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The support properties can be tuned through changing the addition amount of Zr. As a result, the formation and stability of Co species can be regulated, then, the relationships between different Co species and reaction pathways have been revealed. [Display omitted] TiO 2 , ZrO 2 and a series of TiO 2 -ZrO 2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO 2 (3CT), 3 wt% Co/ZrO 2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO 2 (CO 2 -ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C 2 H 4 yield, C 2 H 6 conversion and CO 2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV–vis diffuse reflectance spectra (UV–vis DRS), H 2 temperature-programmed reduction (H 2 -TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO 4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co2+-TiZrO 4 structure. Furthermore, the presence of Ov and Ti3+can facilitate the high dispersion and stabilization of Co2+, as well as suppressing the severe reduction of Co2+, leading to superior ethane oxidative dehydrogenation activity. Besides, less Co0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction; however, more Co0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Relationship between ODH of ethane and electrochemical properties. • Optimal catalyst with Nb in the lattice and on the surface is n -type semiconductor. • Relationship between density of non-stoichiometric oxygen and selectivity to C 2 =. • Relationship between electrochemical properties and selectivity to C 2 =. In the present article, a relationship between the catalytic performance in the oxidative dehydrogenation of ethane (ODHE) for Nb-doped NiO catalysts and their electrochemical properties has been proposed. To do so, highly stable and selective Nb-doped NiO catalysts for the ODHE to ethylene have been synthesized by optimizing synthesis parameters such as the amount of oxalic acid in the synthesis gel and the calcination temperature. These catalysts have been characterized by means of XRD, HRTEM, Raman and UV–vis diffuse reflectance spectroscopies, TPR and XPS. Moreover, Electrochemical Impedance Spectroscopy (EIS), capacitance measurements (Mott-Schottky analysis) and cyclic voltammetries studies were also carried out. Electrochemical characterization indicates changes in the type of semiconductivity: p -type for samples calcined at 350 °C and the sample prepared in the absence of oxalic acid and calcined at 500 °C, to n -type for samples prepared in the presence of oxalic acid in the synthesis gel and calcined at 500 °C. According to the obtained results, the most selective catalysts present a low Nb-incorporation on the NiO lattice with a large amount of tiny Nb 2 O 5 nanoparticles covering NiO crystallites. This work presents, for the first time, a complete electrochemical characterization of Nb-doped NiO catalysts showing a correlation between electrochemical properties and catalytic performance. [ABSTRACT FROM AUTHOR]

Ethylene is mainly produced by steam cracking of naphtha or light alkanes in the current petrochemical industry. However, the high-temperature operation results in high energy demands, high cost of gas separation, and huge CO2 emissions. With the growth of the verified shale gas reserves, oxidative dehydrogenation of ethane (ODHE) becomes a promising process to convert ethane from underutilized shale gas reserves to ethylene at a moderate reaction temperature. Among the catalysts for ODHE, MoVNbTeOx mixed oxide has exhibited superior catalytic performance in terms of ethane conversion, ethylene selectivity, and/or yield. Accordingly, the process design is compact, and the economic evaluation is more favorable in comparison to the mature steam cracking processes. This paper aims to provide a state-of-the-art review on the application of MoVNbTeOx catalysts in the ODHE process, involving the origin of MoVNbTeOx, (post-) treatment of the catalyst, material characterization, reaction mechanism, and evaluation as well as the reactor design, providing a comprehensive overview of M1 MoVNbTeOx catalysts for the oxidative dehydrogenation of ethane, thus contributing to the understanding and development of the ODHE process based on MoVNbTeOx catalysts. [ABSTRACT FROM AUTHOR]

Ethylene is mainly produced by steam cracking of naphtha or light alkanes in the current petrochemical industry. However, the high-temperature operation results in high energy demands, high cost of gas separation, and huge CO2 emissions. With the growth of the verified shale gas reserves, oxidative dehydrogenation of ethane (ODHE) becomes a promising process to convert ethane from underutilized shale gas reserves to ethylene at a moderate reaction temperature. Among the catalysts for ODHE, MoVNbTeOx mixed oxide has exhibited superior catalytic performance in terms of ethane conversion, ethylene selectivity, and/or yield. Accordingly, the process design is compact, and the economic evaluation is more favorable in comparison to the mature steam cracking processes. This paper aims to provide a state-of-the-art review on the application of MoVNbTeOx catalysts in the ODHE process, involving the origin of MoVNbTeOx, (post-) treatment of the catalyst, material characterization, reaction mechanism, and evaluation as well as the reactor design, providing a comprehensive overview of M1 MoVNbTeOx catalysts for the oxidative dehydrogenation of ethane, thus contributing to the understanding and development of the ODHE process based on MoVNbTeOx catalysts.

