Microporous crystalline silicoaluminophosphates: Effect of synthesis conditions on the physicochemical and catalytic properties in the reaction of methanol to C2-C4 olefins conversion

Effect of the synthesis parameters (reaction mixture composition, crystallization temperature and duration) on the physicochemical and catalytic properties of microporous crystalline silicoaluminophosphates (SAPOs) has been studied. Methods for the directional control of phase composition, degree of crystallinity, morphology and size of SAPO crystals crystallized from colloidal silicoaluminophosphate sols stabilized in tetraethylammoniun hydroxide solution as a template have been developed. It has been determined that the use of more severe synthesis conditions (increase in temperature and duration of crystallization) leads to the formation of larger crystals and a growth in the concentration of medium strength sites in the samples, which causes a rapid deactivation of the samples in the reaction of methanol conversion to C₂-C₄ olefins. Crystallization under milder conditions (a decrease in pH and temperature) promotes the acid formation of CHA/AEI intergrowth crystals exhibited a high and steady performance in the methanol conversion for more than 8 h at a total yield of olefins of 95 wt %.     

Effect of the type of silicon source on the physicochemical and catalytic properties of mesoporous silicoaluminophosphate molecular sieves

Silicoaluminophosphates with the ATO structure have been synthesized using two types of silicon source (metakaolin and silica sol). To determine the composition, morphology, and acid properties, SAPO-31 samples have been characterized by various methods. It has been found that the samples synthesized using different silica sources have very different properties. Samples of SAPO-31 synthesized with metakaolin have a higher acidity and are more active in the catalytic hydroisomerization of n-decane as compared with their counterparts prepared with silica sol. The difference in the effect of the type of silicon source has been explained by morphological features of silica particles formed during the dissolution of silicon source (spherical particles of a ~10 nm size in the case of silica sol and nanoplates of a ~1 nm size in the case of metakaolin). On the basis of data on the enhancement of acidic properties in the SAPO-31 samples with an increase in silicon concentration therein, it has been doubted that the SM3 mechanism of incorporation of Si atoms into the aluminophosphate ATO framework really operates (in any of its form). It has been shown that the SM2 mechanism alone operates instead, involving the independent formation of regions with an aluminosilicate composition.     

模板剂对SAPO-34的合成、性质及催化性能的影响

分别以TEA、DEA和TEA+DEA为模板剂进行了SAPO-34分子筛的合成。以TEA为模板剂只能得到CHA/AEI的共生结构产物；以DEA为模板剂能够得到纯相的SAPO-34，但是合成条件比较苛刻；以DEA+TEA为模板剂时，当DEA的量大于总模板剂量的一半时，得到的是纯相SAPO-34。研究了TEA和DEA的不同比例对于晶化产物物化性质的影响。模板剂中DEA的比例的增加，晶化产物中的硅含量增加，孔体积和比表面不断减小，晶粒逐渐增大，酸中心数不断减少，酸强度有所减弱。对合成的分子筛的MTO催化性能进行了研究。随着模板剂中DEA比例的增加， MTO反应产物中乙烯收率降低，而丙烯收率提高，C2=+C3=的选择性逐渐增加。     

原位干胶合成Ni/SAPO-11催化剂中硅含量及配位环境的调控

用原位干胶法合成Ni/SAPO-11双功能催化剂,通过改变初始凝胶中硅添加量调控分子筛骨架硅含量及配位环境,实现对催化剂酸性质的控制。采用XRD、TEM、XPS、SEM、MAS NMR及NH₃-TPD等手段对所得催化剂进行表征,并以正己烷为模型化合物对其异构化性能进行评价。结果表明：增加初始凝胶中的硅添加量对Ni/SAPO-11催化剂的形貌、孔道结构、金属物种类型及分散度并无显著影响,但可促进Si通过SMⅢ同晶取代进入SAPO-11分子筛骨架,硅含量上升,且硅岛结构增多,这使Ni/SAPO-11的酸量在初始凝胶中SiO₂/Al₂O₃摩尔比为0.6时出现最大值。Ni/SAPO-11酸量的增加显著提高了其在正己烷临氢异构化中的活性及异构烃收率,表现出优于Pt/SAPO-11催化剂的异构化性能。     

草酸二甲酯催化加氢制乙二醇铜基催化剂研究进展

合成气经草酸二甲酯加氢制乙二醇是最具工业应用前景的乙二醇合成新工艺。着重介绍了草酸二甲酯非均相加氢Cu基催化剂的研究进展,总结了催化剂的制备方法、载体、助剂等对催化反应性能的影响,初步探讨了反应过程催化剂的活性中心及反应机理。     

