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Ce-incorporated MoVTeNbO catalysts were developed to enhance ethylene productivity of oxidative dehydrogenation of ethane (ODHE) to ethylene. Structural characterizations (XRD, TEM, STEM, Raman, and UV–vis DRS) and DFT calculations revealed that Ce atoms were incorporated into MoVTeNbO framework with maintaining its unique structure ( M1 phase), which is active phase for ODHE. The reducibility of the catalysts was enhanced and both V 5+ and the lattice oxygen species available to ODHE reaction were enriched by incorporation of Ce, confirmed by TPR, XPS, and pulse injection method, respectively. These improved properties enhanced the conversion of ethane while maintaining their excellent selectivity to ethylene for MoVTeNbCeO catalysts. It is noteworthy that 56.2% of ethane conversion and 95.4% of ethylene selectivity were retained for 200 h over MoVTeNbCeO-0.1 catalyst. Ethylene productivity was calculated to be 1.11 kgC 2 H 4 /kg cat  h. The developed catalyst exhibits substantial level of ethylene productivity and stability having the possibility with low production of CO x to make a step forward for industrialization of oxidative dehydrogenation of ethane. [ABSTRACT FROM AUTHOR]

Accurate density measurements on three binary (ethane + carbon dioxide) mixtures with ethane mole fractions of 0.05023, 0.20031, and 0.49954 were carried out at temperatures from T  = (273.15 to 323.15) K with pressures up to the dew-point pressure or 6.0 MPa, whichever was lower. The gas mixtures were prepared gravimetrically and a well-proven two-sinker magnetic suspension densimeter was utilized for the measurements. It was observed that sorption effects have an impact on the reproducibility of the density measurements of up to 0.04%. Considering all measurement uncertainties in temperature, pressure, density, and composition, the relative combined expanded uncertainty ( k  = 2) in density was estimated to be less than or equal to 3.8 × 10 −4 . Relative deviations of the experimental densities from the GERG-2008 equation of state were less than 0.5%, which is clearly within the uncertainty of this equation. Values and uncertainties of the second and third virial coefficients were calculated by correlating the isothermal experimental data to a third-order virial equation. Second interaction virial coefficients were determined as well, and excellent agreement with literature was obtained. The new experimental data presented in this work can be especially used to further improve the performance of multi-parameter equations of state for mixtures, particularly in the vicinity of the dew line. [ABSTRACT FROM AUTHOR]

Unmodified and sulfate-modified SBA-15-supported CrO catalysts were prepared by impregnation method. The physico-chemical properties of the supports and catalysts were determined by nitrogen adsorption/desorption, powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), laser-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (UV-DRS), inductively coupled plasma optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM) and temperature-programmed reduction (TPR) techniques. Oxidative dehydrogenation of ethane to ethylene (ODE) with CO as oxidant was carried out on these catalysts in a fixed-bed reactor at temperatures in the range of 600-700 °C and at atmospheric pressure. The changes in structural and textural properties because of sulfate modification were identified. Sulfate modification affected the nature of interaction of CrO species with the SBA-15 support. During the evaluation, it was observed that sulfate modification enhances ethane conversion and ethylene selectivity of the catalyst. Better dispersion of CrO and the increase in Cr/Cr ratio seem to be the reasons for the higher performance of the sulfate-modified catalysts compared to that of the unmodified catalyst. [ABSTRACT FROM AUTHOR]

The methodology of constructing a phenomenological model for complex heterogeneous catalytic reactions is described in detail. The proposed approach is applicable to development of mathematical models describing the onset of self-oscillations in hydrocarbon oxidation on the transition metal surface. The approach is based on construction of a microkinetic scheme taking into account the formation of main reaction products and intermediates, on estimation of the heat of reaction, activation energy, and preexponential factor for elementary steps and includes development and a subsequent analysis of the corresponding mathematical model. Catalytic reactions are considered in the ideal adsorption layer approximation without taking into account the relationship between coverages and spatial coordinates. Accordingly, the mathematical model is an independent system of ordinary differential equations. This methodology is used to develop a point (lumped) model for ethane oxidation over nickel, which is based on a 36-step microkinetic scheme taking into account the oxidation and reduction of nickel and the formation of total (CO and HO) or partial (CO and H) ethane oxidation products, as well as the dehydrogenation of ethane into ethylene. The proposed model predicts the onset of self-oscillations in this reaction at atmospheric pressure in the temperature range from 850 to 1400 K. The kinetic oscillations are caused by the cyclic oxidation and reduction of nickel. The self-oscillations of the reaction rate are accompanied by oscillations of the catalyst temperature. The results of modeling are compared with experimental data. [ABSTRACT FROM AUTHOR]