[Display omitted] • HYSYS study predicted ethylene ODH yields with new diluents & process technology. • Additional storage for ODH reactor resulted in less downtime & process failures. • An upgrade to improve ethylene ODH profitability could use shale gas as a diluent. A HYSYS simulator was utilized to predict the performance of an ethylene oxidative dehydrogenation (ODH) production facility using alternative diluents and separation technology not currently used in the standard industrial process. An ODH process system was modeled with ethane being fed along with air into a reactor with simultaneous mixing with pure methane to lower the product gas temperature. The methane feed was later separated from the other product gases and eventually fed into a recycle stream. This process was fairly expensive due to the use of a demethanizer within the process recycle stream. Safety and operational improvements for the ODH process was another aspect of this analysis that yielded interesting results. By the inclusion of storage vessels before and after the ODH reactor, the reactor unit can operate even in the event of an upstream or downstream failure, resulting in less downtime for the process. [ABSTRACT FROM AUTHOR]

• The MoVTeNbO catalysts for ODE were modified by Nd, Ge, Ga, Mn additives. • Additives influence on phase composition, surface acidity and elements distribution. • Modification enhances an ethylene space time yield by the factor of ∼1.5. • There is correlation between catalytic activity in ODE and amount of M1 phase. Modification by Nd, Mn, Ga, and Ge substantially affect both physicochemical and catalytic properties of MoVNbTeO oxides in the oxidative dehydrogenation of ethane (ODE). The introduction of modifying additives changes the content of the M1 phase, surface acidity, and surface composition. It does not have an influence on the state of Mo, V, Nb, and Te on catalyst surface, but it induces surface enrichment (Ga, Mn) or depletion (Ge, Nd) by the modifying element. All of these additives have positive effects on catalytic properties at the M/Mo (M = modifying element) ratio of 0.0075 ÷ 0.025. They exhibit an increase of activity and prevent ethylene over-oxidation. The relationship between the rate constant of total ethane transformation and the M1 content confirms that this phase is active in ODE. The correlation between ethylene selectivity and the relative number of intermediate acid sites is revealed, indicating the role of surface acidity on ethylene over-oxidation. [ABSTRACT FROM AUTHOR]

• Bi-modified MoVNbTeO catalysts possess enhanced tolerance toward severe reaction conditions during ODE process. • Incorporated bismuth influences on Te mobility within 6-membered channels of M1 structure. • The improved stability and activity of MoVNbTeO catalysts relates to enhanced Te surface concentration. This work presents the investigation of Bi-modified MoVNbTeO catalysts for oxidative dehydrogenation of ethane (ODE) using the combination of NAP-XPS, in situ XRD and XANES/EXAFS techniques. It was found that introduction of Bi improves the tolerance of catalysts toward severe reaction conditions (high temperature and/or enhanced ethane/oxygen ratio) resulting in a significant decrease in the degree of deactivation. In accordance with NAP-XPS data, the surface/subsurface Te concentration was maintained for Bi-containing MoVNbTeO catalysts even after treatment with a reducing reaction mixture (C 2 H 6 /O 2 >3) at temperatures up to 460 °C. In the case of the unmodified catalyst, such treatment resulted in the surface/subsurface depletion of Te due to the reduction into the Te° state followed by its sublimation into the gas phase. The incorporation of Bi within extended six-membered channels of the M1 structure was suggested based on XANES/EXAFS data. Such incorporation probably influences the mobility of Te within channels, resulting in the limitation of Te diffusion from the particle bulk to the surface. The improved tolerance of catalytically active M1 phase toward severe reaction conditions was confirmed by in situ XRD data during heating in a mixture of 8 wt % C 2 H 6 /He. [ABSTRACT FROM AUTHOR]