Catalytic cracking of isopropylbenzene over hybrid HZSM-12/M41S (M41S = MCM-41 or MCM-48) micro-mesoporous materials

The catalytic cracking of isopropylbenzene was investigaded over hybrid ZSM-12/MCM-41 and HZSM-12/MCM-48 micro-mesoporous materials, in order to verify the effect of the acid site of the accessibility of mesoporous channels combined with the acid sites into the zeolite. The hybrid materials were synthesized by the hydrothermal method using the template mechanism. The obtained materials were characterized by X-ray diffraction and BET isotherms using nitrogen adsorption-desorption at 77 K. The X-ray diffraction patterns presented characteristic peaks of the microporous and mesoporous phases. These analysis revealed the formation of ordered hexagonal MCM-41 or cubic MCM-48 mesoporous phases, associated with the ZSM-12 structure. In order to generate acid sites, the materials were ion exchanged with ammonium chloride solution. The calcined hybrid materials were tested as catalyst for cracking of isopropyl-benzene, using a fixed bed reactor at 450 ^oC and nitrogen gas. The catalytic tests showed that the HZSM-12/AlMCM-41 and HZSM-12/MCM-48 hybrid materials have potential for use in cracking reactions, bening more active than the zeolite or the M41S alone. The catalytic activities of the hybrid materials can be associated with a synergistic effect between the acid sites present on the zeolitic phase and the mesoporous phase. In order to verify how the structure of the hybrid materials may affect and control their catalytic performances, the results were compared with HZSM-12 physically mixed with MCM-41 and MCM-48.     

分级晶化合成SAPO-34分子筛及其催化性能的研究

为调控SAPO-34分子筛的粒径,提高其甲醇制低碳烯烃(MTO)的催化性能,采用分级晶化方式将晶化过程分为四级,依次合成并分离出各级SAPO-34分子筛产品。测定各级产品的平均粒度,并进行XRD,SEM,NMR表征以及MTO催化性能评价,结果表明:相比于相同条件下传统方法制备的SAPO-34分子筛,分级晶化产品的总收率较高,平均粒径较小,MTO反应单程寿命较长,乙烯选择性略高;随分级晶化的进行,SAPO-34分子筛的平均粒径逐渐减小,硅取代磷和铝的SMⅢ机理发生的比例逐渐增大,体系中依次出现了Si(1Si,3Al)和Si(2Si,2Al)结构,粒径较小的三级产品与粒径较大的二级产品在甲醇转化率大于99%时单程寿命和双烯收率均相当。     

乙烯选择性四聚合成1-辛烯研究进展

从乙烯选择性四聚催化体系铬配合物的配体结构(双膦胺型配体、乙基桥连双膦型配体、碳-氮桥连磷胺型配体)、助催化剂和反应机理等方面,综述了近年来乙烯选择性四聚领域内的研究进展,指出过渡金属铬配合物在乙烯选择性齐聚中具有高催化活性、产物高选择性的特点,是制备1-己烯、1-辛烯等线性α-烯烃的主要催化剂,配体结构是影响铬配合物...     

Nanoheterogeneous catalysis: Definition,state, and research prospects (Review)

This review is concerned with the analysis of nanoheterogeneous catalysis (catalysis in heterogeneous-dispersed systems with nanosized particles of the dispersed phase) in the hydroconversion of a vacuum distillation residue, hydrogenation of individual aromatic hydrocarbons and technical mixtures, and Fischer–Tropsch synthesis. For nanoheterogeneous catalysis, in addition to factors that are typical for heterogeneous catalysis, important factors are the size effect, the all-round accessibility of catalytically active species to reagents, the absence of a porous structure, a high efficiency of heat transfer in the dispersion medium, and an extremely low mass concentration of the catalyst in the suspension reactor (0.05–0.5%) at a high concentration of nanoparticles per reactor volume unit (10¹³–10¹⁵ particles per cubic centimeter). A fine tuning of catalytic processes may be performed in nanoheterogeneous catalysis via a change in the morphology, size, and structure of nanoparticles and variation in their concentration in a suspension reactor. In many cases, the aggregation of nanoparticles accompanied by the formation of nanoaggregates may become the decisive factor for the final outcome of the test reaction and special efforts are needed to stabilize the suspension of catalytically active particles. Technologies based on catalysis by nanosized particles of the dispersed phase have undergone benchmark and pilot tests and are entering the period of wide implementation in the hydroconversion of oil vacuum distillation residue and partially in the Fischer–Tropsch synthesis.     

