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.     

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.     

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.     

Oxidative dehydrogenation of ethane and propane over Mn-based catalysts

The catalytic performances of Mn-based catalysts have been investigated for the oxidative dehydrogenation of both ethane (ODE) and propane (ODP). The results show that a LiCl/MnO_x/PC (Portland cement) catalyst has an excellent catalytic performance for oxidative dehydrogenation of both ethane and propane to ethylene and propylene, more than 60% alkanes conversion and more than 80% olefins selectivity could be achieved at 650°C. In addition, the results indicate that Mn-based catalysts belong to p-type semiconductors, the electrical conductivity of which is the main factor in influencing the olefins selectivity. Lithium, chlorine and PC in the LiCl/MnO_x/PC catalyst are all necessary components to keep the excellent catalytic performance at a low temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

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     

Catalytic composites based on yttria stabilized zirconia for oxidative dehydrogenation of ethane

LiCl/YSZ is found to be a very effective catalyst for the oxidative dehydrogenation of ethane. LiCl supported on YSZ-MgO composite shows increase in catalytic activity and ethylene selectivity. Addition of Mn and Sn as promoters to this system leads to 85% ethane conversion, 77% ethylene selectivity and 65% ethylene yield at 662 °C. Use of Li₂O in the place of LiCl results in lower ethylene yields. Further modification is needed to improve the catalyst stability.     

Oxidative Dehyrodimerization of Methane Using Manganese‐based Catalysts Made by Self‐propagating High‐temperature Combustion Synthesis

The self‐propagating high‐temperature synthesis (SHS) method has been used to produce a range of active manganese‐based catalysts for the oxidative dehydrodimerization of methane. Catalytic activity was measured at temperatures between 920 and 1120 K under a range of conditions. In the best case found, the ethylene yield reached about 26 % with a selectivity of 85 % and a methane conversion of 30.2 %. Some ethane, propylene, propane and hydrogen were also obtained. The addition of alkaline elements, promoted by halides, increased the yield of ethylene at the expense of reduced stability. The catalytic activity was found to be enhanced by careful control of SHS conditions and various post‐synthesis treatments of the materials.     

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.     

Sulfated zirconia and iron- and manganese-promoted sulfated zirconia: do they protonate alkanes?

Because of their high activities for alkane conversion, sulfated zirconia and iron- and manganese-promoted sulfated zirconia have been the objects of much recent attention as a possible next generation of solid acid catalysts for alkane conversion. These catalysts have been suggested to be superacidic on the basis of measurements with adsorbed Hammett indicator bases, but published data determined with other adsorbed bases indicate only moderately strong acid sites. The indicator methods are limited by the opaqueness of the materials and by the inability of the methods to probe a possible set of minority sites that might be responsible for the reactivity and catalytic activity for alkane conversions. Another approach to the challenge of estimating the acid strengths of the reactive and catalytic sites is to investigate the reactivities and catalytic activities of the materials for reactions which, for initiation, require donation of protons from a solid acid to a very weakly basic reactant such as an alkane. Such a test reaction is the acid-catalyzed dehydrogenation of alkanes proceeding by the Haag–Dessau mechanism (Olah type chemistry). This review includes a summary of results for conversion of ethane, propane, and n-butane that are consistent with the postulate that iron- and manganese-promoted sulfated zirconia and sulfated zirconia are capable of protonating light alkanes to give carbonium-ion transition states at temperatures as low as 200°C. The data support the postulate that these proton-donation reactions are important at low alkane conversions and in initiating alkane conversions, although conventional carbenium ion reactions predominate at high conversions. This revised version was published online in June 2006 with corrections to the Cover Date.     

H2S Promoted Oxidative Dehydrogenation of Hydrocarbons in Molten Media

The H₂S promoted oxidative dehydrogenation of butane to butadiene can be efficiently carried out if a molten salt medium, e.g. LiCl/KCl, is used to dissipate the heat from the highly exothermic reaction. The reaction is catalyzed by the addition of soluble salts such at Tl₂O₃, BaCl₂ or MnCl₂. Optimization of reaction conditions by varying temperature, space velocity and quantity of promoter results in a 53% olefin yield (5% butenes, 48% butadiene) at 80% butane conversion. The system is also shown to be efficient for the dehydrogenation of ethane to ethylene, propane to propylene, butene to butadiene and ethylbenzene to styrene.     

