不同加铝方式对SAPO-34分子筛合成及MTO催化性能的影响

在水热合成体系中,以三乙胺(TEA)和四乙基氢氧化铵(TEAOH)为混合模板剂,考察了在初始凝胶形成过程中铝源的加入方式对合成SAPO-34分子筛及甲醇制烯烃(MTO)催化性能的影响;通过X射线衍射(XRD)、扫描电子显微镜(SEM)、氮气等温吸附脱附(BET)、²⁹Si固体核磁(²⁹Si MAS NMR)、氨气程序升温脱附(NH₃-TPD)等方法对合成产物进行物性表征,并研究了其在甲醇转化制烯烃(MTO)反应中的催化性能。结果表明,随着首先加铝量的增加,粒径有逐渐变小的趋势,且逐渐出现板层状形貌的SAPO-34分子筛;同时,产物分子筛骨架中Si(4Al)配位结构的数量增加,强酸比例在逐渐增大,且酸密度增加;随着强酸比例和酸密度的提高,SAPO-34分子筛在MTO催化反应中的寿命逐渐延长,丙烯选择性逐渐增大而乙烯选择性逐渐减小。     

不同加铝方式对SAPO-34分子筛合成及MTO催化性能的影响

在水热合成体系中,以三乙胺(TEA)和四乙基氢氧化铵(TEAOH)为混合模板剂,考察了在初始凝胶形成过程中铝源的加入方式对合成SAPO-34分子筛及甲醇制烯烃(MTO)催化性能的影响;通过X射线衍射(XRD)、扫描电子显微镜(SEM)、氮气等温吸附脱附(BET)、~(29)Si固体核磁(~(29)Si MAS NMR)、氨气程序升温脱附(NH_3-TPD)等方法对合成产物进行物性表征,并研究了其在甲醇转化制烯烃(MTO)反应中的催化性能。结果表明,随着首先加铝量的增加,粒径有逐渐变小的趋势,且逐渐出现板层状形貌的SAPO-34分子筛;同时,产物分子筛骨架中Si(4Al)配位结构的数量增加,强酸比例在逐渐增大,且酸密度增加;随着强酸比例和酸密度的提高,SAPO-34分子筛在MTO催化反应中的寿命逐渐延长,丙烯选择性逐渐增大而乙烯选择性逐渐减小。     

酸处理可控制备多级孔SAPO-34及其甲醇制烯烃性能

甲醇制低碳烯烃(MTO)技术既可实施石油替代路线,又能解决低碳烯烃不足的问题,因而具有重要意义.在MTO技术中,SAPO-34分子筛因其高水热稳定性、适宜的微孔结构和酸强度而展现了优异的MTO性能.但SAPO-34分子筛孔道较小,易形成积碳物种而覆盖活性中心,导致分子筛催化剂失活快,反应流程复杂.延长SAPO-34催化剂的单程寿命可减少其再生频率,降低能耗并节约成本.在微孔SAPO-34分子筛中引入介孔或大孔孔道来组成多级孔道结构,可大大促进反应物及产物分子在孔道内的扩散,从而降低积碳速率,延长催化剂寿命.目前,文献中主要采用直接合成路线制备多级孔SAPO-34分子筛,该过程所用的二级模板剂价格较贵,且合成步骤复杂.而采用后处理方法,即先合成SAPO-34分子筛母体,再进行酸碱后处理来制备多级孔SAPO-34分子筛是非常有前景的技术路线.本文首先通过水热合成法制备了立方形貌SAPO-34分子筛,再采用不同种类的酸溶液(硝酸、草酸及丁二酸)对其进行后处理,制备了具有良好相对结晶度的多级孔SAPO-34,考察了酸种类对所得多级孔SAPO-34结构及其MTO性能的影响.研究发现,经硝酸和草酸处理后的样品在特定晶面上出现了蝴蝶状孔道,形成了由微孔、介孔(40–50 nm)和大孔(400–500 nm)组成的多级孔分子筛;其比表面积高达876 m2/g,孔容为0.36 cm3/g,该多级孔道大幅改善了MTO过程中的分子扩散性能.酸后处理过程并没有影响分子筛的化学环境及酸中心强度,却降低了分子筛的强酸中心数量并增加了弱酸中心数量.在多级孔结构及酸中心的协同作用下,其MTO性能得到了大幅度提升:经硝酸和草酸处理后所得多级孔SAPO-34,其MTO寿命(400°C,1 atm,甲醇空速1 h–1)分别由母体的210 min增至360和390 min,低碳烯烃的总选择性由母体的90%提高至92%–94%,并可根据孔道大小调整产物组成,使乙烯选择性在37.4%–51.5%内调变.对比发现,MTO过程中多级孔SAPO-34上的积碳量由母体的15%提高到18%,但积碳速率却由0.071降至0.046 g/min.失活多级孔SAPO-34内的积碳物种主要为较大的分子,其中芘及芘取代物的含量高达73%,而母体SAPO-34中芘及芘取代物的含量则降低至49%.这是因为多级孔SAPO-34内部更大的孔道空间可容纳更多的大分子积碳物种所致.丁二酸处理后的样品未产生多级孔道,却使部分微孔受损且增加了强酸中心数量,导致其更易失活,MTO寿命也降至100 min.选择合适种类的酸溶液进行后处理可控制备多级孔SAPO-34,可大幅改善其MTO性能.     

