A Novel Way to Prepareγ-A1_2O_3 Supported SO_4~(2-)/ZrO_2 Solid Superacid Catalysts for n-Butane Isomerization

The isomerization of n-butane to isobutane, which is a valuable precursor for theproduction of MTBE and alkylated gasoline, on strong acid catalysts is an importantprocess in refining industry. Solid superacid, especially sulfated zirconia, has highcatalytic activity in n-butane isomerization at comparatively low temperatures andtherefore has attracted more attention of researchers in the past twenty years.' However,from the view point of practice, the activity of SZ needs to be improved fur…     

ESR Characterization and Activity of V_2O_5/γ-Al_2O_3 Catalysts for Dehydrogenation of Isobutane

IntroductionIsobutene is the raw material for theproduction of many important chemicals.Thedehydrogenation of isobutane to isobutene oncatalysts Cr2 O3/γ- Al2 O3and Pt/γ- Al2 O3have beenextensively studied and successfully applied inindustry[1,2 ] .The dehydrogenation of isobutane to isobuteneis an endothermic reaction and is limited by thechemical equilibrium.Coke is easy formed on thecatalyst surface and the catalyst is frequentlyregenerated in the running.The oxidativedehydrogenation …     

Selective Oxidation of Isobutane to Methacrylic Acid over Supported V-Mo-P Based Composite Oxide Catalysts

Heteropolyacid, the most popular catalyst for the direct oxidation of isobutane, exhibits high catalytic activity, poor thermal stability and a short lifetime. Therefore, the catalyst requires further research to improve its performance. Catalysts composed of mixed oxides (V2O5, P2O5, or MoO3) supported on silica were prepared by the sol-gel method to catalyze the reaction. Results of XRD, IR, and BET corroborated that the mixed oxides were dispersed homogeneously on the surface of support. The activity of lattice oxygen in the catalysts was studied by TPR, and the chemisorption property of isobutane on the surface of the catalysts was investigated by the TPD method. H2-TPR of the catalysts revealed that the lattice oxygen of the vanadium-based catalysts is more active than that of the molybdenum-based catalysts. The redox property of V or Mo species is slightly affected by other compositions of the series catalysts. The TPD curves illustrate that there are two kinds of adsorptive species of isobutane on     

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.     

Mechanosynthesis and mechanochemical treatment of bismuthdoped vanadium phosphorus oxide catalysts for the partial oxidation of n-butane to maleic anhydride

Three Bi-doped vanadyl pyrophosphate catalysts were prepared via dihydrate route （VPD method）, which consisted of different preparation methods including mechanosynthesis, mechanochemical treatment, and the conventional reflux method. The catalysts produced by the above three methods were characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and temperature programmed reduction （TPR）. Catalytic evaluation for the partial oxidation of n-butane to maleic anhydride （MA） was also carried out. The XRD patterns of all the Bi-doped catalysts showed the main peaks of pyrophosphate phase. Lower intensity peaks were observed for the mechanochemically treated Bi-doped catalyst （VPDBiMill） with two additional small peaks corresponding to the presence of a small amount of V5＋ phase. The TPR profiles showed that the highest amount of active oxygen species, i.e, V4＋–O- pair, responsible for n-butane activation, was removed from VPDBiMill. Furthermore, from the catalytic test results, the graph of selectivity to MA as a function of the conversion of n-butane demonstrated that VPDBiMill was the most selective catalyst. This suggests that the mechanochemical treatment of vanadium phosphate catalyst （VPDBiMill） is a potential method to improve the catalytic properties for the partial oxidation of n-butane to maleic anhydride.     

n-Butane Oxidation over γ-Al2O3 Supported Vanadium Phosphate Catalysts

Four vanadium phosphate catalysts supported onγ-Al_2O_3(20 wt%)were synthesized via wetness impregnation of VOHPO_4·0.5H_2O precursor and calcined for different durations(6,10,30 and 75 h)at 673 K in a reaction flow of n-butane/air mixture.The samples calcined for 6 and 10 h produced only a single phase of(VO)_2P_2O_7.However,the VOPO_4 phase(β-VOPO_4)was detected and became more prominent with only a minor pyrophosphate peaks were found after 30 h of calcination.All these pyrophosphate peaks disappeared after 75 h of calcination.The formation of V~(5 )phase was also observed in the SEM micrographs.The redox properties and the nature of oxidants of the catalysts employed in this study were investigated by H_2-TPR analysis.Selective oxidation of n-butane to maleic anhydride(MA) over these catalysts shows that the percentage of n-butane conversion decreases with the transformation of the catalysts from V~(4 )to V~(5 )phases.An appropriate ratio of V~(5 )/V~(4 )can enhance the performance of the VPO catalyst.However,a higher amount of V~(5 )and its associated oxygen species are responsible to promote the MA selectivity.     

