Oxidative Dehydrogenation of Light Alkanes on Supported Molten Alkali Metal Chloride Catalysts

Potential and limitations of molten alkali metal (Li, Na, and K) chlorides supported on Dy₂O₃/MgO were explored for the oxidative dehydrogenation of lower alkanes, such as ethane and propane. The catalysts have high activity and selectivity to olefins compared to conventional catalysts. Optimum performance is obtained with catalysts on which the alkali metal chloride phase is molten under reaction conditions. Lower chloride melting point correlates with higher selectivity. The high selectivity to ethene or propene is attributed to the high mobility of cations and anions, which facilitates desorption of alkene (limiting further oxidation) and the generation of spatially isolated hypochloride anions acting as the active sites for the primary C–H bond activation.     

The catalytic performance and characterization of a durable perovskite-type chloro-oxide SrFeO3–δClσ catalyst selective for the oxidative dehydrogenation of ethane

The catalytic performances and properties of SrFeO_3-0.190 and SrFeO_3-0.382Cl_0.443 catalysts have been investigated for the oxidative dehydrogenation of ethane (ODE). XRD results showed that both catalysts exhibited oxygen-deficient perovskite-type structures. The inclusion of chloride ions in the SrFeO_3-δlattice matrix can significantly enhance ethene selectivity and ethane conversion. The SrFeO_3-0.382Cl_0.443 catalyst showed an ethane conversion of ca. 90%, an ethene selectivity of ca. 70%, and an ethene yield of ca. 63% under the reaction conditions: C₂H₆:O₂:N₂ = 2:1:3.7, temperature 680°C, and space velocity 6000 ml h^-1 g^-1. With the increase of space velocity, ethane conversion decreased, whereas ethene selectivity increased over SrFeO_3-0.382Cl_0.443. Lifetime studies showed that the perovskite-type chloro-oxide catalyst was durable. The results of O₂-TPD and TPR experiments illustrated that the implanted chloride ions caused the oxygen nature of SrFeO_3-δ to change. By regulating the concentration of oxygen vacancies and the Fe⁴⁺/Fe ratio in this perovskite-type chloro-oxide catalyst, one can generate a durable chloro-oxide catalyst for the ODE reaction with excellent performance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lithium-chloride-promoted sulfated zirconia catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane over sulfated-zirconia-supported lithium chloride catalysts has been systematically investigated. The optimal experimental parameters were obtained. It is found that sulfation of zirconia increases the catalytic activity. 2–3.5 wt% lithium chloride on sulfated zirconia catalysts exhibit high catalytic activity for oxidative dehydrogenation of ethane, with particularly high activity for ethene production. 70% selectivity to ethene at 98% ethane conversion, giving 68% ethene yield, is achieved over 3.5 wt% LiCl/SZ at 650°C.     

The importance of heterogeneous and homogeneous reactions in oxidative coupling of methane over chloride promoted oxide catalysts

The formation of ethene from ethane and methane in a silica reactor has been studied both in the presence and in the absence of chloride-containing catalysts. Some homogeneous conversion of ethane to ethene occurs in the gas phase through direct dehydrogenation, oxidative dehydrogenation, and, when HCl is present, chlorine radical induced reactions. Methyl chloride is detected in the gas phase but has no influence on the conversion of ethane to ethene. It is shown that under typical catalytic conditions, when a chloride-modified catalyst is used, ethane is mostly produced in the catalyst bed.     

Highly Selective Supported Alkali Chloride Catalysts for the Oxidative Dehydrogenation of Ethane

Binary, ternary and quaternary molten eutectic alkali chloride catalysts, supported on mildly redox active oxides, were investigated for the oxidative dehydrogenation of ethane. The influence of different support oxides, on the catalytic performance, as well as that of different anions (bromide vs. chloride) and cations in a chloride eutectic system were studied. Metal oxides which react with chlorides are not suitable and lead to substantial deactivation. Especially supports forming volatile chlorides induce irreversible chloride depletion. Bromides catalyze oxidative dehydrogenation of ethane with higher rates, but lower olefin selectivities, highlighting the similarities and differences of Cl^? and Br^? in the redox cycle. Two catalysts were identified having olefin selectivities up to 98 % at 70 % ethane conversion, which ranges among the highest selectivities reported for ethane ODH.     

