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作者简介:

张强(1979-),女,副教授,博士,研究方向为催化材料。E-mail:xyz@upc.edu.cn。

通信作者:

张强(1979-),女,副教授,博士,研究方向为催化材料。E-mail:xyz@upc.edu.cn。

中图分类号:TQ 032

文献标识码:A

文章编号:1673-5005(2024)01-0197-09

DOI:10.3969/j.issn.1673-5005.2024.01.022

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目录contents

    摘要

    通过引入含铜分子筛晶种作为铜源、10 h快速合成出Cu-SAPO-34分子筛,并与传统的水热合成法和铜胺络合物引入铜源的方式进行对比,同时利用XRD、SEM、IR、TPD和微反等手段表征样品的结构和甲醇制烯烃(MTO)催化性能。结果表明:与常规合成方法相比,快速合成法可在10 h制备出结晶度在86.24%,固体收率达到94.65%的Cu-SAPO-34分子筛,其乙烯+丙烯选择之和达到81.26%;与添加铜胺络合物相比,加入含铜分子筛晶种的方式引入铜元素,更合适于快速合成法,避免了铜无法与分子筛骨架结合的问题;通过调整含铜分子筛晶种的性质及加入量,可以快速合成晶粒直径在470 nm的纳米Cu-SAPO-34分子筛,固体收率达到96.72%,乙烯+丙烯选择之和达到86.24%。

    Abstract

    Cu-SAPO-34 molecular sieves were rapidly synthesized with introduced copper zeolite seed as copper source for 10 h, which were compared with the traditional hydrothermal synthesis method and copper amine complex introduced copper source. Meanwhile, the structure and methanel to olefin (MTO) catalytic performance of the sample were characterized by XRD, SEM, IR, TPD and micro reaction. The results show that the Cu-SAPO-34 molecular sieve with a crystallinity of 86.24% and solid yield of 94.65% could be prepared by rapid synthesis method in 10 h, and the sum of ethylene and propylene selectivity reaches 81.26%. Compared with the addition of copper amine complex, the introduction of copper by adding copper seed is more suitable for rapid synthesis and avoids the problem that copper cannot combine with molecular sieve framework. Nanosized Cu-SAPO-34 molecular sieves with grain diameter of 470 nm could be rapidly synthesized by adjusting the properties and adding amount of Cu-SAPO-34 seed, in which the solid yield is 96.72%, and the ethylene and propylene selectivity is 86.24%.

  • SAPO-34具有适中的孔径、酸性和较高的水热稳定性,在膜、吸附剂和石油化学反应等领域都有着重要的应用,尤其是含金属的MeAPSO-34分子筛在甲醇转化制烯烃的反应过程中逐渐表现出更高的乙烯和丙烯选择性,特别是Cu-SAPO-34和Zn-SAPO-34。水热合成法是目前此类分子筛最常见的制备方法,常常需要2 d甚至更长的晶化时间来保证产品的结晶度和固体收率,致使生产成本较高。因此大量研究被用于SAPO-34分子筛的快速合成。通过提高晶化温度或使用昂贵模板剂可将晶化温度缩短至24 h[1-2]。Liu等[3]通过在凝胶中加入络合剂,如柠檬酸、酒石酸,乙二胺四乙酯等,可将晶化温度缩短至40~120 min,但需要使用昂贵的四乙基氢氧化铵为模板剂。Wu等[4]采用微波辅助合成的方法,仅晶化0.75 h就获得了20 nm的球状纯相SAPO-34分子筛,但此时酸中心数量较少,并且需要特殊的设备。含金属的MeAPSO-34分子筛的快速合成研究很少,主要原因是MeAPSO-34分子筛的快速合成不仅要促进硅磷铝原料的快速链接,也要保证金属离子快速进入分子筛骨架中。Xiao等[5]用四乙烯五胺(TEPA)先与Cu2+络合,得到Cu-TEPA络合物,从而将骨架外的铜物种直接引入CHA笼结构中。但Cu的引入也极大地影响了Si进入SSZ-13骨架,大量的初始Si物种仍然在溶液中,对SSZ-13的收率产生较大影响。Raquel等[6]仍以TEPA作为铜络合剂,同时使用小有机分子二乙胺作为共模板剂,发现Cu-SAPO-34分子筛固体收率超过90%。王家明等[7]也报道了TEPA可以明显促进铜物种进入Cu-SAPO-34骨架中,从而缩短分子筛的晶化时间。但这种方法的晶化时间仍超过24 h。笔者研究以三乙胺模板剂与柠檬酸络合物复配的方式缩短分子筛的晶化时间,通过添加含铜分子筛晶种的方式引入铜源,快速合成Cu-SAPO-34分子筛。