Effects of Cs-substitution and partial reduction on catalytic performance of Keggin-type phosphomolybdic polyoxometalates for selective oxidation of isobutane

The catalytic performance of Cs-substituted phosphomolybdic salts was studied for selective oxidation of isobutane. The results of activity tests revealed that 360 °C was the optimal reaction temperature. It was demonstrated that oxidizing sites not only took dominating part in the activation of isobutane, but also influenced the product distribution. Besides, appropriate Cs addition led to moderate acidity of catalysts, favoring the selectivity to desired products. Furthermore, to obtain partially reduced catalysts, different calcination atmospheres were investigated and certain proportion of Mo~(5+) produced during calcination was crucial for the redox reaction. The catalyst calcined in N_2 showed the highest yield of MAA(7.0%). Fe-substitution enhanced the activity of catalysts by rapid reoxidation of Mo~(5+).     

Effect of Cr and Co Promoters Addition on Vanadium Phosphate Catalysts for Mild Oxidation of n-Butane

In this study, Cr and Co promoted, as well as unpromoted vanadium phosphate (VPO) catalysts were synthesized by the reaction of V2O5 and o-H3PO4 in organic medium followed by calcination in n-butane/air environment at 673 K. The physico-chemical properties and the catalytic behavior were affected by the addition of Cr and Co dopants. H2-TPR was used to investigate the nature of oxidants in the unpromoted and promoted catalysts. The results showed that both the Cr and Co promoters remarkably lowered the temperature of the reduction peak associated with V5 . The amount of oxygen species originated from the active phase, V4 , removed was significantly increased for Co and Cr-promoted catalysts. Both Cr and Co dopants improve strongly the n-butane conversion without sacrificing the MA selectivity. A good correlation was observed between the amount of oxygen species removed from V4 phase and the activity for n-butane oxidation to maleic anhydride. This suggested that V4 -O was the center for the activation of n-butane.     

Effect of alcohol solvents treated ZrO（OH）2 hydrogel on properties of ZrO2 and its catalytic performance in isosynthesis

A series of ZrO2 catalysts were prepared by treating ZrO(OH)2 hydrogel with different alcohol solvents (C2-C4 alcohols) and calcining under N2 flow at 773 K for 3 h. The obtained ZrO2 catalysts were systematically characterized by the methods of N2 adsorption-desorption, powder X-ray diffraction, NH3 temperature-programmed desorption, and CO2 temperature-programmed desorption. The catalytic performance of each catalyst was evaluated in the selective synthesis of iso-C4 (isobutene and isobutane) and light olefins (C2= ～C4= ) from CO hydrogenation. The specific surface area increased for the ZrO2 catalysts obtained by treating ZrO(OH)2 hydrogel with different alcohol solvents. The amounts of both acidic and basic sites on the catalyst surface increased obviously. The catalytic activity (CO conversion) of ZrO2 catalysts also increased after the treatment with different alcohol solvents. The highest activity was obtained over the catalyst which was pretreated with isopropanol. However, alcohol solvent treatment retarded the transformation of ZrO2 crystal structure from tetragonal phase to monoclinic phase, and subsequently resulted in the decrease of monoclinic phase in ZrO2, which led to the decrease of olefin selectivity in corresponding hydrocarbon products (C2=～C4= /CH).     

Colloidal Dispersion of Nano-Ru/SiO2 in PEG and its Application for Hydrogenation of Benzene

The conversion of benzene to cyclohexane, a key intermediate in adipic acid production, is still the most important industrial hydrogenation reaction of monocyclic arenes. Traditionally, benzene hydrogenation is performed with heterogeneous catalysts such…     

Impact of molecular structure on the lubricant squeeze-out between curved surfaces with long range elasticity

The properties of butane (C4H10) lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and elastic properties of the solid surfaces. We consider the linear n-butane and the branched isobutane. For the linear molecule, well defined molecular layers develop in the lubricant film when the width is of the order of a few atomic diameters. The branched isobutane forms more disordered structures which permit it to stay liquidlike at smaller surface separations. During squeezing the solvation forces show oscillations corresponding to the width of a molecule. At low speeds (<0.1 ms) the last layers of isobutane are squeezed out before those of n-butane. Since the (interfacial) squeezing velocity in most practical applications is very low when the lubricant layer has molecular thickness, one expects n-butane to be a better boundary lubricant than isobutane. With n-butane possessing a slightly lower viscosity at high pressures, our result refutes the view that squeeze-out should be harder for higher viscosities; on the other hand our results are consistent with wear experiments in which n-butane were shown to protect steel surfaces better than isobutane.     

