碳催化剂用于异丁烷直接脱氢制异丁烯

异丁烯用途广泛,被认为是除乙烯和丙烯外最重要的基础化工原料.异丁烯的来源主要是石油裂化过程中产生的碳四馏分,但随着对其需求量的逐年增加,分离法已逐渐无法满足,因此异丁烷直接脱氢工艺逐渐受到工业界和学术界的重视.铬系和铂系催化剂是两类传统工业催化体系,但铬对环境污染严重,铂作为贵金属成本较高,而且现有工艺大多存在催化剂稳定性较差需要反复再生的问题.近年来碳材料用于烷烃氧化脱氢反应的研究较多,并表现出较高的活性和稳定性,甚至有研究组提出金属催化剂在反应中快速生成的活性积碳(active coke)可能是真正的催化活性中心.但氧化脱氢反应不同于直接脱氢,需在反应中加入氧气,这在实际生产中会带来一系列问题：考虑到烷烃的爆炸极限,实际应用时反应气必须稀释,这不利于产物的收集;而且氧气会导致反应物过度氧化产生CO和CO2等副产物,也限制了氧化脱氢工艺在工业上的应用和发展.
　　我们研究组将椰壳碳、煤质碳和碳纳米管等碳材料作为催化剂用于催化异丁烷直接脱氢反应,发现碳催化剂表现出较高的催化活性：在625 oC,椰壳碳上异丁烷转化率和异丁烯选择性分别为70%和78%,连续反应3d后仍能维持34%的转化率,且选择性基本不变.与铬基催化剂相比,碳催化剂在稳定性方面表现出更大优势.我们进一步采用N2吸脱附、X射线光电子能谱(XPS)、傅里叶变换红外光谱(FTIR)和场发射扫描电子显微镜(FE-SEM)等手段对反应前后的碳催化剂进行了详细表征. N2吸脱附结果表明,椰壳碳比表面积高达1190.2 m2/g,这可能是其具有较高催化活性的原因;而结合催化剂活性数据,对比反应前后椰壳碳催化剂比表面积和异丁烷转化率可知,两者呈现近乎线性的相关性,进一步证实比表面积大小对碳催化剂催化活性有重要影响. XPS谱图证明椰壳碳在反应前表面除了有少量硅(0.73%)外,不存在金属氧化物等杂质,证实碳材料无需负载氧化物等即可表现出较高的催化活性;反应后沉积的积碳附着在催化剂表面,使硅含量降低至0.47%;催化剂中氧含量也由4.43%降低至3.78%,同时有碳酸盐生成. FTIR谱图进一步证实反应前的椰壳碳表面有丰富的有机官能团,但反应开始后有机官能团很快消失,而催化剂仍保持较高的催化活性,因此有机官能团并非碳催化剂催化活性高的必要因素,这与文献中已报道的结果不同. FE-SEM照片中观察到反应后椰壳碳催化剂表面形成积碳,随着反应时间延长积碳明显增多,这与XPS结果一致.
　　碳材料具有来源广泛、绿色环保等显著优势,可作为一种新的催化体系应用于异丁烷直接脱氢反应,无需负载其他物质或添加氧化性气体即可表现出良好的催化活性和稳定性,其比表面积对催化活性有重要影响,反应中产生的积碳导致催化剂比表面积下降进而降低其催化活性,而有机官能团的存在对催化活性影响不大.     

异丁烷脱氢催化剂的研究

本文对异丁烷脱氢反应制异丁烯过程催化剂体系及其反应机理进行了述评,指出异丁烷脱氢依然是最有潜力的转化途径,但非贵金属高效催化剂的研制是其关键.详细总 结了不同载体和助剂对脱氢反应的影响,尤其是载体和助剂的酸碱性以及载体的孔结构.弱 酸中心有利于异丁烷脱氢反应的发生,较小的孔结构能提高反应的选择性.催化剂的抗积炭 性能研究表明: 载体表面的弱酸位和活性组分在表面的高分散度以及碱性助剂的加入,有 利于提高催化剂的抗积炭性能.对异丁烷的脱氢反应机理的研究进行了阐述.     

