【作者】 戴卫理；

【导师】 关乃佳；

【作者基本信息】 南开大学 ， 材料物理与化学， 2012， 博士

【摘要】 甲醇替代石油制烯烃（MTO）的可持续路线，近些年引起了人们的研究兴趣。本文利用水热的方法合成了一系列具有不同孔道结构的硅铝磷酸盐（SAPO）分子筛和磷酸盐（AlPO）分子筛，在固定床的条件下考察了其在MTO反应中的催化活性，并结合多种表征手段对影响MTO反应的因素以及反应的机理进行深入的研究。在相同反应条件下首先对具有不同孔道结构和B酸含量的SAPO类分子筛进行MTO活性评价，并结合¹H MAS NMR，in-situ UV/Vis, GC-MS以及TGA等手段对催化剂的B酸含量及孔道结构对MTO反应的影响进行详细分析。结果表明，具有一维十元环孔道和中等B酸含量的SAPO-41分子筛具有良好的MTO催化活性和较长的寿命。首次利用NH3吸附以及¹H高速魔角旋转固体核磁（¹H MAS NMR）对SAPO-34分子筛在MTO反应过程中B酸及苯基碳正离子的变化过程进行定量表征。结果表明样品上的B酸在MTO反应过程中是逐渐被消耗或覆盖的，而苯基碳正离子则先生成后逐渐被消耗。此外，结合MTO的活性数据可知，B酸的完全消耗并不是催化剂失活的直接原因，而苯基碳正离子的完全消耗可能与催化剂的失活有直接的联系。通过焙烧温度的控制，对三维十二元环孔道结构的SAPO-46分子筛上模板剂不完全焙烧造成的有机杂质对MTO催化活性的影响进行了详细的分析。研究表明低温焙烧的SAPO-46样品具有良好的初活性。GC-MS的结果表明低温下模板剂不完全焙烧形成的甲苯有机杂质在反应初期起到活性“烃池”物种的作用，甲醇与该物种按照“烃池”机理的方式断裂生成低碳烯烃。首次合成具有不同孔道结构和微量B酸的AlPO类分子筛，并将其用到MTO反应中进一步探索B酸对MTO反应的影响。利用in situ FTIR，is situ UV/Vis，¹H MAS NMR，¹³C MAS NMR以及TGA等手段对特定的AlPO分子筛上B酸变化过程以及有机物种的形成和消耗过程进行深入的研究，首次发现微量的B酸足以引发MTO反应，适宜的孔道结构与微量的B酸可以获得优异的MTO性能。首次利用¹H脉冲梯度场固体核磁（¹H PFG NMR）手段对乙烯和乙烷探针分子在不同MTO反应时间后的SAPO-34样品上的扩散情况进行研究。并结合in situ UV/Vis，¹³C MAS NMR以及¹H MAS NMR等手段讨论MTO反应过程中有机物种和B酸的变化过程。然后综合以上多种表征结果对MTO反应过程中SAPO-34催化剂失活的原因进行详细分析。结果表明，MTO反应过程中积碳的形成对SAPO-34分子筛孔道的扩散性能有一定的影响，但催化剂失活并不是由积碳导致的孔道完全堵塞造成的，进一步证实积碳造成的B酸和苯基碳正离子活性位的完全覆盖则可能是其失活的直接原因。更多还原

【Abstract】 As an oil-free process to obtain olefins, the conversion of methanol to olefins（MTO） on microporous solid acids has attracted significant attentions. In the presentstudy, several types of silicoaluminophosphates （SAPO） and aluminophosphates（AlPO） with different framework structure were synthesized via hydrothermalmethods and applied as MTO catalysts in fixed-bed reactor. The mechanism of MTOreaction and the factors influencing MTO conversion were investigated by means of aseries of characterization techniques.The catalytic performances of SAPO-type samples with different amounts ofBr nsted acid sites and different framework structure were studied under the sameconditions. The effects of Br nsted acid sites and framework structure on MTOconversion were studied by¹H MAS NMR, in-situ UV/Vis, GC-MS and TGAanalysis. The results indicated for the first time that SAPO-41with one-dimensional10-ring pores and a significant concentration of Br nsted acid sites could be goodcatalyst for MTO, or more generalized MTH, reaction.The accessible Br nsted acid sites and benzene-based carbenium ions on workingSAPO-34catalysts after different MTO reaction time were measured via a novelmethod consisting of ammonia adsorption and quantitative¹H high speed MAS NMRspectroscopy for the first time. The results indicated that the accessible Br nsted acidsites were gradually consumed during the MTO process, but the benzene-basedcarbenium ions were firstly formed and then gradually consumed. The totalconsumption/coverage of benzene-based carbenium ions, instead of the totalconsumption/coverage of Br nsted acid sites, is the direct reason for catalystdeactivation.The effects of organic impurities originated from the incomplete combustion oforganic template on MTO reaction were studied over SAPO-46withthree-dimensional12-ring pore structures. SAPO-46samples calcined at lowertemperatures exhibited good initial MTO activity. GC-MS results indicated the tolueneoriginated from the incomplete combustion of organic template may be the primaryhydrocarbon pool or the precursor for the formation of primary hydrocarbon pool thatinduces the initial MTO reaction. Under MTO reaction conditions, residual toluene inSAPO-46can be transformed to polymethylbenzenes and alkylnaphthalenes, i.e. thewell-known active hydrocarbon pool species for MTO process. In order to study the effects of trace amounts of Br nsted acid sites on MTOconversion. Several AlPO-type molecular sieves with different framework structureand trace amounts of Br nsted acid sites were synthesized and studied as possibleMTO catalysts. The changes of Br nsted acid sites and organic species during MTOconversion were studied by in situ FTIR, is situ UV/Vis,¹H MAS NMR,¹³C MASNMR and TGA analysis. Based on the results, it is revealed that trace amounts ofBr nsted acid sites are enough to realize MTO reaction. Moreover, good MTOperformances can be obtained on catalysts with trace amounts of Br nsted acid sitesand suitable framework structure.SAPO-34obtained after MTO conversion times of0to30min were investigatedby¹H PFG NMR spectroscopy for studying the self-diffusivities of ethane and ethene.The MTO reaction over SAPO-34were investigated by in situ UV/vis,¹³C MASNMR, and¹H MAS NMR spectroscopy giving insights into the organic deposits andacid sites in different periods of the catalyst lifetime. The results indicated that theorganic deposits can lead a growing hindrance of molecular diffusion in the pores ofSAPO-34. However, the deactivation of SAPO-34was not caused by the block ofpore, but should be due to the cover of benzene-based carbenium ions by coke.更多还原