Mo—V—Te—Nb-O催化剂在丙烷氧化制丙烯酸反应中活化条件的研究

研究了Mo—V—Te—Nb—O催化剂在丙烷选择氧化制丙烯酸反应中的活化条件，从预处理气氛、预处理温度及预处理时间等方面作了较为详细的研究。实验发现，经一种特殊气氛预处理的Mo—V—Te—Nb—O催化剂在丙烷选择氧化制丙烯酸反应中具有非常好的催化活性，在最佳活化条件下，其丙烷转化率由活化前的15％提高到27％，丙烯酸选择性则由38％提高到70％。     

MoVTeNbO_x催化剂焙烧条件对丙烷氧化制丙烯酸的影响

制备了Mo1V0.25Te0.13Nb0.12Ox催化剂,研究了焙烧条件（焙烧方式、焙烧气氛和焙烧温度）对该催化剂在丙烷选择氧化制丙烯酸反应中的影响。结果表明,两段间歇式焙烧要优于一段式连续焙烧所得催化剂的催化效果,适宜的预焙烧温度既有利于脱除挥发性物质和化学结合水,又能避免活性组分氧化生成不利的晶相;在惰性气氛中焙烧所得催化剂的催化效果要优于在弱氧化性气氛中焙烧,丙烷转化率和丙烯酸收率随着焙烧温度的升高先增加后减小,在600 ℃时达到最大值。     

丙烷直接氧化制丙烯酸的研究进展及展望

丙烷直接氧化制丙烯酸是近年来烃类催化氧化的热点课题。MoVTeNbOx复合金属氧化物催化剂被认为是目前对于该反应催化性能最好的一类催化剂。作者针对在丙烷直接氧化制丙烯酸领域中影响MoVTeNbOx系列金属氧化物催化性能的因素及将来可能开发的烃类选择氧化反应新工艺两方面进行综述。     

MoVTeNbO催化剂的研究新进展及展望

论述了近年来国内外对丙烷氧化制丙烯酸反应机理的研究,复合金属氧化物催化剂MoVTeNbO的研究新进展。重点介绍了制备MoVTeNbO催化剂的几种新方法和催化剂制备过程中组成变化和催化剂中活性相组成对催化剂性能的影响,并展望了未来的发展趋势。     

丙烷选择氧化金属氧化物催化剂的研究进展

综述了多组分金属氧化物催化剂对非均相选择氧化反应的一般特性，包括酸特性和氧物种的性质及在催化反应中结构／晶相状态的变化。并对丙烷选择氧化的机理及Mo—V—Sb(Te)—Nb—O多组分混合金属氧化物的晶相结构及性能进行了总结。     

VMo/γ-Al_2O_3催化剂上丙烷氧化脱氢制丙烯

以浸渍法制备VMo/γ-Al_2O_3和VMo Mg/γ-Al_2O_3催化剂,考察其催化丙烷氧化脱氢制丙烯的反应活性,采用XRD、UV-Vis DRS和In suit IR对催化剂进行表征。结果表明,V负载质量分数为3%、Mo负载质量分数为7%时的3V7Mo/γ-Al_2O_3催化剂表现出较好的催化性能;添加Mg后催化剂的催化性能有所改善,反应温度500℃时,丙烷转化率为18.19%,丙烯选择性74.76%。丙烷和丙烯在3V7Mo/γ-Al_2O_3和3V7Mo4Mg/γ-Al_2O_3催化剂上吸附后,C—H键的H与催化剂活性中心的晶格氧发生作用形成H—O键,且3V7Mo4Mg/γ-Al_2O_3催化剂上出现C—O键的温度比3V7Mo/γ-Al_2O_3催化剂高,表明加入Mg有利于提高丙烯选择性。     

