Effect of the rhenium additive to VOx/TiO2 and MoOx/TiO2 catalysts on their properties in oxidative dehydrogenation of propane

VO_x/TiO₂ and MoO_x/TiO₂ catalysts with the addition of Re (Re/V or Mo = 0.5) were synthetized and tested in oxidative dehydrogenation of propane and in reduction by propane. XPS measurements showed depletion of the surface in Re. The Re additive does not affect the total conversion of propane, but increases the selectivity to propene. The effect is more pronounced for the MoO_x/TiO₂ catalyst. The increase in the selectivity to propene is accompanied with the increase in the reducibility of the catalysts.     

Synergetic effect between NiO and Ni3V2O8 in propane oxidative dehydrogenation

The oxidative dehydrogenation (ODH) of propane was investigated on Ni-V-O catalysts in a wide range of vanadium contents (5-40%). The addition of a small amount of vanadium significantly increased the catalytic activity of NiO for oxidative dehydrogenation of propane to propene. The formation of propene has a good correlation with the coexistence of NiO and Ni₃V₂O₈. This result strongly suggests that a synergetic effect exists between them in Ni_XV_1-XO_Y (X = 0.95 to 0.6). The best results were obtained with a high Ni/V ratio (e.g. X = 0.95 to 0.85). The active sites and selective oxygen species are discussed. The influence of the catalyst preparation technique and the redox properties of the catalyst were also examined.     

How Strain Affects the Reactivity of Surface Metal Oxide Catalysts

Highly dispersed molybdenum oxide supported on mesoporous silica SBA‐15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2–2.5 Mo atoms nm^?2). X‐ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO₄ units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature‐programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O‐K‐edge at high Mo loadings are explained by distorted MoO₄ complexes. Limited availability of anchor silanol groups at high loadings forces the MoO₄ groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity.     

Iron-Doped Nickel Molybdate with Enhanced Oxygen Evolution Kinetics

Electrochemical water splitting is one of the potential approaches for making renewable energy production and storage viable. The oxygen evolution reaction (OER), as a sluggish four-electron electrochemical reaction, has to overcome high overpotential to accomplish overall water splitting. Therefore, developing low-cost and highly active OER catalysts is the key for achieving efficient and economical water electrolysis. In this work, Fe-doped NiMoO₄ was synthesized and evaluated as the OER catalyst in alkaline medium. Fe³⁺ doping helps to regulate the electronic structure of Ni centers in NiMoO₄, which consequently promotes the catalytic activity of NiMoO₄. The overpotential to reach a current density of 10 mA cm⁻² is 299 mV in 1 m KOH for the optimal Ni_0.9Fe_0.1MoO₄, which is 65 mV lower than that for NiMoO₄. Further, the catalyst also shows exceptional performance stability during a 2 h chronopotentiometry testing. Moreover, the real catalytically active center of Ni_0.9Fe_0.1MoO₄ is also unraveled based on the ex situ characterizations. These results provide new alternatives for precious-metal-free catalysts for alkaline OER and also expand the Fe-doping-induced synergistic effect towards performance enhancement to new catalyst systems.     

具备高首周库仑效率的高性能锂离子电池负极材料Li2Ni2(MoO4)3@C的制备

采用常规的固相反应法结合机械球磨制备了含碳质量分数23.7%的Li₂Ni₂（MoO₄）₃@C复合材料,并应用于锂离子电池负极。与纯Li₂Ni₂（MoO₄）₃相比,Li₂Ni₂（MoO₄）₃@C具有优异的电化学性能,在电流密度为200 mA·g^-1时,50周循环后,可逆容量高达845 mAh·g^-1。值得注意的是,Li₂Ni₂（MoO₄）₃@C的首周库仑效率高达85%。此外,运用循环伏安法对Li₂Ni₂（MoO₄）₃@C复合物存储锂行为进行了初步探索。     

Comparative study of coke deposition on catalysts in reactions with and without oxygen