• Impact of the axial effective thermal conductivity (k eff,z) on hot spots prediction. • Adequate characterization of k eff,z from adiabatic experimental conditions. • Considering k eff,z is crucial to avoid runaway mispredictions. • Evaluation of the Oxidative Dehydrogenation of Ethane industrial reactor model. The impact of axial conductive heat transfer on the simulation and prediction of hot spots and, more particularly, runaway, within an industrial-scale wall-cooled packed-bed reactor with low tube-to-particle diameter ratio (d t /d p ∼ 3) has been assessed in this work. To this purpose, the effective axial conductivity (k eff,z) was first determined from adiabatic experiments in a bench-scale packed bed in the absence of reaction. Next, non-adiabatic and non-isothermal bench-scale and industrial-scale packed bed experimental data were used in the assessment of the impact of axial heat conduction on the prediction of the temperature profile. The so-called Pseudo-local Internal Heat Transfer Approach (PL-IHTA) was used for the adequate description of the radial temperature gradients. Finally, an industrial-scale wall-cooled packed bed reactor for the highly exothermic catalytic oxidative dehydrogenation of ethane was modeled to assess the impact of the axial thermal conductivity on temperature profile simulations. When disregarding axial heat conduction or adopting literature-based values for k eff,z , determined from either experiments at low d t /d p ratios (<8) and Re p ≤ 1000 or high d t /d p ratios (>8) and Re p ≤ 700 at a wide panel of operating configurations, runaway is simulated at conditions where it has not been observed experimentally or a negligible hot-spot prediction is obtained. When considering the k eff,z determined for the specific reactor configuration in this work, hot spots are predicted at Re p of 700 and 1400, but no runaway. The discrepancies between experimental findings and temperature profiles simulated using literature-based values for k eff,z indicate the need for a specific determination of k eff,z in packed bed reactors with low d t /d p ratio to more accurately predict hot spots, resulting in more reliable reactor design and operation. [ABSTRACT FROM AUTHOR]

From macro- to nano-engineering of a promising CeO 2 -ZrO 2 -doped NiO-Al 2 O 3 /Ni-foam catalyst has been demonstrated for the oxidative dehydrogenation of ethane to ethylene (ODE), through facial wet chemical etching of a Ni-foam followed post modification with CeO 2 and ZrO 2 . The NiO-Al 2 O 3 /Ni-foam (denoted as NANF) achieved a high ethane conversion of 25.2% but with a very low ethylene selectivity of 43.1% at 450 °C. ZrO 2 -doping of the NANF led to a remarkable improvement in the ethylene selectivity but serious deterioration of activity while the CeO 2 -doping showed an opposite effect. Co-doping of the NANF using optimal amount of CeO 2 and ZrO 2 markedly promoted not only the activity but also the selectivity to ethylene. For example, over the 1CeO 2 -5ZrO 2 -NANF (CeO 2 :1 wt%, ZrO 2 :5 wt%) catalyst, a high ethane conversion of 40.3% was obtained with a 60.6% ethylene selectivity for a feed gas of C 2 H 6 /O 2 /N 2 = 1/1/8 at 500 °C and a gas hourly space velocity of 18,000 cm 3 g −1 h −1 , corresponding to a high ethylene productivity of 510 g Ethylene kg cat −1 h −1 . In nature, co-doping with CeO 2 and ZrO 2 synergistically tamed the NiO for selective H-abstraction of the ethane molecules other than over oxidation of them. [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]

