Study of vanadium based mesoporous silicas for oxidative dehydrogenation of propane and n-butane

The comparative study of catalytic performance of V-containing high-surface mesoporous siliceous materials (HMS, SBA-16, SBA-15 and MCM-48) in oxidative dehydrogenation of propane and n-butane (C₃-ODH and C₄-ODH, respectively) was carried out. The aim of study was to investigate effect of silica support texture on the speciation of vanadium complexes and its impact on catalytic behavior in both above mentioned reactions is reported. Prepared catalysts were characterized by XRF for determination of vanadium content, XRD, SEM and N₂-adsorption for study of morphology and texture, and H₂-TPR and DR UV-vis spectroscopy for determination of vanadium complex speciation. All prepared materials were tested in propane and n-butane ODH reaction at 540 °C and obtained catalytic results were correlated with their structural and surface characteristics. On the basis of obtained data we conclude that the structure of mesoporous silica support plays decisive role in the case of application of catalysts in n-butane ODH reaction, whereas catalytic performance of investigated catalysts in propane ODH reaction is comparable for all investigated structures. Catalytic performance of investigated materials in C₃-ODH and C₄-ODH can be correlated with population of all tetrahedrally coordinated VO_x complexes and only isolated monomeric VO_x complexes, respectively.     

Oxidative dehydrogenation of propane to propene, 1: Kinetic study on V/MgO

The reaction kinetics of the oxidative dehydrogenation of propane to propene over a V/MgO catalyst were studied. Both propane and propene oxidation kinetics were measured independently to quantify the rates of the parallel and consecutive reactions to propene and carbon oxides. Specific experiments to evaluate reaction products effects showed that water inhibited reaction rates but co‐feeding CO₂ or propene had no measurable effect on selectivity or conversion. Kinetic data generated under integral reactor conditions and over an inert membrane reactor have also been used to estimate the kinetic parameters. Selectivity decreased as the oxygen partial pressure increased; however, propene yield was relatively insensitive to oxygen concentration. A dual site Mars‐van Krevelen model characterizes the reaction kinetics well. The role of lattice oxygen was established by alternating pulses of propane and oxygen. This redox model is able to predict the experimental tendencies observed in the three types of reactor studied.     

A generalized kinetic model for the partial oxidation of n-butane to maleic anhydride under aerobic and anaerobic conditions

The kinetics of n-butane oxidation for the production of maleic anhydride (MA) over a commercial VPO catalyst has been investigated under aerobic and anaerobic conditions and at a temperature range of 400-. A kinetic model that can be applied under both aerobic and anaerobic conditions is presented. The model considers three types of oxygen: adsorbed oxygen, surface lattice oxygen and sub-surface lattice oxygen. Both adsorbed and surface lattice oxygen are considered active for the production of maleic anhydride and CO_x.     

Oxidative dehydrogenation of n-butane on V/MgO catalysts. Influence of the type of contactor

A comparative study of the catalytic performance of a selective V-Mg-O catalyst in the oxidative dehydrogenation of n-butane is presented using three different types of reactor: (i) an adiabatic fixed-bed reactor; (ii) a fluidized-bed reactor; and (iii) an in situ redox fluidized-bed reactor. The results obtained indicate that the in situ redox fluidized-bed reactor outperforms the conventional fixed- and fluidized-bed reactors, especially at high n-butane conversions. Thus, a selectivity to C₄ olefins of 54% at n-butane conversions of 60% was achieved at 550°C using an in situ redox fluidized-bed reactor while selectivities to C₄-olefins lower than 43% were obtained on the other reactor types under the same reaction conditions (isoconversion and reaction temperature). This revised version was published online in July 2006 with corrections to the Cover Date.     