镓对Pt-K/Al2O3催化剂在丙烷脱氢中活性的影响

以Al_2(SO_4)_3和NaAlO_2为原料,采用双铝法合成拟薄水铝石,再经高温焙烧制备了活性氧化铝载体。采用分步等体积浸渍法,在氧化铝载体上负载Ga、K和Pt,制备催化剂,并考察催化剂对丙烷脱氢制丙烯的催化性能。通过BET比表面分析,简单探讨了催化剂结构与催化剂失活再生的关系。结果表明,同时添加质量分数为1.5%的Ga和1.5%的K,制备的0.3Pt-1.5Ga-1.5K/Al_2O_3催化剂,对丙烷脱氢制丙烯有较高的催化活性,反应1h后,丙烷的转化率和丙烯的选择性分别为46.2%和81.3%。催化剂失活的主要原因是积碳覆盖了活性位,再生后,催化剂活性基本可以恢复到初始状态。     

信息与动态

中国石油兰州石化研究院丙烯酸催化剂获中国专利金奖在第九届中国专利颁奖大会上,由中国石油兰州石化研究院科研人员自主研发的一种复合多金属氧化物催化剂被国家知识产权局授予专利金奖。该催化剂开创了使用国产化催化剂生产丙烯酸的先河,为我国丙烯酸工业的快速发展奠定了坚实基础。该复合多金属氧化物催化剂是丙烯氧化制丙烯醛、丙烯酸催化剂的核心技术。丙烯氧化制丙烯醛、丙烯酸催化剂属于一种多元复合氧化物,主要应用于丙烯氧化制丙烯醛、丙烯酸,异丁烯氧化制甲基丙烯醛等反应中。中国石油兰州石化研究院从20世纪70年代中期开始进行丙…     

丙烷在复合金属氧化物上的选择氧化与氨氧化

综述了复合金属氧化物催化剂（CMO）上丙烷选择氧化制取丙烯酸和氨氧化制取丙烯腈的反应过程及水和氨在其中的作用，介绍了丙烷选择氧化和氨氧化过程中具有活性和选择性的晶相性质，并对今后的研究进行了展望。     

丙烷选择氧化制丙烯酸MoVTeNbO催化剂研究进展

对丙烷选择氧化制丙烯酸的3类催化剂进行了分析,指出了它们未来的研究方向,重点对MoVTeNbO催化剂上丙烷氧化反应机理进行了探讨,总结了人们对该催化剂晶相结构认识的差异,复合金属氧化物催化剂研究的重点是准确掌握催化剂结构．性能关系,实现具有特定晶相结构催化剂的重现性。     

M1 to M2 Phase Transformation and Phase Cooperation in Bulk Mixed Metal Mo–V–M–O (M=Te, Nb) Catalysts for Selective Ammoxidation of Propane

In the present study we systematically explored hydrothermal synthesis of bulk mixed metal Mo–V–(Te–Nb)–O catalysts and investigated the bulk characteristics of the resulting M1 and M2 phases as well as their roles in the selective ammoxidation of propane. It was found that unlike Mo–V–Te–Nb–O M1 phases, the Mo–V–Te–O M1 phases may be quantitatively transformed into M2 phases of the same chemical composition indicating that Nb stabilizes the M1 structure. The stabilizing role of Nb and Te was further observed in high resolution TEM studies of Mo–V–(Te–Nb)–O catalysts which indicated that structural order and the M1 phase domain size progressively decreased in this order: Mo–V–Te–Nb–O > Mo–V–Te–O > Mo–V–O. The cooperation between the M1 and M2 phases in propane ammoxidation to acrylonitrile was observed only at low propane conversions suggesting that the M1 phase is the only crystalline phase required for the activity and selectivity of the Mo–V–Te–Nb–O catalysts in propane ammoxidation to acrylonitrile at practical propane conversions.     