天然气和二氧化碳转化制合成气的研究──Ⅱ．催化剂失活与再生

采用ＸＲＤ，ＸＰＳ技术，配合比表面、孔结构测定和催化微反技术，研究了天然气和ＣＯ２转化制合成气催化剂失活机制和再生条件。发现催化剂失活主要是由于活性中心Ｎｉ０聚集并形成晶相，因而降低了催化剂表面活性中心数，其次是由于部分活性中心形成难还原的ＮｉＡ１２Ｏ４物种和催化剂比表面降低。找到了一种催化剂再生的最佳条件，通过使用晶相分散剂Ｂ可以使催化剂恢复到新鲜催化剂的活性。     

A study of Pt/WO<Subscript>4</Subscript><Superscript>2−</Superscript>/ZrO<Subscript>2</Subscript> catalyst deactivation in the hydroisomerization of heptane and a heptane–benzene mixture

The dynamics of the catalytic properties of a Pt/WO₄ ^2?/ZrO₂ catalyst (17 mol % WO₄ ^2?) in the hydroisomerization of heptane and a heptane–benzene mixture as a function of reaction time and temperature has been studied. It has been found that the heptane conversion decreases in the initial reaction period (within 2 h) and the isohexane selectivity symmetrically increases at 170–280°C, with the benzene hydrogenating activity decreasing at 250°C and higher temperatures. The observed changes in catalytic properties are attributed to the partial deactivation of both the acid and hydrogenation components of the catalyst. X-ray photoelectron spectroscopy has revealed the formation of carbon deposits on the catalyst surface; the structure of the deposits is determined by the reaction medium composition. The composition of the products formed on the catalyst after heptane hydroisomerization is mostly represented by aliphatic polymers of the “poly-С_хН_y” type, which are capable of blocking the active sites that catalyze the cracking reactions. The addition of benzene to heptane has led to the formation of graphite-like carbon deposits; this feature is apparently responsible for a decrease in both the acidity and hydrogenation activity of the catalyst. The phase state and textural characteristics of the catalysts are stable under the isomerization reaction conditions.     

丙烯齐聚非均相催化剂的研究进展

综述了近10年来丙烯齐聚非均相催化剂的研究进展,讨论了催化剂载体的种类、结构和性质,金属阳离子种类、价态和迁移规律等对丙烯齐聚反应的影响,并对催化剂活性中心、反应中间体的形成和催化反应机理进行了深入的论述。指出丙烯齐聚非均相催化剂存在的主要问题活性中心易流失,提出了丙烯齐聚非均相催化剂的研究和开发应以能够稳定活性中心的载体和添加剂为重点。     

Methanol to lower olefins conversion in a slurry reactor: Effects of acidity and crystal size of silicoaluminophosphate catalysts

Effects of the crystal size and acidity of silicoaluminophosphates on their catalytic behavior in the methanol to lower olefins conversion in a slurry reactor have been studied. It has been found that an increase in the crystal size of silicoaluminophosphate causes a reduction in its catalytic activity, which is due to an increase in diffusion limitations for both reagents and reaction products. An increase in the number of acid sites and their localization on the outer catalyst layer improve the time stability of silicoaluminophosphate performance and the selectivity of methanol conversion to lower olefins.     

嵌入表面分子方法及其在CO加氢催化反应中的应用

嵌入表面分子方法是描述非均相催化反应中所定义的活性中心的新方法。该法是将活性中心看作一个“表面分子”。嵌入表面分子方法强调了在非均相催化中需要考虑生成键的思想并充分利用其它化学领域尤其是均相催化方面的成键理论。利用这一方法较详细地分析了以合成气为原料、以负载型的铑为催化剂进行反应生成Ｃ２以上含氧化合物及烃类等产物机理。     

The multiple-site nature of ethylene polymerization catalysts based on zirconyl carboxylates

Zirconyl carboxylates in combination with alkylaluminum chlorides were shown to be active catalysts for the reaction of ethylene polymerization. It was found that the molecular-mass distribution of ethylene oligomers depends considerably on the donor-acceptor properties of a modifier of the catalytic system. The optimal conditions for obtaining the C₄–C₈ and C₈–C₁₈ fractions of linear α-olefins with yields of 75–80%, respectively, were determined. Experimentally observed deviation of the composition of oligomerization products from the statistical distribution of the Schulz-Flory type is caused by the multistie character of the catalytic system used. Modifiers that provide the formation of catalytic centers with higher coordination unsaturation (type I) promote the selective formation of the C₄–C₈ fraction (95%). Modifiers capable of forming semilabile ligands (type II) lead to an increase in the yield of the middle, C₆–C₁₀ and C₈–C₁₈ fractions. Modifiers with stronger chelating properties (type III) direct the process toward the formation of macromonomers and polymers of ethylene.     