Performance of metal‐oxide‐promoted LiCl/sulfated‐zirconia catalysts in the ethane oxidative dehydrogenation into ethene

The effects of some transition‐ and lanthanide‐metal oxides in LiCl/sulfated‐zirconia (SZ) catalysts on catalytic behavior in the oxidative dehydrogenation of ethane were investigated. It is found that modification of LiCl/SZ by metal oxides significantly improves the catalytic activity and ethene yield. Among those additives, Ni and Nd oxides show the best promoting effect in terms of ethane conversion and ethene yield. 93% ethane conversion with 83% selectivity to ethene has been achieved over the Nd₂O₃–LiCl/SZ catalyst at 650°C. In addition, those oxide‐promoted LiCl/SZ catalysts are also found to exhibit a longer stability in catalytic performance. Metal‐oxide additives change the chemical structure and surface redox properties, which accounts for the enhancement of activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

V–BaCO3 catalysts for the oxidative dehydrogenation of ethane

A new type of supported vanadium oxide catalyst V–BaCO₃, which consists of barium orthovanadate Ba₃(VO₄)₂ and BaCO₃ phases, has been used in the oxidative dehydrogenation of ethane. The catalyst with the ratio of V/Ba from 0.1 to 0.3 exhibited high catalytic activity for oxidative dehydrogenation of ethane, with particularly high activity for ethene production.     

A Comparison of Catalytic Oxidative Dehydrogenation of Ethane Over Mixed V-Mg Oxides and Over Those Prepared via a Mesoporous V-Mg-O Pathway

The catalytic oxidative dehydrogenation of ethane was investigated in a fixed-bed tubular microreactor at 500, 550 and 600 °C and a space velocity of 35 027ml g^-1h^-1. Two kinds of V-Mg oxides catalysts containing various V/Mg atomic ratios were employed. One group of catalysts was prepared by the solid reaction between fine powders of vanadium pentoxide and magnesium nitrate and the other ones were obtained from mesostructured V-Mg-Os. For the former catalysts, it was found that the selectivity to ethene increased and the conversion of ethane passed through a maximum with increasing V/Mg atomic ratio. For the catalysts obtained from the mesoporous materials, an optimum V/Mg atomic ratio was found, for which the conversion of ethane and the selectivity to ethene were maxima. Compared with the mixed-oxide catalysts, those obtained from the mesoporous materials exhibited much higher yields to ethene. Several new phases, such as pyro-Mg₂V₂O₇, ortho-Mg₃(VO₄)₂ and meta-MgV₂O₆, formed between magnesia and vanadia, were identified by XRD in the mixed V-Mg oxide catalysts; they may be responsible for the catalytic activity. In the catalysts prepared from mesoporous V-Mg-O, a V₂O₃ phase, which may contain highly dispersed magnesium, was identified and suggested to be responsible for the higher catalytic performance.     

Pt0.02Sn0.003Mg0.06 on γ-alumina: a stable catalyst for oxidative dehydrogenation of ethane

The advantages of two-step oxidative dehydrogenation as an alternative method for manufacturing small alkenes are outlined. In a nutshell, the process is based on separating the gaseous oxygen and hydrocarbon feeds in time. In the first step, alkanes are dehydrogenated in the presence of a solid oxygen carrier (without gaseous oxygen). Subsequently, the carrier is reoxidised using a gaseous feed. This process requires a dehydrogenation catalyst that is selective and stable under severe redox cycling. In search for such a catalyst, we prepare and study various platinum/tin catalysts supported on alumina. The catalysts are doped with either magnesia or potassium oxide. The activity, selectivity, and stability of these catalysts in the dehydrogenation of ethane to ethylene are then investigated under severe redox cycling conditions (600 °C and 10% (v/v) oxygen in the regeneration step). Pt_0.02Sn_0.003Mg_0.06 is found to be the most stable combination. The catalysts’ dispersion and the metal–support interactions are studied using transmission electron microscopy (TEM) and temperature-programmed hydrogen desorption (TPD). The effects of the (earth)alkali promoter and the interaction between the metal catalyst and support are discussed.     