Characterization and catalytic studies of PVD synthesized Mo/V/Nb/Te oxide catalysts

Multicomponent Mo/V/Nb/Te oxide catalysts were synthesized using physical vapor deposition (PVD) onto the substrates of Si wafers and of honeycomb cordierites. The PVD films were prepared at different metal deposition sequences and were subsequently calcined at different temperatures and environment (air or N₂). The PVD films on Si wafer were characterized using several surface techniques, including X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and secondary ion mass spectrometry (SIMS). In parallel, PVD films on cordierites were evaluated in a fixed-bed reactor for the selective oxidation of propane to acrylic acid. The combined synthesis, characterization, and reactor studies provided clear evidence that the surface compositions and the catalytic properties of the Mo/V/Nb/Te oxide catalysts depend strongly on the metal deposition sequence, calcination temperature, and calcination environment.     

Preparation, Characterisation and Catalytic Behaviour of a New TeVMoO Crystalline Phase

TeM_xMo_1.7O mixed oxides (M = V and/or Nb; x = 0-1.7) have been prepared by calcination of the corresponding salts at 600 °C in an atmosphere of N₂. A new crystalline phase, with a Te/V/Mo atomic ratio of 1/0.2-1.5/1.7, has been isolated and characterised by XRD and IR spectroscopy. This phase is observed in the TeVMo or TeVNbMo mixed oxide but not in the TeNbMo mixed oxide. The new crystalline phase shows an XRD pattern similar to Sb₄Mo₁₀O₃₁ and probably corresponds to the M1 phase recently proposed by Aouine et al. (Chem. Commun. 1180, 2001) to be present in the active and selective MoVTeNbO catalysts. Although these catalysts present a very low activity in the propane oxidation, they are active and selective in the oxidation of propene to acrolein and/or acrylic acid. However, the product distribution depends on the catalyst composition. Acrolein or acrylic acid can be selectively obtained from propene on Nb-free or Nb-containing TeVMo catalysts, respectively. The presence of both V and Nb, in addition to Mo and Te, appears to be important in the formation of acrylic acid from propene.     

Influence of gel composition in the synthesis of MoVTeNb catalysts over their catalytic performance in partial propane and propylene oxidation

MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different molar compositions (Mo/Te ratio from 2 to 6 and Nb/(V + Nb) ratio from 0 to 0.7) in the synthesis gel leading to different crystalline phases distribution and catalytic behaviour in the partial oxidation of both propane and propylene to acrylic acid. Chemical analysis indicates that the composition of samples before and after the heat-treatment changes, especially the Te-content, since a significant amount of Te is lost during the heat-treatment step when the amount of oxalate (from niobium oxalate) increases in the synthesis gel. Thus, the nature of the crystalline phases and the catalytic performance of heat-treated materials will be related to the final chemical composition. On the other hand, only the catalysts presenting Te₂M₂₀O₅₇ (M = Mo, V, Nb) crystalline structure, the so-called M1 phase, were active and selective in the partial oxidation of propane to acrylic acid. Moreover, all catalysts were active and relatively selective to the formation of O-containing products, i.e. acrolein and/or acrylic acid, during the partial propylene oxidation although the more active ones were those presenting M1 phase.     

Structural organization of catalytic functions in Mo-based oxides for propane selective oxidation

Several single phasic MoVO-based mixed oxides, all of which have a layer structure in the direction of c-axis and a high dimensional arrangement of metal octahedra in a–b plane, were synthesized by hydrothermal method and their catalytic performance in the selective oxidation of propane to acrylic acid were compared in order to elucidate structure effects on catalytic property and roles of constituent elements. It was clearly demonstrated that the catalyst with the particular arrangement of MO₆ (M = Mo, V) octahedra forming slabs with pentagonal, hexagonal and heptagonal rings in (0 0 1) plane of orthorhombic structure was exclusively superior both in the propane oxidation activity and in the selectivity to acrylic acid to the other related Mo- and V-based layer oxide catalysts consisting of either pentagonal or hexagonal ring unit. The role of constituent elements was clarified by the comparison of catalytic performance of MoVO, MoVTeO and MoVTeNbO, all of which have the same orthorhombic structure. Mo and V, which were indispensable elements for the structure formation, were found to be responsible for the catalytic activity for propane oxidation. Te located in the central position of the hexagonal ring promoted the conversion of intermediate propene effectively, resulting in a high selectivity to acrylic acid. The introduced Nb occupied the same structural position of V and the resulting catalyst clearly showed the improved selectively to acrylic acid particularly at high conversion region, because the further oxidation of acrylic acid to CO_x was suppressed.     

