Selective oxidation of isobutane over Mo-V-Te mixed oxide catalysts with different tellurium contents

A series of MoV_0.3Te_x (x = 0−0.3) mixed oxides were prepared and investigated for the selective oxidation of isobutane. Among them, MoV_0.3Te_0.23 showed the best methacrolein and methacrylic acid selectivity (as high as 17% and 16%, respectively), and the yield to methacrolein and methacrylic acid reached 3.6% and 3.5%, respectively, at 21.3% isobutane conversion at 440°C.     

水热法合成的MoVTeNbOx多组分氧化物催化剂上异丁烷的选择氧化

采用水热法合成了MoVTeNbOx多组分氧化物催化剂, 并用XRD, ICP, BET和SEM等方法对催化剂进行了表征, 考察了MoVTeNbOx多组分氧化物催化剂的组成、反应温度和空速对异丁烷选择氧化反应性能的影响. 其中组成为MoV0.3Te0.17Nb0.12Ox的催化剂显示出最好的催化活性和选择性, 在673 K下, 异丁烷的转化率为10.8%, 甲基丙烯醛(MAL)和甲基丙烯酸(MAA)的收率累积达到6.5%.     

Effect of calcination conditions on the catalytic behavior of Te-Mo mixed oxide catalysts in oxidation of isobutane and isobutene

A series of Te-Mo-O catalysts were prepared by decomposing (NH₄)₆TeMo₆O₂₄·nH₂O telluromolybdate under different conditions and tested for the selective oxidation of isobutane and isobutene. Characterization results showed that their structure and properties depend on the calcination conditions. Catalytic tests showed that molybdenum may be the key element for the activation of isobutane, whereas the selective oxidation of isobutene to methacrolein might proceed mainly on the surface of a TeMo-containing crystalline phase.     

The Effect of Nb Loading on Catalytic Properties of Ni/Ce0.75Zr0.25O2 Catalyst for Methane Partial Oxidation

In this study,the effect of Nb loading on the catalytic activity of Ce_(0.75)Zr_(0.25)O_2-supported Ni catalysts was studied for methane partial oxidation.The catalysts were characterized by BET,H_2 chemisorption,XRD,TPR,TEM and tested for methane partial oxidation to syngas in the temperature range of 400-800℃at atmospheric pressure.The results showed that the activity of methane partial oxidation on the catalysts was apparently dependent on Nb loading.It seemed that the addition of Nb lowered the catalytic activity for methane partial oxidation and increased the extent of carbon deposition. This might be due to the strong interaction between NiO and Nb-modified support and reduction of surface oxygen reducibility.     

Cr掺杂的丙烷选择氧化制丙烯酸高效催化剂

在丙烷选择氧化制丙烯酸催化剂MoVTeNbOx的活性相M1基础上掺杂一定量的Cr,当Cr/Nb摩尔比为0.002时,催化剂具有很高的丙烯酸选择性(78.3%)和收率(50.7%);并采用X射线衍射、X射线光电子能谱、程序升温还原、O2程序升温脱附、NH3程序升温脱附和异丙醇氧化等手段对催化剂的构效关系进行了探讨.结果表明,适量Cr的添加可调节催化剂表面Mo6+,V5+和Te4+等物种含量,提高催化剂的氧化能力,使丙烷转化率增加.同时,适量Cr的添加使得催化剂表面酸强度下降,酸性位点数量减少,从而抑制丙烯酸的深度氧化,提高了丙烯酸选择性.     

Catalytic activity of V-substituted Cs2Te0.2H0.6 + xPMo12 ? xVxOn heteropoly compounds in selective oxidation of isobutane

A series of Cs₂Te_0.2H_{0.6 + x} PMo_{12 − x} V _x O _n (x = 0–3) heteropoly compounds has been prepared and tested in the partial oxidation of isobutane. Catalytic tests show that at 350°C very high selectivity to methacrylic acid (60.1%) can be achieved at isobutane conversion of 12.2% over a Cs_2.0Te_0.2H_1.6PMo₁₁VO _n catalyst with only one molybdenum atom per unit cell substituted by vanadium. The presence of Te⁴⁺ in the heteropoly compounds appears to interfere with the dehydrqgenation step and favor the formation of methacrolein and methacrylic acid.     

