乙苯脱氢催化剂的发展动态

通过对乙苯脱氢制苯乙烯工业催化剂演变过程的分析。认为近年催化剂组成已经历由Ｆｅ－Ｋ－Ｃｒ系列向Ｆｅ－Ｋ－Ｃｅ系列以及由高钾含量向低钾含量的过渡。催化剂制备工艺也有诸多改进,颗粒形状由传统圆柱形向齿轮柱形及三叶柱形等异型颗粒演变。关于催化活性本质的研究渐趋活跃,多数研究者认为活性相是Ｋ２ｆｅ２Ｏ４钾流失是催化剂在正常操作条件下逐渐老化的根本原因。     

SO2/O2 dehydrogenation of ethylbenzene

In the SO₂ dehydrogenation of ethylbenzene to styrene using alkalized alumina or titania catalysts, addition of small amounts of oxygen results in (1) higher styrene yields at equivalent SO₂ concentrations, or (2) equivalent styrene yields with lower SO₂ requirements. By staging the oxygen additions, styrene yields of greater than 80% are achieved at SO₂ levels as low as 0.15 mole/mole ethylbenzene when 0.45 mole O₂ is added in increments of 0.15 mole. The low SO₂ concentration and staging of the oxygen result in a high selectivity (94%) for the reaction to styrene by minimizing both byproduct formation and combustion.     

Characterization and activity of V2O5/CeO2-MgO catalyst in the dehydrogenation of ethylbenzene to styrene

Supported vanadia catalyst was impregnated on CeO₂-MgO and characterized by N₂ adsorption, XRD, XPS, TPR and solid NMR. The vanadia species dispersed well on the support surface with vanadia content up to 10 wt%. At higher vanadia content, the non-active Mg₃(VO₄)₂ was formed. Vanadium oxides existing on the support surface as tetrahedral vanadium were observed. An ethylbenzene conversion of 43% and styrene selectivity of 91% were obtained with the 10V₂O₅/CeO₂-MgO catalyst.     

Iron oxide-based honeycomb catalysts for the dehydrogenation of ethylbenzene to styrene

Corning has recently developed a novel extrusion method to make bulk transition metal oxide honeycomb catalysts. One area of effort has been iron oxide-based catalysts for the dehydrogenation of ethylbenzene to styrene, a major chemical process that yields worldwide 20 MM tons/yr. In industry, the monomer is synthesized mostly in radial-flow fixed-bed reactors. Because of the high cross-sectional area for flow and shallow depth of the catalyst bed in these reactors, low reactor pressure gradients are maintained that favors the yield and selectivity for styrene formation. However, the radial-flow design has inherent detractions, including inefficient use of reactor volume and large temperature gradients that decrease catalyst service life. The overall economics of the process can be improved with parallel-channel honeycomb catalysts and axial flow reactors. The simple axial flow design of honeycomb catalysts provides low-pressure drop, while making more efficient use of reactor volume, with better heat and mass transfer characteristics compared to a conventional radial packed bed. An important part of this concept is the ability to fabricate a wide family of dehydrogenation catalyst compositions into honeycombs with the requisite chemical, physical, mechanical, and catalytic properties for industrial use. The ethylbenzene dehydrogenation (EBD) honeycomb catalysts developed by Corning have compositions similar to those commonly used in industry and are prepared with the same catalyst and promoter precursors and with similar treatments.

However, to enable extrusion of catalyst precursors into honeycomb shapes, especially at cell densities above 100 cell/in.², Corning’s process compensates for the high salt concentrations and the high pH of the batch material that would otherwise prevent or impede honeycomb extrusion. The improved rheological characteristics provide the necessary plasticity, lubricity, and resiliency for honeycomb extrusion with sufficient binder strength needed before calcination to the final product. Iron oxide-based honeycombs after calcination are strong and possess macroporosity and high surface area. In bench-scale testing, particular honeycomb catalyst compositions exhibited 60–76% ethylbenzene conversion with styrene selectivity of 95–91%, respectively, under conventional reaction conditions without apparent deactivation or loss of mechanical integrity.     

Screening of catalysts for the oxidative dehydrogenation of ethylbenzene

The oxidative dehydrogenation of ethylbenzene to styrene on various oxide catalysts has been investigated. The catalysts examined are classified into six types, considering their catalytic behavior. In general, acidic catalysts show high selectivity. The most effective catalyst has been found to be the SnO₂-P₂O₅ catalyst prepared from Sn(OH)₂ and phosphoric acid. The effects of partial pressures and reaction temperature have been studied and suitable reaction conditions for the SnO₂-P₂O₅ catalyst have been determined.     

