双模板剂法SAPO-34分子筛的合成及其MTO催化性能调变
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摘要
以四乙基氢氧化铵(TEAOH)和二乙铵(DEA)为混合模板剂,在低投料硅铝比[n (SiO_2)∶n (Al_2O_3)=0.2]及低模板剂用量[n (模板剂)∶n (Al_2O_3)=1.9]下,考察了两种模板剂比例的调变对合成的SAPO-34分子筛物化性能及其催化甲醇制烯烃反应(MTO)催化性能的影响。研究发现,通过改变两种模板剂比例,可以明显调变SAPO-34分子筛晶粒尺寸、硅分布(晶粒表面和体相的硅分布)、硅原子的配位环境,从而影响其MTO催化反应的效果。在低模板剂用量制备的SAPO-34产品中,晶粒尺寸是影响其催化寿命的最主要因素,小晶粒分子筛因其扩散路径短有利于延长催化寿命。此外,硅分布也是影响催化寿命的因素之一,表面富硅的分子筛导致外表面积炭程度大于晶内积炭,积炭趋势由外向内发展,加速分子筛"假性"失活。硅分布还影响MTO反应产物分布,表面富硅分子筛外表面更易发生非择形催化,显著提高C_4～C_6等产物的选择性,不利于目标产物双烯(乙烯+丙烯)选择性的提高。
SAPO-34 molecular sieve was synthesized by using a dual-template(TEAOH and DEA),under the conditions of low silica content [n(SiO_2)∶n(Al_2O_3)=0.2] and low template content[n(template) : n(Al_2O_3)=1.9] in the starting gel. The effect of TEAOH/DEA ratio on the physicochemical properties of SAPO-34 molecular sieve and its catalytic performance in the methanol to olefin(MTO) reaction were investigated. It has been found that the ratio of TEAOH and DEA have significant effect on the crystal size, Si distribution and coordination environment of framework Si. The crystal size and Si distribution are the major factors to determine the catalytic lifetime of MTO. Due to its short diffusion pathway, small crystals prolong the catalytic lifetime, while SAPO-34 with Si-rich surface leads to more carbon deposition on the surface than interior, which causes the"fictitious"deactivation of molecular sieves. Si distribution also determines the product profiles of MTO reaction, for example, the crystals with Si-rich surface would favor the non-shape selectivity catalysis, leading to more C_4～C_6 hydrocarbon products and thus suppressing the selectivity of ethylene + propylene.
SAPO-34 molecular sieve was synthesized by using a dual-template(TEAOH and DEA),under the conditions of low silica content [n(SiO_2)∶n(Al_2O_3)=0.2] and low template content[n(template) : n(Al_2O_3)=1.9] in the starting gel. The effect of TEAOH/DEA ratio on the physicochemical properties of SAPO-34 molecular sieve and its catalytic performance in the methanol to olefin(MTO) reaction were investigated. It has been found that the ratio of TEAOH and DEA have significant effect on the crystal size, Si distribution and coordination environment of framework Si. The crystal size and Si distribution are the major factors to determine the catalytic lifetime of MTO. Due to its short diffusion pathway, small crystals prolong the catalytic lifetime, while SAPO-34 with Si-rich surface leads to more carbon deposition on the surface than interior, which causes the"fictitious"deactivation of molecular sieves. Si distribution also determines the product profiles of MTO reaction, for example, the crystals with Si-rich surface would favor the non-shape selectivity catalysis, leading to more C_4～C_6 hydrocarbon products and thus suppressing the selectivity of ethylene + propylene.
引文
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[20]何长青,刘中民,杨立新,等.模板剂对SAPO-34分子筛晶粒尺寸和性能的影响[J].催化学报,1995,16(1):33-37.HE Changqing,LIU Zhongmin,YANG Lixin,et al.Effect of template on crystallite size and properties of SAPO-34 molecular sieve[J].Chinese Journal of Catalysis,1995,16(1):33-37.
[21]QIN Z X,SHEN B J,YU Z W,et al.A defect-based strategy for the preparation of mesoporous zeolite Y for high-performance catalytic cracking[J].Journal of Catalysis,2013,298(2):102-111.
[22]SCHUNK S A,DEMUTH D G,SCHULZ-DOBRICK B,et al.Element distribution and growth mechanism of large SAPO-5 crystals[J].Microporous Materials,1996,6(5/6):273-285.
[23]SINHA A K,SEELAN S.Characterization of SAPO-11 and SAPO-31synthesized from aqueous and non-aqueous media[J].Applied Catalysis A:General,2004,270(1):245-252.