脱铝丝光分子筛应用于MTP反应:Al的落位和晶体形貌的影响

甲醇制烯烃/丙烯工艺(MTO/MTP)是当前煤基碳资源绿色催化转化的重要过程之一.在MTO/MTP工艺中,分子筛通常面临低碳烯烃选择性低、水热稳定性差和寿命短等挑战.开发高选择性和高稳定性的分子筛催化剂对煤基乙烯/丙烯等化学品的工业生产具有重要意义.本文选择了具有12元环孔道的低硅丝光分子筛(Si/Al=6)为母体,对...     

晶粒大小对ZSM-5分子筛甲醇制低碳烯烃催化性能的影响

对三种HZSM-5分子筛进行Ca改性,获得两组酸性接近的催化剂,考察了晶粒大小对甲醇制低碳烯烃(MTO)反应的影响。通过进一步与Na改性的比较,探讨了Ca在催化反应中的作用。采用扫描电镜(SEM)测定晶粒大小及形貌,氨气程序升温脱附(NH3-TPD)及吡啶红外吸附(Py-IR)表征催化剂的酸性。MTO催化性能测定结果表明,HZSM-5的低碳烯烃选择性较低且下降较快,催化活性降低也快;Ca改性降低酸性,提高了低碳烯烃选择性和催化稳定性;晶粒大小主要影响催化稳定性,小晶粒分子筛催化剂稳定性更好。高Ca含量改性效果更好;钠改性也提高了低碳烯烃选择性,但其稳定性较差。对于HZSM-5和Ca/HZSM-5,小晶粒的催化剂具有较好的催化稳定性。提出Ca参与了催化反应,MTO是一个酸碱协同作用的催化过程。     

Synthesis of Low Silica SAPO-34 by In Situ Pretreatment and Its Catalytic Performance in the Methanol-to-Olefins (MTO) Reaction

A series of low-silica SAPO-34 molecular sieves with a tunable silica content were synthesized through a facile in situ pretreatment strategy under different pretreatment condition. The effects of the pretreatment condition on the crystal phases, chemical composition, morphology and acidity of SAPO-34 were characterized by XRD, XRF, SEM, N₂ adsorption-desorption, NH₃-TPD and ²⁹Si MAS NMR. The obtained low-silica SAPO-34 exhibits higher catalytic performance in the MTO reaction than conventional SAPO-34 due to the moderate acidity and larger surface areas. Sample S4 with a Si content of Si/(Si+Al+P)=0.053 showed the prolonged catalytic lifetime of 204 min and remarkably improved selectivity for ethylene and propylene reaching up to 86.58 %, which was 34 % and 4.16 % higher than the reference sample.     

Catalytic conversion of methanol to olefins over rare earth (La, Y) modified SAPO-34

SAPO-34 modified with lanthanum and yttrium exhibited higher selectivity to light olefins, lower methane formation, and longer lifetime (prolonged by 20%) than the parent SAPO-34 in the process of methanol conversion to olefins. The modified catalytic performance could be ascribed to the incorporation of La³⁺ and Y³⁺ into the framework of SAPO-34.     