低水比乙苯脱氢制苯乙烯催化剂的开发

在铁系催化剂基础上通过引入活性助剂、选择性助剂、抗积炭助剂及创造条件促使铁钾形成K₂Fe₂₂O₃₄晶相，开发出了能适应低水比条件下使用的催化剂。1 000 h稳定性试验和催速老化试验结果表明，催化剂具有良好的活性稳定性，强度高，可以应用于工业装置。     

CO2氧化乙苯脱氢制苯乙烯钒基氧化物催化剂研究进展

与现有乙苯直接脱氢工艺技术相比,CO₂氧化乙苯脱氢工艺具有缓解直接脱氢热力学平衡限制、苯乙烯选择性高、能耗低和二氧化碳资源化利用等显著优势,有望成为一条从乙苯生产苯乙烯的绿色工艺路线。为此,在总结乙苯直接脱氢反应体系和现有工业技术特点、面临的问题和发展方向的基础上,本文较为全面地分析了CO₂氧化乙苯脱氢的特点和反应机理,探讨了现有催化剂体系普遍快速失活的关键原因,表明高性能催化剂研究依然是推进CO₂氧化乙苯脱氢工业化应用的关键。鉴于钒基氧化物催化剂表现出较高的活性,成为近年来CO₂氧化乙苯脱氢相关研究关注的重点。为此,从钒物种含量及其聚集态结构、催化剂的氧化还原和酸碱性、催化剂表面积炭及其作用等角度,综合分析了活性中心结构、反应机理等方面的相关研究进展,认为孤立态V⁵⁺及其含量可能是决定钒基氧化物催化剂活性的关键,其稳定性主要取决于催化剂的氧化还原特性,而积炭对催化剂活性和稳定性的影响则与其组成和石墨化程度密切相关。基于上述认识,认为强化CO₂的高效活化、抑制V⁵⁺的深度还原等是今后钒基氧化物催化剂研究的重点发展方向,而利用移动固定床或提升管反应器等进行工艺优化,对推进CO₂氧化乙苯脱氢工业化应用具有重要的研究价值。     

Chromia-alumina catalysts for the dehydrogenation of propane prepared by a modified method of codeposition

A method for preparing chromia-alumina catalysts for the dehydrogenation of propane, enabling us to increase the activity and thermal stability of a catalyst relative to currently known catalysts, is proposed. Chromia-alumina catalysts were prepared for the first time using a modified method of codeposition, in which a suspension of chromium and aluminum hydroxides was subjected to a high-temperature treatment (550°C). The proposed method is simple and allows us to reduce the number of stages in the preparation of the catalyst. The phase composition and texture of the catalyst, and the formation and properties of surface-active forms in dependence on the conditions of catalyst preparation, were studied using a set of physicochemical methods. The selected conditions of catalyst preparation ensured high specific surface area and a stable bond between the surface forms of chromium and the support, hindering the formation of the catalytically low-activity form α-Cr₂O₃ during calcination. In this work, we synthesized and studied laboratory samples of a chromia-alumina catalyst with different contents of chromium (2.8–11.3 wt %). With respect to the main parameters (conversion of propane, selectivity to propylene, and resistance to coke formation), the catalyst was as good as more active samples known from the literature and exhibited high activity at low chromium contents (2.8–5.5 wt %). This method of catalyst preparation is protected by a patent of the Russian Federation and recommended for improving industrial technology.     

Fe2O3-K2O系乙苯脱氢催化剂贮存稳定性研究

对存放在不同环境下的Fe₂O₃-K₂O系乙苯脱氢催化剂的稳定性进行了研究。在潮湿环境下贮存30天的样品，其机械强度下降50％，磨耗率上升至新鲜样品的7～9倍，脱氢活性降低1/2。热重分析结果表明，潮湿环境中存放的样品，会大量吸收环境中的水分，导致催化剂在脱氢反应过程中钾的流失，从而引起了催化剂性能的劣化。     

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO₂‐Al₂O₃ catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO₂‐Al₂O₃ catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N₂ adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O₂ volumetric chemisorption, H₂‐O₂ titration, and transmission electron microscopy. We have shown that Ga³⁺ cations are incorporated into the cubic fluorite structure of CeO₂, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO₂ is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016     

GS-HA低水比乙苯脱氢催化剂的开发

通过组合铈源和引入固定钾显著提高了催化剂的活性和耐低水比的能力,开发成功了新一代GS-HA低水比催化剂,该催化剂具有低水比条件下失活速率慢、活性高的特点。在二段负压绝热评价装置上,一、二反入口温度分别为615℃和620℃,乙苯液体空速为0.5 h-1,水比为1.15(wt),二反出口压力-50 kPa条件下,乙苯转化率为67.0%,苯乙烯选择性大于96.8%。催速老化试验结果表明,该催化剂的失活速率为-0.007 974%/h,优于最新引进催化剂。     

