Al2O3 Nanosheets Rich in Pentacoordinate Al3+ Ions Stabilize Pt‐Sn Clusters for Propane Dehydrogenation

In heterogeneous catalysis, supports play a crucial role in modulating the geometric and electronic structure of the active metal phase for optimizing the catalytic performance. A γ‐Al₂O₃ nanosheet that contains 27 % pentacoordinate Al³⁺ sites can nicely disperse and stabilize raft‐like Pt‐Sn clusters as a result of strong interactions between metal and support. Consequently, there are strong electronic interactions between the Pt and Sn atoms, resulting in an increase in the electron density of the Pt sites. When used in the propane dehydrogenation reaction, this catalyst displayed an excellent specific activity for propylene formation with >99 % selectivity, and superior anti‐coking and anti‐sintering properties. Its exceptional ability to maintain the high activity and stability at ultrahigh space velocities further showed that the sheet construction of the catalyst facilitated the kinetic transfer process.     

Novel KF-TiO2catalysts for oxidative dehydrogenation of isobutane

A novel type of catalysts, KF-TiO₂, efficient for the oxidative dehydrogenation (ODH) of isobutane is presented. The effect of KF content and calcination temperature was studied. In the reaction conditions explored, the best performance (73 % selectivity to isobutene at 10.5 % conversion of isobutane) was observed over a catalyst with KF/TiO₂ = 0.2 (mol/mol). The surface properties of the catalysts were investigated by SPS (Surface Photo-voltage Spectroscopy) and XPS. The promotion effect of KF in the catalysts can be attributed to the formation of an oxyfluoro-compound, K₂Ti₄O₈F₂.     

Dehydrogenation of isobutane in the presence of carbon dioxide over supported vanadium oxide catalysts

Summary The dehydrogenation of isobutane to isobutene in the presence of carbon dioxide was carried out over supported vanadium oxide catalysts. The influence of the support on the catalytic performance was investigated. The isobutane conversion and isobutene selectivity in the presence of carbon dioxide were compared with the results obtained during the dehydrogenation reaction in the presence of helium (inert gas). The catalysts were characterized by temperature-programmed techniques (TPR, TPD-NH₃, TPD-CO₂).     

NiO/Al_2O_3催化剂上二氧化碳气氛下异丁烷耦合脱氢制异丁烯

研究了二氧化碳气氛下NiO/Al2O3催化剂上异丁烷脱氢制异丁烯的反应性能,考察了助剂K2O对NiO/Al2O3催化性能的影响。结果表明,与在惰性气氛下的反应相比,在二氧化碳气氛下异丁烷脱氢与逆水煤气变换反应耦合,促进了异丁烷脱氢反应,异丁烯的收率得到提高。助剂K2O的加入,能降低催化剂的酸性,减缓反应过程中催化活性物种NiO的过度还原,并抑制异丁烷裂解及积炭生成等副反应,从而提高了异丁烯的收率以及催化剂的稳定性。     

Isobutane Dehydrogenation Assisted by CO2 over Silicalite‐1‐Supported ZnO Catalysts: Influence of Support Crystallite Size

The ZnO catalysts supported on Silicalite‐1 zeolites with different crystallite sizes (0.08, 0.35, 1 and 1.7 μm, respectively) and 5% Zn were synthesized via an incipient wetness method. The catalysts were characterized by XRD, N₂ adsorption, SEM, TEM‐EDX, DRIFT spectra and NH₃‐TPD, and their catalytic performance in isobutane dehydrogenation assisted by CO₂ was investigated. The catalytic activity is strongly dependent on the crystallite size of Silicalite‐1 support. The ZnO/S‐1‐0.35 catalyst with ca. 0.35 μm crystallite size displays the highest activity, affording an initial isobutane conversion of 51.0% and 74.5% isobutene selectivity. This can be attributed to a higher amount of acid sites present on this catalyst as well as the largest amount of nest silanols possessed by the S‐1‐0.35 support.     