Catalysts based on Si-Mo heteropoly compounds (HPC) supported on carriers were investigated in oxidative dehydrogenation of ethane (ODE) to ethylene. Determination of the effect of reaction parameters and the nature of catalyst on composition and distribution of products was carried out. The optimal reaction conditions: C 2 H 6 – 20.0%, O 2 – 2.5%, N 2 – 57.5%, H 2 O – 20.0%, space velocity – 8000 h −1 , contact time – 0.45 s were installed. Ethylene yields exceeding 42% with selectivity above 87% were obtained over novel Pb-Si-Mo heteropoly compound catalysts under oxidative dehydrogenation of ethane at 1023 K. Water vapor in the composition of reaction mixture increases the yield and selectivity of ODE products. Supporting of Si-Mo HPC on aluminosilicate does not destroy the Keggin molecular structure and increases its thermal stability. Reduction of heteropoly acid (HPA) molecule in methane atmosphere is different from the reduction in hydrogen atmosphere. [ABSTRACT FROM AUTHOR]

Phase-pure M1 catalysts with different post-treatments have been prepared from the same precursor slurry by hydrothermal synthesis and used to study the key factors influencing their performance in the oxidative dehydrogenation of ethane (ODHE) process. Different purification processes (i.e. steam treatment and hydrogen peroxide treatment) result in different tellurium (Te) contents and V 5+ concentration in the catalysts. Catalytic tests reveal that there is a direct correlation between the amount of V 5+ present in the catalysts and the catalytic activity. A hydrogen peroxide treatment increases the V 5+ concentration and decreases the Te content which can improve the catalytic activity and stability in comparison with the steam treatment. A post-treatment with oxalic acid improves the catalyst surface area (54 m 2 /g) but causes some vanadium leaching. The phase-pure M1 catalyst calcined at 650 ̊C and purified by H 2 O 2 shows the best catalyst productivity of 0 .77 kg C 2 H 4 /kg cat /h at 73% ethane conversion and 85% ethylene selectivity in ODHE process. The formation of reduced Te(0) aggregates blocking the active sites is identified as a main reason for catalyst deactivation. A low Te content favors a stable catalyst with less risk of Te aggregation. However, at harsh operating conditions (i.e. high oxygen concentration and high reactor temperature) the performance of phase-pure M1 catalysts with a low Te content can also reduce obviously due to the formation of a new (V, Nb)-substituted θ-Mo 5 O 14 and MoO 2 phases. [ABSTRACT FROM AUTHOR]

Abstract: Using a high-pressure shock tube facility, the ignition delay times of stoichiometric C2H6/H2/O2 diluted in argon were obtained behind reflected shock wave at elevated pressures (p = 1.2, 4.0 and 16.0 atm) with ethane blending ratios from 0 to 100%. The measured ignition delay times were compared to the previous correlations, and the results show that the ignition delay times of ethane from different studies exhibit an obvious difference. Meanwhile, numerical studies were conducted with three generally accepted kinetic mechanisms and the results show that only NUIG Aramco Mech 1.3 agrees well with the measurements under all test conditions. Sensitivity analysis was made to interpret the poor prediction of the other two mechanisms. Furthermore, the effect of ethane blending ratio on the ignition delay times of the mixtures was analyzed and the results show that ethane blending ratio gives a non-linear effect on the auto-ignition of hydrogen. Finally, chemical interpretations on this non-linear effect were made from the reaction pathway analysis and normalized H radical consumption analysis. [Copyright &y& Elsevier]

Abstract: The (vapor+liquid) equilibrium data for binary system of (ethane+ethanol) at three temperatures (295, 303, and 313)K were measured using a designed pressure–volume–temperature (PVT) apparatus. A wide range of pressures, (1 to 5)MPa, were considered for the measurements. The phase composition, saturated density, and viscosity of liquid phase were measured for each pressure and temperature. The experimental (vapor+liquid) equilibrium data were compared with the modeling results obtained using the Peng–Robinson and Soave–Redlich–Kwong equations of state. [Copyright &y& Elsevier]

