沸石对于亚硝胺的吸附和裂解

Adsorption and decomposition of N-nitrosamines on zeolites

采用气相色谱 质谱 (GC MSD)、程序升温表面反应 (TPSR)等技术研究吡咯烷亚硝胺 (NPYR)和二甲基亚硝胺 (NDMA)等亚硝胺在NaY ,HY ,NaZSM 5 ,HZSM 5等沸石上的气相和液相吸附及催化分解 ,并剖析其产物分布 :NaZSM 5与NaY沸石上NPYR裂解产物与热裂解产物非常相近 .而H型沸石如HZSM 5与HY上发生了H+ 参与的催化裂解反应 ,产物则是以亚硝胺还原及开环物种为主 .亚硝胺在H+ 型与Na+ 型沸石上分别是以酸催化及自由基热裂化进行裂解反应的 ,沸石上的质子酸中心是沸石催化降解亚硝胺的活性中心 .ZSM 5沸石能够从溶液中强吸附NPYR类亚硝胺 ,而且在常温下很难解吸 ,这将有利于沸石在环境保护中消除亚硝胺的污染 .和 773K活化的NaY沸石相比 ,未经活化样品的NPYR TPSR谱图上裂解产物NOx 的峰形状及峰位置基本不变 ;据此可推测 ,沸石上已吸附的水不仅不影响NPYR的吸附 ,而且可能有助于NPYR的裂解 .

In this short paper,adsorption and catalytic decomposition of N-nitrosamines such as NDMA and NPYR on NaY,HY,HZSM-5 and NaZSM-5 zeolites were investigated by use of GC-MSD,TPSR techniques,and the products distribution were also analyzed.Of zeolite catalysis dramatically lowers the temperature needed for the degradation of N-nitrosamines.Degradation of NDMA on NaZSM-5 or NaY zeolites produced mainly cyano derivative same as that of pyrolysis,while on HZSM-5 or HY dimethylamine became the dominant product as the GC-MS spectra demonstrated.Consequently different reactions are proposed to occur on the zeolites with proton or sodium ions.On the former the Bronsted acid sites probably play the role of main catalytic sites,hence N-nitrosamines degrades to amines while on the latter N-nitrosamines decomposed through radical reaction process,similar as pyrolysis. Zeolite can selectively adsorb N-nitrosamines from solution,but degradation of NDMA or NPYR on zeolite kept to high temperature,indicating the strong adsorption of NPYR on zeolite ZSM-5 which means no N-nitrosamines can desorb from the adsorbent at ambient temperature. Unlike pyrolysis by which the conversion of NPYR was only 1.3% at 593?K while NDMA did not react noticeable,NPYR began to decompose at 523?K on zeolite NaY and NDMA at 593?K.Degradation of N-nitrosamines strongly depends on the pore structure of zeolite, and the acid sites of zeolite accelerate degradation of N-nitrosamines,so that NDMA began to decompose at 513?K on HZSM-5 zeolite but at 553?K on NaZSM-5.However,activation of zeolite NaY at 773?K seems to have almost no influence on TPSR of NPYR,since similar TPSR spectrum was found of both activated and non-activated samples;so that zeolite can be used for removing N-nitrosamines pollution without activation.