Oxidative dehydrogenation of ethane over Dy2O3/MgO supported LiCl containing eutectic chloride catalysts

The catalytic oxidative dehydrogenation of ethane with alkali and alkaline earth metal chloride modified LiCl supported on Dy₂O₃/MgO (MD) was studied. Eutectic mixtures of alkali and alkaline earth metal chloride with LiCl are formed on the support surface decreasing so the melting point of pure LiCl to temperatures as low as 366 °C (Li-K-MD). All samples had weak basicity decreasing in the order: Li-K-MD < Li-Sr-MD Li-Ba-MD < Li-Na-MD < Li-MD. Physisorbed and chemisorbed CO₂ species are identified for all materials studied by in situ IR spectroscopy. Bidentate carbonate species are the most abundant on Li-MD, while on modified samples bi- and unidentate carbonate species exist. The catalyst activity increases with decreasing basicity. Catalyst selectivity increases with increasing reaction temperature and is constant above a threshold temperature. The maximum ethene selectivity is directly correlated with the melting point of the eutectic melt on the catalyst support.     

Selective Conversion of Ethane to Ethene via Oxidative Dehydrogenation Over Ca-doped ThO2 Using CO2 as Oxidant

Ca-doped ThO₂, synthesized by solution combustion method was tested for dehydrogenation of ethane with CO₂. Doping ThO₂ with Ca resulted in the creation of oxide ion vacancies and an increased conversion of ethane compared to pure ThO₂. On Th_0.75Ca_0.25O₂ selectivity to ethene was 97 at 46% ethane conversion at 725 °C. Well-known reference catalysts like 5%Cr/TS-1 or OMS-2 showed significantly lower selectivity, but the former was more active under the same conditions.     

Ni–Nb–O mixed oxides as highly active and selective catalysts for ethene production via ethane oxidative dehydrogenation. Part II: Mechanistic aspects and kinetic modeling

In this work, transient and SSITKA experiments with isotopic ¹⁸O₂ were conducted to study the nature of oxygen species participating in the reaction of ethane oxidative dehydrogenation to ethylene and obtain insight in the mechanistic aspects of the ODH reaction over Ni-based catalysts. The study was performed on NiO, a typical total oxidation catalyst, and a bulk Ni–Nb–O mixed-oxide catalyst (Ni_0.85Nb_0.15) developed previously [E. Heracleous, A.A. Lemonidou, J. Catal., in press], a very efficient ethane ODH material (46% ethene yield at 400 °C). The results revealed that over both materials, the reaction proceeds via a Mars–van Krevelen-type mechanism, with participation of lattice oxygen anions. However, the ¹⁸O₂ exchange measurements showed a different distribution of isotopic oxygen species on the two materials. The prevalent formation of cross-labelled oxygen species on NiO indicates that dissociation of oxygen is the fast step of the exchange process, leading to large concentration of intermediate electrophilic oxygen species on the surface, active for the total oxidation of ethane. Larger amounts of doubly exchanged species were observed on the Ni–Nb–O catalyst, indicating that doping with Nb makes diffusion the fast step of the process and suppresses formation of the oxidizing species. Kinetic modeling of ethane ODH over the Ni_0.85Nb_0.15 catalyst by combined genetic algorithm and nonlinear regression techniques confirmed the above, since the superior model is based on a redox parallel-consecutive reaction network with the participation of two types of active sites: type I, responsible for the ethane ODH and ethene overoxidation reaction, and type II, active for the direct oxidation of ethane to CO₂. The kinetic model was able to successfully predict the catalytic performance of the Ni_0.85Nb_0.15 catalyst in considerably different experimental conditions than the kinetic experiments (high temperature and conversion levels).     