Aerogel VOx/MgO catalysts for oxidative dehydrogenation of propane

VO_x/MgO aerogel catalysts were synthesized using three different preparation methods: by mixing the aerogel MgO support with dry ammonium vanadate, by vanadium deposition from a precursor solution in toluene, and by hydrolysis of a mixture of vanadium and magnesium alkoxides followed by co-gelation and supercritical drying. The latter aerogel technique allowed us to synthesize mixed vanadium–magnesium hydroxides with the surface areas exceeding 1300 m²/g. The synthesized catalysts were studied by a number of physicochemical methods (XRD, Raman spectroscopy, XANES and TEM). A common feature of all synthesized samples is the lack of V₂O₅ phase. In all cases vanadium was found to be a part of a surface mixed V–Mg oxide (magnesium vanadate), its structure depending on the synthesis method. The VO_x/MgO mixed aerogel sample had the highest surface area 340 m²/g, showed higher catalytic activity and selectivity in oxidative dehydrogenation of propane compared to the catalysts prepared by impregnation and dry mixing. The addition of iodine vapor to the feed in 0.1–0.25 vol.% concentrations was found to increase to propylene yield by 40–70%.     

催化剂上丙烷氧化脱氢制丙烯

以浸渍法制备VMo/γ-Al₂O₃和VMoMg/γ-Al₂O₃催化剂,考察其催化丙烷氧化脱氢制丙烯的反应活性,采用XRD、UV-Vis DRS和In suit IR对催化剂进行表征。结果表明,V负载质量分数为3%、Mo负载质量分数为7%时的3V7Mo/γ-Al₂O₃催化剂表现出较好的催化性能;添加Mg后催化剂的催化性能有所改善,反应温度500 ℃时,丙烷转化率为18.19%,丙烯选择性74.76%。丙烷和丙烯在3V7Mo/γ-Al₂O₃和3V₇Mo₄Mg/γ-Al₂O₃催化剂上吸附后,C—H键的H与催化剂活性中心的晶格氧发生作用形成H—O键,且3V₇Mo₄Mg/γ-Al₂O₃催化剂上出现C—O键的温度比3V₇Mo/γ-Al₂O₃催化剂高,表明加入Mg有利于提高丙烯选择性。     

用于二乙醇胺脱氢反应的铜锰系催化剂制备条件的研究

研究了铜锰系催化剂并流共沉淀法的制备条件对二乙醇胺催化脱氢反应性能的影响。结果表明,在铜锰原子比为1、溶液浓度0.4 mol·L^-1、沉淀pH为12、沉淀温度70　℃、焙烧温度550 ℃和还原温度210 ℃时,催化剂性能最好。在反应温度150 ℃和压力0.8 MPa,催化剂用量为二乙醇胺质量10%的反应条件下反应 5 h,亚氨基二乙酸盐收率可达93.2%。     

脱氢用Pd/C催化剂制备及其工艺优化

采用浸渍法制备了一种脱氢专用Pd/C催化剂,研究了其在四氢咔唑脱氢反应中的应用。利用响应面分析法对Pd/C催化剂制备的pH、炭浆体积和反应时间进行了优化,得出最佳工艺条件:pH=7.86,炭浆体积139.76 mL,反应时间75.70 min,咔唑收率接近100%。     

沉淀方式对二乙醇胺催化脱氢铜锰催化剂性能的影响

研究了沉淀方式对铜锰催化剂二乙醇胺脱氢反应性能的影响,并采用XRD和H_2-TPR分别对催化剂结构和还原性能进行了表征。结果表明,分步沉淀法制备的催化剂对二乙醇胺脱氢具有更高的活性(91.9%)和亚氨基二乙酸选择性(96.2%),有利于改善锰溶出的影响,催化剂重复使用率高。H_2-TPR研究发现,分步沉淀法制备的催化剂具有更好的还原性能;XRD测试表明,分步沉淀法有利于催化剂中CuO的分散。     

氧化铝载体老化温度对长链烷烃脱氢催化剂性能的影响

采用油柱成型法制备球形氧化铝,考察了氧化铝载体老化温度对长链烷烃脱氢催化剂性能的影响,通过强度、堆积密度、BET和NH₃-TPD等手段对载体进行表征。结果表明,老化温度对载体表面的酸强度和酸量有较大影响。随着老化温度的升高,酸强度及酸量逐渐变大,使长链烷烃脱氢过程中单烯烃收率降低。     