Effect of calcination temperature on characteristics of sulfated zirconia and its application as catalyst for isosynthesis

The effect of catalyst calcination temperature (450 °C, 600 °C, and 750 °C) on catalytic performance of synthesized and commercial grade sulfated zirconia catalysts towards isosynthesis was studied. The characteristics of these catalysts were determined by using various techniques including BET surface area, XRD, NH₃- and CO₂-TPD, ESR, and XPS in order to relate the catalytic reactivity with their physical, chemical, and surface properties. It was found that, for both synthesized and commercial sulfated zirconia catalysts, the increase of calcination temperature resulted in the increase of monoclinic phase in sulfated zirconia, and the decrease of acid sites. According to the catalytic reactivity, at high calcination temperature, lower CO conversion, but higher isobutene production selectivity was observed from commercial sulfated zirconia. As for synthesized sulfated zirconia, the isobutene production selectivity slightly decreased with increasing calcination temperature, whereas the CO conversion was maximized at the calcination temperature of 600 °C. We concluded from the study that the difference in the calcination temperatures influenced the catalytic performance, sulfur content, specific surface area, phase composition, the relative intensity of Zr³⁺, and acid-base properties of the catalysts.     

Supported Ni–W–O Mixed Oxides as Selective Catalysts for the Oxidative Dehydrogenation of Ethane

Mixed Ni–W–O catalysts (with a W/(Ni + W) atomic ratio of 0.3) supported on γ-Al₂O₃ or on mesoporous alumina have been prepared, characterized and tested in the oxidation of ethane. For comparison unsupported and supported NiO as well as bulk Ni–W–O mixed oxides catalysts have also been studied. Supported Ni–W–O materials show interesting catalytic performances in the oxidative dehydrogenation of ethane. They show similar catalytic activities than the corresponding unsupported Ni–W–O catalysts. However, the selectivity to ethylene over supported catalysts was higher than that achieved over unsupported samples (the selectivity to ethylene followed the trend: mesoporous-supported > γ-Al₂O₃-supported > unsupported Ni–W–O). In addition, it has also been observed that Ni–W–O catalysts are more efficient than the corresponding W-free NiO catalysts. The discussion of the catalytic results will be undertaken on the basis of the modification of active sites of NiO when incorporating WO₃ and/or metal oxide supports.     

Ni–Nb–O mixed oxides as highly active and selective catalysts for ethene production via ethane oxidative dehydrogenation. Part I: Characterization and catalytic performance

This work demonstrates the high potential of a new class of catalytic materials based on nickel for the oxidative dehydrogenation of ethane to ethylene. The developed bulk Ni–Nb–O mixed oxides exhibit high activity in ethane ODH and very high selectivity (∼90% ethene selectivity) at low reaction temperature, resulting in an overall ethene yield of 46% at 400 °C. Varying the Nb/Ni atomic ratio led to an optimum catalytic performance for catalysts with Nb/Ni ratio in the range 0.11–0.18. Detailed characterization of the materials with several techniques (XRD, SEM, TPR, TPD-NH₃, TPD-O₂, Raman, XPS, electrical conductivity) showed that the key component for the excellent catalytic behavior is the Ni–Nb solid solution formed upon the introduction of niobium in NiO, evidenced by the contraction of the NiO lattice constant, since even small amounts of Nb effectively converted NiO from a total oxidation catalyst (80% selectivity to CO₂) to a very efficient ethane ODH material. An upper maximum dissolution of Nb⁵⁺ cations in the NiO lattice was attained for Nb/Ni ratios ⩽0.18, with higher Nb contents leading to inhomogeneity and segregation of the NiO and Nb₂O₅ phases. A correlation between the specific surface activity of the catalysts and the surface exposed nickel content led to the conclusion that nickel sites constitute the active centers for the alkane activation, with niobium affecting mainly the selectivity to the olefin. The incorporation of Nb in the NiO lattice by either substitution of nickel atoms and/or filling of the cationic vacancies in the defective nonstoichiometric NiO surface led to a reduction of the materials nonstoichiometry, as indicated by TPD-O₂ and electrical conductivity measurements, and, consequently, of the electrophilic oxygen species (O⁻), which are abundant on NiO and are responsible for the total oxidation of ethane to carbon dioxide.     