异丁烷脱氢制异丁烯体系的热力学分析

对等温反应条件下的异丁烷脱氢制异丁烯反应进行了热力学分析,以获得等温反应条件下,压力和温度或其他反应条件与异丁烷脱氢反应的自由能ΔrG与热焓值ΔrH之间的关系。考察了不同反应条件(压力、温度和进料方式等)对于异丁烷脱氢反应的转化率的影响,为今后异丁烷脱氢制异丁烯工艺的开发提供热力学基础数据的支持。     

不同载体负载的Cr基催化剂催化CO2氧化异丁烷脱氢制异丁烯

制备了介孔分子筛MSU-1,γ-A12O3,AC(活性炭)和MgO负载的CrOx催化剂,并考察了其催化CO2氧化异丁烷脱氢制异丁烯反应性能.结果表明,各催化剂活性的顺序为:CrOx/MSU-1 ＞CrOx/A12O3＞ CrOx/AC＞ CrOJMgO.其中在CrOx/MSU-1催化剂上,异丁烷的转化率和异丁烯的收率分...     

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。     

异丁烷脱氢催化剂V-O-Al水热-流体干燥法合成

负载型 V2 O5催化剂被广泛应用于烃的氧化、低碳烃的氧化脱氢及 NOx的 NH3 还原等催化反应[1～ 3 ] .对于低碳烃脱氢 ,Cr2 O3 和 Pt体系研究较多 ,而 V2 O5体系则鲜有报道[4 ,5] .水热合成方法是合成各种分子筛的常用方法 ,同时也被广泛用于合成多种无机功能材料 (如纳米材料 ,     

异丁烷催化脱氢制异丁烯Cr2O3／Al2O3体系催化剂

对异丁烷催化脱氢催化剂进行了研究。助催化剂Ｋ２Ｏ,ＣｕＯ的引入改进了Ｃｒ２Ｏ３／Ａｌ２Ｏ３催化剂的活性和抗积炭性能。同时考察了原料气空速、反应温度以及催化剂制备的焙烧温度对Ｋ２Ｏ－ＣｕＯ－Ｃｒ２Ｏ３／Ａｌ２Ｏ３催化剂反应性能的影响。ＸＲＤ谱图表明,Ｃｒ２Ｏ３在催化剂中高分散,７００℃焙烧的催化剂中出现的ＫＣｕＯ晶相对催化剂活性不利。用ＮＨ３－ＴＰＤ和ＣＯ２－ＴＰＤ检测了催化剂表面的酸碱中心,表明助     

异丁烷直接脱氢制异丁烯的催化剂的研究进展

从热力学和反应机理角度概述了异丁烷直接脱氢和氧化脱氢的差异;从活性中心性质、失活与再生、助催化剂以及载体方面综述了目前广泛研究的异丁烷直接脱氢制异丁烯的催化剂,包括PtSn-、CrO_x-、GaO_x基和金属硫化物催化剂,并分析了各类催化剂的优缺点及目前的研究方向。简述了其他类型的脱氢催化剂,包括Mo/MgAl_2O_4、碳基材料、Co-、Ni_2P-、VO_x基催化剂等。分析了目前脱氢技术面临的问题以及未来的研究方向。     

异丁烷在钼酸锌上的催化氧化脱氢

研究了钼酸锌对异丁烷氧化脱氢反应的催化作用,考察了原料气中烷氧体积比、N₂及水蒸汽对反应结果的影响.提高反应原料气中的烷氧体积比能够提高异丁烯选择性,但也会降低异丁烷的转化率.原料气中加入N₂不利于反应;而加入水蒸汽可提高异丁烯选择性.催化剂表面主要是弱酸中心,对反应有利.     

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.     

Influence of impregnation conditions on the activity of CrOx/Al2O3 catalysts in dehydrogenation of isobutane in fixed bed reactor

The development of catalysts for dehydrogenation of light paraffin hydrocarbons in a fixed bed reactor is of great importance for the world petrochemical industry. The preparation of granules (~3 mm in diameter) of CrO_x/Al₂O₃ catalysts is hindered by such problems as homogeneous distribution of active component and modifiers, high strength of granules, etc. In this paper, the alumina support dissolution in the impregnating solution containing chromic acid and the opportunity to apply vacuum impregnation to minimize this effect in the preparation of CrO_x/Al₂O₃ catalysts are discussed. A series of catalysts is synthesized at different impregnation pressures (1, 0.85, and 0.7 atm), characterized by a complex of physical–chemical methods (low-temperature N₂ adsorption, SEM, XRD, TPR-H₂), and tested in isobutane dehydrogenation. The use of vacuum impregnation is shown to lead to the reduction of the specific surface area of the catalysts from to 91 to 56 m²/g and the growth of content of CrO_x phases that decreases the catalytic activity in dehydrogenation. The isobutylene yield at 610 °C decreases from 68% to 54% for the catalyst prepared at P = 0.7 atm as compared with the one prepared at atmospheric pressure. The high activity and stability are connected with the hierarchical structure of the alumina support and homogeneous chromia distribution on its surface.     