Abstract: In a typical industrial catalyst, a small amount of catalytically active species is finely dispersed inside a large amount of porous support material. The reactor volume is mainly occupied by the catalyst support, not by the catalytic species itself. The use of fluidised nanoparticles as catalyst without the need of a support may result in drastic reduction in catalytic reactor volume for major savings in capital and operating costs. Here we report for the first time the use of fluidised NiO nanoparticles to catalyse ethane–oxygen reaction at temperatures of 240–420°C. Our data indicate that the fluidised NiO nanoparticles exhibit very different characteristics from the traditional porous catalyst. The lack of a rigid porous structure in the fluidised NiO nanoparticle catalyst allows ethyl radicals to desorb from the catalyst surface into the gas phase to initiate further gas-phase radical chain reactions. Therefore, the ethane–oxygen reaction catalysed by the fluidised NiO nanoparticles shows some typical behaviour of gas-phase reactions. In contrast, the rigid porous structure in the NiO/SiO2 catalyst does not allow the radicals to desorb from catalyst surface into the bulk gas phase. [Copyright &y& Elsevier]

Abstract: Spatial reactor profile measurements are a novel tool in chemical reaction engineering research. In this technique species concentrations or molar flow rates, phase temperatures and spectroscopic information are measured as function of the axial coordinate in a continuous flow tubular reactor. The obtained spatial gradients can be analyzed in terms of kinetic and mechanistic information about the reaction under study. The advantage of the spatial profile technique is that transient data are obtained at steady state and that it can be applied at temperature and pressure conditions relevant for industrial application. After a detailed description of the method various application examples are discussed such as methane catalytic partial oxidation on rhodium and platinum coated foam catalysts, methane oxidative coupling in the gas phase and oxidative dehydrogenation of ethane to ethylene on a supported molybdenum oxide catalyst. It is demonstrated how information about film transport limitation and reaction pathways can be extracted. The importance of spatial reactor profiles for validation of microkinetic models is highlighted for gas phase methane oxidative coupling at elevated pressure. Finally the idea of spatially resolved Raman spectroscopy using an optical fiber sensor is demonstrated and key parameters such as spatial resolution and position accuracy are determined. [Copyright &y& Elsevier]

Abstract: This contribution presents a theoretical study of a multitubular packed-bed membrane reactor for the ethane to ethylene oxidative dehydrogenation reaction over a highly active and selective Ni–Nb–O mixed oxide catalyst. This theoretical study takes into account the radial composition and temperature profiles using a two-dimensional pseudo-homogeneous model on the reaction side. The feasibility and convenience of using this novel design, as well as the influence of the main operating variables on the reactor performance, are analyzed. The introduction of the membrane leads to lower oxygen partial pressures inside the catalyst tubes, which results in an improved selectivity to ethylene (lower heat generation rates) and high effective heat transfer area per unit volume. The multitubular membrane reactor enables significant ethylene productions per tube and milder temperature profiles than a conventional wall-cooled fixed-bed reactor. Operating conditions have to be carefully adjusted to avoid undesired oxygen accumulation inside the tubes. The presence of small amounts of oxygen at the reactor inlet significantly improves the ethylene production rates. [ABSTRACT FROM AUTHOR]

Abstract: Sub-brown dwarfs (SBD) might originate either around a star or in solitary fashion. These bodies can retain atmospheres composed of molecular gases, which, upon cooling, have basal pressures of tens of bars or more. Pressure-induced opacity of these gases prevents such a body from eliminating its internal radioactive heat and its surface temperature can exceed the melting point of the life-supporting solvent for an extended period of time. Earth life uses water as a solvent but synthesis of observational data makes it possible to conceive chemical reactions that might support life involving non-carbon compounds, occurring in solvents other than water. In this paper a non-polar solvent is considered: ethane. Thermodynamic requirements to be fulfilled by a hypothetic gas constituent of a life-supporting SBD atmosphere are studied. Three gases are analyzed: nitrogen, carbon dioxide and methane. For thermodynamic reasons carbon dioxide is excluded from the list of candidate gases. We show that bodies with ethane oceans are possible in interstellar space. This may happen on SBD of (significantly) smaller or larger mass than the Earth. Generally, in case of SBD smaller in size than the Earth, the atmosphere exhibits a convective layer near the surface and a radiative layer at higher altitudes while the atmosphere of SBDs larger in size than Earth does not exhibit a convective layer. The prescribed thermodynamic state of ethane on the surface has some influence on the features of the atmosphere. The atmospheric mass of a life-hosting SBD of Earth size is two or three orders of magnitude larger than the mass of Earth atmosphere. [Copyright &y& Elsevier]