MoVO, MoVTeO and MoVTeNbO mixed oxides, prepared hydrothermally and heat-treated in N 2 at 400, 500 or 600 °C, are active and selective catalysts in the oxidative dehydrogenation (ODH) of ethane, although their catalytic behaviour strongly depends on the composition and the activation temperature of the material. Thus, the selectivity to ethylene over samples heat-treated at 400 or 600 °C, decreases according to the following trend: MoVTeNb-600 > MoV-400 > MoVTe-600 > MoVTe-400 > MoVTeNb-400 >> MoV-600 (with catalysts heat-treated at 500 °C presenting an intermediate performance). This catalytic performance can be explained to a high extent by the presence of the M1 phase in the best catalysts. Interestingly, the temperature of formation and decomposition of the M1 phase strongly depends on the chemical composition of the catalysts, leading to different trends depending on the heat-treatment temperature. Not only the presence of the M1 phase determines the catalytic performance but also the V4+/V5+ ratio in the surface of catalysts. Additionally, a comprehensive brand-new electrochemical characterization of the catalysts has been carried out for MoV-based samples with M1 phase. Accordingly, the best catalytic behaviour in terms of selectivity to ethylene in the ethane ODH was observed in those materials presenting higher charge-transfer resistances at the interfacial active parts and n -type semiconductivity with few O-vacancies. Besides, lower current densities obtained in cyclic voltammetries (related to low electrochemical activity) has been associated with higher selectivity in the ODH reaction. [Display omitted] • Comparison of different MoVO, MoVTeO and MoVTeNbO M1 phase catalysts in ethane ODH. • The M1 crystalline phase is key to obtain good selectivity to ethylene in ethane ODH. • Catalytic performance optimized by the higher presence of surface V4+ species. • Correlations between electrochemical and catalytic properties in M1-based materials. [ABSTRACT FROM AUTHOR]

The incorporation of hydrodynamics in an industrial wall-cooled packed bed reactor model is essential to describe the performance of highly exothermic oxidation reactions. Although the conventional hydrodynamic approach (CHA), Navier-Stokes equations coupled to Darcy-Forchheimer terms, has been the most used approximation to describe velocity profiles in these packed bed reactors, it is itself inconsistent and the computation time for its numerical solution, when coupled to the reactor model, is still demanding. This work is aimed at developing a practical but reliable hydrodynamic approach (PHA) to describe velocity profiles in packed bed reactors presenting a low tube to particle diameter ratio. In this approach, velocity profiles are described at the core and close to the wall of the reactor. The core model makes use of the Darcy-Forchheimer equation (DFE), and the wall model makes use of Navier-Stokes equations (NSE) using an effective viscosity to account for turbulence. The PHA predicts similar results to those obtained by the CHA and properly fits velocity observations from packed beds with a tube to particle diameter ratio (d t /d p ) ranging from 3 to 6. The PHA allows the estimation of both turbulent viscosity (μ t ) involved in the viscous term of the NSE and parameters influencing viscous (α) and inertial (β) flow resistances in Darcy and Forchheimer terms, respectively. Then, hydrodynamics is coupled to a heat transport model accounting for conductive anisotropy to fit temperature observations in absence of reaction from a pilot-scale packed bed reactor with a d t /d p = 3.048. Hydrodynamics and heat transfer results are, then, transferred to a pseudo heterogeneous reactor model to simulate the behavior of a novel technology to perform the oxidative dehydrogenation of ethane on a multimetallic MoVNbTeO formulation. This is the first study modeling this reactor system accounting for hydrodynamics, information that is essential for its conceptual design in future studies. Finally, it is worth stressing that the PHA, coupled to the heat transport model or the reactor model, leads to significantly lower computation times than the CHA, which is attributed to the analytical rather than numerical solution of the former. [ABSTRACT FROM AUTHOR]

This paper investigates the oxidative dehydrogenation of ethane to produce ethylene at low temperatures (500 °C) in metallic structured substrates. To check this point, the FeCrAlloy® monoliths with different channel sizes (289–2360 cpsi) were prepared. The monoliths were coated with a Ni/Al2O3 catalyst (by washcoating of alumina and the latter nickel impregnation) and characterized by Scanning Electron Microscopy and Energy-Dispersive X-ray analysis (SEM-EDX), Temperature-Programmed Reduction (TPR), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The catalytic results showed that all monoliths coated with ~300 mg of catalyst presented similar ethane conversion (15%) at 450 °C. However, the lowest selectivity to ethylene was found for the monolith with the lower channel size and the higher geometric surface area, where a heterogeneous catalyst layer with Ni enriched islands was generated. Therefore, it can be said that the selectivity to ethylene is linked to the distribution of Ni species on the support (alumina). Nevertheless, in all cases the selectivity was high (above 70%). On the other hand, the stability in reaction tests of one of the coated monoliths was done. This structured catalyst proved to be more stable under reaction conditions than the powder catalyst, with an initial slight drop in the first 8 h but after that, constant activity for the 152 h left.