Selective Oxidation of Isobutane over NH4CsFePVMoAs Heteropolycompound Catalysts

A series of NH4Cs1.5Fe0.08HxPVMo11AsαOy heteropolycompound catalysts for the selective oxidation of isobutane, having Keggin structure, were synthesized by using co-precipitation method. The catalysts were characterized by FT-IR, H2-TPR, TG-DTA, SEM and XRD. Effects of the As content,reaction time, reaction temperature and molar ratio of isobutane to oxygen in feedstock on the activity and selectivity of the catalyst were investigated. The activation energy of the catalysts was measured by kinetics researches. Results showed the introduction of Cs^ into the catalysts shortened the stable period of them and enhanced their catalytic activity for the selective oxidation of isobutane. The highest conversion of isobutane and the total selectivity to liquid products were 18.6% and 81.2%, respectively,which were obtained at 380 *(3 with a space velocity of 975h^-1 over the NH4Cs1.5Fe0.08HxPVMo11 As0.3Oy heteropolycompound catalyst. It is confirmed that completely oxidized products were controlled well.     

Novel KF-TiO2catalysts for oxidative dehydrogenation of isobutane

A novel type of catalysts, KF-TiO₂, efficient for the oxidative dehydrogenation (ODH) of isobutane is presented. The effect of KF content and calcination temperature was studied. In the reaction conditions explored, the best performance (73 % selectivity to isobutene at 10.5 % conversion of isobutane) was observed over a catalyst with KF/TiO₂ = 0.2 (mol/mol). The surface properties of the catalysts were investigated by SPS (Surface Photo-voltage Spectroscopy) and XPS. The promotion effect of KF in the catalysts can be attributed to the formation of an oxyfluoro-compound, K₂Ti₄O₈F₂.     

Dehydrogenation of isobutane in the presence of carbon dioxide over supported vanadium oxide catalysts

Summary The dehydrogenation of isobutane to isobutene in the presence of carbon dioxide was carried out over supported vanadium oxide catalysts. The influence of the support on the catalytic performance was investigated. The isobutane conversion and isobutene selectivity in the presence of carbon dioxide were compared with the results obtained during the dehydrogenation reaction in the presence of helium (inert gas). The catalysts were characterized by temperature-programmed techniques (TPR, TPD-NH₃, TPD-CO₂).     

Study of the acid-base properties of SiO2-supported NiMoO4 catalysts by temperature-programmed desorption: effect of the support

The acid-base properties of several NiMoO₄ catalysts supported on two silicas and prepared by different methods have been studied by temperature-programmed desorption of NH₃. The catalytic behavior in the oxidative dehydrogenation of isobutane for two NiMoO₄ catalysts with different acid-base properties are compared.     

Highly active Mo-V-Te-Nb-O catalysts obtained by eliminating surface Te0 for selective oxidation of propane to acrylic acid

Different methods were used to eliminate the negative effect of surface Te⁰ in Mo-V-Te-Nb-O catalysts. The characterization and catalytic results showed that the best catalytic performance was obtained on the catalyst prepared by addition of HNO₃, and the excellent catalytic behavior could be attributed to the elimination of surface Te⁰ and the optimum synergetic effect between the M1 and M2 phases.     

Short Te …︁ Te bonding contacts in a new layered ternary telluride: Synthesis and crystal structure of 2D Nb3GexTe6 (x ≃ 0.9)

The new layered ternary compound Nb₃Ge_xTe₆ (x ? 0.90) was prepared by direct combination of the elements taken in the stoichiometric proportions 3 : 1 : 6, heated at 1 000 °C for 10 days in silica tubes and quenched to room temperature. The phase crystallizes in the orthorhombic symmetry, space group Pnma (#62), with the following single crystal refined parameters: a = 643.18(5) pm, b = 1391.98(11)pm and c = 1 154.07(5) pm, with Z = 4. The structure was refined to an R of 3.4% (R_w = 4.6%), with 1969 independent reflexions and 49 parameters. The structure is based on the close stacking of trigonal prismatic (TP) slabs in the AA/BB mode. The slabs can be seen as built up from face sharing biprisms, which are filled either by one or by two niobium cations situated in the middle of the trigonal prisms. The germanium is located in the middle of the common face of two prisms, leading to a rather unusual anionic square coordination. The refinements showed that this latter cation does not fill completely its square site. No cation was found in the van der Waals gap between the slabs. The mean d_{Ge? Te} distance (276.5 pm) is in agreement with Ge^II cations, while some Te …? Te distances (from 333.84 to 361.65pm) are too short for anions in a simple contact. These bonding distances, already mentionned in some MTe₂ compounds, are to be ascribed to charge transfer in the structure, with a partial oxidation state for the tellurium anions. Short Nb? Nb and Nb? Ge distances (292.0 and 281.3 pm, respectively) imply intercationic bonding within the slabs.     