Two types of catalysts, i.e. Pt/γ Al₂O₃ and Cu/Na-ZSM-5, were used to investigate the catalyst activity and amount of coke formation on the spent catalysts. The reactions of particular interest were the hydrocarbon oxidation and the SCR of NO with and without O₂. Propane and propene were used as the hydrocarbon sources. The reaction conditions were as follows: reaction temperature =170–500°C, GHSV=4,000 hr⁻¹, TOS=2 hr, feed composition depending on each reaction, but the composition of gases were fixed as HC=3,000 ppm, NO=1,000 ppm and O₂=2.5%, using He balance. It was found that both the case of Pt/γ Al₂O₃ and the case of Cu/Na-ZSM-5, propene provided higher conversion and coke deposition than propane in the presence or the absence of O₂ and/or NO. For Pt/γ Al₂O₃ catalyst, in case of the absence of oxygen reactions, the propene conversion dropped more rapidly than the propane conversion. Finally the reaction of propene gave a lower percent of hydrocarbon conversion than the reaction of propane. Additionally, propene had a higher percent selectivity of coke formation for the reaction with the absence of oxygen, but propane had a higher percent selectivity of coke formation for the reaction with the presence of oxygen. For Cu/Na-ZSM-5, in the system with absence and presence of oxygen, the addition of oxygen caused a significant change in % coke selectivity. With the presence of NO_x, the percent conversion of both propane and propene decreased and that the % coke selectivity of propane decreased, whereas that of in propene increased.     

Phase formation in the Li2MoO4-A2MoO4-NiMoO4 (A = K, Rb, Cs) systems, the crystal structure of Cs2Ni2(MoO4)3, and color characteristics of alkali-metal nickel molybdates

The subsolidus regions of the Li₂MoO₄-A₂⁺MoO₄-NiMoO₄ (A⁺ = K, Rb, Cs) systems at 510°C have been triangulated by the intersecting-joins method. The A₂MoO₄-Li₂Ni₂(MoO₄)₃, Li₂MoO₄-A₂Ni₂(MoO₄)₃, A₂Ni₂(MoO₄)₃-Li₂Ni₂(MoO₄)₃ (A = K, Rb, Cs), and ALiMoO₄-A₂Ni₂(MoO₄)₃ (A = K, Rb) joins have been investigated. The subsolidus phase formation study has also been completed by spontaneous flux crystallization. No triple salts have been identified, but only compounds belonging to the boundary binary systems. The crystal structure of Cs₂Ni₂(MoO₄)₃ (a = 10.7538 ?, Z = 4, space group P2₁3, R = 0.0082) belonging to the langbeinite type has been determined. It is built of a three-dimensional framework of vertexsharing MoO₄ tetrahedra and NiO₆ octahedra and cesium ions occupying large out-of-framework cavities. All alkali-metal nickel molybdates are yellow. These compounds are usable as pigments, as judged from their reflection spectra and calculated color characteristics, namely, colorfulness (C), lightness (L), and hue (H).     

Synthesis,Characterization, and Chemical Vapor Transport of Solid Solutions in the MgMoO4‐NiMoO4 System

Two solid solution series exist in the system MgMoO₄‐NiMoO₄. The α‐Ni_1–yMg_yMoO₄ solution series, isostructural to α‐NiMoO₄, is thermodynamically stable at ambient conditions for compositions between 0 % and about 75 % magnesium content. The solution series β‐Mg_1–xNi_xMoO₄, isostructural to MgMoO₄ and the high temperature β modification of NiMoO₄, is thermodynamically stable at ambient conditions for compositions with < 25 % nickel content. A complete solid solution series β‐Mg_1–xNi_xMoO₄ exists at higher temperatures (> 823 K). The transition temperature for the α → β transition decreases with increasing magnesium content. The coexistence of both polymorphs at room temperature in samples with a wide range of composition is a result of the kinetic inhibition of the phase transition β → α. The chemical vapor transport of β‐Mg_1–xNi_xMoO₄ solid solutions with chlorine was investigated. Crystals with a nickel content up to 25 % were synthesized in temperature gradients 1273 K → 1223 K or 1273 K → 1173 K. Deposited nickel richer crystals are destroyed during cooling down to room temperature due to the phase transition. The observed distinctive nickel enrichment during the transport process is in good agreement with predictions by thermodynamic modeling.     

