高酸位多级孔超稳Y型沸石的制备及催化性能

Synthesis and Catalytic Performance of Hierarchical Ultrastable Y-Type Zeolite with Ubstantially Increasing Acid Sites

以表面活性剂十六烷基三甲基溴化铵(CTABr)为模板剂,在水热体系对水蒸气处理后的超稳Y型(USY)沸石进行晶化处理,获得高酸量和高水热稳定性的USY‑c‑w样品。利用X射线衍射、扫描电子显微镜、透射电子显微镜、固态核磁共振、N_(2)吸附-脱附、NH_(3)‑程序升温脱附、傅里叶变换红外光谱及吡啶红外对所制备催化剂的物化性质进行详细表征。选用1,3,5‑三异丙苯(TIPB)催化裂化作为探针反应,研究制备的催化剂的催化性能,并与工业USY沸石进行对比。结果表明,再次水热晶化后,样品的硅铝骨架局部重构,非骨架铝重新进入沸石骨架,合成样品的硅铝比(n_(Si)/n_(Al))由10降至3.0;再晶化后的USY沸石,不仅具有丰富的介孔结构,并且具有更多的弱酸和中强酸位点。在TIPB裂解反应中,再晶化后的USY沸石表现出比原样品更优异的催化性能。

Ultrastable Y‑type(USY)zeolite catalysts with high acid content and high hydrothermal stability(USY‑c‑w)were obtained by crystallizing an industrial USY‑zeolite in a traditional hydrothermal system with the help of a surfactant cetyltrimethylammonium bromide(CTABr).The physicochemical properties of as‑synthesized USY‑zeolite samples were analyzed by X‑ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),solid‑state NMR,N_(2) adsorption‑desorption,ammonia temperature programmed desorption(NH_(3)‑TPD),FT‑IR,and pyridine infrared spectroscopy(Py‑IR).Catalytic cracking of 1,3,5‑triisopropylbenzene(TIPB)was selected as a probe reaction to investigate the catalytic performance of as‑synthesized catalysts and compare it with that of the industrial USY‑zeolite.The results exhibited that after hydrothermal re‑crystallization,the framework of USY‑zeolite suffered from a partial reformation.Desilicication by steam or alkali treatment results in the formation of a large number of silanol nests,which reacts with Al species resulting from the non‑framework aluminum in the USY‑zeolite and then promotes the formation of the“new”framework Al.This offers as‑synthesized sample with a less Si/Al ratio(n_(Si)/n_(Al))and with increasing acid sites.The increased Al content in the zeolite framework was confirmed by the results of XRD,FT‑IR,X‑ray energy dispersive spectrum(EDS),and NMR.For example,the framework Si/Al ratio decreased from 10(industrial USY‑zeolite)to 3.0(USY‑045‑07C).The NH_(3)‑TPD experiment and Py‑IR provided direct evidence supporting the increased acidity in as‑synthesized catalysts.Moreover,the results obtained by the N_(2) adsorption‑desorption experiment,SEM,and TEM also showed that abundant mesopores were also introduced into as‑synthesized samples with more weak acid sites along with more medium‑strong acid ones.During the catalytic cracking of TIPB,as‑synthesized USY‑c‑w showed more excellent catalytic performance with higher conversion of TIPB than the reference sample.