Hβ沸石表面酸性质的研究

Study on the Surface Acid Properties of Hβ Zeolite

采用四乙基氢氧化铵为模板剂，分别以铝酸钠和拟薄水铝石为铝源合成了β沸石，经硝酸铵溶液离子交换、柠檬酸处理及高温焙烧后制得Ｈβ沸石．采用ＮＨ３ＴＰＤ， 吡啶吸附态ＩＲ，２９Ｓｉ ＮＭＲ 及２７Ａｌ ＮＭＲ 技术研究了Ｈβ沸石的酸性位及脱铝与补铝过程． 结果表明，经柠檬酸处理后Ｈβ沸石酸强度减弱，总酸量增加，弱酸量增加的幅度大于强酸量增加的幅度，Ｂ酸量增加，Ｌ酸变化不明显． 柠檬酸处理具有脱铝与补铝的双重功能，脱铝可能主要发生在Ｓｉ（２Ａｌ） 位，补铝可能主要发生在Ｓｉ（０Ａｌ）Ｄ位．Ｈβ沸石的酸性及酸度与β沸石的合成条件、离子交换条件及酸处理条件密切相关，在一定的Ｓｉ／Ａｌ 比（１０～１５） 范围内， Ｈβ沸石的酸度决定于骨架硅的铝配位数及其分布．

A method of increasing the amount of acid sites, specially Brnsted acid site, of Hβ zeolite is reported. Hβ samples were prepared through ion exchange with NH 4NO 3 solution, citric acid treatment and 550 ℃ calcination for as synthesized zeolite Beta used NaAlO 2 and α Al 2O 3·H 2O respectively as aluminium source, and characterized by NH 3 TPD, Pyridine IR, 29 Si NMR and 27 Al NMR. It is found that through citric acid treatment, the characteristics of Hβ zeolite change: acid strength decreased, total acid amount increased, Brnsted acid sites increased and Lewis acid sites unvaried.The citric acid treatment of zeolite Beta may have the function of both dealuminization at Si(2Al) site and realuminization at Si(0Al) D site. Therefore the acidity and acid sites of Hβ zeolite are proved to be related to the conditions of synthesis, ion exchange and acid treatment of zeolite Beta, and determined by number and distribution of Al in framework Si configuration in a certain Si/Al ratio range of Hβ(10 15).