The template-induced mesoporous Ni–Al oxide catalysts synthesized by a template-assisted self-assembly route show the good mobility of selective oxygen species and tuned physico-chemical properties, thus promoting their catalytic performance and stability for the oxidative dehydrogenation of ethane using O 2 as an oxidant. [Display omitted] • Template-induced mesoporous Ni–Al mixed oxides are successfully prepared. • Structural effect and strong interaction are crucial to enhance ODHE performance. • Template-induced mesoporous Ni–Al mixed oxides exhibit preferable ODHE performance. • Adding template significantly enhances coking resistance. • Ni–Al–F127 catalyst shows a C 2 H 4 yield of 37.3 % and prominent stability for 150 h. Oxidative dehydrogenation of ethane is a potential industrial process to produce ethylene. In this work, the template-induced mesoporous Ni–Al mixed oxide catalysts synthesized by the template-assisted self-assembly method were investigated for the oxidative dehydrogenation of ethane to ethylene using O 2 as an oxidant. The template-induced structure evolution is an effective means to modulate physico-chemical properties of the Ni–Al mixed oxide, thus, it further improves the catalytic performance. All the mesoporous Ni–Al–template catalysts present higher C 2 H 6 conversions and C 2 H 4 selectivities than bulk NiO and non-porous Ni–Al–O catalysts in the temperature range of 350–500 °C. Meanwhile, up to 49.6% C 2 H 6 conversion and 75.3% C 2 H 4 selectivity (37.3% of C 2 H 4 yield) can be obtained over Ni–Al–F127 catalyst at 500 °C. And the mesoporous Ni–Al–F127 catalyst exhibits a superior stability after a long run. The structure–performance correlation indicates that the remarkable catalytic performance is ascribed to the synthesis driven structural effect. The strong interaction between Ni and Al cations caused by the addition of template promotes the formation of small NiO particles and the better dispersion of NiO, which decreases the content of non-selective oxygen species and increases the availability of lattice oxygen. [ABSTRACT FROM AUTHOR]

Flexible structured catalysts based on Ni and Zr deposited on a ceramic paper made of SiO 2 -Al 2 O 3 and ZrO 2 fibers showed to be active and selective for the Oxidative Dehydrogenation of Ethane. Zirconium promoter strongly interacted with nickel oxide and produced structural changes that affected the NiO redox behavior, crystal growth and lattice order which enhanced selectivity towards ethylene. The variation of the concentration of the precursor solution used and the addition of zirconia short fibers, affected the catalytic performance. The lower the concentration of the solution used to incorporate the catalyst, the better the catalytic performance. The addition of zirconia fibers also showed beneficial effects on ethylene production. [ABSTRACT FROM AUTHOR]

The present work investigates the preparation of NiCe/γ-Al 2 O 3 coated cordierite monoliths for oxidative dehydrogenation of ethane (ODE) reaction through a two steps procedure: the primer deposition of a γ-Al 2 O 3 coating consisting in a mixture of micro and nanoparticles via the washcoating method and the latter incorporation of the active phase by impregnation. Moreover, a modification in these two steps was made: the suppression of some calcination steps to save energy in the manufacture process. The structured catalysts, named as Ni(X)Ce(Y)-M, where X = 13 or 19 wt%. Ni and Y = 5 or 8 wt%. Ce respectively, with respect to the alumina loading, were characterized by SEM/EDX, XRD, FTIR, LRS and XPS, and their catalytic activity was tested in the ODE reaction. Furthermore, their mechanical resistance to vibration was studied. Similar results corresponding to the un-promoted system are also presented for comparison. It was found that the co-impregnation of nickel and cerium was affected by the suppression of some calcinations: a preferential absorption of Ce rather than Ni occurred, generating at the end a catalytic coating with a higher Ce/Ni ratio than that of the precursor solution and a lower Ni loading than that of Ni(13)-M. On the other side, in the NiCe-based catalysts the properties of the active sites remained the same despite the increment in the active phase, at a fixed Ce/Ni nominal atomic ratio of 0.17. In the case of the Ni(19)Ce(8)-M system, although the Ni/Al atomic ratios were found lower than those of the nominal ones by EDX and XPS and ethylene selectivity decayed, ethane conversion resulted markedly higher, leading to an improved ethylene yield. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ni and Ni–Ce/Al2O3 coatings on metallic foams were active and selective for the ODE. [•] The cerium addition increased considerably the ethylene productivity. [•] Catalytic features of the structured systems depend on the calcination temperature. [•] The presence of chromium in the catalytic coatings mainly affects the selectivity. [•] The structured systems showed higher ethylene productivity than powder catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Ni and Ni–Ce oxides alumina-supported formulations onto alpha-alumina foams were prepared, characterized and evaluated in the oxidative dehydrogenation of ethane (ODE) reaction. The catalysts were appropriately deposited on ceramic foams with a uniform, mechanically stable coverage. Besides, the structured systems were active and selective in the ODE reaction, demonstrating that the incorporation method was successful to obtain adequate active sites. Cerium markedly improved the ethane conversion due to a synergistic effect with nickel oxide, thus leading to a significant increment in ethylene productivity compared to that of the cerium-free system. An optimal Ce/Ni ratio was found which maximized the catalytic performance. [Copyright &y& Elsevier]