钾改性对Au/ZSM-5催化剂上正丁烷裂解性能的影响

采用负压沉积沉淀法制备了负载型Au/HZSM-5催化剂,采用X射线衍射（XRD）、透射电镜（TEM）、Ｘ射线光电子能谱（XPS）、NH3-TPD、紫外可见漫反射（UV-vis）等技术对催化剂进行了表征分析,并考察了催化剂对正丁烷裂解性能的影响。结果表明,Au金属成功负载到HZSM-5催化剂上,并且金颗粒的尺寸受负载量的影响,其中1.0%Au/HZSM-5催化剂中的金颗粒粒径最小,约为5～10nm。钾离子作为一种碱性离子可以调节载体酸性,随着K离子的引入xK-Au/HZSM-5催化剂的酸性逐渐降低,使Au0的电子结合能更高。相对于HZSM-5,2.0Au/HZSM-5催化剂对于正丁烷的转化率从13.1%提升到了37.5%,对丙烯的选择性从17.2%提升到了52.5%。随着K离子的引入,催化剂对于丁烯以及异丁烷的选择性有所提高,当K离子负荷为0.08%时,对丁烯的选择性从3.8%提高到36.9%,负荷为0.1%时,对异丁烷的选择性由2.8%提升到51.8%。但原料转化率低于2.0Au/HZSM-5,这可能与K的加入降低催化剂酸改性有关。此外通过研究Au/HZSM-5用K+修饰得知Au+离子是Au/HZSM-5催化剂转化正丁烷主要活性中心。     

Mechanism studies of the conversion of 13C-labeled n-butane on zeolite H-ZSM-5 by using 13C magic angle spinning NMR spectroscopy and GC-MS analysis

By using 13C MAS NMR spectroscopy (MAS = magic angle spinning), the conversion of selectively 13C-labeled n-butane on zeolite H-ZSM-5 at 430-470 K has been demonstrated to proceed through two pathways: 1) scrambling of the selective 13C-label in the n-butane molecule, and 2) oligomerization-cracking and conjunct polymerization. The latter processes (2) produce isobutane and propane simultaneously with alkyl-substituted cyclopentenyl cations and condensed aromatic compounds. In situ 13C MAS NMR and complementary ex situ GC-MS data provided evidence for a monomolecular mechanism of the 13C-label scrambling, whereas both isobutane and propane are formed through intermolecular pathways. According to 13C MAS NMR kinetic measurements, both pathways proceed with nearly the same activation energies (E(a) = 75 kJ mol(-1) for the scrambling and 71 kJ mol(-1) for isobutane and propane formation). This can be rationalized by considering the intermolecular hydride transfer between a primarily initiated carbenium ion and n-butane as being the rate-determining stage of the n-butane conversion on zeolite H-ZSM-5.     

Vibrational overtone spectroscopy of saturated hydrocarbons dissolved in liquefied Ar, Kr, Xe, and N2

This article presents a collection of vibrational overtone spectra of hydrocarbons in cryogenic solutions. Vibrational overtone spectra of ethane and propane dissolved in liquid argon and n-butane and isobutane dissolved in liquid krypton were recorded between 5000 and 14,000 cm(-1). Spectral regions for the first four overtones were measured using a Fourier transform spectrophotometer. The fifth overtone (Deltaupsilon = 6) spectra were recorded with a double beam (pump-probe) thermal lens technique using concentrations as low as 10-3 mole fraction. We obtained the C-H (Deltaupsilon = 6) spectra of (a) liquid ethane at 100 K and ethane in solutions in liquid Ar at 92 K and liquid N2 at 85 K, (b) liquid propane at 148 K and propane in liquid Ar at 93 K, (c) n-butane in liquid Kr at 129 K, (d) n-pentane in liquid Xe at 160 K, and (e) isobutane liquid at 135 K and isobutane in liquid Kr at 130 K. Local-mode parameters were calculated for primary, secondary, and tertiary C-H oscillators in solution and compared with gas-phase local-mode parameters. The peak frequency shift (Deltaomega) from gas phase to solution is explained by the change in harmonic frequency and anharmonicity in solution with respect to the gas-phase values. The bandwidth (Deltaomega1/2) of the (Deltaupsilon = 6) C-H absorption bands of ethane in solution can be explained in terms of collisions with the solvent molecules.     