Aminated MCM-41-tethered Wilkinson''s complex: active immobilized catalyst precursor for cyclohexene hydroformylation

CuO/Ce_0.7Sn_0.3O₂ catalysts were prepared for the catalytic oxidation of CO. The catalysts were characterized by means of CO-TPD, XRD and TPR. A synergistic interaction between CuO and Ce_0.7Sn_0.3O₂ is responsible for the high activity of carbon monoxide at low temperature.This revised version was published online in December 2005 with corrections to the Cover Date.     

A kinetic study of oxidative dehydrogenation of isobutane to isobutylene over chromium oxide supported on lanthanum carbonate

Kinetics of oxidative dehydrogenation of isobutane to isobutylene over chromium oxide supported on lanthanum carbonate was studied. The formation rate of isobutylene was found to be first order in isobutane and zero order in oxygen concentration and the rate limiting step was the regeneration of active sites by the gas phase oxygen. The formation of CO₂ was due to the consecutive oxidation of isobutylene which occurred on the same active sites used for isobutylene formation, not by the parallel oxidation of isobutane.     

钒氧化物催化CO2氧化异丁烷脱氢的研究

采用溶胶-凝胶法制备了一系列钒氧化物催化剂,并用于CO₂氧化异丁烷脱氢反应. 采用X射线衍射、低温N₂吸附-脱附、O₂程序升温氧化、程序升温表面反应和原位傅里叶变换红外光谱等方法研究了催化剂的性质. 反应结果表明,尽管所有钒氧化物催化剂的丁烯选择性都大于85%,但随着催化剂组成和制备方法的改变,催化活性和稳定性差异显著. 其中,12 wt% V₂O₅/Ce_0.6Zr_0.4O₂（7 wt%）-Al₂O₃的催化活性最高,而6 wt% V₂O₅-Ce_0.6Zr_0.4O₂（7 wt%）-Al₂O₃的稳定性最佳. 关联分析催化反应结果与催化剂表征表明,钒氧化物的催化活性取决于VO_x物种的结晶度和分散度,而催化剂表面所积重质焦炭的特性是决定催化剂稳定性的关键. 非稳态反应和原位光谱结果确认,CO₂氧化异丁烷脱氢遵循Mars-van Krevelen氧化还原机理.     

Keggin-type H4PVMo11O40-based catalysts for the isobutane selective oxidation

Cesium heteropolysalts Cs₃PMo₁₂O₄₀ and HCs₃PVMo₁₁O₄₀ were synthesized by modifying the preparation conditions in order to get materials with a much higher surface area than the original Keggin-type heteropolyacids (H₃PMo₁₂O₄₀ and H₄PVMo₁₁O₄₀). These solids were used as carriers for the dispersion of H₄PVMo₁₁O₄₀ heteropolyacid by the incipient wetness impregnation technique. The textural and structural properties of supports and catalysts were examined by scanning electron microscopy, N₂ adsorption-desorption isotherms and Raman spectroscopy. The supported catalysts were studied before and after red/ox pretreatments by X-ray photoelectron spectroscopy, which showed that both the surface composition and oxidized to reduced species ratio depend on the used carrier. The catalytic performances of these novel supported catalysts in the selective oxidation of isobutane to methacrylic acid and methacrolein were studied. The best catalytic properties were obtained when H₄PVMo₁₁O₄₀ was supported on HCs₃PVMo₁₁O₄₀. The isobutane conversion and yield of the desired oxygenates increased along the unsupported H₄PVMo₁₁O₄₀ < H₄PVMo₁₁O₄₀/Cs₃PMo₁₂O₄₀ < H₄PVMo₁₁O₄₀/HCs₃PVMo₁₁O₄₀ series.