[24]TIAN P,LI B,XU S,et al.Investigation of the crystallization process of SAPO-35 and Si distribution in the crystals[J].Journal of Physical Chemistry C,2013,117(8):4048-4056.
[25]AKOLEKAR D,BHARGAVA S,GORMAN J,et al.Formation of small pore SAPO-44 type molecular sieve[J].Colloids&Surfaces A:Physicochemical&Engineering Aspects,1999,146(1/2/3):375-386.
[26]YANG M,TIAN P,WANG C,et al.A top-down approach to prepare silicoaluminophosphate molecular sieve nanocrystals with improved catalytic activity[J].Chemical Communications,2014,50(15):1845-1847.
[27]TAN J,LIU Z,BAO X,et al.Crystallization and Si incorporation mechanisms of SAPO-34[J].Microporous and Mesoporous Materials,2002,53(1-3):97-108.
[28]LEE K,LEE S,JUN Y,et al.Cooperative effects of zeolite mesoporosity and defect sites on the amount and location of coke formation and its consequence in deactivation[J].Journal of Catalysis,2017,347:222-230.
[29]ZHENG J,DING J,JIN D,et al.The tailored synthesis of nanosized SAPO-34 via time-controlled silicon release enabled by an organosilane precursor[J].Chemical Communications,2017,53(45):6132-6135.
[30]ASKARI S,HALLADJ R,SOHRABI M.Methanol conversion to light olefins over sonochemically prepared SAPO-34 nanocatalyst[J].Microporous and Mesoporous Materials,2012,163(163):334-342.
[31]KONG C,ZHU J,LIU S,et al.SAPO-34 with a low acidity outer layer by epitaxial growth and its improved MTO performance[J].RSCAdvances,2017,7(63):39889-39898.
[2]WANG P,YANG D,HU J,et al.Synthesis of SAPO-34 with small and tunable crystallite size by two-step hydrothermal crystallization and its catalytic performance for MTO reaction[J].Catalysis Today,2013,212(2):62.e1-62.e8.
[3]AGHAEI E,HAGHIGHI M.Effect of crystallization time on properties and catalytic performance of nanostructured SAPO-34 molecular sieve synthesized at high temperatures for conversion of methanol to light olefins[J].Powder Technology,2015,269:358-370.
[4]CAI D,MA Y,HOU Y,et al.Establishing discrete ising model for zeolite deactivation:inspiration from the game of Go[J].Catalysis Science&Technology,2017,7(12):2375-2640.
[5]WANG C,YANG M,ZHANG W,et al.Organophosphorous surfactantassistant synthesis of SAPO-34 molecular sieve with special morphology and improved MTO performance[J].RSC Advances,2016,6(53):47864-47872.
[6]SUN Q,WANG N,GUO G,et al.Ultrafast synthesis of nano-sized zeolite SAPO-34 with excellent MTO catalytic performance[J].Chemical Communications,2015,51(91):16397-16400.
[7]赵飞,李渊,张岩,等.对比SSZ-13和SAPO-34分子筛在甲醇制烯烃中的研究进展[J].化工进展,2017,36(1):166-173.ZHAO Fei,LI Yuan,ZHANG Yan,et al.Research progress of SSZ-13and SAPO-34 zeolites for methanol to olefins[J].Chemical Industry and Engineering Progress,2017,36(1):166-173.
[8]DAI W,CAO G,YANG L,et al.Insights into the catalytic cycle and activity of methanol-to-olefin conversion over low-silica AlPO-34zeolites with controllable Br?nsted acid density[J].Catalysis Science&Technology,2017,7(3):607-618.
[9]ZHONG J,HAN J,WEI Y,et al.Recent advances of the nanohierarchical SAPO-34 in the methanol-to-olefin(MTO)reaction and other applications[J].Catalysis Science&Technology,2017,7(21):4905-4923.
[10]VOMSCHEID R,BRIEND M,PELTRE M J,et al.The role of the template in directing the Si distribution in SAPO zeolites[J].Journal of Physical Chemistry,1994,98(38):9614-9618.
[11]LI Z,MARTINES-TRIGUERO J,YU J,et al.Conversion of methanol to olefins:stabilization of nanosized SAPO-34 by hydrothermal treatment[J].Journal of Catalysis,2015,329:379-388.
[12]刘广宇,田鹏,刘中民.二乙胺导向合成SAPO-34及与其它模板剂的对比[J].催化学报,2012,33(1):174-182.LIU Guangyu,TIAN Peng,LIU Zhongmin.Synthesis of SAPO-34molecular sieves templated with diethylamine and comparison with other templates[J].Chinese Journal of Catalysis,2012,33(1):174-182.