氧化铝载体对Pt-Sn-K/γ-Al2O3催化剂上异丁烷脱氢性能的影响

采用盐酸回流法和氨水沉淀法合成了氧化铝载体,并通过络合真空浸渍法制备了不同来源氧化铝负载的Pt-Sn-K/γ-Al₂O₃催化剂。利用N₂物理吸附、CO脉冲吸附、H₂程序升温还原、NH₃程序升温脱附、热重等手段对Pt-Sn-K/γ-Al₂O₃催化剂进行了表征,以异丁烷脱氢为探针反应研究了氧化铝载体对该催化剂脱氢性能的影响。结果表明,与由盐酸回流法合成的载体制备的催化剂相比,采用氨水沉淀法合成的氧化铝载体制备的Pt-Sn-K/γ-Al₂O₃催化剂表面具有较小的Pt颗粒和较弱的酸性分布,其脱氢活性及异丁烯选择性更优。14 d的连续运行数据显示,由氨水沉淀合成的载体制备的催化剂,其抗积炭能力更强,反应后催化剂的积炭石墨化程度更低,因而具有更好的稳定性;在该催化剂上,异丁烷初始转化率为56.67%,14 d后仍能达到34.71%,异丁烯初始选择性为80%,7 d后维持在94%左右。     

Physicochemical study of catalysts for the oxidative dehydrogenation of isobutane: Cobalt,nickel, and manganese molybdates

Temperature-programmed desorption and IR spectroscopic studies of the physicochemical properties of cobalt, nickel, and manganese molybdates are reported. These properties are correlated with the catalytic properties of the molybdates in the oxidative dehydrogenation of isobutane with atmospheric oxygen. It is demonstrated by an analysis of the IR spectra of the molybdates that the isobutene yield grows as the proportion of tetrahedrally coordinated molybdenum in the catalyst structure increases in isobutane dehydrogenation. NiMoO₄ has the highest surface concentration of strong acid sites, and it binds adsorbed isobutene more strongly than the other catalysts     

Adsorptive separation of isobutene and isobutane on Cu3(BTC)2

The metal organic framework material Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate) has been synthesized using different routes: under solvothermal conditions in an autoclave, under atmospheric pressure and reflux, and by electrochemical reaction. Although the compounds display similar structural properties as evident from the powder X-ray diffraction (XRD) patterns, they differ largely in specific surface area and total pore volume. Thermogravimetric and chemical analysis support the assumption that pore blocking due to trimesic acid and/or methyltributylammoniummethylsulfate (MTBS) which has been captured in the pore system during reaction is a major problem for the electrochemically synthesized samples. Isobutane and isobutene adsorption has been studied for all samples at different temperatures in order to check the potential of Cu3(BTC)2 for the separation of small hydrocarbons. While the isobutene adsorption isotherms are of type I according to the IUPAC classification, the shape of the isobutane isotherm is markedly different and closer to type V. Adsorption experiments at different temperatures show that a somewhat higher amount of isobutene is adsorbed as compared to isobutane. Nevertheless, the differential enthalpies of adsorption are only different by about 5 kJ/mol, indicating that a strong interaction between the copper centers and isobutene does not drive the observed differences in adsorption capacity. The calculated breakthrough curves of isobutene and isobutane reveal that a low pressure separation is preferred due to the peculiar shape of the isobutane adsorption isotherms. This has been confirmed by preliminary breakthrough experiments using an equimolar mixture of isobutane and isobutene.     

CATALYTIC OXYDEHYDROGENATION OF ISOBUTANE OVER LITHIUM-BASED OXIDES

研究了一些锂基氧化物对异丁烷的催化氧化脱氢作用，其中Ｌｉ２ＳｎＯ３显示出优良的催化性质，Ｌｉ２ＭｎＯ３，ＬｉＦｅ５Ｏ８和ＬｉＡｌ５Ｏ８对异丁烯的选择性较差，而Ｌｉ２ＣｅＯ３，ＬｉＦｅＯ２和ＬｉＺｎＯ２在反应条件下不稳定。系列ＬｉＳｎＯ催化剂的ＣＯ２ＴＰＤ分析表明，当ＳｎＯ２转化为Ｌｉ２ＳｎＯ３时，在表面形成了碱中心，它有利于异丁烯从催化剂表面脱附。Ｏ２ＴＰＤ和Ｈ２ＴＰＤ结果表明，此时吸附的氧物种数量降低，异丁烯的深度氧化受到抑制。Ｌｉ２ＳｎＯ３中晶格氧物种的活性对异丁烷催化氧化脱氢可能是适宜的，但不利于深度氧化。     

Coupling dehydrogenation of isobutane in the presence of carbon dioxide over chromium oxide supported on active carbon

The dehydrogenation of isobutane （IB） to produce isobutene coupled with reverse water gas shift in the presence of carbon dioxide was investigated over the catalyst Cr2O3 supported on active carbon （Cr2O3/AC）. The results illustrated that isobutane conversion and isobutene yield can be enhanced through the reaction coupling in the presence of carbon dioxide. Moreover, carbon dioxide can partially eliminate carbonaceous deposition on the catalyst and keep the active phase （Cr2O3）, which are then helpful to alleviate the catalyst deactivation.     