Highlights: [•] Novel catalytic papers were prepared for oxidative dehydrogenation of ethane. [•] The papers present an interconnected network structure with fibers covered by alumina. [•] The systems exhibit NiO as active phase and show high activity for ODE. [•] Catalytic paper with Ce/Ni=0.17 atomic ratio showed the highest productivity. [ABSTRACT FROM AUTHOR]

Abstract: MoVTe(Sb)NbO catalysts have been prepared using the slurry method and tested as catalysts for the oxidative dehydrogenation of ethane. The influence of both the addition of silica to the starting slurry during the preparation and of a final heat treatment under nitrogen at 873K after the dissolution of the M2 phase formed concomitantly to the active M1 active phase has been studied. While the parameters change the texture of the catalysts without modification of the catalytic sites, they have opposite effects on catalytic properties. The addition of silica increases the conversion without modifying the selectivity to ethylene and the final heat treatment decreases the conversion but increases the selectivity. These effects have been explained respectively by a decrease of the agglomeration and sintering of the M1 phase crystallites and a decrease of the number of small pores, where total oxidation takes place. These effects could be leveraged to optimize the preparation protocol and obtain more efficient catalysts for the oxidative dehydrogenation of ethane. [Copyright &y& Elsevier]

Abstract: In this paper we present the synthesis, characterization and catalytic behaviour in the oxidative dehydrogenation of ethane of NiO–CeO2 mixed oxides. The addition of cerium oxide to NiO strongly modifies its catalytic performance, although the changes in the catalytic behaviour depend on the catalyst composition. The incorporation of low amounts of cerium oxide to NiO multiplies the productivity to ethylene in the oxidative dehydrogenation of ethane by a factor of ca. 7, which is the result of an increase in both catalytic activity and selectivity to ethylene. The enhanced activity has been related to the remarkable increase of the surface area of catalyst and the low crystal sizes of NiO that takes place when a tiny amount of cerium oxide is incorporated to the NiO. The higher selectivity to ethylene has been related to the modification of the nature of Ni–O species, which implies a lower production of carbon oxides. On the other hand, high activity and selectivity is also observed over catalysts rich in cerium (with Ni/Ce ratios between 0.2 and 3). In this case, a different mechanism can be proposed in which the high capacity of CeO2 to bomb oxygen from bulk to surface and the partial formation of NiO and Ce1−x Ni x O2 facilitates a faster reoxidation of active Ni-sites by a synergic effect improving catalytic activity. [Copyright &y& Elsevier]

Abstract: Ni–W–O mixed oxides were prepared through the evaporation of aqueous solutions of nickel nitrate and ammonium tungstate and calcined in air at 500°C for 2h. The catalysts were characterized by several techniques (N2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO, and 18O/16O isotope exchange) and tested in the oxidative dehydrogenation of ethane. The catalytic activity and catalyst reducibility decrease when the W content increases. Thus, nickel sites seem to be the active centers for ethane activation in these catalysts. However, the selectivity to ethylene strongly changes depending on the Ni/W ratio. In W-rich catalysts, in which NiWO4 and WO3 are mainly observed, a strong influence of ethane conversion on the selectivity to ethylene is observed. However, in Ni-rich catalysts, in which NiO crystallites and WO x nanoparticles are mainly observed, ethane conversion hardly influences the selectivity to ethylene. It has been demonstrated that the nature of the Ni sites and the characteristics and number of the acid sites determine the catalytic behavior of these catalysts. The presence of Lewis acid sites with high acid strength in W-rich catalysts facilitates the decomposition of ethylene during ethane oxidation. [Copyright &y& Elsevier]