Catalytic behavior of nanostructured sulfated zirconia promoted by alumina: Butane isomerization

Promotion of sulfated zirconia with alumina (ASZ) improves its catalytic activities in n-butane isomerization. The activity and stability of the sulfated zirconia catalysts are investigated in three different nanostructures: ASZ supported on MCM-41, ASZ nanoparticles, and Al-promoted mesoporous sulfated zirconia. The increase of activity was determined primarily by the amount of aluminum addition and the temperature of calcination. The remarkable activity and stability of the Al-promoted catalysts are due to an improved distribution of acid sites strength. The Al loadings in all three catalysts can be adjusted so that optimum catalytic activities for butane isomerization could be found. The increase of butane conversion can be as high as 6 times of that in un-promoted SZ catalysts. This is due to an enhanced amount of weak Brønsted acid sites with intermediate strength on the optimal catalysts. For nanoparticle form of sulfated zirconia, the activity is most steady which is related to the optimum distribution of weak Brønsted acid. On the other hand, too much strong Brønsted acid leads to rapid decay of activity because of coking and cracking. The overall reaction mechanism of the isomerization of n-butane over sulfated zirconia was discussed to understand the details in product distribution.     

Hydroisomerization of n-hexane over gallium-promoted sulfated zirconia

Gallium-promoted sulfated zirconia (GSZ) catalysts were prepared by impregnation of zirconium hydroxide with aqueous Ga₂(SO₄)₂ followed by calcination. Isomerization of n-hexane was studied over GSZ at 150 °C, 2.0 MP, WHSV 2 and H₂/hexane (molar) ratio of 5. In comparison to sulfated zirconia (SZ), the conversion of n-hexane over Gallium-promoted sulfated zirconia (GSZ) was greatly improved and it remained stable at 85%. In particular, almost all the products were isomers of hexane and the selectivity of 2,2-DMB reached 20%. The results of characterization indicated that the addition of gallium onto SZ catalyst showed little difference in acid strength between SZ and GSZ catalysts while the redox properties of the SZ catalyst changed with addition of gallium. The transformation of SZ crystalline from metastable tetragonal phase, the more active phase, to monoclinic phase was retarded with the addition of gallium. Furthermore, the simultaneous promotion of Pt and Ga brings the production distribution very close to the equilibrium one.     

Oxidative Dehydrogenation of Propane on Calcium Hydroxyapatites Partially Substituted with Vanadate

Solid solutions of phosphate and vanadate calcium hydroxyapatites were synthesized and the catalytic activities for the oxidative dehydrogenation of propane to propylene on those catalysts were examined. Although the conversion of propane and the selectivity to propylene were 7.6 and 3.5% on calcium hydroxyapatite (CaHAp), the incorporation of vanadate to CaHAp by V/P=0.05 (atomic ratio) resulted in the enhancement of the conversion and the selectivity to 17.2 and 52.4%, respectively, corresponding to those on Mg₂V₂O₇ under the same reaction conditions (14.0 and 50.9%, respectively).     

Well-dispersed Ceria-promoted Sulfated Zirconia Supported on Mesoporous Silica

Ceria-promoted sulfated zirconia (CeSZ) was supported on mesoporous molecular sieve of pure-silica MCM-41 (abbreviated as CeSZ/MCM-41). It was prepared by direct impregnation of metal sulfate onto the as-synthesized MCM-41, followed by solid state dispersion and thermal decomposition. The resultant catalysts were characterized by TG, XRD, nitrogen physisorption and TEM. It was showed that the hollow tubular structure of MCM-41 was retained, even with ZrO₂ loading as high as 60 wt.%. Most of CeSZ was well dispersed on the interior surface of the ordered mesopores, following a slight twist of the channels. The catalytic activity of CeSZ/MCM-41 was studied in the octadecanol oxidation. The improved performance of CeO₂-promoted catalysts was attributed to the high dispersion of sulfated zirconia (SZ) and the introduction of CeO₂ enhancing the oxidation ability of catalysts by retarding the transformation of zirconia from highly catalytic active metastable tetragonal phase to monoclinic phase.     