Dehydrogenation of propane in the presence of carbon dioxide over oxide-based catalysts

In the present study, we show the advantages of CO₂ use for the dehydrogenation of propane to propene on the basis of thermodynamic considerations and some experimental results. Several metal oxides Ga₂O₃, Cr₂O₃, Fe₂O₃ unsupported and supported on g- Al₂O₃ and SiO₂ were tested. Ga₂O₃ catalyst was found to be an effective agent for dehydrogenation of propane to propene. The yield of propene at 873 K was 30.1 %. This revised version was published online in June 2006 with corrections to the Cover Date.     

钼掺杂LaVO4上丙烷氧化脱氢

研究了钼掺杂LaVO4催化剂的丙烷氧化脱氢催化性能.加入钼对丙烷氧化脱氢反应有很好的助催化作用.当丙烷转化率恒定在10％和20％时，丙烯选择性在LaMo0.1V0.9O4.05上分别达到了56％和43％，而在LaVO4上仅为36％和22％，这归结为钼掺杂催化剂上有利于丙烯生成的可活动氧物种的增加和催化剂氧化还原性的改变.     

ZrO2‐Based Alternatives to Conventional Propane Dehydrogenation Catalysts: Active Sites,Design, and Performance

Non‐oxidative dehydrogenation of propane to propene is an established large‐scale process that, however, faces challenges, particularly in catalyst development; these are the toxicity of chromium compounds, high cost of platinum, and catalyst durability. Herein, we describe the design of unconventional catalysts based on bulk materials with a certain defect structure, for example, ZrO₂ promoted with other metal oxides. Comprehensive characterization supports the hypothesis that coordinatively unsaturated Zr cations are the active sites for propane dehydrogenation. Their concentration can be adjusted by varying the kind of ZrO₂ promoter and/or supporting tiny amounts of hydrogenation‐active metal. Accordingly designed Cu(0.05 wt %)/ZrO₂‐La₂O₃ showed industrially relevant activity and durability over ca. 240 h on stream in a series of 60 dehydrogenation and oxidative regeneration cycles between 550 and 625 °C.     

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.     

Kinetic investigation of propane oxidation on diluted Mo1–V0.3–Te0.23–Nb0.125–Ox mixed-oxide catalysts

Reaction kinetics and proposed mechanism for the oxidation of propane over diluted Mo₁–V_0.3–Te_0.23–Nb_0.125–O _x are described. The kinetic study allowed determination of the orders of propane disappearance, propene formation, CO _x formation, and acids formation. The results show that selective oxidation of propane to propylene over this catalyst follows the Langmuir-Hinshelwood mechanism. Deep oxidation of propane to carbon dioxide is first order with respect to hydrocarbon, and partial order (0.21) with respect to oxygen. The selective oxidation of propane to acrylic acid is half order with respect to hydrocarbon and partial order (0.11) with respect to oxygen, while water does not participate directly in propane transformation. The result also shows that the overall reaction consists of three parallel process channels. One main sequence of consecutive reactions leads to the desired product.     

Ferric Single-Site Catalyst Confined in a Zeolite Framework for Propane Dehydrogenation

Non-oxidative dehydrogenation of propane is a highly efficient approach for industrial preparation of propene that is commonly catalyzed by noble Pt or toxic Cr catalysts and suffers from coking. In this work, ferric catalyst confined in a zeolite framework was synthesized by a hydrothermal procedure. The isolated Fe in the framework formed distorted tetrahedra, which were beneficial for the selective dehydrogenation of propane and reached over 95 % propene selectivity and over 99 % total olefins selectivity. This catalyst had a silanol-free structure and was oxygen tolerant, hydrothermally stable, and coke free, with a deactivation constant of 0.01 h⁻¹. This study provided guidance for the synthesis of structural heteroatomic zeolite and efficient propane non-oxidative dehydrogenation over early transition metals.     

Oxidation of propane over substituted Keggin phosphomolybdate salts

Ammonium salts, (NH₄)₆HPMo₁₁MO₄₀ (M = Ni, Co, Fe), have been investigated for the oxidation of propane, with molecular oxygen, at temperature ranging between 380 °C and 420 °Cafter in-situ pre-treatment performed at two heating rate of 5 or 9 °C/min. They were characterized by BET method, XRD, ³¹P NMR, UV-Vis and IR techniques. The catalysts were found active in the propane oxidation and selective to propene or acrolein, in particular for samples pre-treated with the heating rate of 9 °C/min.     