长链烷烃脱氢失活催化剂的表征及其烧炭再生温度研究

以N2物理吸附-脱附、压汞、热重和CO脉冲化学吸附催化剂物化表征手段对工业失活长链烷烃脱氢催化剂进行表征,并考察烧炭再生温度对催化剂活性的影响.结果表明,与新鲜催化剂相比,失活催化剂比表面积和总孔容略有下降,孔径分布向小孔方向移动.通过氧化烧炭可使催化剂活性部分恢复.O2-N2混合气(O2体积分数1%)气氛氧化烧炭适宜...     

Optimization of V2O5–MgO/TiO2 catalyst for the oxidative dehydrogenation of propane effect of magnesia loading and preparation procedure

The effect of magnesia loading and preparation procedure of vanadia on titania catalysts on the physicochemical characteristics and the performance in propane oxidative dehydrogenation were investigated. A series of magnesia promoted vanadia catalyst (5 wt% V₂O₅) with varying amounts of MgO (1.9--10 wt%) were synthesized by synchronous and sequential deposition on titania support. The catalysts were characterized using several techniques (BET, XRD, H₂-TPR and NH₃)-TPD). Both MgO loading and preparation procedure affect the catalyst surface properties and the behavior in the oxidative dehydrogenation of propane. Magnesia addition results in drastic increase in propene selectivity, while the effect on activity is negative. The activity is inversely related with the magnesia loading. Deposition of V₂O₅ on previously prepared MgO/TiO₂ presents a beneficial effect in the activity of the sample. The role of acidity and reducibility is explored. There is no correlation between reducibility and activity of the catalysts, whereas the acidity seems to influence the catalytic performance. Catalyst containing 5 wt% V₂O₅ and 1.9 wt% MgO prepared by sequential deposition of V₂O₅ on already doped with MgO titania exhibits the most interesting results.     

Effect of alkali metals additives to V2O5/TiO2 catalyst on physicochemical properties and catalytic performance in oxidative dehydrogenation of propane

The effect of alkali metal additives Li, K, and Rb to V₂O₅/TiO₂ catalyst on the rate of catalyst reduction with propane and reoxidation with oxygen, sorption of propene, and the electron work function has been examined. The results have been correlated with the catalytic performance in oxidative dehydrogenation, ODH, of propane. It has been found that the rates of reduction, reoxidation and the ODH of propane decrease in the order: VTi>LiVTi>KVTi>RbVTi. The activation energies of the reduction and reoxidation are not, however, affected by the presence of the alkali metals. The same sequence has been observed for the work function values of the catalysts. It is argued that alkali metal poisons the centres of the hydrocarbon activation. The yield and selectivity to propene in the ODH of propane increase, however, for the promoted catalysts, following the above sequence. This effect is ascribed to the decrease in the heat of the propene adsorption, which is due to the increase in the basicity and decrease in acidity on the promoted catalysts.     

Sn对V2O5/Al2O3催化剂在异丁烷脱氢反应中的影响

以Al₂O₃为载体,采用等体积浸渍法制备了负载型高分散氧化钒催化剂（12%V₂O₅/Al₂O₃）,并选择Sn作为助剂对12%V₂O₅/Al₂O₃催化剂的表面性质进行调控,采用XRD、N₂等温吸脱附、NH₃-TPD、H₂-TPR、XPS、TEM和Raman光谱等方法对催化剂进行表征,结合活性评价实验,研究了催化剂表面物种分散状态、酸性和活性物种价态的变化与异丁烷脱氢活性和稳定性之间的关系。表征结果显示,Sn对V₂O₅/Al₂O₃表面的酸性和V物种在催化剂表面的分布和价态具有一定的调节作用,当Sn质量分数为1%时,氧化锡在催化剂表面分散均匀,对表面积和孔结构影响较小,同时,表面酸性变化较小,表面低价态的钒物种增多。活性评价结果表明,该催化剂在临氢反应条件下保持了最佳的脱氢活性及稳定性,异丁烷脱氢反应480min后,异丁烷转化率为46.8%,异丁烯收率为39.8%。     