  • 1 试验

  • 1.1 试验试剂

  • 磷酸、三乙胺(TEA)、硅溶胶、四乙烯五胺、硝酸铜、柠檬酸,均为国药集团化学试剂有限公司分析纯试剂;拟薄水铝石,中国铝业股份有限公司;硅溶胶(SO2质量分数为30%),青岛微纳硅胶科技有限公司。

  • 1.2 合成方法

  • 1.2.1 晶种的合成方法

  • 将拟薄水铝石置于水中,搅拌10 min后缓慢滴入磷酸,待溶液成为均匀的胶状后,依次加入晶种、硅溶胶、铜胺溶液(硝酸铜与四乙烯五胺(TEPA)水溶液)和三乙胺模板剂(TEA)。所有物料加完后,搅拌4 h后将凝胶转移至晶化釜中,在110℃下预晶化4 h,升温至180℃晶化48 h,最后将固体产物离心洗涤干燥,得到Cu-SAPO-34。组成配比(质量分数)为Al2O3∶SiO2∶P2O5∶TEA∶H2O∶TEPA = 1.0∶0.4∶1.0∶2.5∶50∶0.2。根据合成晶种中的金属铜质量分数分别为0、3%、4%和5%,将晶种命名为Cu0、Cu3、Cu4和Cu5。

  • 1.2.2 常规方法合成Cu-SAPO-34分子筛

  • Cu-SAPO-34分子筛分2种方式引入铜,方法1是在凝胶中加入铜胺溶液的方法,方法2是凝胶中加入含铜的分子筛晶种。

  • 方法1:将拟薄水铝石置于水中,搅拌10 min后缓慢滴入磷酸,待溶液成为均匀的胶状后,依次加入不含铜分子筛晶种(Cu0)和铜胺溶液、硅溶胶和三乙胺模板剂(TEA)。所有物料加完后,搅拌4 h后将凝胶转移至晶化釜中,于180℃晶化10 h,将固体产物离心洗涤干燥,最终得到Cu-SAPO-34。组成配比(质量分数)为Al2O3∶SiO2∶P2O5∶TEA∶H2O∶TEPA = 1.0∶0.4∶1.0∶2.5∶50∶0.2。该分子筛命名为C-TEPA样品。

  • 方法2:制备步骤及配比与方法1的相同。但不加入铜胺溶液,而是加入含铜分子筛晶种(Cu3),晶化时间为180℃晶化10 h,该分子筛命名为C-Cu3样品。

  • 1.2.3 快速法合成Cu-SAPO-34分子筛

  • 方法1:将拟薄水铝石置于水中,搅拌10 min后缓慢滴入磷酸,待溶液成为均匀的胶状后,依次加入不含铜分子筛晶种(Cu0)、铜胺溶液、硅溶胶、三乙胺模板剂(TEA)和柠檬酸(CA)。所有物料加完后,搅拌4 h后将凝胶转移至晶化釜中,于180℃晶化10 h,将固体产物离心洗涤干燥,最终得到Cu-SAPO-34。组成配比(质量分数)为Al2O3∶SiO2∶P2O5∶TEA∶H2O∶TEPA = 1.0∶0.4∶1.0∶2.5∶50∶0.2。该分子筛命名为K-TEPA样品。