Methanol-to-Olefin Conversion over Zeolite Catalysts: Active Intermediates and Deactivation

Methanol-to-olefin (MTO) conversion over various zeolites with different topologies, Si/Al molar ratios, and crystallite sizes were investigated to verify the effects of pore shape and size, acidity, and external surface area on the catalytic activity, product selectivity, and deactivation. The IR and electron spin resonance (ESR) study of zeolite catalysts used in MTO also proceeded to deduce the active intermediates formed in their cages or pores. The zeolites with 8 membered-ring (MR) pore entrances such as CHA, ERI, LTA, and UFI commonly exhibited high selectivity to lower olefins due to their small entrances, but the CHA catalyst with the smallest cage maintained its activity longer than other 8MR zeolites. The slow condensation of polymethylbenzene (PolyMB) to polyaromatic hydrocarbons (PAH) on MOR zeolite with a high Si/Al molar ratio due to its low concentration of strong acid sites resulted in a slow deactivation. The extremely small crystallites of H-SAPO-34 and H-ZSM-5 less than 100 nm showed an adverse effect in MTO; while the large crystallites above 1,000 nm also exhibited poor catalytic performance because of their small external surface. The study of IR regarding the adsorbed and occluded materials on zeolites demonstrated the effect of pore shape and size on the active intermediates: the zeolites with larger pores and cages allowed the formation of alkylbenzenes with long alkyl groups which preferred to be condensated to PAH. The well-resolved hyperfine splitting of ESR spectra observed on H-SAPO-34 used in MTO clearly illustrated the presence of hexamethylbenzenium radical cations. The small intersections of phosphorous-modified H-ZSM-5 allowed the formation of tetramethylbenzenium radical cations in MTO. The formation of PolyMB radical cations, their role as active intermediates and the effect of topology, acidity, and crystallite size of zeolites on their deactivation were discussed.     

ZSM-5酸改性对甲醇芳构化性能的影响

利用硝酸、草酸和酒石酸溶液对ZSM-5分子筛进行改性,并采用XRD、SEM、NH₃-TPD、XRF、²⁷Al MAS NMR、吡啶吸附红外光谱和N₂吸附-脱附对ZSM-5分子筛结构、酸量、比表面积及孔体积等物化性质进行表征分析。在反应温度为422℃,甲醇质量空速为4.74 h^-1的条件下,考察了ZSM-5分子筛的催化活性。结果表明,采用不同酸改性ZSM-5分子筛,影响了分子筛的比表面积、酸性及孔体积,从而改变了催化剂的催化性能。在甲醇芳构化（MTA）反应中,酸改性后的分子筛表现出良好的催化活性,且草酸改性后的催化剂表现出较高的催化活性及选择性,反应8 h时,芳烃及BTX收率分别达到57.40%和39.40%。     

PdSAPO－5分子筛在甲醇转化反应中的催化性能及机理

用连续－脉冲激反应色谱评价了不同ＳＡＰＯ－５分子筛及一步法合成的ＰｄＳＡＰＯ－５催化剂对甲醇制烯烃（ＭＴＯ）反应的催化性能，用ＴＰＤ－ＭＳ及１３ＣＣＰＭＡＳＮＭＲ研究了其催化反应机理．结果表明，ＰｄＳＡＰＯ－５比ＳＡＰＯ－５和Ｐｄ／ＳＡＰＯ－５有更高的烯烃选择性，这是由于反应物凝胶中加入的钯对分子筛的酸性具有调节作用，加入不同形式的钯源，其调节作用有较大的差别，并使分子筛上甲醇及生成的二甲醇的脱附温度不同．此外，钯还充当了脱氢中心，可从二甲基已基氧离子中脱下一个氢原子，从而有利于乙烯的生成．ＮＭＲ结果表明，此类催化剂上的结炭存在多种形式．反应生成乙烯的甲氧基离子主要是二甲基乙基氧离子；甲醇在此类催化剂的部分钯粒子上脱氢生成ＣＨ２Ｏ．     

DFT计算结合固体NMR研究富铝SSZ-13的铝分布和Br?nsted酸性

具有菱沸石(CHA)结构的SSZ-13分子筛在甲醇制烯烃(MTO)及柴油机车尾气氨选择性催化还原(NH_3-SCR)反应中具有重要的应用,采用富铝SSZ-13可以调节MTO反应的烯烃选择性和提升NH_3-SCR的低温脱硝活性,因此SSZ-13中的铝含量和分布与对应的酸性决定了其催化性能。本文采用密度泛函理论结合固体核磁共振实验研究了富铝和富硅HSSZ-13的Al位置与Br?nsted酸强度的内在关系。通过计算取代能发现,对于孤立Al位,质子位于Al周围4个不同O位时能量差异较小,最稳定的B酸位点是O(1)―H。对于富铝SSZ-13,两个Al原子位于同一六元环的对位是Al-Si-Si-Al (NNNN)序列中最稳定的结构,而Al-Si-Al (NNN)序列中能量最优的Al分布是两个铝原子排布于六棱柱上下不同的六元环上。通过计算最稳定构型下的质子亲和势、NH3脱附能和吸附氘代乙腈后的1H NMR化学位移,发现富铝SSZ-13中含有Si(2Al)分布的NNN序列导致了其Br?nsted酸强度弱于高硅的分子筛。分峰拟合29Si魔角旋转核磁共振(MASNMR)谱图表明富铝SSZ-13中Si(2Al)的含量在43%以上,而吸附氘代乙腈后的1H MAS NMR实验显示富铝SSZ-13的桥羟基化学位移向低场移动,进一步证明富铝SSZ-13具有较弱的Br?nsted酸强度。     