Abstract: The catalytic reactions between O2 and hydrocarbons are an important class of reactions in energy and chemical industries. This study aims to investigate the complicated reactions involving reactive radicals on the catalyst surface and in the gas phase during the partial oxidation/combustion of light alkanes. In order to avoid intra-particle transport constraints associated with the traditional porous catalysts, a non-porous nickel mesh catalyst has been used in this study for the partial oxidation of ethane with O2 at 625°C at atmospheric pressure. The catalytic effects of the nickel mesh strongly depended on the flow rate of gas reactants passing through the mesh. At a low gas flow rate, the nickel mesh catalyst showed negative effects for the oxidation of ethane. At a high gas flow rate, the same catalyst showed positive catalytic effects. Our results can be explained by considering the selective/preferential adsorption and desorption of different radicals onto and from the catalyst surface. It is believed that the desorption of some surface generated radicals (e.g. OH radicals) may be greatly affected by the thickness of the mass transfer gas film around the mesh wires, which in turn is affected by the gas flow rate passing through the mesh. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to apply fuzzy/possibilistic optimization focus in the context of the pyrolysis of ethane. The methodology is based on the fact that minimal/maximal values of these parameters are target values along the year rather than fixed real numbers. The fuzzy model is obtained taking into account the behaviour of the ethane conversion, steam/hydrocarbon ratio, inlet pressure and inlet temperature. The results demonstrated that the degree of optimism, α =1, describes better the real behaviour of the process with an equilibrium approach dimensionless parameter (EA) below 0.65 and a minimum total cost of US$ 2.55. [Copyright &y& Elsevier]

Abstract: A benchmark calculation of the atomization energy of the ‘simple’ organic molecule C2H6 (ethane) has been carried out by means of W4 theory. While the molecule is straightforward in terms of one-particle and n-particle basis set convergence, its large zero-point vibrational energy (and anharmonic correction thereto) and nontrivial diagonal Born–Oppenheimer correction (DBOC) represent interesting challenges. For the W4 set of molecules and C2H6, we show that DBOCs to the total atomization energy are systematically overestimated at the SCF level, and that the correlation correction converges very rapidly with the basis set. Thus, even at the CISD/cc-pVDZ level, useful correlation corrections to the DBOC are obtained. When applying such a correction, overall agreement with experiment was only marginally improved, but a more significant improvement is seen when hydrogen-containing systems are considered in isolation. We conclude that for closed-shell organic molecules, the greatest obstacles to highly accurate computational thermochemistry may not lie in the solution of the clamped-nuclei Schrödinger equation, but rather in the zero-point vibrational energy and the diagonal Born–Oppenheimer correction. [Copyright &y& Elsevier]

Abstract: The use of a conventional porous catalyst in the study of the pyrolysis of ethane (or any hydrocarbon) is complicated because reactions take place both on the catalyst surface and in the gas phase (including pores). A non-porous nickel mesh catalyst was used to study the catalytic pyrolysis of C2H6 in a quartz tubular reactor at 750°C. Our experimental results strongly indicate that the radicals formed on the catalyst surface could easily desorb from the catalyst surface when the gas film around the mesh wires was thinned by increasing the gas flow rate passing through the mesh. The desorption of radicals from the catalyst surface greatly limited the formation of coke on the catalyst surface, leading to sustained high catalytic activities even in pure C2H6 at 750°C. The catalyst could have dual roles. It could act as a chain reaction terminator by providing a surface for the chain termination reactions to take place. The mesh catalyst could also act as a chain reaction re-initiator by providing additional radicals into the gas phase in which the desorbed radicals re-initiate and participate in the chain reactions. The dual roles of the mesh catalyst were largely responsible for the changes in net product formation rates and product distribution (e.g. the C2H4/CH4 ratio). [Copyright &y& Elsevier]

Models of Cr(III)–silica were used to study C&bond;H activation in ethane by oxidative addition as a possible route to catalytic dehydrogenation. This mechanism involves a formal double oxidation of chromium and a minimum energy crossing point (MECP) was located on the seam between the quartet spin potential energy surface of Cr(III) and the doublet spin potential energy surface of Cr(V). Subsequent to the change of spin state, the C&bond;H activation path passes through a transition state on the doublet potential surface, leading to the formation of an ethylhydridochromium(V) complex. This complex represents only a shallow minimum on the potential energy surface and β-hydrogen transfer to complete the catalytic cycle must therefore take place in the extension of the C&bond;H activation step. The combination of a significant activation energy and a small pre-exponential factor in the rate constant makes C&bond;H activation by oxidative addition an unlikely mechanism for dehydrogenation in this system. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Density functional theory in its B3LYP variant has been used to study the reaction of Ti+ (4F) with ethane in the gas phase. The potential energy surface corresponding to [Ti, C2, H6]+, has been examined in detail at the B3LYP/6-311++G(3df,3pd)//B3LYP/6-311+G(d,p) level of theory. The quality of this theoretical method has been calibrated against the available thermochemical data. Three activation branches, C—H, C—C, and synchronous C—H and C—C bond activations, were proposed along the reaction coordinates, and two new mechanisms, the sequential 1,1-H2 elimination and the concerted elimination of CH4, were found. [ABSTRACT FROM AUTHOR]