  • 方法2:制备步骤及配比与方法1的相同。但不加入铜胺溶液,而是加入含铜分子筛晶种(Cu3),该分子筛命名为K-Cu3样品。加入Cu4和Cu5晶种合成的样品分别为K-Cu4和K-Cu5。

  • 合成的2个系列的Cu-SAPO-34分子筛,具体差异如表1所示。

  • 表1 样品的合成条件及其理论铜负载量

  • Table1 Synthetic conditions of sample and its theoretical copper loading capacity

  • 注:(1)铜负载量都为理论值,数值为质量分数,等于原料投料时的w(Cu)/w(SiO2+P2O5+Al2O3+CuO);(2)固体收率根据原料投料的质量计算,等于w(产物)/w(SiO2+P2O5+Al2O3+CuO+晶种)。

  • 1.3 分析测试

  • 采用丹东浩源公司型号为DX-2700BH的X射线衍射仪分析合成的分子筛的晶相结构。采用S-4800型扫描电子显微镜表征分子筛催化剂的形貌特征和晶粒。采用荷兰PANalytical公司生产的X射线荧光光谱仪测定样品的铜含量。采用美国Quantachrome公司生产的Quadrasorb SI型多功能吸附仪上测量分子筛催化剂的比表面积和孔容。采用美国Bruker公司生产的Tensor 27型傅里叶变换红外光谱仪测量SAPO-34分子筛和MeAPSO-34分子筛的骨架振动情况和表面羟基振动等。采用日本Hitachi公司生产的U-4100型紫外可见分光光度计测定样品的紫外光谱,以硫酸钡(BaSO4)为参比标准,波数范围是200~800 nm。采用北京彼奥德电子技术有限公司生产的PCA-1200型全自动多功能吸附仪进行样品的NH3-TPD表征,以测量样品的酸性质。

  • 1.4 性能评价

  • 采用固定床反应器进行分子筛MTO(甲醇制烯烃)反应性能的评价。将焙烧后的分子筛压片,筛分出粒径为0.250~0.377 mm的颗粒,装于不锈钢反应器中,以纯甲醇(分析纯)为原料,空速为10 h-1,反应温度为450℃。气体由德国Bruker公司生产的450-GC型气相色谱仪分析。

  • 2 结果分析

  • 2.1 晶体结构和收率

  • 分别使用常规合成法和快速合成法制备Cu-SAPO-34分子筛,并考察金属引入方式对分子筛结晶度和收率的影响(表1和图1)。所有样品均在2θ=9.9、13.0、17.9、20.5和25°附近具有相关的衍射峰,证明合成的样品为Cu-SAPO-34分子筛。

  • 采用常规法时,两种铜源的引入方式明显影响分子筛的结晶度和收率。采用添加铜胺络合物引入铜源合成的C-TEPA样品结晶度为60.71%,以含铜的分子筛晶种为铜源合成的C-Cu3分子筛的结晶度为92.50%,二者的收率分别为62.06%和81.99%。说明含铜的分子筛晶种不仅具有替代铜胺络合物作为铜源的作用,还具有加快Cu-SAPO-34分子筛晶化速度作用。含铜和不含铜晶种的结晶度基本相同,说明Cu-SAPO-34分子筛结晶度和收率的差别不是由于晶种结晶度大小的影响引起的(图1(a))。与不含铜的晶种(Cu0)相比,含铜晶种(Cu3)颗粒尺寸更小(图2),更容易在合成凝胶中解聚,形成较小的晶核,减少了晶核形成时间,更有利于晶体快速生长。为此分子筛的结晶度较高,收率也有所增加[8]

