摘要
以马尔可夫链近似模拟丝光沸石脱铝过程．用ＭｏｎｔｅＣａｒｌｏ方法计算脱铝丝光沸石中骨架Ｓｉ－Ａｌ近邻分布｛Ｓｉ（ｎ－Ａｌ）；ｎ＝０－４｝和Ａｌ－Ａｌ次邻分布｛Ａｌ（ｍ－Ａｌ）；ｍ＝０－３｝随铝浓度的演化．为使Ｓｉ－Ａｌ近邻分布与对脱铝丝光沸石样品的２９ＳｉＭＡＳＮＭＲ观测相符，而得到丝光沸石弱酸铝易于解脱的结论，这个结论与八面沸石弱酸铝易于解脱相反．根据计算丝光沸石脱铝的开始阶段，强酸中心，Ａｌ（０－Ａｌ）．的数量急剧下降，由此预言脱铝丝光沸石的酸性将明显低于相同Ｓｉ／Ａｌ的原粉，这个预言不难直接得到实验检验．
Abstract The dealumination process is non--equilibrium which ends up with a metastuble state.Therefore the St, Al distribution in the framework of the dealuminatCd mordenites is quite different from the parent mordenitC. It has been found that the seSt MAS NMR speCtra of thedcaluminated mordcnite samples were evidently different from the parent mordenite sampleswith corresponding St / Al framework ratios.In order to describe the St, Al distribuhon in the framework or dealuminated mordenites, itis necessary to follow with the starting state of parent material a simulation of thedealumination.In the present work, the continuous dealuminahon is studied by a discrete stochastic process i.e. the Markov chain with stationary transitions and countable state space. The simulationis based on the assumphons of first--order kinetics and that the strong--acid AIO4 sites arepreferentially removed for mordcnites. By this procedure the state variables, St(mAI) andAl(n--Al), of the metastable states with diITcrent degree ofdealumination can be calculated.The calculated evolutions of St(n--Al) upon the Al content of dealuminated mordenites canthen explain the 'gSi MAS NMR sPCctra or the dealuminated mordenite samples for co,responding St / Al framework ratios.For the mordenite, that the isolated strong--acid sites, Al(0--Al), arc prefcrcnhally removedwhich is different from the faujasite. Based on the fact, the Monte Carlo simulation shows thatthe number of strong--acid will decrease rapidly during the dealumination process. A furtherpredication that the acidity is always weakened in dealuminated mordenitc samples comparedwith mordenites synthesized with the same aluminium content will be easily checked by experiments.
