SAPO-18/SAPO-34共晶分子筛的合成及表征

以三乙胺(TEA)和N,N-二异丙基乙胺(DIEA)为双模板剂经恒温水热晶化法合成了SAPO-18(AEI结构)与SAPO-34(CHA结构)两相共生的SAPO分子筛.考察了DIEA用量、硅铝比及晶化时间等因素的影响,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)和氨气程序升温脱附(NH3-TPD)等手段对所得样品的晶相、形貌和酸性进行了表征.结果表明,当n(DIEA)/n(Al_2O_3)=0.2,n(Si O_2)/n(Al_2O_3)=0.6,晶化时间为4 d时,得到形貌规整,结晶度高且AEI/CHA结构比为74∶26的共生相SAPO分子筛.随着晶化时间的延长,SAPO-18在AEI/CHA共生相中所占比例逐渐上升,表明SAPO-5,SAPO-34和SAPO-18三者中SAPO-18的热力学稳定性最高.二甲醚制烯烃(DTO)催化性能测试结果表明,AEI/CHA共晶结构比为74/26的共生相分子筛具有较高的催化活性和双烯(C_2~=+C_3~=)选择性(84.29%),同时积碳生成速率较慢.

Synthesis and Characterization of Intergrowth Structured SAPO-18/SAPO-34?

SAPO-18(AEI structure) and SAPO-34(CHA structure) intergrowth structured silicoaluminophos-phate molecular sieves were synthesized hydrothermally with trimethylamine(TEA) and N,N-diisopropylethyl-amine(DIEA) as double templates. Influencing factors, such as DIEA content, SiO2 / Al2 O3 molar ratio and crystallization time were investigated in detail. The crystalline phase, morphology and acidic property of the products were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and tempera-ture-programmed desorption of ammonia(NH3-TPD), respectively. The results showed that well crystallized, morphology uniformed AEI/ CHA intergrowth structured silicoaluminophosphate molecular sieves with AEI/CHA= 74 / 26 could be synthesized under the following synthesis conditions: n ( DIEA) / n ( AEI) = 0. 2, n(SiO2 ) / n(Al2 O3 )= 0. 6 and the crystallization time 96 h. The extending of crystallization time resulted in the disappearance of SAPO-5 and the gradual increase of AEI/ CHA proportion. It is therefore concluded that the thermodynamic stability of SAPO-5, SAPO-34, SAPO-18 increased in this order. Dimethylether-to-olefins (DTO) reaction was chosen to test the catalytic performance of the prepared catalysts. The prepared catalyst using TEA-DIEA as double templates exhibited excellent catalytic performance in DTO ( dimethyl ether to olefins) process. The conversion of dimethylether and selectivity of ethylene and propylene are up to 100%and 84. 29% , respectively.