  • 采用快速合成法时,两种引入铜的方式对分子筛结晶度和收率的影响规律与常规法合成规律类似。使用含铜分子筛晶种的方法引入铜源可以得到更高的分子筛结晶度和固体收率。但采用Cu-TEPA为铜源合成的样品,经离心洗涤后分为上下2层,上层为淡蓝色固体,而下层为紫色固体。通常铜的二价水合离子呈蓝色,铜单质呈紫色。经XRD分析,上层为Cu-SAPO-34分子筛,下层除了SAPO-34分子筛衍射峰外,在2θ=43.34和50.49°处都出现了明显的衍射峰,这2个峰是Cu单质的典型特征峰,说明样品中存在大量未结合到骨架的金属铜衍射峰。这是因为快速合成法[4]使用了柠檬酸作为络合剂,与铝离子等相互作用,形成[Al1-2P1-2O4-10]/[Si1-2Al2PO7-9][Cit]纳米团簇,生产了亚稳态的分子筛晶体,加快分子筛生长速度。但采用该方法合成Cu-SAPO-34时,柠檬酸与铜离子也会生成络合物,生成的铜物种游离于骨架外,形成金属铜;同时也使得柠檬酸无法与Al原子螯合,导致柠檬酸促进分子筛快速晶化的效果减弱,固体收率仅为48.62%。当使用含铜分子筛晶种作为铜源时,避免了柠檬酸与二价铜离子的络合,合成的样品中不含明显的铜的特征峰,固体收率达到94.65%,证明该方法可以在短时间内合成Cu-SAPO-34。此外,以含铜分子筛晶种为铜源时,对比常规合成法和快速合成方法,采用快速合成法合成样品的结晶度略低,为86.24%,收率较高,说明柠檬酸的加入会略微降低晶体的完整性,但会加快晶体的生长速度。

  • 通过增加分子筛晶种的铜含量,降低晶种的加入量,合成出样品铜含量相同的K-Cu4和K-Cu5分子筛。与K-Cu3相比,二者的结晶度略有降低,样品的固体收率略有增加。说明在此合成范围内,晶种的结晶度和晶粒尺寸等性质变化不大,晶种用量的变化对结晶度和收率的影响不大。

  • 表1荧光光谱分析仪测量显示,铜的实际负载量要比理论负载量要高,这可能是由于在制备过程中,铜原子几乎都进入到分子筛骨架中,而合成凝胶中可能仍有残留的Si、Al和P等原料没有完全消耗,从而导致铜的负载量普遍比理论计算值高。但快速合成法具有促进凝胶中硅铝相结合的作用,为此快速合成法制备样品的铜含量要低于常规方法合成的样品。

  • 图1 样品的XRD谱图

  • Fig.1 XRD patterns of samples

  • 图2 不同晶种的SEM图

  • Fig.2 SEM diagrams of seed crystals

  • 2.2 晶体形貌和孔结构分析

  • 图3为不同合成方法制备的Cu-SAPO-34分子筛的SEM图。可以看出,添加铜胺络合物作为铜源,采用常规方法合成的C-TEPA样品和快速合成法合成的K-TEPA样品的晶粒粒径约为2~3 μm,并含有较多未晶化完全的晶体,与XRD表征得到的相对结晶度较低相吻合。K-TEPA样品表面不如C-TEPA表面光滑,与K-TEPA样品结晶不完全,含有较多的金属铜有关。

  • 当以含铜分子筛晶种为铜源时,采用常规方法合成的C-Cu3样品和快速合成法合成的K-Cu3样品中都为大晶粒和小晶粒共存的状态。大晶粒粒径与C-TEPA和K-TEPA样品相似,为2~3 μm;小晶粒的晶粒粒径为100~500 nm,并且有许多堆叠码垛结构。Wang等[9]也发现了大、小晶粒共存的现象,当在Cu-SAPO-34合成体系中加入纯SAPO-34分子筛时,Cu-SAPO-34往往在SAPO-34分子筛的外表面生成更小的晶体。Zhang等[10]在使用磷酸预处理后的晶种合成SAPO-34时,发现有大量的微米级和纳米级共生晶体,也出现晶体码垛堆叠等情况。这可能与凝胶中的晶种含量有关,但晶种含量过多时,晶种无法解体成小微晶作为晶核,则会留存在合成体系中成为大颗粒。也有文献指出晶种的溶解程度不同,较大的颗粒会在釜底沉淀,形成较大晶粒的分子筛[11]