In order to probe the thermal stability and reactivity of ethyl intermediates on Pt-Sn alloy catalysts, we have synthesized these species by reaction of H atoms with adsorbed ethylene on a () R30°-Sn/Pt(111) surface alloy. Adsorbed ethyl groups are stable until 376 are they react to evolve ethane, ethylene, and H2. The activation energy for ethyl dehydrogenation isEdehyd* 97 kJ mol, which istwicethat reported on Pt(111). In addition, we place a lower limit ofEdehyd* 97 kJ mol on the barrier to ethyl hydrogenation on this alloy. [ABSTRACT FROM AUTHOR]

ZSM-5 and Y zeolites, γ-alumina, and silica modified by solid-state redox reaction with zinc, gallium, manganese, and iron were studied in the conversion of cyclohexane and the nonoxidative conversion of ethane. The catalytic behavior was related to acid properties characterized by temperature-programmed desorption of ammonia (TPAD). [Copyright &y& Elsevier]

The reaction of Fe+ (6D) with ethane in the gas-phase was re-examined at B3LYP/6-311++G(3df,3pd)//B3LYP/6-311+G(d,p) level of theory to explore new characteristic of the C–C and C–H bond activations in alkanes. Two different mechanisms from those described in the early works are shown: one is the concerted elimination of CH4 against the consecutive addition–elimination mechanism, and the other is the 1,1-H2 elimination vs. general 1,2-H2 elimination. Although these alternative pathways are unimportant experimentally as they involve high-energy transition states, it may improve our understanding for the activation mechanism of the C–C and C–H bond in alkane. [Copyright &y& Elsevier]

Oxidative dehydrogenation of ethane to ethylene was studied using variously prepared Li/Dy/Mg/Cl mixed metal oxides as catalysts. The catalytic performance was found to be strongly dependant on the method of preparation and the LiCl content of the solids. Ethylene yields of up to 77% were obtained with catalysts prepared by precipitation of the catalyst precursors with an equimolar mixture of NH4Cl and HCl, and subsequent calcination in synthetic air (i.e., absence of CO2). Both highest ethylene yields and best long-term stability were achieved with catalysts having the highest chloride loading. Based on kinetic data and high-temperature XRD measurements (under controlled atmosphere), a new reaction mechanism is proposed wherein the active sites of the catalytic system are postulated to reside in molten LiCl, supported on Dy2O3/MgO. Oxygen is solved dissociatively in the LiCl melt forming the catalytically active hypochlorite OCl-. With increasing temperature, OCl- decomposes to O• + Cl- or O- + Cl•. The two radical species are highly oxidative and can readily activate an alkane by homolytic hydrogen abstraction. The so-created alkane radicals react further with OH to form an olefin and H2O. At low temperatures, a regime of high apparent activation energy has been determined for high chloride loadings, while at high temperatures and low chloride loadings, a second regime with lower activation energy was found. It is suggested that the first regime is controlled by reaction kinetics, whereas the second regime is diffusion-controlled. Which of the two regimes predominates is strongly dependent on the reaction temperature and the structure and composition of the catalyst. [ABSTRACT FROM AUTHOR]

Oxydehydrogenation of ethane as a route to ethylene has the attractive feature of removing the thermodynamic equilibrium conversion limitation of the simple dehydrogenation. For example, in the dehydrogenation of ethane to ethylene, the maximum conversion possible at 1000 °C is 51%, while essentially complete (100%) conversion is possible even at ambient conditions. The best catalysts discovered to date are those from Union Carbide's work (in the late 1970s and early 1980s), which operate at 300-400 °C. These reducible Mo–V–Nb oxide catalysts are thought to react via a surface ethoxide intermediate on a Mo or V site that can then undergo a β-elimination process to form ethylene. On the other hand, the surface ethoxide can be oxidized further to form surface acetate, which leads to acetic acid on hydrolysis with water. Aside from these low-temperature reducible catalysts, many catalysts containing reducible metal oxides and non-reducible metals are known to convert ethane to ethylene at 500-800 °C. It is proposed that these catalysts are essentially dehydrogenation catalysts where the H2 formed from straight dehydrogenation or during a surface intermediate stage after H-abstraction is converted to H2O, thereby shifting the dehydrogenation equilibrium. Therefore, the big question, the challenge, and the opportunity remains as to whether true oxydehydrogenation is possible at relative low-to-moderate temperatures? This challenge/opportunity will be discussed in the backdrop of some of the recent advances in alkane activation. [ABSTRACT FROM AUTHOR]