsic reaction coordinate approach to find the most favorable reaction pathways. The hydration effect is found to be mainly the destabilization of the methoxy intermediates. An alternative reaction pathway with a lower apparent barrier is presented. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Catalytic effects on methanol oxidation produced by cathodization of platinum electrodes

A catalytic effect is found for methanol oxidation after new active surface states are produced on polycrystalline platinum by potentiostatic cathodization in acid media at room temperature. This procedure originates surface states not available on the original polycrystalline electrodes with unexpected cyclic voltammetric responses; i.e., at least four new peaks below 0.9 V are observed. The cathodization process also induces a rearrangement of the bulk platinum oxide, showing a defined peak at 1.2 V. The appearance of these new states is also proven by open-circuit potential decays. The electrocatalytic activity of these new surfaces in methanol oxidation is compared with that of the untreated electrodes by electrochemical impedance spectroscopy, chronoamperometry, and cyclic voltammetry. The cathodic procedure enhances the methanol oxidation voltammetric current peaks with charge density values higher than those on untreated platinum. The integration of chronoamperometric plots over 10 min in methanol acid media presents the largest difference between 0.6 and 0.7 V with respect to the original surface. Analysis of the impedance data shows that the values of polarization resistance for methanol oxidation on the cathodically treated platinum are lower than those of the original surface. According to the time constant values for methanol oxidation, the original surface can be considered less tolerant of the formation of catalytic poisons. A discussion of the most likely mechanism for the formation of the new active sites on platinum is presented here, assuming the presence of hydrogen subsurface states, ordered water clusters, and low-coordinated platinum atoms.     

Dehydrogenation of methanol to formaldehyde over titanium alloys

The dehydrogenation of methanol to formaldehyde has been studied in the temperature range between 523 and 723 K over titanium alloys. The FeTi alloy showed a high selectivity for the formation of formaldehyde. Addition of zinc increased the specific rate of formaldehyde formation with a simultaneous decrease in its selectivity.

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523 723 K . FeTi . Zn .

     

涂覆在堇青石上的负载贵金属催化剂催化氧化甲醛的性能研究

将催化性能优异的负载贵金属催化剂与拟薄水铝石(Al OOH)溶胶混合,制备得到均匀的料浆,采用料浆涂覆法将其负载到堇青石蜂窝陶瓷基体上,考察了Al OOH含量对涂层形貌、负载量、涂层牢固度的影响,并对合成的整体式催化剂进行催化氧化甲醛性能测试。结果表明,合成的负载贵金属催化剂Pt粒子粒径为1.14nm时,可在17℃完全降解甲醛;涂覆过程中Al OOH含量越高,载体负载量越大,但过高易导致孔道堵塞,涂覆不均和涂层龟裂;超声振荡测试表明,Al OOH含量对涂层牢固度影响不大,当Al OOH含量为8(wt)%时,负载型蜂窝陶瓷的催化效果和涂覆效果最佳,可以在60℃下完全降解甲醛。     

Surface properties of Fe?Mo?O catalysts and their activity in methanol oxidation to formaldehyde

The Fe^III–Mo^VI–O catalyst was prepared from iso-ortho-Fe(OH)₃ and -FeOOH. The catalysts differed markedly in their activity in methanol oxidation depending on the biography of their iron(III) oxide. The catalytic properties were found to depend on the pore structure of the catalyst.

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Fe(III)–Mo(VI)–O, --Fe(OH)₃ -FeOOH. , . , .

     

Preparation of iron molybdate catalysts for methanol to formaldehyde oxidation based on ammonium molybdoferrate(II) precursor

It was demonstrated that iron molybdate catalysts for methanol oxidation can be prepared using Fe(II) as a precursor instead of Fe(III). This would allow for reduction of acidity of preparation solutions as well as elimination of Fe(III) oxide impurities which are detrimental for the process selectivity. The system containing Fe(II) and Mo(VI) species in aqueous solution was investigated using UV–Vis spectroscopy. It was demonstrated that three types of chemical reactions occur in the Fe(II)–Mo(VI) system: (i) formation of complexes between Fe(II) and molybdate(VI) ions, (ii) inner sphere oxidation of coordinated Fe(II) by Mo(VI) and (iii) decomposition of the Fe–Mo complexes to form scarcely soluble Fe(III) molybdate, Mo(VI) hydrous trioxide and molybdenum blue. Solid molybdoferrate(II) prepared by interaction of Fe(II) and Mo(VI) in solution was characterized by EDXA, TGA, DTA and XRD and a scheme of its thermal evolution proposed. The iron molybdate catalyst prepared from Fe(II) precursor was tested in methanol-to-formaldehyde oxidation in a continuous flow fixed-bed reactor to show similar activity and selectivity to the conventional catalyst prepared with the use of Fe(III).     