  • 图3 不同方法合成的Cu-SAPO-34分子筛的SEM图

  • Fig.3 SEM diagrams of Cu-SAPO-34 zeolite synthesized by different methods

  • 通过逐渐降低加入晶种的使用量合成K-Cu4和K-Cu5样品,其中大颗粒晶粒的数量逐渐减少。K-Cu5样品中晶粒相对均匀,晶粒粒径约470 nm。通常样品的晶粒较小,结晶度略低,这与表1数据显示样品的结晶度偏低规律相同。说明通过减少晶种用量,样品中晶粒更均匀,合成纳米级的晶粒。也说明晶种用量减少后更容易解聚成小的晶体碎片,并作为晶核中心,生长成新的晶体。与小晶粒晶种更容易促进分子筛生长规律类似。

  • 表2为不同方法合成的Cu-SAPO-34分子筛的比表面积和孔体积。无论是快速合成法还是常规合成法,与通过铜氨络合物的形式引入铜合成样品相比,含铜分子筛晶种形式引入铜合成的样品的总比表面积和介孔表面积都较大(K-Cu3> K-TEPA;C-Cu3>C-TEPA)。这是因为含铜分子筛晶种合成的样品的结晶度都较高,晶体碎片较少,不会堵塞分子筛孔口。此外分子筛含有一定量的小晶粒,晶粒越小,样品的比表面积越大,表明小晶粒分子筛具有较大比表面积[12]

  • 对比不同合成方法,相同的铜引入方式,快速合成法合成样品的比表面积大于常规方法合成的样品(K-Cu3>C-Cu3;K-TEPA>C-TEPA)。说明采用快速合成法合成时,柠檬酸与磷铝形成的络合物更容易促进碎片快速生长成较少缺陷的晶体。

  • 采用快速合成时,晶种的用量减少,小晶粒分子筛数量增多,比表面积增加(K-Cu5> K-Cu4> K-Cu3)。

  • 表2 Cu-SAPO-34分子筛的比表面积和孔体积

  • Table2 Specific surface area and pore volume of Cu-SAPO-34 zeolite

  • 2.3 骨架振动分析

  • 图4为4个Cu-SAPO-34分子筛样品和纯的SAPO-34分子筛对比的骨架振动红外谱图。可以看出,SAPO-34分子筛的骨架振动红外谱带分别位于635、700和110 cm-1处,1100 cm-1处的谱带可以归因于TO4四面体的不对称伸缩振动,635 cm-1处的谱带属于双六元环的振动,而700 cm-1处的T-O-T的伸缩振动[13-15]。对于4个Cu-SAPO-34分子筛样品来说,所有骨架振动谱带与纯SAPO-34分子筛的振动谱带都类似,但一些结构敏感的谱带的峰位发生轻微偏移。可以看出,与SAPO-34分子筛相对应的635和700 cm-1处的峰分别漂移至615和665 cm-1处,这主要是由于铜原子进入分子筛骨架引起的,而且峰的强度也有所变化,以含铜分子筛晶种的方式引入铜合成的样品在635和700 cm-1处的振动峰强度明显大于铜胺法制备的样品,表明含铜分子筛晶种的方式更有利于促进铜在骨架的结合。

  • 图4 SAPO-34分子筛骨架振动红外谱图

  • Fig.4 FT-IR spectra of SAPO-34 molecular sieve framework

  • 图5为4个Cu-SAPO-34分子筛的紫外可见DRS光谱图。所有样品在200~260 nm波长段都显示出宽带,这主要归因于骨架内或者骨架外的Al四面体中的Al-O电荷转移[16]。此外,在260~350 nm波长处可以观察到弱带,这一部分主要归因于金属四面体[17-19],表明金属在固体中的存在形式为MeO4,而不是金属氧化物的八面体构型,说明在4个样品中都有Cu进入了分子筛骨架。