乙炔选择性加氢催化剂的结构及性能调控

催化加氢可以有效去除乙烯原料气中微量的乙炔。通过综述近年来国内外以Pd基催化剂为主的关于调控乙炔选择性加氢催化剂结构及反应性能方面的相关研究和进展,探讨了活性组分粒径、形貌对催化剂吸/脱附乙烯性能的影响;评述了添加助剂形成的合金或者金属间化合物,利用其几何效应提高活性中心分散度,利用电子效应优化电子性质使反应关键步骤的吸脱附行为发生改变;阐述了通过调控载体对金属原子锚定,使金属的分散度提高进而获得优异的催化性能;叙述了不同制备方法对催化剂结构及催化性能的影响。指出提高催化剂性能是当今研究的重中之重,未来负载型催化剂的研究方向依旧是构建高乙烯选择性和良好稳定性的高分散乃至单原子催化剂。     

Cu-Fe/ZrO2催化苯胺和CO2合成二苯基脲反应

以Cu-Fe/ZrO₂为催化剂、乙腈为溶剂,进行苯胺与CO₂合成二苯基脲(DPU)反应,考察了反应条件对该反应的影响和催化剂的重复使用性能,推测了Cu-Fe/ZrO2对该反应的催化作用机理。结果表明,苯胺与CO2合成DPU反应的适宜条件为催化剂与苯胺质量比0.10、乙腈/苯胺体积比1.0、反应温度160℃、CO₂初始压力1 MPa、反应时间7 h;在此条件下,苯胺转化率、DPU产率及其选择性分别为5.5%、5.3%和96.9%。Cu-Fe/ZrO²催化剂表面存在3类活性中心,即Cu-Fe金属位M、Lewis酸位Zrⁿ⁺和Lewis碱位Zr－O^-,在它们的协同作用下实现了苯胺与CO₂合成DPU的反应。催化剂重复使用4次后失活,活性组分Cu的流失是其失活的主要原因。     

外加硅对REHY分子筛及其催化剂性能的影响

考察了外加硅源对ＲＥＨＹ分子筛及其催化剂性能的影响。试验结果表明，在分子筛中外加适量的硅，可以提高其骨架的完整性，提高分子筛的结晶度，调变分子筛的酸强度分布。用该富硅分子筛作为活性组分制备的烃类裂化催化剂，具有活性高、积炭量低和较强的抗重金属污染能力。     

Ethane aromatization on Ga-Pt/HZSM-5 zeolites prepared by solid-state modification

The results of a comparative study of the catalytic properties of gallium and platinum pentasil (ZSM-5) zeolites, prepared according to the solid-state modification and impregnation techniques, in the ethane aromatization reaction are reported. It has been found that the procedure for the preparation of bimetallic catalysts has no substantial effect on their activity and selectivity for aromatic hydrocarbons. The formation of the active sites of the catalysts obtained by solid-state modification was investigated with the use of X-ray diffraction and X-ray photoelectron spectroscopy, and it has been supposed that Ga-Pt clusters similar to the species revealed earlier in bimetallic pentasil catalysts prepared by impregnation are produced as a result of topochemical reactions involving hydrogen. Based on the catalytic and physicochemical data, a reaction scheme for the ethane aromatization on Ga-Pt/HZSM-5 is proposed, which suggests the involvement of bimetallic clusters in a key step, the dehydrogenation of ethane followed by the formation of ethylene oligomers and their dehydrocyclization.     

Pt/SO42-/ZrO2-Al2O3在正己烷异构化反应中的催化行为

采用连续流动的固定床微反装置考察了Pt/SO24-/ZrO2-Al2O3(PSZA)在正己烷异构化反应中的催化行为。采用NH3-TPD、H2-TPR及TG表征了催化剂的酸性、还原性能及硫物种含量。结果表明,PSZA的初始异构化催化活性几乎不受反应温度的影响,而稳定性则与反应温度密切相关。低温下反应,催化剂在短时间内迅速失活,而提高反应温度可大大提高PSZA的反应稳定性。PSZA具有良好的再生性能,与新鲜催化剂相比,多次再生后的催化剂异构化催化活性基本没有变化。PSZA在低温下的快速失活与其催化活性中心产生的机理有关,而与其硫损失或硫物种的还原无关。在异构化反应过程中,催化剂通过氢溢流可产生强酸活性中心,并在反应过程中不断被消耗;在高温下通过氢溢流不断产生新的强酸中心,使催化活性保持稳定;而低温下氢溢流难以发生,消耗的强酸活性中心不能及时补充,使催化活性下降。