Electrocatalytic oxidation of formaldehyde and methanol on Ni(OH)2/Ni electrode

A nickel hydroxide-modified nickel electrode (Ni(OH)₂/Ni) was successfully prepared by the cyclic voltammetry (CV) method and the electrocatalytic properties of the electrode for formaldehyde and methanol oxidation have been investigated respectively. The Ni(OH)₂/Ni electrode exhibits high electrocatalytic activity in the reaction. A new method has been developed for formaldehyde determination at the nickel hydroxide-modified nickel electrode and the experimental parameters were optimized. The oxidation peak current is linearly proportional to the concentration of formaldehyde in the range of 7.0 × 10^?5 to 1.6 × 10^?2 M with a detection limit of 2.0 × 10^?5 M. Recoveries of artificial samples are between 93.3 and 103.5%. The effect of scan rate and methanol concentration on the electrochemical behavior of methanol were investigated respectively.     

Role of the structural and electronic properties of molybdenum trioxide catalysts on the structure-sensitive oxidation of methanol to formaldehyde

Summary As catalysts for selective oxidation, molybdenum trioxide catalysts—prepared by two different methods—have been investigated. The results of vapor-phase oxidation of methanol are discussed on the basis of the acidic property, oxidizing functions, and the crystallographic structure of the catalysts. It was found that the acidic property is not the sole factor deciding the catalytic activity. Electrical conductivity measurements proved that molecular oxygen in the gas feed is necessary for maintaining the catalysts active. The difference in the catalytic activity and selectivity were reasonably interpreted in view of the structure sensitivity of those catalysts. A redox mechanism is also discussed in this paper.

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Der Einfluß von strukturellen und elektronischen Eigenschaften von Molybdäntrioxidkatalysatoren auf die struktursensitive Oxidation von Methanol zu Formaldehyd

Zusammenfassung Auf zwei verschiedene Arten hergestellte Molybdäntrioxidkatalysatoren wurden für selektive Oxidationen untersucht. Die Ergebnisse der Dampfphasenoxidation von Methanol werden auf Basis der sauren Eigenschaften, der oxidierenden Funktionen und der kristallographischen Struktur der Katalysatoren diskutiert. Es wurde festgestellt, daß die sauren Eigenschaften zur Erklärung der entscheidenden Wirksamkeit der Katalysatoren nicht alleine verantwortlich sind. Elektrische Leitfähigkeitsmessungen zeigten, daß molekularer Sauerstoff im zugeleiteten Gas zur Erhaltung der katalytischen Aktivität notwendig ist. Die Unterschiede in der Katalysatoraktivität und der Selektivität sind aus der Struktur der Katalysatoren zu erklären. Es wird ein adäquater Redox-Mechanismus diskutiert.

     

Catalytic properties of oxides in vapor phase oxidation of acetone

The temperature dependences of the rate of oxidation of acetone vapors by oxygen on oxide surface catalysts: V₂O₅, Co₃O₄., MoO₃ and TiO₂ (rutile), and the industrial catalyst VKSh were determined. A series of the catalytic activity of the above surface catalysts was established. The relationship between the catalytic properties of the oxides in the oxidation of acetone and their redox and acid-base characteristics was analyzed. The catalytic activity of the oxides in the oxidation reaction of acetone and methanol were compared.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 114–117, January–February, 1988.     

Catalytic oxidation of methanol on Pd metal and oxide clusters at near-ambient temperatures

Supported Pd clusters catalyze methanol oxidation to methyl formate with high turnover rates and >90% selectivity at near ambient temperatures (313 K). Metal clusters are much more reactive than PdO clusters and rates are inhibited by the reactant O(2). These data suggest that ensembles of Pd metal atoms on surfaces nearly saturated with chemisorbed oxygen are required for kinetically-relevant C-H bond activation in chemisorbed methoxide intermediates. Pd metal surfaces become more reactive with increasing metal particle size. The higher coordination of surface atoms on larger clusters leads to more weakly-bound chemisorbed species and to a larger number of Pd metal ensembles available during steady-state catalysis. Chemisorbed oxygen removes H-atoms formed in C-H bond activation steps and inhibits methoxide decomposition and CO(2) formation, two functions essential for the high turnover rates and methyl formate selectivities reported here.     

Catalytic conversion of methane to methanol over Cu-mordenite

Methane can be converted to methanol over copper-exchanged mordenite at 200 °C. Methanol could be recovered at the end of the reactor. This multi-step reaction opens the possibility for methane to methanol conversion in a closed catalytic cyclic reaction system.     

Catalytic effects of ruthenium and osmium spontaneous deposition on platinum surfaces toward methanol oxidation

The influence of ruthenium and osmium spontaneous deposition on polycrystalline platinum in sulfuric acid was studied by conventional electrochemical techniques. The inhibition of the hydrogen adatom voltammetric profile by the foreign adatoms was used to calculate the degree of surface coverage of ruthenium, osmium, and a mixture of both metal ions from solutions of different composition. Methanol adsorption and oxidation were compared on bare platinum, platinum/ruthenium, platinum/osmium, and ternary compounds, considering the efficiency of methanol oxidation per hydrogen adatom displaced by the foreign metal on platinum.