Abstract: Gamma-alumina-supported MoO x , MoVO x (Mo/V=11) and MoVPO x (Mo/V=11, V/P=1) catalysts were prepared and their properties studied by several techniques (EDX-SEM, XRD, XPS, LRS, TPR). Acid–base and catalytic properties were determined by carrying out 2-propanol decomposition and oxidative dehydrogenation of ethane to ethene, respectively. In situ X-ray diffraction and X-ray photoelectron spectroscopy after pre-treatment were carried out in redox conditions (with H2/N2, C2H6/N2 as reducing and O2/N2 as oxidant). The catalytic performance increases along MoO x

Abstract: Vanadium-exchanged Ti, Zr, and Sn-pyrophosphates have been prepared as cubic phase and tested for the oxidative dehydrogenation of ethane in the temperature range 550–700°C in a fixed bed reactor. The catalysts have been characterised by XRD, XPS, BET surface area and TPR experiments. Vanadium exchange does not modify the cubic structure of the materials but thermal treatment under reducing or reaction conditions results in a significant loss of Sn-pyrophosphate structure, whereas Ti and Zr-pyrophosphates remain stable. All samples are active for the reaction and vanadium-Ti-pyrophosphate provides the best catalytic performances. The exchanged catalysts show a very good selectivity to ethylene, even at quite high ethane conversion, which has been attributed to the great vanadium site isolation. [Copyright &y& Elsevier]

X-ray Photoelectron Spectroscopy (XPS) has been used to investigate titania-supported vanadyl phosphates (VOPO4) with respect to thermal treatments and catalytic runs in the oxidative dehydrogenation (ODH) of ethane. The surface characterization of monolayer (9.6 wt.%) and sub-monolayer (6.5 wt.%) VOPO4 samples has been performed after calcination in air and after catalytic tests at different temperature (T=450 and 550 °C). Vanadyl phosphates are well dispersed on the TiO2 surface. The oxidation state, surface distribution and evolution of vanadium and titanium species have been analysed by the V 2p3/2 and Ti 2p3/2 peak-fitting procedures. The interaction with the support allows the formation of different vanadium species, V5+ phosphate, V5+ and V4+ oxide species, whose relative fraction depends both on the nature of the support and on the samples treatments. The amount of tetravalent vanadium species in the samples progressively increases as effect of the temperature. Surface modifications of the titania support are evidenced by XPS after impregnation, calcination and catalytic tests. [Copyright &y& Elsevier]

Combinatorial methodologies are emerging as powerful tools in heterogeneous catalysis. Previously, we have established a strong correlation between catalysts prepared as thin films for high-throughput primary screening to those prepared in bulk for secondary screening in a multi-channel fixed bed (MCFB) microreactor for the ethane oxidative dehydrogenation process [Proc. Natl. Acad. Sci. U.S.A. 96 (1999) 11077]. Numerous catalysts with improved performance over literature compositions were also reported. With this high-throughput technology, tens of thousands of new compositions have been synthesized and tested. In this paper, we describe in detail the discovery of a new class of catalysts with extraordinary performance improvements. These catalysts contain Ni, Nb, and Ta or Co mixed oxides. The respective ternary systems were first screened in a thin film form (∼200 μg catalyst loading). Then they were scaled up to 50 mg level and screened in an MCFB microreactor. The optimal compositions were Ni0.62Ta0.10Nb0.28Ox and Ni0.62Ta0.20Nb0.18Ox. They convert 20.5% of ethane with 86.2% selectivity to ethylene and 20.0% of ethane with 86.1% selectivity to ethylene at 300 °C, respectively, as compared to 3.3% conversion of ethane with 82.9% selectivity to ethylene for the state-of-the-art catalyst Mo0.72V0.26Nb0.02Ox under identical testing conditions. One of these compositions, Ni0.62Ta0.10Nb0.28Ox, was further scaled up to 5 g and tested in a conventional bench scale reactor. The performance improvement is consistent with measurements made on the MCFB microreactor. [Copyright &y& Elsevier]