Influence of SBA-15 support on CeO2–ZrO2 catalyst for the dehydrogenation of ethylbenzene to styrene with CO2

Pure oxides of ceria (CeO₂) and zirconia (ZrO₂) were prepared by precipitation method and a catalyst comprising of 25 mol% of CeO₂ and 75 mol% of ZrO₂ (25CZ) mixed metal oxide was prepared by co-precipitation method and also a catalyst with 25 wt% of 25CZ (25 mol% of CeO₂ and 75 mol% of ZrO₂) and 75 wt% SBA-15(25/25CZS) was prepared by precipitation–deposition method. Aqueous NH₃ solution was used as a hydrolyzing agent for all the precipitation reactions. These catalysts were characterized by X-ray diffraction and nitrogen adsorption–desorption techniques for the confirmation of SBA-15 structural intactness. All these catalysts were found to be effective for the oxidative dehydrogenation of ethylbenzene (ODHEB) to styrene in the presence of CO₂ and also it was observed that there was a sequential enhancement in the catalytic activity from individual oxides to mixed oxides followed by supported mixed oxide catalysts. Of the catalysts studied in this work, the supported 25/25CZS catalyst exhibited the superior activity, which was about 10–20 times higher than the activity of bulk single oxides in terms of turn over frequency.     

MgAl2O4 spinel prepared by mechanochemical synthesis used as a support of multimetallic catalysts for paraffin dehydrogenation

The catalytic performance in n-butane dehydrogenation of bimetallic PtSn, PtGa and PtIn, and trimetallic PtSnIn and PtSnGa catalysts (with low metal contents) supported on a MgAl₂O₄ prepared by a novel mechanochemical synthesis was evaluated both in flow and pulse equipment. The influence of the addition of different promoters (Sn, Ga and In) to Pt on the activity, selectivity and deactivation in the n-butane dehydrogenation reaction was studied. Stability experiments through successive reaction-regeneration cycles were carried out for selected catalysts. In order to correlate the properties of the metallic phase of the catalysts with the catalytic behavior, several characterization techniques were used, such as test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), TPR, XPS, H₂ chemisorption and TEM. Bimetallic PtSn catalyst has a better catalytic behavior than PtIn and PtGa ones. For PtSnM (M: In or Ga) catalysts, whereas Ga addition to the bimetallic catalyst does not practically modify the dehydrogenation performance, the addition of In produces an increase of the activity and the selectivity to butenes. Characterization results indicate the presence of geometric effects for the PtSn catalyst, and geometric and electronic effects for PtIn and PtGa ones. For trimetallic catalysts, the presence of a close contact between Pt, Sn and In or Ga in both trimetallic catalysts was found, mainly due to geometric effects like blocking and dilution of the active sites by the promoters. In stability experiments, the trimetallic PtSnIn/MgAl₂O₄ catalyst clearly displays the best catalytic performance along reaction-regeneration cycles, though PtSnGa and PtSn catalysts also showed a very good behavior through the successive cycles. The characterization of these catalysts after cycles shows that their metallic phases are slightly modified along the cycles.     

CuO–CeO2/Al2O3 /FeCrAl monolithic catalysts prepared by sol-pyrolysis method for preferential oxidation of carbon monoxide

This work describes a new technique, sol-pyrolysis method, for depositing CuO–CeO₂on FeCrAl honeycomb supports. The monolithic catalysts prepared by the method presented good adhesion stability in ultrasonic and thermal shock tests. The principle of the deposition and the role of the support were studied and analyzed by SEM, XRD, TG-DTA, TPR and XPS techniques. The results showed that the active components adhered to the support via three stages. High surface energy of the crystal nuclei and the interaction between the active components and the support promoted adhesion stability. Moreover, the presence of the support influenced distribution and interaction of the active components, but had no obvious effect on catalytic performance. The CuO–CeO₂/Al₂O₃/FeCrAl monolithic catalysts were applied for the preferential oxidation of carbon monoxide in rich-hydrogen gases and revealed high activity and good selectivity under the presence of 15%CO₂ and 10%H₂O.     