Oxydehydrogenation of propane over Mg-V-Sb-oxide catalysts. I. Reaction network

Magnesium vanadates have been shown by various groups to be active oxydehydrogenation catalysts for the conversion of light paraffins to the corresponding olefins. The olefins produced have significant commercial value in petroleum and petrochemical industry. Recently, we reported that doping of the magnesium vanadates with antimony, antimony-phosphorus, or boron, produces catalysts with significantly better selectivities to olefins than those of the parent undoped catalysts. Among these, the composition Mg₄V₂SbO_x was selected for further study of propane oxydehydrogenation and its reaction network. At 500°C and atmospheric pressure, the selectivity to propylene decreases monotonically from 75% to 5% as propane conversion is increased from 2% to 68%. An analysis of the reaction network reveals, that propylene is the only useful first formed product, that CO_x is produced largely by sequential oxidation of the in situ formed propylene, but also to a lesser extent direct from propane by a deep oxidation route. The presence of two parallel pathways for CO_x formation is of interest, as it suggests that partial and deep oxidations may occur at different surface sites or involve different forms of reactive oxygens. Both of these might be amenable to electronic modification by substitution or doping to achieve higher propylene selectivities and yields at higher propane conversions, or their catalytic behavior might be advantageously alterable through site isolation of the paraffin activation centers.     

乙烷脱氢催化剂研究进展

乙烯是重要的有机化工原料,随着乙烯需求量的不断增加以及石油资源的日益匮乏,乙烷脱氢已成为乙烯增产的重要途径。乙烷脱氢制乙烯受到越来越多的关注,乙烷脱氢催化剂逐步改善。本文首先介绍了近年来国内外乙烷脱氢制乙烯的研究现状,然后从催化剂制备方法、性能以及应用等方面对乙烷催化脱氢催化剂和乙烷氧化脱氢催化剂的研究进行了总结,并对其进行了系统分类。催化脱氢是低碳烷烃转化为烯烃的有效途径,烯烃选择性高,受到热力学平衡限制,能耗较高。氧化脱氢由于氧化剂的引入打破了热力学平衡限制,能够有效抑制焦炭的生成,减少能量消耗。然而,深度氧化反应难于控制,乙烯的选择性低。因此,选取合适的催化脱氢催化剂,尽可能提高乙烷单程转化率、降低能耗是乙烷脱氢的关键。     

Electrophilic chlorination of methane over superacidic sulfated zirconia

Catalytic chlorination of methane was studied over SO ₄ ^2– /ZrO₂, Pt/SO ₄ ^2– /ZrO₂, and Fe/Mn/SO ₄ ^2– /ZrO₂ solid superacid catalysts. The reactions were carried out in a continuous flow reactor under atmospheric pressure, at temperatures below 240°C, with a gaseous hourly space velocity of 1000 ml/g h and a methane to chlorine ratio of 4 to 1. At 200°C with 30% chlorine converted the selectivity in methyl chloride exceeds 90%. At more elevated temperatures, the selectivity decreases but stays above 80% in methyl chloride at 225°C using the sulfated zirconia catalysts. The selectivity can be enhanced by adding platinum to sulfated zirconia catalysts. An iron and manganese-doped catalyst exhibited excellent selectivities at somewhat lower conversions. Methyl chloride is obtained at 235°C in selectivities greater than 85%. No chloroform or carbon tetrachloride is formed. The electrophilic insertion involves electron-deficient metal-coordinated chlorine into the methane C-H bond.Catalysis by solid superacids, 29. For part 28 see ref. [14].