Study On Organic Hybridization Of Extra-Large-Pore SAPO-CLO Molecular Sieve And Their Catalytic Performance On Propene Oligomerization

Extra-large-pore molecular sieves have received great attention because of its potential advantages in catalysis,adsorption and separation of bulky molecules.At present,this type of molecular sieve has the problems of high synthetic cost and poor water-resistance stability.In this thesis,a new extra-large-pore silicoaluminophosphate SAPO-CLO molecular sieve was modified with organic hybridization using in situ grafting method.The influence of the modification on their physicochemical properties was systematically studied by the combination of multiple characterization techniques,and their catalytic performance was comparatively evaluated using propene oligomerization as a model reaction.SAPO-CLO molecular sieves with different silicon contents were synthesized by ionothermal method.Combining multiple characterization methods,it was proved that silicon has been successfully substituted in the molecular sieve framework,giving rise to relatively strong Br(?)nsted acid sites.With the increase of silicon content,the catalytic activity of SAPO-CLO in propene oligomerization was significantly improved.The reaction products were mainly propene dimer C6 olefins with selectivity>30%.Compared with 8-ring SAPO-LTA with comparable activity,SAPO-CLO was more likely to produce bulkier olefins.The deactivated SAPO-CLO could be perferctly recovered by high-temperature calcination,demonstrating its high structural stabitity during these processes.Methylphosphonic acid and phenylphosphonic acid were used as phosphorus sources to synthesize methyl and phenyl hybrid AlPO-CLO respectively;methyltrimethoxysilane and phenyltrimethoxysilane were used as silicon sources to synthesize SAPO-CLO molecular sieve with methyl hybridization and phenyl hybridization,respectvely.It was found that the introduction of a small amount of organic phosphorus and siliconehad little influence on the crystallization of the-CLO structure,and the water-resistance stabilityof the methyl hybrid SAPO-CLO after removing the template agent was significantly improved.The catalytic activity of SAPO-CLO after hybridization with organic silicon was lower than that of non-hybridized SAPO-CLO but higer than aluminophosphate molecular sieve A1PO-CLO,and the catalytic activity of methyl hybrid SAPO-CLO was higher than that of phenyl hybrid SAPO-CLO.These results indicate that organic silicon was more difficult to substituted into the framework than inorganic silicon,and small-size organic silicon was relatively easier to incorporated in the framework.Compared with the organic silicon hybridization,the organic phosphine hybridization resulted in higher catalytic activity,which indicates that the organic phosphine hybridization was beneficial for silicon substitution into the framework.After organic hybridization,there was no obvious change of the product selectivity.