Oxidative dehydrogenation of ethane over alkali‐metal doped sulfated zirconia catalysts

Alkali‐metal doped sulfated zirconia catalysts were tested for the oxidative dehydrogenation of ethane into ethene. The effects of metal precursor compounds and acidic anion promoters on the catalytic activity in this reaction were studied. It was found that sulfation of zirconia increases the selectivity of ethane towards ethene. Lithium‐, sodium‐, and potassium‐doped sulfated zirconia catalysts showed quite different activities in this reaction. Sulfated zirconia doped with lithium catalysts were found to be effective for the oxidative dehydrogenation of ethane, giving over 90% selectivity to ethene and 25% ethene yield at 650 °C. © 1999 Society of Chemical Industry     

Effect of oxygen capacity and oxygen mobility of supported Mg3(VO4)2 catalysts on the performance in the oxidative dehydrogenation of n-butane

Vanadium-magnesium oxide (Mg₃(VO₄)₂) catalysts supported on Al₂O₃, ZrO₂, MgO, and CeO₂ were prepared by a wet impregnation method, and they were applied to the oxidative dehydrogenation of n-butane. Effect of oxygen capacity and oxygen mobility of supported Mg₃(VO₄)₂ catalysts on the catalytic performance in the oxidative dehydrogenation of n-butane was investigated. Experimental results revealed that large oxygen capacity of the catalyst was favorable for obtaining high catalytic activity at the initial stage of reaction, while facile oxygen mobility of the catalyst led to stable catalytic activity during the catalytic reaction in the oxidative dehydrogenation of n-butane.     

The effect of potassium on the selective oxidation ofn-butane and ethane over Al2O3-supported vanadia catalysts

The catalytic properties of undoped and K-doped (K/V atomic ratio of 0.5) Al₂O₃-supported vanadia catalysts (4.5 wt% of V₂O₅) for the oxidation ofn-butane and ethane were studied. Isolated tetrahedral V⁵⁺ species are mainly observed in both undoped and K-doped samples. The incorporation of potassium decreases both the reducibility of surface vanadium species and the number of surface acid sites. Potassium-free vanadium catalysts show a high selectivity during the oxidative dehydrogenation (ODH) of ethane but a low selectivity during the ODH ofn-butane. However, the presence of potassium on the vanadium catalysts strongly influences their catalytic properties, increasing the selectivity to C₄-olefins fromn-butane and decreasing the selectivity to ethene from ethane. The role of the acid-base characteristics of catalysts on selectivity to ODH reactions is proposed.On leave from the Department of Industrial Chemistry and Materials, V. le Risorgimento 4, 40136 Bologna, Italy.     

Effect of promoters on catalytic performance of Cr/SiO2 catalysts in oxidative dehydrogenation of ethane with carbon dioxide

Several acidic and basic oxide promoted Cr/SiO₂ catalysts were prepared and investigated in oxidative dehydrogenation of ethane in the presence of carbon dioxide. The effects of SO₄ ^2–, WO₃ and alkali metal oxides (Li₂O, Na₂O, and K₂O) on the catalytic activity were studied. It is found that sulfation of silica produces a positive effect on ethane conversion and ethylene yield while tungstation and addition of strong basic promoters (alkali metal oxides) suppress the catalytic activity. Characterization indicates that the varying activity of the promoted catalysts can be attributed to the difference in acid/base property and redox potential.     

Effect of Oxygen Capacity and Oxygen Mobility of Pure Bismuth Molybdate and Multicomponent Bismuth Molybdate on their Catalytic Performance in the Oxidative Dehydrogenation of n-Butene to 1,3-Butadiene