多级SAPO-34的合成及其在甲醇制烯烃反应中的催化性能

针对SAPO-34在甲醇制烯烃（MTO）催化过程中易于失活的问题,采用水热法合成了具有不同粒径及多级孔SAPO-34。详细研究了铝源、硅源对SAPO-34分子筛晶粒尺度的调控性能及二次模板剂对多级孔SAPO-34合成的影响。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、傅立叶变换红外（FT-IR）、N₂吸附-脱附,透射电子显微镜（TEM）以及NH₃-TPD等手段对合成的材料进行了表征。结果表明采用不同铝源可以实现对SAPO-34粒径的有效调控,二次模板剂的引入可以在纳米SAPO-34晶粒内部创造出孔壁晶化的晶内介孔结构。在甲醇制烯烃的催化反应过程中,大颗粒SAPO-34具有较高的低碳烯烃的选择性,多级SAPO-34因为纳米化或介孔的引入使得微孔孔道有效缩短,提高了其在MTO催化反应过程中的稳定性,但是对低碳烯烃的选择性受到抑制,而对油品的选择性则因为外表面积的增大而显著增加。     

多级SAPO-34的合成及其在甲醇制烯烃反应中的催化性能

针对SAPO-34在甲醇制烯烃(MTO)催化过程中易于失活的问题,采用水热法合成了具有不同粒径及多级孔SAPO-34。详细研究了铝源、硅源对SAPO-34分子筛晶粒尺度的调控性能及二次模板剂对多级孔SAPO-34合成的影响。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶变换红外(FT-IR)、N2吸附-脱附,透射电子显微镜(TEM)以及NH3-TPD等手段对合成的材料进行了表征。结果表明采用不同铝源可以实现对SAPO-34粒径的有效调控,二次模板剂的引入可以在纳米SAPO-34晶粒内部创造出孔壁晶化的晶内介孔结构。在甲醇制烯烃的催化反应过程中,大颗粒SAPO-34具有较高的低碳烯烃的选择性,多级SAPO-34因为纳米化或介孔的引入使得微孔孔道有效缩短,提高了其在MTO催化反应过程中的稳定性,但是对低碳烯烃的选择性受到抑制,而对油品的选择性则因为外表面积的增大而显著增加。     

镁改性对HZSM-5分子筛催化乙烯制丙烯的影响

采用等体积浸渍法制备了一系列不同Mg含量(0–1.0%)的HZSM-5分子筛。利用X射线衍射(XRD)、N_2吸附/脱附、铝魔角旋转固体核磁共振(~(27)AlMASNMR)、~(29)SiMASNMR、氨-程序升温脱附(NH_3-TPD)和吡啶吸附傅里叶变换红外(Pyridine-IR)光谱等技术对改性前后样品的结构和酸性进行了详细表征,在常压连续流动固定床反应器上考察其对乙烯转化制丙烯(ETP)反应的催化性能,评价了反应条件和Mg改性的影响。结果表明,在温度为550°C、乙烯体积空速GHSV=3000 h~(-1)的适宜反应条件下,0.5%适量镁改性HZSM-5导致乙烯转化率有所下降,但丙烯选择性增加到45%以上,而副产物芳烃的选择性降到8%以下。反应前样品的酸性表征和反应后积碳样品的TPO及~(13)CCP/MASNMR谱图分析表明适量镁改性使HZSM-5分子筛的总酸量和强B酸量减少而中强酸量增加,从而提高了丙烯的选择性,但是过量的镁改性使分子筛的总酸量明显减少,导致催化剂的活性显著下降。     

H-ZSM-5分子筛不同孔道处的酸位在甲醇制烯烃反应中的催化作用

甲醇制烯烃(MTO)作为一条由煤、天然气和生物质等含碳资源制备重要有机化学品的非石油路线,近年来备受关注.作为MTO催化剂,分子筛的骨架拓扑结构和酸性质对于其催化活性、反应路径和产物分布等具有重要的影响.H-ZSM-5分子筛是一种典型的MTO反应催化剂,酸位可以分布在MFI拓扑结构的直孔道、正弦孔道和交叉位点处.虽然目...     