SO42-/ZrO2-Al2O3催化剂表面酸性质对正丁烷异构化反应性能的影响研究

采用“沉淀-浸渍”法制备一系列不同硫酸负载量的SO₄^2-/ZrO₂-Al₂O₃催化剂,利用N₂吸附-脱附、Py-FTIR、XRD等手段对催化剂进行表征。在常压、200 ℃、H₂：C₄=2：3和质量空速为3 h^-1的反应条件下,在固定床微型反应评价装置上考察了硫酸负载量对SO₄^2-/ZrO₂-Al₂O₃催化正丁烷异构化反应性能的影响。Py-FTIR结果表明,硫酸化处理为催化剂表面提供了丰富的Brønsted酸性位,其中,强Brønsted酸性位在正丁烷异构化反应中起重要作用,因此,硫酸化处理可显著提高正丁烷异构化活性,而Lewis酸性位与之没有直接关系。     

Pt-SO42-/ZrO2固体超强酸上异丁烷与丁烯烷基化反应

由异丁烷和1-丁烯烷基化合成高辛烷值汽油虽已被广泛用于工业生产,但由于液体酸催化剂存在许多缺点,寻找固体酸催化剂——分子筛、磺酸树脂及固体超强酸已受到国内外学者的广泛重视。对超强酸的研究多集中在SO_4~(2-)/氧化物催化剂上,此类催化剂的酸强度高、热稳定性好、制备简单,对异丁烷、1-丁烯烷基化具有较高的反应活性,但存在着积炭、寿命     

异丁烷脱氢催化剂的研究

本文对异丁烷脱氢反应制异丁烯过程催化剂体系及其反应机理进行了述评,指出异丁烷脱氢依然是最有潜力的转化途径,但非贵金属高效催化剂的研制是其关键.详细总 结了不同载体和助剂对脱氢反应的影响,尤其是载体和助剂的酸碱性以及载体的孔结构.弱 酸中心有利于异丁烷脱氢反应的发生,较小的孔结构能提高反应的选择性.催化剂的抗积炭 性能研究表明: 载体表面的弱酸位和活性组分在表面的高分散度以及碱性助剂的加入,有 利于提高催化剂的抗积炭性能.对异丁烷的脱氢反应机理的研究进行了阐述.     

正丁烷脱氢制正丁烯催化剂

综述了对正丁烷脱氢制备正丁烯的催化剂体系,包括有氧脱氢中钒基催化剂、钼酸盐系列和焦磷酸盐系列催化剂;催化脱氢中贵金属Pt系催化剂、以ZSM-5分子筛为载体的催化剂以及膜反应器。探讨了正丁烷脱氢动力学,并在Mars-van Krevlen和 Eley-Rideal机理模型动力学基础上归纳了正丁烷氧化脱氢及直接脱氢的机理。讨论了正丁烷催化剂的影响因素,比较了各类催化剂的特点并对其进行展望,认为ZSM-5分子筛将可能成为正丁烷脱氢制正丁烯的新的研究热点。     

Solid-phase microextraction: investigation of the metabolism of substances that may be abused by inhalation

Purified liquefied petroleum gas (LPG), a mixture of butane, isobutane, and propane, is commonly abused by inhalation. Little is known about the mammalian metabolism of these substances. Metabolism of other hydrocarbons, including n-hexane and cyclohexane, has been studied in vitro using a range of liver preparations, with metabolites analyzed by static headspace techniques. Solid-phase microextraction (SPME) for sampling metabolites in the headspace of incubates of volatile compounds with activated rat liver microsomes is investigated. Cyclohexanol and cyclohexanone were formed from cyclohexane and 1-, 2-, and 3-hexanol and 2-hexanone from n-hexane as predicted. Secondary alcohols are found for the other compounds studied, except for propene and isobutane, together with 2-propanone and 2-butanone from propane and n-butane, respectively. Samples from three individuals who died following LPG abuse contained a range of putative n-butane metabolites: n-butanol, 2-butanol, 2,3-butanediol, 3-hydroxy-2-butanone, and 2,3-butanedione. To our knowledge, the last three compounds have not been proposed as metabolites of n-butane in man. These might be produced through similar metabolic pathways to those of n-hexane and n-heptane. The findings indicate the value of SPME for investigating the metabolism of volatile substances and for detecting and monitoring exposure to these compounds.     

正丁烷和异丁烷在改性纳米HZSM-5上的芳构化反应

用脉冲微反装置评价了正丁烷和异丁烷在氢型和锌改性的纳米ZSM-5催化剂上的反应活性和芳构化选择性.结果表明,在550℃下,异丁烷在氢型和不同锌负载量的纳米ZSM-5催化剂上的转化率都远高于正丁烷,但其芳构化选择性低于正丁烷.脱甲基活化是异丁烷和正丁烷的重要活化方式,也是影响其芳构化选择性的主要因素.锌改性在提高异丁烷和正丁烷转化率的同时,也促进了正丁烷和异丁烷的脱甲基活化.在混合丁烷进料反应的情况下,正丁烷和异丁烷的转化率与其单独进料时十分接近,这说明正丁烷和异丁烷共存时不会发生明显的竞争吸附和反应.纳米ZSM-5因晶粒度小,孔道短和微孔扩散阻力低而有利于异丁烷转化.