     

Isothermal Reduction Behaviour of Some Metal Molybdates. Selective light alkane oxydehydrogenation and/or olefins partial oxidation

The reduction profile of several unpromoted and promoted metal molybdate catalysts was investigated correlating their reducibility with the reactivity in catalysis. Using the stoichiometric α- and β-nickel molybdate compounds it was observed that the reduction rate was significantly affected by the nature of the phase. The results show thatβ-NiMoO₄ phase led to a significant increase in the reduction rate with respect to α phase. The increased resistance to reduction by hydrogen due to the structure of the catalytic system is reported. It was found that there is a relationship between the reducibility of the catalysts and selectivity to dehydrogenation products, indicating that the lattice oxygen plays an important role in the reaction. The effect of MoO₃, TeO₂ and Te₂MoO₇ added to NiMoO₄ systems onthe reducibility of the catalyst and on the propylene oxidation were also studied. It wasobserved that the reduction rate was significantly affected by the nature of the doping element. The results show that NiMoO₄–MoO₃ combination led toa significant increase of the reduction resistance of the nickel molybdate while TeO₂ or Te₂MoO₇ addition increases its oxygen depletion rate.Ni–Mo–O systems (Mo/Ni>1) were found to favour low CO_x selectivity, high selectivity to C₃H₄O and C₃H₄O₂ and good propylene conversion. In presence of TeO₂ and Te₂MoO₇ doped Ni–Mo–O system both acrolein and propylene conversion were increased with respect to the undoped system. Ni–Mo–Te–O catalysts have been found to have a reducibility trend which fits well with the acrolein and acrylic acid formation from propylene oxidation in presence of molecular oxygen. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pt/TiO2催化剂上CO氧化反应动力学研究

利用沉积沉淀法制备了Pt/TiO₂催化剂, 将其在不同温度下焙烧, 以得到不同颗粒尺寸的Pt. 并将这些样品用于CO催化氧化反应以及反应动力学研究. 结果表明: 焙烧温度对催化剂有明显影响, Pt 颗粒尺寸随着焙烧温度的升高而增加; 与此同时, CO催化活性随焙烧温度的升高呈先增加后降低的趋势, 其中, 400℃焙烧的样品表现出最高的催化活性. 反应动力学结果表明, 催化剂上CO氧化反应表观速率方程为r=5.4×10^-7p_CO^0.17p_O2^0.36,说明在该催化剂上CO氧化遵循Langmuir-Hinshelwood机理. 同时, 对催化剂进行了CO化学吸附红外光谱和O₂化学吸附表征. 结果表明, 随着焙烧温度的升高, 催化剂上CO和O₂吸附量均呈现先升高后降低的趋势, 这与反应结果和反应动力学方程一致, 说明反应受到催化剂表面上CO和O₂吸附浓度的影响. 而在400℃焙烧的催化剂上, CO和O₂吸附量均最高, 因此其反应活性也最好. 这可能是焙烧过程影响了Pt 和TiO₂之间的相互作用引起的.     

Study of the interaction of hydrogen with palladium-containing catalysts of methane oxidation

The reaction of palladium-containing catalysts PdCl₂/SiO₂ [ratio of the components 0.3:100 (molar)] with H₂ (300°C) after methane oxidation leads to the formation of RH: methane, ethane, propane, n-butane, and isobutane. The sources of RH are PdC_x — products of incomplete oxidation of CH₄ — as well as organic impurities in silica gel. Additions of NaCl (NaCl:SiO₂ = 7:100) triple the yield of RH. Catalysts with additions of H₂SO₄ (H₂SO₄:SiO₂ = 40.100) are not hydrogenated to RH.L. M. Litvinenko Institute of Physico-Organic Chemistry and Coal Tar Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg Street, Donetsk 340114, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 177–181, May–June, 1996. Original article submitted July 20, 1995.     

烷基膦酸促进负载磷钨酸催化异丁烷/丁烯烷基化反应

异丁烷/丁烯烷基化是生产高辛烷值汽油的重要反应,目前主要采用液体强酸为催化剂,而固体催化剂用于该反应的性能均不理想。我们设计合成出十六烷基膦酸(HDPA)修饰的氧化硅负载型磷钨酸纳米多级结构催化剂(HDPA-HPW/SiO2),其结构与悬铃木果实相似。通过X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、透射电子显微镜镜(TEM)、氮气吸附-脱附、异丁烷吸附-脱附等对该催化剂进行了表征,并使用固定床微型反应器评价了其对异丁烷/丁烯烷基化反应的催化性能。结果表明,HDPA的外围修饰增强了催化剂对烃类反应物的吸附,减少了烯烃聚合副反应和催化剂表面积碳的产生,提高了高辛烷值产物的选择性,延长了催化剂的寿命。