Pure bismuth molybdate (γ-Bi₂MoO₆) and multicomponent bismuth molybdate (Co₉Fe₃Bi₁Mo₁₂O₅₁) catalysts were prepared by a co-precipitation method, and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene. The Co₉Fe₃Bi₁Mo₁₂O₅₁ catalyst showed a better catalytic performance than the γ-Bi₂MoO₆ catalyst in terms of conversion of n-butene and yield for 1,3-butadiene, indicating that the multicomponent bismuth molybdate was more efficient than the pure bismuth molybdate in the oxidative dehydrogenation of n-butene. It was revealed that the crucial factor determining the catalytic performance of Bi–Mo-based catalyst in the oxidative dehydrogenation of n-butene is not the amount of oxygen in the catalyst involved in the reaction (oxygen capacity) but the intrinsic mobility of oxygen in the catalyst involved in the reaction (oxygen mobility). The enhanced catalytic performance of Co₉Fe₃Bi₁Mo₁₂O₅₁ was due to its facile oxygen mobility.     

Oxidative Dehydrogenation of Ethane Over Zirconia‐Supported Lithium Chloride Catalysts

A series of Li‐doped catalysts on zirconia or sulfated zirconia were prepared and investigated in the catalytic reaction of ethane oxidative dehydrogenation into ethylene. It is found that zirconia and sulfated zirconia supports prepared by different methods show varying nature and thus influence the catalytic performance of their supported Li catalysts in this reaction. Li catalysts doped on the sulfated zirconia prepared by a two‐step method can exhibit high ethane conversion, selectivity towards ethylene and ethylene yield as well as a stable catalytic performance. The Li precursors also affect the catalytic behavior. LiCl doped on sulfated zirconia can give high ethane conversion and ethylene selectivity. Addition of transitional and lanthanide metal oxides to the LiCl/SZ system significantly improves the activity and yield of ethylene in the oxidative dehydrogenation of ethane. Among the oxides studied, NiO and Nd₂O₃ demonstrate the best promoting effect in terms of catalytic conversion and ethylene yield.     

The effect of alkali promoters in oxidative coupling of methane with Mn-oxide catalysts

The catalytic oxidalive coupling of metnane to ethylene and ethane with manganese oxide catalysts promoted with alkali metal and alkali metallic-chloride has been studied at atmospheric pressure in a fixed bed flow reactor. The main studies of reaction were carried out over maganese oxide catalysts promoted with sodium chloride and the structure and surface morphology of these catalysts was characterized by an X-ray diffraction and a scanning electron microscope. The powdered MnO₂ was changed into Mn₂O₃, and MnO₂ containing alkali metallic-chlorides was not changed to new ternary oxides but changed into Mn₃O₄ and/or Mn₂O₃ at higher calcination temperature(above 780°C). The optimum content of NaCl promoted was 10–20wt%, an in over 10wt%, the conversion and the selectivity were kept constant. The main factor on deactivation of catalysts was the loss of thepromoter(NaCl). The addition of alkali metal salts to manganese oxide catalyst has enhanced C₂(C₂H₄ + C₂H₆) selectivity due to neutralizing acid sites more than the electronic factor. It was confirmed that chlorine in alkali metallicchloride has enhanced the formation of C₂H₄, resulting in a good C₂-yield (up to 25.7%).     

Promoting effect of carbon dioxide on the dehydrogenation and aromatization of ethane over gallium‐loaded catalysts

Ga₂O₃ and Ga₂O₃/TiO₂ catalysts were found to be effective agents for the dehydrogenation of ethane to ethene in the presence of carbon dioxide at 650 °C. The activity of the Ga₂O₃ and Ga₂O₃/TiO₂ catalysts in the presence of CO₂ was 2–4 times higher than that without CO₂. Ethene yields reached ca. 20–25% and selectivity was ca. 70–90% at 650°C in the 17% ethane and 83% CO₂ feed at an SV of 9,000 ml/(g‐cat h). The presence of CO₂ markedly promoted dehydrogenation of ethane over Ga₂O₃ and Ga₂O₃/TiO₂ catalysts. Furthermore, the promoting effect of CO₂ on the aromatization of ethane and ethene over a Ga₂O₃+H/ZSM‐5 catalyst was also observed above 650 °C. Aromatics yields were higher than those without CO₂. This revised version was published online in July 2006 with corrections to the Cover Date.