水热脱铝ZSM-5/Y复合分子筛的表征和催化裂化性能

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.     

IR and29Si NMR investigation of the influence of alkaline modification on the structure of hydrothermally dealuminated Y zeolites

The change in the structure of NH₄NaY zeolite (53 % NH₄ ⁺, Si/Al = 2.37) after hydrothermal treatment at 873 K followed by modification with aqueous KOH solution at 353 K was studied by IR and²⁹Si NMR spectroscopy. It has been shown that hydrolytic cleavage of the Al-O bond of the deammoniated zeolite sites by hydrothermal treatment predominates in the framework groups Si(OAl) _n (OSi)_4–n ,n=2, 3. Molecular water adsorbed on such a sample exists as hydrogen-bonded associates with hydrogen bonds of various strengths reaching that in ice-like structures (the band at 2468 cm^–1). Treatment with an alkali results in partial regeneration of the normal bridge bonds. The exchange of the protons of the terminal silanol groups with the alkaline cation prevents those groups from participating in the regeneration process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 387–391, March, 1994.     

基于多步高阶差分格式求解时域Maxwell方程

提出基于无穷维哈密尔顿系统及分裂算子理论的多步高阶差分格式,求解时域Maxwell方程.在时间方向上,针对Maxwell方程采用不同阶数的辛算法进行差分离散;在空间方向上,采用四阶差分格式进行差分离散.探讨多步高阶差分格式的稳定性及数值色散性,最后给出数值计算结果.结果表明,五级四阶格式为最有效的多步高阶差分格式,具有高精度、占用较少的计算机资源等优点,适用于长时间的数值模拟.     

On the construction of a nonlinear recursive predictor

In this paper, we present a novel approach for constructing a nonlinear recursive predictor. Given a limited time series data set, our goal is to develop a predictor that is capable of providing reliable long-term forecasting. The approach is based on the use of an artificial neural network and we propose a combination of network architecture, training algorithm, and special procedures for scaling and initializing the weight coefficients. For time series arising from nonlinear dynamical systems, the power of the proposed predictor has been successfully demonstrated by testing on data sets obtained from numerical simulations and actual experiments.     

短时交通流复杂动力学特性分析及预测

为揭示短时交通流的内在动态特性,利用非线性方法对交通流混沌特性进行识别,为短时交通流的预测提供基础.基于混沌理论对交通流时间序列进行相空间重构,利用C-C算法计算时间延迟和嵌入维数,采用Grassberger-Procaccia算法计算吸引子关联维数,通过改进小数据量法计算最大Lyapunov指数来判别交通流时间序列的混沌特性.针对局域自适应预测方法在交通流多步预测中预测器系数无法调节的问题,提出了交通流多步自适应预测方法.通过实测数据计算,结果表明:2,4和5 min三种统计尺度的交通流时间序列均具有混沌特性;改进的小数据量法能够准确地计算出最大Lyapunov指数;构建的交通流多步自适应预测模型能够有效地预测交通流量的变化.为智能交通系统诱导和控制提供了依据.     

高硅Y沸石的研制及性能——Ⅱ.沸石孔结构及吸附性能

LiNaY沸石经SiCl₄气相同晶脱铝补硅后制得系列高硅铝比、高结晶度的Y沸石,用低温氮吸附法,求得样品对N₂的吸附—脱附等温线,从而计算其比表面和孔体积,并采用BJH模型计算孔径分布。用真空重量法测定了四种C₆化合物(正己烷,2,3-二甲基丁烷、苯、环己烷)的吸附等温线,探讨吸附量与吸附物的性能(极性、几何构型)、吸附量与吸附剂脱铝深度的关系。从而得到,经SiCl₄同晶取代后Y沸石的孔结构和表面性质与脱铝深度的关系。     

Formation of Alkali‐Aluminosilicate Layers on Thermochemically Dealuminated Y Zeolites by Alkaline Leaching

Zeolite Y was steamed at 873 K for 7 h. This thermochemical treatment increases the Si/Al ratio of the zeolite framework from 2.4 to 3.8 under the formation of non‐framework aluminium species. Successive leaching in 0.25 M KOH at 353 K for 24 h decreases the Si/Al ratio of the zeolite to 2.6 due to the formation of a X‐ray amorphous potassium aluminosilicate surface layer.