手性双哌啶衍生物用于甲基三氧化铼催化烯烃不对称环氧化反应

以N-烷基-4-哌啶酮为原料,制备了几个手性双哌啶衍生物配体.以尿素-过氧化氢复合物(UHP)为氧化剂,甲醇为溶剂,将这些配体用于甲基三氧化铼(MTO)催化的前手性烯烃的环氧化反应,考察了各种反应参数对催化剂催化性能的影响.结果表明,手性双哌啶衍生物的加入可降低MTO的催化活性,但可提高环氧化物的选择性;这些配体对前手性烯烃的环氧化反应有较低的手性诱导作用,对映体过量值(ee值)只有4%-11%.讨论了对映选择性低的原因.     

Preparation of modified Ce-SAPO-34 catalysts and their catalytic performances of methanol to olefins

The modified Ce-SAPO-34 catalysts were prepared with three methods, i.e., the liquid ion exchange with air calcination, impregnation with air calcination and impregnation with steam calcination methods. The catalytic performances of the catalysts for methanol to olefins were investigated. The properties of the catalysts were characterized using XRD, BET, XRF, FT-IR and NH₃-TPD. The results indicated that compared to the SAPO-34 catalyst the catalyst prepared with the impregnation and air calcination prolonged the lifetime by 40 min and improved the selectivity to ethylene by 5% (mol) and the catalyst prepared with the impregnation and steam calcination showed the best modification effect, prolonging the lifetime by 70 min and improving the ethylene selectivity by 10% (mol). The catalyst prepared with the liquid ion exchange showed similar behaviour as the SAPO-34 catalyst. It was verified that the porous structure and surface acidity of these catalysts determined their catalytic behaviors.     

固体酸催化剂结构与催化反应机理的核磁共振研究

Solid acid catalysts have been widely used in advanced petrochemical processes because of their environmental friendliness, high product selectivity, and easy product separation. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a well-established tool for structure determination and dynamic study of various functional materials. In this review, we focus mainly on our research using solid-state NMR to characterize the acid properties and elucidate the catalytic reaction mechanism of solid acid catalysts. The acid strength of solid acids can be quantitatively measured from the chemical shifts of adsorbed probe molecules such as pyridine, acetone, trialkylphosphine oxides, and trimethylphosphine. The spatial proximity and synergetic effect of various acid sites on solid acid catalysts can be ascertained by two-dimensional (2D) double-quantum magic angle spinning (DQ MAS) NMR spectroscopy. Additionally, in situ solid-state NMR spectroscopy can be used to explore heterogeneous catalytic reaction mechanisms by monitoring the evolution of the reactants, intermediates, and products.     

Tuning the product selectivity of SAPO-18 catalysts in MTO reaction via cavity modification

The AEI cavity of SAPO-18 catalyst was modified with zinc cations with the conventional ion exchange procedure. The cavity modification effectively tunes the product selectivity, and shifts the products from mainly propylene to comparable production of ethylene and propylene in methanol to olefin (MTO) reaction. The incorporation of zinc ions and the generation of bicyclic aromatic species in the AEI cavity of SAPO-18 catalysts introduce additional diffusion hindrance that exert greater influence on the relatively bulky products (e.g. propylene and higher olefins), which increase the selectivity to small-sized products (e.g. ethylene). It appears that the incorporated zinc cations facilitate the generation of lower methylbenzenes which promote the generation of ethylene. The cavity modification via incorporating zinc ions effectively tunes the product selectivity over SAPO molecular sieves with relatively larger cavity, which provides a novel strategy to develop the potential alternative to SAPO-34 catalysts for industrial MTO reaction.     

High Ethylene Selectivity in Methanol-to-Olefin (MTO) Reaction over MOR-Zeolite Nanosheets

Precisely controlled crystal growth endows zeolites with special textural and catalytic properties. A nanosheet mordenite zeolite with a thickness of ca. 11 nm, named as MOR-NS, has been prepared using a well-designed gemini-type amphiphilic surfactant as bifunctional structure-directing agent (SDA). Its benzyl diquarternary ammonium cations structurally directed the formation of MOR topology, whereas the long and hydrophobic hexadecyl tailing group prevented the extensive crystal growth along b axis. This kind of orientated crystallization took place through the inorganic–organic interaction between silica species and SDA molecules present in the whole process. The thin MOR nanosheets, with highly exposed (010) planes and 8-membered ring (MR) windows, exhibited a much improved ethylene selectivity (42.1 %) for methanol-to-olefin (MTO) reactions when compared with conventional bulk MOR crystals (3.3 %).