A set-up for fast parallel preparation and testing of catalytic materials is presented. A commercial synthesis robot is used for automated parallel preparation of catalyst libraries. An adapted method for the synthesis of supported multicomponent catalytic material by sequential impregnation of an alumina support with different precursor solutions is described. It is shown that the catalytic performance of the materials prepared with the synthesis robot is comparable to manually prepared materials. In testing materials for the oxidative dehydrogenation of light alkanes to olefins a 64 multi-channel ceramic reactor module was used being connected to a fast GC/MS analysis. The reactor module is suitable for parallel testing of heterogeneous catalysts for various gas-phase reactions close to conventional laboratory conditions. Reliability and efficiency of the reactor are illustrated for the oxidative dehydrogenation of propane and ethane. [Copyright &y& Elsevier]

[Display omitted] • Al 2 O 3 -Supported NiO improve the catalytic performance of bulk NiO in ethane ODH. • NiO-support interaction determine selectivity to ethylene. • NiO-support interaction determine the reducibility of catalysts. • High selectivity related also with a higher number of nickel and oxygen. vacancies. Nickel oxides supported on γ-alumina (Ni-loading from 5 to 30 wt% NiO) have been synthesized and tested in the oxidative dehydrogenation (ODH) of ethane in order to determine the importance of the NiO-support interaction. The best performance was achieved by the catalyst with 15 wt% NiO; higher NiO-loadings lead to the formation of unselective bulk-like NiO and lower Ni-loadings present high proportion of free alumina surface sites. The presence of oxalic acid and/or niobium in the synthesis gel resulted in the formation of NiO particles with similar size, but higher crystallinity and reducibility than the standard 15 wt% NiO catalyst. The obtained results have revealed that, in addition to NiO crystal size, the nickel oxide-support interaction determines the catalytic performance of these catalysts. [ABSTRACT FROM AUTHOR]

• Discrimination of electrophilic and lattice oxygen by mathematical decoupling. • Acetate species represents key surface intermediate for carbon dioxide formation. • Predominant production of carbon monoxide from ethene decomposition. • Adequacy and significance of model parameter verified by statistical methods. • Sensitivity analyses reveal dependency of ethene formation on model parameters. An intrinsic kinetic model for the selective production of ethene via oxidative dehydrogenation of ethane over the M1 phase of MoVTeNb mixed metal oxides is presented. Formation of acetic acid, carbon monoxide and carbon dioxide has been incorporated using a holistic reaction mechanism. The proposed model is based on two different oxygen sites, namely, lattice oxygen causing carbon-hydrogen bond cleavage and electrophilic surface oxygen responsible for the formation of carbon-oxygen bonds. It is found that carbon dioxide exclusively originates from decarboxylation of acetate species, while ethene selectively reacts to CO. Consumption and formation of all species are well predicted by the proposed model. Sensitivity analyses demonstrate the strong impact of the initial carbon-hydrogen cleavage on the net ethene production rate. Moreover, regeneration of lattice oxygen sites is found to become rate-determining at oxygen-lean conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the oxidative dehydrogenation of ethane to produce ethylene at low temperatures (500 °C) in metallic structured substrates. To check this point, the FeCrAlloy® monoliths with different channel sizes (289–2360 cpsi) were prepared. The monoliths were coated with a Ni/Al2O3 catalyst (by washcoating of alumina and the latter nickel impregnation) and characterized by Scanning Electron Microscopy and Energy-Dispersive X-ray analysis (SEM-EDX), Temperature-Programmed Reduction (TPR), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The catalytic results showed that all monoliths coated with ~300 mg of catalyst presented similar ethane conversion (15%) at 450 °C. However, the lowest selectivity to ethylene was found for the monolith with the lower channel size and the higher geometric surface area, where a heterogeneous catalyst layer with Ni enriched islands was generated. Therefore, it can be said that the selectivity to ethylene is linked to the distribution of Ni species on the support (alumina). Nevertheless, in all cases the selectivity was high (above 70%). On the other hand, the stability in reaction tests of one of the coated monoliths was done. This structured catalyst proved to be more stable under reaction conditions than the powder catalyst, with an initial slight drop in the first 8 h but after that, constant activity for the 152 h left. [ABSTRACT FROM AUTHOR]