Dehydrogenation of Isobutane to Isobutene with Carbon Dioxide over SBA‐15‐Supported Chromia‐Ceria Catalysts

A series of SBA‐15‐supported chromia‐ceria catalysts with 3% Cr and 1%–5% Ce (3Cr‐Ce/SBA) were prepared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N₂ adsorption, SEM, TEM‐EDX, Raman spectroscopy, UV–vis spectroscopy, XPS and H₂‐TPR, and their catalytic performance for isobutane dehydrogenation with CO₂ was tested. The addition of ceria to SBA‐15‐supported chromia improves the dispersion of chromium species. 3Cr‐Ce/SBA catalysts are more active than SBA‐15‐supported chromia (3Cr/SBA), which is due to a higher concentration of Cr⁶⁺ species present on the former catalysts. The 3Cr‐3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570 °C after 10 min of the reaction.     

Oxidation of isobutane over hydrothermally synthesized Mo-V-Te-Nb-O mixed oxide catalysts

MoV_0.3Te_0.17 and MoV_0.3Te_0.17Nb_0.12 catalysts were prepared by a hydrothermal synthesis route and tested for the oxidation of isobutane and isobutene. Characterization results showed that the structure and property of Mo-V-Te-based catalysts are relatively different depending on the presence of the Nb element. Catalytic tests showed that the selectivity of methacrolein can comparatively be improved by the addition of Nb into the MoV_0.3Te_0.17 catalyst for the selective oxidation of isobutane.     

Catalytic dehydrogenation of propane to propylene over highly active PtSnNa/γ-Al_2O_3 catalyst

This paper reports a new fabrication method of the PtSnNa/γ-Al₂O₃ catalyst through ball milling, which is more stable and active than the commercial catalyst.     

Effect of chelating agents on catalytic performance of Cr/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> dehydrogenation catalysts

Chromia/alumina (Cr₂O₃/γ-Al₂O₃) catalysts with addition of chelating agents (citric acid or oxalic acid) were prepared by the incipient impregnation method. The resulting catalysts with different citric acid (CA) or oxalic acid (OA) contents were applied to the dehydrogenation of isobutane to isobutene. The influence of chelating agents on the catalysts was investigated by means of BET, SEM, H₂-TPR, NH₃-TPD, and TG-DTG. The results showed that the Cr₂O₃/γ-Al₂O₃ catalysts with addition of CA or OA exerted slightly increase on specific surface area. The addition of the chelating agents as expected, determined a general decrease in the surface acidity. The catalysts with CA or OA have a better anti-coking ability by inhibiting the side reaction of cracking and carbon formation. The addition of CA or OA for preparing these catalysts resulted in a beneficial effect on the reducibility of the Cr species to diminish the reduction temperature. The appropriate content of chelating agents could improve dispersion of metal species in the γ-Al₂O₃ support. The catalytic activity showed an important enhancement when the metal species was impregnated in the presence of CA or OA.     

金属离子修饰的Ru-Pt/γ-Al2O3催化p-CNB选择性加氢

催化还原法制备卤代苯胺因具有产品质量好、收率高和三废少等优点而日益受到重视．近年来,研究较多的是高分子化合物稳定的Pt,Pd,Ru单金属或双金属胶体催化剂以及负载型单金属或双金属催化剂．用第三金属组分修饰的胶体催化剂的催化性能更好,但反应后催化剂与产物分离     

Trimerization of Isobutene Over Solid Acid Catalysts

Oligomerization of isobutene is a very promising reaction not only for the production of isobutene oligomers such as trimers but also for the separation of isobutene from C₄ mixtures. Several solid acid catalysts have been applied for the continuous oligomerization of isobutene in liquid phase. This review analyzes the trimerization of isobutene over various solid acid catalysts such as zeolites, oxides (zirconias and titanias) and acid resins. Trimers selectivity increases with increasing isobutene conversion, irrespective of catalysts such as zeolites and acid resins. Very stable operation with high trimers selectivity is accomplished with WO _x /ZrO₂ catalyst having tetragonal zirconia or various zeolite catalysts with high Lewis acid site-to-Brønsted acid site ratio (LA/BA ratio). For a good performance, acid resins should be macroporous and strong acid (sulphonic acid group) with high acid concentration. Inorganic catalysts are superior to acid resins because the deactivated inorganic materials can be regenerated by simple calcination. The WO _x /ZrO₂ catalyst may be applied to a commercial process because about several thousand tons of isobutene can be oligomerized per one ton of zirconia catalyst in a catalytic cycle without regeneration. The oligomerization of isobutene may be improved further because the reaction has been started only recently and no research has been done for the optimization of the reaction and catalysts. It is expected to develop a new inorganic catalyst having suitable acidity, LA/BA ratio and phase, etc. by further research. The isobutene trimers, with or without hydrogenation, may be used for various purposes, and the importance of this trimerization reaction will be increased considering the expected surplus of isobutene due to the banned use of methyl-tert-butyl ether.     

