摘要
ZSM-5/Y是一种通过原位合成方法制备的新型复合分子筛材料,用XRD、IR光谱、N2吸附/脱附等手段,研究了水热处理对ZSM-5/Y物化性质的影响,并以正己烷为原料考察了样品的催化裂化性能.结果表明,与机械混合样品相比,在550℃和700℃水热处理条件下,复合分子筛中的Y型沸石相具有更好的结晶保留度.复合分子筛的中孔孔径分布范围大于机械混合分子筛,但复合分子筛样品所表现出的中、大孔体积小于相应的机械混合分子筛.吡啶吸附定量IR研究表明,550℃水热处理使复合分子筛的B酸量和L酸量减少;而机械混合样品则是B酸量和L酸量变化很小.进一步700℃水热处理则使B和L酸量都大量减少.与氢型样品相比,550℃脱铝样品的正己烷裂化活性显著增加,700℃脱铝后活性明显降低.产物分布的分析表明活性的提高与反应机理的改变有关.
ZSM-5/Y composite zeolite, a new composite material synthesized in situ from NaY gel, was dealuminated by hydrothermal treatment to study the effect of dealumination on physicochemical properties (undertook with XRD, IR spectroscopy, N-2 adsorption /desorption) and catalytic activity (in n-hexane cracking). Compared to the mechanical mixtures, Y phases of the composites had better retained crystallinity under steaming at 550 degreesC and 700 degreesC. Steaming resulted in the loss of microporosity of the crystalline material but the increase of mesoporous structure (5 similar to 30 nm at 550 degreesC and 5 similar to 40 nm at 700 degreesC). The size of the mesopore distribution of dealuminated composites was larger than the dealuminated mechanical mixtures, but their macro- and mesopore volume was smaller. Quantitative IR studies of pyridine sorption showed Bronsted and Lewis acid sites of the composite after dealuminated at 550 degreesC decreased (mainly the medium strength acid sites). Compared to the hydrogen type zeolite, the catalytic activity of the dealuminated zeolite for n-hexane cracking increased greatly after 550 degreesC dealumination, and then decreased by further dealumination. The analysis of the product distribution showed that the enhanced activity was related to the change of reaction mechanism.
出处
《物理化学学报》
SCIE
CAS
CSCD
北大核心
2004年第8期854-859,共6页
Acta Physico-Chimica Sinica
基金
中国石油天然气股份有限公司(030806-04-02)资助项目~~