  • 图5 Cu-SAPO-34分子筛的紫外可见DRS光谱图

  • Fig.5 UV-vis DRS spectra of Cu-SAPO-34 zeolite

  • 2.4 酸性分析

  • AlPO-34分子筛中的酸性主要来源于Si元素。Si主要通过两种方式进入分子筛骨架[20]。在晶化前期,Si与Al、P一起参与分子筛骨架的构建,此时Si配位结构多为Si(4Al)配位结构,而在晶化后期Si发生SMⅡ和SMⅢ取代机制,通过取代骨架中的Al原子和磷铝对,形成Si(nAl)(n= 0、1、2、3)多种配位结构。n越小,表明取代的Si越多,则需要补偿电荷的质子也越多,对应酸位点上的酸强度越强。当过渡金属被引入到SAPO-34分子筛骨架时,其会通过影响Si的配位状态来进一步影响MeAPSO-34分子筛的酸性质[21-23]

  • 如图6和表3所示,采用快速合成法与常规合成方法制备的K-Cu3和C-Cu3总酸量分别为0.82和0.81 mmol/g,相差不大,但快速合成法制备的K-Cu3的弱酸量较小,为0.13 mmol/g,弱酸的峰温却偏高,说明采用快速合成法合成的样品更有利于提高中强酸和强酸量,提高酸强度。低温199℃附近的脱附峰是因分子筛表面缺陷位点的羟基集团引起,如 POH,SiOH 和 AlOH 等,在甲醇转化过程起到了将甲醇转化为二甲醚的作用,对二甲醚转化成烯烃的作用微弱[24-25];高温364℃附近的脱附峰是因桥羟基(—SiOHAl—)上吸附的 NH3 分子脱附引起,是甲醇转化过程中的主要活性位点[26]。合成方法造成的铜含量的差别对分子筛的酸性影响不大。

  • 对比铜的引入方式发现,C-TEPA 的酸性为0.69 mmol/g,明显小于C-Cu3的酸性,说明通过使用含铜分子筛晶种引入铜的方法合成样品具有更强的酸性,这种适当高的酸量有利于分子筛保持高的甲醇转化率。这与分子筛相应的结晶度的规律相同,说明分子筛晶化更完全,分子筛的酸性越大。

  • 随着加入晶种量的减少,制备的K-Cu4和K-Cu5总酸性变化不成规律。强酸酸量变化不大,但峰温却向高温偏移,说明酸性略有增强。此外,弱酸量有所增加,说明分子筛的缺陷结构增多,这与分子筛的结晶度略有降低,以及晶粒变小的规律相符。

  • 图6 不同合成方法制备的Cu-SAPO-34分子筛NH3-TPD表征

  • Fig.6 Characterization of Cu-SAPO-34 zeolite NH3-TPD prepared by different synthesis methods

  • 表3 不同样品酸位分布及其酸量

  • Table3 Acid distribution and acid content of different samples

  • 2.5 甲醇转化性能

  • 表4为不同条件合成的Cu-SAPO-34分子筛的MTO转化性能。可以看出,分子筛中的铜无论以铜胺络合物的形式引入还是以含铜分子筛晶种的形式引入,快速合成法合成的样品的转化率和烯烃收率都大于常规方法合成的样品(K-TEPA>C-TEPA;K-Cu3>C-Cu3),说明快速合成法更有利于提高烯烃选择性。从表3的酸性数据看出快速合成法制备样品具有更强的酸性,更容易促进甲醇转化。并且快速合成法合成的样品的丙烯收率要大于常规合成法,这是因为快速合成法合成样品晶粒的碎片较少,样品的比表面积较大,孔容发达,有利于烯烃的生成和脱附。