Catalytic oxidative activation of light alkanes over Mo–V-based oxides having controlled surface

An arrangement of catalytically active elements of Mo, V, and Te in an oxide solid with a single crystallographic phase was successfully done by the hydrothermal synthetic method. A black solid powder with a rod-shape (by SEM) was obtained. This catalyst material was first air-treated at 280°C for 2 h, by which Te was stabilized in the structure. The air-treated sample was then heat-treated at 600°C in a nitrogen stream. It was revealed by XRD analysis that this treatment made the solid in a well-crystallized state. Finally, in order to break the rods into fine powders, the well-crystallized rod-shaped material was ground, by which a face of the cross-section of the rods seems to be preferentially appeared. Thus obtained catalyst, Mo₆V₃Te₁O _x , showed a high activity for the selective oxidation of propane to acrylic acid at 360°C. Since the grinding was found to be the most effectual determinant in the propane conversion and the acrylic acid formation, the surface on the cross-section part of the rod-shaped crystals is active for the selective oxidation. It was assumed that all the elements of Mo, V, and Te arrange in this surface and effectively promote the consecutive oxidation from propane to acrylic acid via propene and acrolein.     

Inhibition of Propylene Oxidation to Acrylic Acid by Amorphous Overlayers on MoV(Nb)TeO Based M2 Catalysts

One of the most effective catalysts for the selective oxidation of propane to acrylic acid (AA) and ammoxidation to acrylonitrile (AN) is the MoV(Nb,Ta)(Te,Sb)O system, comprised of two phases, with M1 the major catalyst and M2 the co-catalyst in symbiosis with M1, converting intermediately formed propylene to the respective desired end products. An improvement in either phase should enhance the overall desired yields of a combined M1/M2 conglomerate. The current study concentrates on the M2 phase (variously substituted and/or doped) where depending on composition and preparation technique crystalline materials or crystalline materials with amorphous overlayers are obtained. Crystalline M2 catalysts without amorphous overlayers are vastly superior to those encumbered with overlayers. In a comparative study the former give a maximum AN yield of ~45% in propylene ammoxidation, the latter ~24%. In the selective oxidation of propylene to acrylic acid, the difference in performance between the two types of catalysts becomes enormous: The crystalline M2 catalyst gives a maximum AA yield of ~34% while the Te–molybdate overlayered M2 a meager ~3%. Doping of crystalline M2 phase with P significantly enhances AA yields over the base and should be seriously considered in future attempts to improve M1/M2 propane/propylene catalyst systems.     

The influence of additives and their concentration on the selectivity of catalysts based on heteropoly compounds in the reaction of propane oxidation

The catalytic properties and X-ray phase structure of molybdophosphoric heteropoly acid modified with Sb, W, and Nb ions have been studied in the reaction of propane oxidation. The additive of Nb ions increases the total activity of catalyst and its selectivity to acrolein and acrylic acid and decreases the selectivity to propylene. The concentration of Nb ions in samples is varied from 0.025 to 1 mol %. The concentration of Nb ions at a level of 0.025–0.1 mol % has the most profound effect on the reaction selectivity and the yield of mild oxidation products. The reaction selectivity depends on both the concentration of added niobium and the reaction conditions. The growth in the reaction temperature increases the conversion and selectivity to acrolein and reduces the selectivity to acrylic acid and propylene. The use of reaction mixture with higher propane concentrations decreases sharply the selectivity to acrolein. The obtained data can be explained by the possibility of the rearrangement of Nb ions between the cationic and anionic sublattices of heteropoly acids and by the change in the ratio between the acrolein and acrylic acid formation rates. The development and application of heteropoly compounds modified with niobium permits to increase the yield of target products in the partial propane oxidation.