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.     

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.     

无粘结剂ZSM-11催化剂上异丁烯直接胺化生成叔丁胺

叔丁胺是一种重要的化工原料和中间体,广泛应用于制备橡胶促进剂、医药、农药和着色剂等下游产品.异丁烯在分子筛催化剂上直接胺化生产叔丁胺是一个经济环保过程,其中ZSM-5和BEA分子筛的催化性能优于其它系列分子筛.ZSM-11与ZSM-5分子筛具有相似的孔道结构,我们以前的实验结果表明,与ZSM-5相比,ZSM-11表现出更优越的芳构化反应性能,在干气中乙烯低温芳构化方面也有明显优势.在此基础上,我们进行无粘结剂ZSM-11分子筛催化剂合成,并应用于异丁烯直接胺化生产叔丁胺反应.传统水热技术合成的分子筛通常为粉末,机械强度不能达到实际应用的要求,在工业化过程中分子筛粉末一般需要加入粘结剂成型使其具备一定的机械强度和形状,但是粘结剂会降低分子筛催化剂的活性和选择性,有可能会引发一些副反应,因此无粘结剂分子筛催化剂引起人们广泛关注.无粘结剂分子筛是指分子筛颗粒中不含惰性粘结剂或只含有少量粘结剂,主要依靠分子筛晶粒间的相互作用支撑存在,具有一定形状、尺寸和机械强度的催化材料.无粘结剂分子筛催化剂中分子筛含量较高,可利用的有效表面积较大,在离子交换及工业催化等方面具有明显优势.本文采用水热合成的ZSM-11分子筛原粉与二氧化硅机械混合(ZSM-11/SiO2=70/30)挤条后,通过气固相合成法制备了无粘结剂ZSM-11分子筛催化剂(Cat-C).作为对比,还分别制备了ZSM-11和SiO2机械混合(ZSM-11/SiO2=70/30)样品HZSM-11+SiO2及ZSM-11和氧化铝机械混合(ZSM-11/Al2O3=70/30)样品HZSM-11+Al2O3.利用X射线衍射、透射电镜、NH3程序升温脱附和吸附吡啶红外光谱等对分子筛催化剂的物理化学性能进行了表征.同时,以这些分子筛样品为催化剂,在固定床反应装置上进行了异丁烯胺化反应评价,反应条件为270℃,5.0 MPa,氨烯比为4和异丁烯空速0.5 h?1.结果表明,与HZSM-11+SiO2和HZSM-11+Al2O3相比,Cat-C上叔丁胺生成速率最高.关联催化剂物化性能和反应性能发现,催化剂孔道结构与叔丁胺生成并不存在明显的关联性,而较多的Br?nsted酸和较少的Lewis酸才是Cat-C具有良好反应性能的主要原因.具有一定机械强度的无粘结剂ZSM-11分子筛催化剂制备简单,在异丁烯直接胺化过程中叔丁胺生成速率高,具有很好的工业化应用前景.     

Geometric and electronic factors in paraffin dehydrogenation on bimetallic platinum catalysts

Summary Relationships between specific activity of bimetallic platinum catalysts in paraffin dehydrogenation and atomic sizes of promoters (i) and enthalpies of alloying with platinum (ii) were considered. The leading role of the size (geometric) effect was demonstrated.     

Oxidative dehydrogenation of isobutane to isobutylene over supported transition metal oxide catalysts

Para-selectivity of ZSM-5 zeolites with similar bulk Si/Al ratio, but different particle size and surface Al concentration has been investigated in toluene disproportionation. Results showed that enhancedpara-selectivity is a consequence not only of the particle size but also of the external surface aluminium concentration in the particles.     

Effect of carriers and additives on the activity and stability of copper-based catalysts for the dehydrogenation of cyclohexanol

A continuous process for the dehydrogenation of cyclohexanol to cyclohexanone on copper-based catalysts was described. The catalysts were characterized by XRD, XPS and TPR, and Cu⁰ was found to be the active site for the copper-based catalysts studied. The two carrier catalysts were proved to be more active than the single carrier ones, and the Cr additive, which mainly existed as the CuCr₂O₄ phase on the catalyst’s surface, was found to have a significant effect on the activity and stability of the Cu-Cr-Mg-Al catalyst.