Mixed-oxide catalysts involving V, Nb and Si obtained by a non-hydrolytic sol–gel route: preparation and catalytic behaviour in oxydative dehydrogenation of propane

One-step non-hydrolytic condensation reactions, starting from VO(OⁱPr)₃ and NbCl₅, have been used for the first time to prepare Nb-V oxide catalysts. Different materials containing the NbVO₅ phase at different purity levels have been obtained, after thermal treatments, depending on the experimental conditions. The synthetic procedure has also been applied to prepare ternary Nb-V-Si oxide systems. From preliminary catalytic reaction studies it appears that the catalysts so prepared are promising with respect to their interesting performances in the oxidative dehydrogenation (ODH) of propane. It has also been found that -Sb₂O₄, physically blended with the Nb-V oxide materials, could act as an appropriate promoter to improve the catalytic performances of these systems.     

Anaerobic catalytic oxidation of hydrocarbons in moving heat waves. Case simulation: Propane oxidative dehydrogenation in a packed adiabatic V-Ti oxide catalyst bed

The model simulation study has shown that the anaerobic process of oxidative dehydrogenation of propane under periodic alteration of feeding between propane and air may be realized in adiabatic catalyst beds in a stable continuous cyclic mode in a two-reactor scheme. In the case of an appropriate choice of process parameters (cycle duration and feeding flow rates) the process appears to be autothermal, i.e. it does not require any inlet gas preheating for stable operation. Compared with a similar steady-state adiabatic process, the proposed process is characterized with much lower maximum catalyst temperatures, giving the way to process pure propane without diluting it with inert gases, thus simplifying the downstream procedure of product separation. Predicted propylene yield is competitive with the one for the steady-state adiabatic process, while sufficient technological benefits of the new technology are expected (decrease in energy consumption and minimization of heat-exchange environment, process safety improvement, suppression of coke formation and efficient coke incineration).     

改性铁酸锌催化剂的合成及其丁烯氧化脱氢活性

采用共沉淀法制备铁酸锌催化剂,考察改性元素Mg、B、Zr、Ce、La对铁酸锌催化剂结构和丁烯氧化脱氢性能的影响。采用XRD、TEM和N_2吸附-脱附对镧改性铁酸盐催化剂进行金属元素组成的优化研究,确认镧元素在催化剂中存在的形态和作用。结果表明,La改性铁酸锌催化剂晶粒粒径(20～50) nm,具有较大的比表面,主要活性组分是α-Fe_2O_3和ZnFe_2O_(4,)催化剂的活性随着Fe含量的升高而升高,n(Fe)∶n(Zn)∶n(La)=4∶1∶1催化剂具有最高的催化活性,反应温度380℃时,其TOF值2.1×10~(-3) mol_(butene)·mol_(surface-Fe)·s~(-1)。     

AFM investigation of solid product layers of MgSO4 generated on MgO surfaces for the reaction of MgO with SO2 and O2

The nucleation, growth and arrangement of MgSO₄ product layers during the reaction of single-crystal MgO with SO₂ and O₂ were investigated via atomic force microscopy (AFM). The morphology of the single-crystal MgO surface after reacting with SO₂ and O₂ consisted of three-dimensional cone-shaped MgSO₄ product islands. Most of the islands appeared at locations with terraces, steps and kinks. With increasing reaction time, small product islands grew to large islands, finally coalescing into continuous islands. The nucleation, growth and arrangement of the solid products on the reactant surface are controlled by thermodynamics and kinetics. The morphology of the MgSO₄ product islands is governed by the competition between the intrinsic chemical reaction rate and the product molecular diffusion rate, which are both significantly affected by the reaction temperature. As the reaction temperature increases, the mean size of the MgSO₄ islands increases while the island density decreases. The nucleation, growth and arrangement of the solid product layers and the product layer morphology on the solid reactant surface directly affect the mechanism of the gas–solid reaction.