VO_x/SBA-16催化CO_2氧化乙苯脱氢性能

采用等体积浸渍法制备了不同钒负载量的VOx/SBA-16催化剂,通过XRD、N_2吸附、H_2-TPR和TGA表征和催化剂性能评价,研究了VO_x/SBA-16催化剂对CO_2氧化乙苯脱氢制苯乙烯的催化性能。结果表明,VO_x/SBA-16催化剂具有良好的乙苯脱氢活性,钒负载量为1.2 mmol/g的催化剂活性最佳,乙苯转化率可达57.6%,苯乙烯选择性98.6%。VO_x/SBA-16催化剂上的乙苯脱氢活性和稳定性明显高于VO_x/MCM-41,是由于SBA-16载体畅通的三维孔道结构更有利于钒物种的高度分散和反应介质的扩散,提高了催化剂的可还原性能,减缓了积炭的生成。     

VO_x/SBA-16催化CO_2氧化乙苯脱氢性能

采用等体积浸渍法制备了不同钒负载量的VOx/SBA-16催化剂,通过XRD、N_2吸附、H_2-TPR和TGA表征和催化剂性能评价,研究了VO_x/SBA-16催化剂对CO_2氧化乙苯脱氢制苯乙烯的催化性能。结果表明,VO_x/SBA-16催化剂具有良好的乙苯脱氢活性,钒负载量为1.2 mmol/g的催化剂活性最佳,乙苯转化率可达57.6%,苯乙烯选择性98.6%。VO_x/SBA-16催化剂上的乙苯脱氢活性和稳定性明显高于VO_x/MCM-41,是由于SBA-16载体畅通的三维孔道结构更有利于钒物种的高度分散和反应介质的扩散,提高了催化剂的可还原性能,减缓了积炭的生成。     

Amorphous porous MxTi mixed oxides as catalysts for the oxidative dehydrogenation of ethylbenzene

The properties of different metal‐oxide‐doped porous titanium oxides as catalysts for the oxidative dehydrogenation of ethylbenzene were investigated. Amorphous porous mixed oxides based on the amorphous titania matrix with selected metal ion centers as active sites have been prepared by an acid‐catalyzed sol–gel method. The dehydrogenation of ethylbenzene was studied in a continuous gas phase flow reactor under different reaction temperatures at ambient pressure. Among the 23 catalysts studied the amorphous porous AM‐Cr₅Ti mixed oxide is the most promising catalyst. At 350 °C a 75% selectivity to styrene at a 29% conversion of ethylbenzene was obtained. BET, HRTEM, XRD, GC, MS, TGA and optical microscopy were employed to characterize the fresh and used AM‐Cr₅Ti catalyst. This revised version was published online in August 2006 with corrections to the Cover Date.     

Screening of amorphous metal–phosphate catalysts for the oxidative dehydrogenation of ethylbenzene to styrene

The gas-phase oxidative dehydrogenation of ethylbenzene to styrene was carried out by using as catalyst a series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe = Al/Ca = 1) mixed systems: FeAl(PO₄)₂ and Ca₃Al₃(PO₄)₅, that were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. These results were compared to those obtained with 24 commercial inorganic solids (several metal oxides, sulfates and phosphates). Reactions were also carried out without oxygen, under non-oxidative conditions, where the catalytic activity was always appreciably lower than under oxidative conditions. Experimental results indicated that the oxidative gas-phase dehydrogenation of ethylbenzene to styrene could be related to the total number of acid and basic sites of catalysts, so that this reaction probably needs selected acid–basic pairs for coke formation, where the oxidative dehydrogenation process is developed.

The main practical conclusion of the catalyst screening was that the best results were obtained with the synthesized amorphous AlPO₄, where 43% ethylbenzene conversion and 99.7% styrene selectivity were achieved. A very reduced number of commercial inorganic solids like Al₂(SO₄)₃, Cr₂(SO₄)₃, Fe₂(SO₄)₃, NiSO₄, Al₂O₃ and Fe₂O₃ were also able to obtain an acceptable catalytic behavior, with conversions ranging between 18 and 23% and selectivity in the 95–100% range. Among the other synthesized solids, Ni₃(PO₄)₂-A-450 was the only metal phosphate exhibiting results in such a range. All the other catalysts studied were rather inactive and/or selective. Additional experiments carried out at longer times on stream (3.5 h) and longer contact times (W/F 0.254 and 0.654) confirmed the superior catalytic behavior of amorphous AlPO₄. Consequently, this solid could be a good candidate for application as a catalyst in the industrial oxydehydrogenation of ethylbenzene to styrene.     

H2S promoted oxidative dehydrogenation of ethylbenzene to styrene

The technique of using mixtures of H₂S/O₂ and H₂S/SO₂ to selectively dehydrogenate hydrocarbons in the presence of suitable catalysts has been applied to the production of styrene from ethylbenzene. The mechanism of the reaction is discussed and results are presented on the influence of different catalysts and the optimization of processing variables such as temperature, space velocity and reactant concentrations. Styrene yields as high as 75% have been achieved under optimum conditions.