Effect of cerium addition on catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

The effect of cerium addition on the catalytic performance of propane dehydrogenation over PtSnNa/ZSM-5 catalyst has been investigated by reaction tests and some physicochemical characterization such as XRD,BET,TEM,XPS,NH 3-TPD,H 2 chemisorption,TPR and TPO techniques.It has been found that with suitable amount of cerium addition,the platinum dispersion increased,while the carbon deposition tended to be eliminated easily.In these cases,the presence of cerium could not only realize the better distribution of metallic particles on the support,but also strengthen the interactions between Sn species and the support.Additionally,XPS spectra confirmed that more amounts of tin could exist in oxidized form,which was advantageous to the reaction.In our experiments,PtSnNaCe(1.1 wt%)/ZSM-5 catalyst exhibited the best catalytic performance.After running the reaction for 750 h,propane conversion was maintained higher than 30% with the corresponding selectivity to propylene of about 97%.     

Improvements in selectivity and stability of Rh catalysts modified by SnBu4. dehydrogenation of isobutane to isobutene

RhSn/SiO₂ bimetallic catalysts prepared via an organometallic route have proved to be very active and selective toward several hydrogenation reactions. In this work these catalysts were studied for the dehydrogenation of isobutane to isobutene. It was found that Rh/SiO₂ monometallic catalysts had a null selectivity to isobutene, and this selectivity increased up to more than 90% after the addition of tin, using SnBu₄ as precursor.     

有序介孔Sn-SBA-15负载铂催化剂上丙烷脱氢性能的提高

丙烷脱氢制丙烯能够将低级烷烃转变成烯烃,是有效扩大丙烯来源的生产工艺.铂锡催化剂用于丙烷催化脱氢的主要缺点是稳定性差、选择性低,通过稳定锡的氧化态可以大大改善催化剂的脱氢性能及稳定性.本文采用一锅水热合成法制备了一系列高比表面积具有高度有序介孔结构的Sn掺杂的Sn-SBA-15材料,并作为载体负载铂催化剂用于丙烷脱氢反应.同时利用传统浸渍法(IM)合成了Sn/SBA-15-IM材料作为对比.结合X射线衍射(XRD)、BET比表面积和孔体积测试、红外光谱(FT-IR)、X射线光电子能谱、H2程序升温脱附(H2-TPD)、热重分析(TGA)、扫描电镜和透射电镜等多种物理化学表征手段研究了Sn-SBA-15材料和催化剂的结构性质及其丙烷脱氢反应性能.XRD和BET比表面积和孔体积测试结果表明,水热合成法原位引入助剂Sn不影响载体SBA-15的有序孔道结构,同时能够保持较大的比表面积.传统浸渍法引入Sn会堵塞载体孔道,载体比表面积及孔道有序度下降.Sn掺杂进入SBA-15骨架能够增强Sn物种与载体的相互作用,有利于Sn物种在反应过程中保持氧化态,提高催化剂丙烷脱氢反应的活性及选择性.当Sn掺杂量增至2.0 wt％时,Pt,Sn组分与载体之间的相互作用减弱,催化剂中Sn0物种所占比例增多,导致催化剂丙烷脱氢性能下降.在丙烷脱氢反应过程中,一锅法引入Sn的催化剂上反应活性和稳定性明显优于浸渍法引入Sn的催化剂.其中,Pt/0.5 Sn-SBA-15催化剂表现出最优的丙烷脱氢性能,丙烷转化率为43.8％,丙烯选择性为98.5％.     

Effect of calcination conditions on the catalytic behavior of Te-Mo mixed oxide catalysts in oxidation of isobutane and isobutene

A series of Te-Mo-O catalysts were prepared by decomposing (NH₄)₆TeMo₆O₂₄·nH₂O telluromolybdate under different conditions and tested for the selective oxidation of isobutane and isobutene. Characterization results showed that their structure and properties depend on the calcination conditions. Catalytic tests showed that molybdenum may be the key element for the activation of isobutane, whereas the selective oxidation of isobutene to methacrolein might proceed mainly on the surface of a TeMo-containing crystalline phase.