[13]CHAE H,PARK I,SONG Y,et al.Physicochemical characteristics of SAPO-34 molecular sieves synthesized with mixed templates as MTOcatalysts[J].Journal of Nanoscience&Nanotechnology,2010,10(1):195-202.
[14]YE L,CAO F,YING W,et al.Methanol conversion on SAPO-34catalysts synthesized by tri-templates[J].MRS Online Proceedings Library Archive,2010,1279.
[15]LEE Y,BAEK K,JUN K.Methanol conversion on SAPO-34 catalysts prepared by mixed template method[J].Applied Catalysis A:General,2007,329(10):130-136.
[16]WANG P,LV A,HU J,et al.The synthesis of SAPO-34 with mixed template and its catalytic performance for methanol to olefins reaction[J].Microporous&Mesoporous Materials,2012,152(4):178-184.
[17]MASOUMI S,TOWFIGHI J,MOHAMADALIZADEH A,et al.Tritemplates synthesis of SAPO-34 and its performance in MTO reaction by statistical design of experiments[J].Applied Catalysis A:General,2015,493:103-111.
[18]代跃利,王磊,刘德阳.用于催化甲醇制烯烃的SAPO-34分子筛合成的研究进展[J].化工进展,2015,34(3):731-737.DAI Yueli,WANG Lei,LIU Deyang.Progress in the synthesis of SAPO-34 molecular sieve for the conversion of methanol to olefins[J].Chemical Industry and Engineering Progress,2015,34(3):731-737.
[19]CHAN W,MIAO Y,PENG T,et al.Dual template-directed synthesis of SAPO-34 nanosheet assemblies with improved stability in the methanol to olefins reaction[J].Journal of Materials Chemistry A,2015,3(10):5608-5616.
[20]何长青,刘中民,杨立新,等.模板剂对SAPO-34分子筛晶粒尺寸和性能的影响[J].催化学报,1995,16(1):33-37.HE Changqing,LIU Zhongmin,YANG Lixin,et al.Effect of template on crystallite size and properties of SAPO-34 molecular sieve[J].Chinese Journal of Catalysis,1995,16(1):33-37.
[21]QIN Z X,SHEN B J,YU Z W,et al.A defect-based strategy for the preparation of mesoporous zeolite Y for high-performance catalytic cracking[J].Journal of Catalysis,2013,298(2):102-111.
[22]SCHUNK S A,DEMUTH D G,SCHULZ-DOBRICK B,et al.Element distribution and growth mechanism of large SAPO-5 crystals[J].Microporous Materials,1996,6(5/6):273-285.
[23]SINHA A K,SEELAN S.Characterization of SAPO-11 and SAPO-31synthesized from aqueous and non-aqueous media[J].Applied Catalysis A:General,2004,270(1):245-252.
[24]TIAN P,LI B,XU S,et al.Investigation of the crystallization process of SAPO-35 and Si distribution in the crystals[J].Journal of Physical Chemistry C,2013,117(8):4048-4056.
[25]AKOLEKAR D,BHARGAVA S,GORMAN J,et al.Formation of small pore SAPO-44 type molecular sieve[J].Colloids&Surfaces A:Physicochemical&Engineering Aspects,1999,146(1/2/3):375-386.
[26]YANG M,TIAN P,WANG C,et al.A top-down approach to prepare silicoaluminophosphate molecular sieve nanocrystals with improved catalytic activity[J].Chemical Communications,2014,50(15):1845-1847.
[27]TAN J,LIU Z,BAO X,et al.Crystallization and Si incorporation mechanisms of SAPO-34[J].Microporous and Mesoporous Materials,2002,53(1-3):97-108.
[28]LEE K,LEE S,JUN Y,et al.Cooperative effects of zeolite mesoporosity and defect sites on the amount and location of coke formation and its consequence in deactivation[J].Journal of Catalysis,2017,347:222-230.
[29]ZHENG J,DING J,JIN D,et al.The tailored synthesis of nanosized SAPO-34 via time-controlled silicon release enabled by an organosilane precursor[J].Chemical Communications,2017,53(45):6132-6135.
[30]ASKARI S,HALLADJ R,SOHRABI M.Methanol conversion to light olefins over sonochemically prepared SAPO-34 nanocatalyst[J].Microporous and Mesoporous Materials,2012,163(163):334-342.
[31]KONG C,ZHU J,LIU S,et al.SAPO-34 with a low acidity outer layer by epitaxial growth and its improved MTO performance[J].RSCAdvances,2017,7(63):39889-39898.