  • 对比铜的引入形式可以看出,以铜胺络合物的方式引入铜元素制备的样品(C-TEPA和K-TEPA)结晶度较低,总酸量较少,可供甲醇转化的酸性位数量不足,所以甲醇转化率较低,在反应进行20 min后,甲醇转化率分别为79.31%和80.35%,失活速度快。而以含铜分子筛晶种的形式引入铜合成的样品,特别是快速法制备的样品 K-Cu3甲醇转化率在20 min后仍超过95%,并且乙烯和丙烯的选择性之和也比其他样品高(K-Cu3>K-TEPA; C-Cu3>C-TEPA)。尽管K-Cu3与K-TEPA反应结果相差不大,但K-TEPA样品不均匀,样品存在分层现象,固体收率低,从放大实用性角度考虑,不太适合采用该方法合成样品。说明无论哪种合成方法,以含铜分子筛晶种的形式引入铜元素更有利于提高甲醇转化率和烯烃选择性。

  • 随着晶种加入量减少, K-Cu3、K-Cu4和K-Cu5的酸性变化不大,但弱酸比例增加。在酸性足够的情况下,弱酸量增加,可以避免氢转移反应,有利于增加烯烃选择性[27-28]。此外,分子筛的晶粒变得更小,由微米和纳米的混合晶粒形态,变为粒径均匀的纳米晶粒。与具有微粒尺寸晶体的常规SAPO-34相比,粒径小于500 nm的SAPO-34催化剂具有最佳的催化性能[29-30]。这种纳米尺寸的分子筛(K-Cu5)更有利于烯烃快速从分子筛空腔扩散出孔道,避免二次反应的发生,从而乙烯+丙烯选择性最高,达到86.24%。Zn-SAPO-34分子筛在475℃下,乙烯+丙烯选择性通常能达到81%[31]。Zn或Cu改性的SAPO-34分子筛乙烯+丙烯选择性也约为75%[32]。说明本方法制备的Cu-SAPO-34具有较高的乙烯和丙烯选择性。

  • 表4 不同方法合成的Cu-SAPO-34分子筛的 MTO转化性能

  • Table4 MTO catalytic performance of Cu-SAPO-34 zeolites prepared by different synthesis methods

  • 3 结论

  • (1)与铜胺络合物法引入铜元素(C-TEPA)相比,使用含铜分子筛晶种的方式引入铜源(C-Cu3)更有利于提高分子筛的结晶度和固体收率,乙烯+丙烯选择性之和达到79.36%。

  • (2)与常规方法合成的样品相比,快速合成法制备的K-Cu3分子筛结晶度较高,固体收率高于常规法合成的样品,达到94.08%。其甲醇转化率和烯烃收率高于常规方法合成的样品C-Cu3,乙烯+丙烯选择性之和达到81.26%。

  • (3)降低晶种的加入量,合成晶粒更均匀的小晶粒样品K-Cu5的乙烯和丙烯选择性分别为51.09%和35.15%,乙烯+丙烯选择性之和为86.24%。

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    • [29] WANG Q,WANG X,LIU Y,et al.Controlled synthesis of hierarchically porous SAPO-34 zeolites with tailored crystal size and morphology[J].Chemical Physics Letters,2022,794:139513-139519.

    • [30] LIU H Y,KIANFAR E.Investigation the synthesis of nano-SAPO-34 catalyst prepared by different templates for MTO process[J].Catalysis Letters,2021,151(3):787-802.

    • [31] ZHONG J,HAN J,WEI Y,et al.Increasing the selectivity to ethylene in the MTO reaction by enhancing diffusion limitation in the shell layer of SAPO-34 catalyst[J].ChemComm,2018,54:3146-3150.

    • [32] HUANG H,YU M,ZHANG Q,et al.Insights into NH4-SAPO-34 preparation procedure:effect of the number of ammonium exchange times on catalytic performance of Zn-modified SAPO-34 zeolite for methanol to olefin reaction[J].Microporous and Mesoporous Materials,2020,295:109971-109977.

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