Preparation of lithium molybdenum oxide bronzes by a temperature gradient flux growth technique

Single crystals of the violet-red Li_0.9Mo₆O₁₇, violet-blue Li_0.32MoO₃, and the new blue Li_0.04MoO₃ bronzes have been grown by a temperature gradient flux growth method in evacuated quartz ampoules. Optimal growth conditions determined for each of the phases are reported. Li_0.9Mo₆O₁₇ is monoclinic, and a quasi-two-dimensional metallic conductor at room temperature, similar to K_0.9Mo₆O₁₇ · Li_0.04MoO₃ appears to be a new intercalation compound of MoO₃.     

Role of CO2 in dehydrogenation of propane over CrOX/SiO2 catalyst with low Cr content

When ethene alone was contacted with silica supported cobalt catalyst (Co/SiO₂), ethene homologation took place with considerable activity. Moreover, the propene metathesis reaction was suppressed ca. 1/6 fold as much as in the case using MoO_X/SiO₂ catalyst. The possibility of selective homologation with a lower activity for metathesis was suggested for the cobalt-based catalyst system.     

Thermal activation of typical oxidative dehydrogenation catalyst precursors belonging to the Ni−Mo−O system

NiMoO₄ obtained by calcination of precursors has been shown to be a very effective catalyst for oxidative dehydrogenation of propane into propene. Preparation conditions and thermal decomposition of two precursors have been studied by TG-DTA, HTXRD, FFT-IR, and thermo-desorption coupled to mass spectroscopy in order to determine their composition and to define the best treatment to favour the oxidative dehydrogenation process. The selectivity and activity for propane transformation into propene are very different depending on the nature of the precursor and of the active phases obtained after thermal activation. The more selective high-temperature β phase of NiMoO₄ has been obtained at a lower temperature (500°C) than previously reported (700°C).     

Solid solutions of Ni and Co molybdates in silica-dispersed and bulk catalysts prepared by sol-gel and citrate methods

Silica-dispersed catalysts based on cobalt, nickel and mixed Ni-Co molybdates of various compositions are prepared by a sol-gel procedure from silicon alkoxides, metal nitrates and ammonium heptamolybdate. For comparative purposes, the corresponding bulk molybdates are obtained by the citrate route. The polymorphism and the textural properties of these catalysts are investigated by means of X-ray diffraction, UV-visible diffuse reflectance spectroscopy and Raman spectroscopy. Their surface and textural characteristics are investigated by X-ray photoelectron spectroscopy and nitrogen or krypton physisorption. In the sol-gel prepared catalysts, the β-phase of Ni_1−xCo_xMoO₄, which is the most active phase in the oxidative dehydrogenation of light alkanes, is stabilized over the whole composition range. In the analogous bulk catalysts prepared by the citrate method, this phase is stabilized only at high Co content (x?0.55). Dispersion of the active phase in silica is shown to improve the propene productivity in comparison with bulk catalysts obtained by citrate or coprecipitation methods.     

Die Lichtabsorption des Ni2+ und Co2+ in Molybdaten(VI)

Zusammenfassung Die Lichtabsorption von CoMoO₄, Co_0,1Mg_0,9MoO₄, NiMoO₄ und Ni_0,1Mg_0,9MoO₄ wird untersucht. Es zeigt sich, daß die verschiedenartigen Strukturen bei MolybdatenM ^IIMoO₄ (M ^II=Mg, Mn, Ni, Co) durch Unterschiede in der Kristallfeld-stabilisierung derM ^II bedingt sind.

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The absorption of light by CoMoO₄, Co_0,1Mg_0,9MoO₄, NiMoO₄ and Ni_0,1Mg_0,9MoO₄ has been investigated. It was found that the different types of structure of the molybdatesM ^IIMoO₄ (M ^II=Mg, Mn, Ni, Co) are due to differences of the crystal field stabilization ofM ^II.

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