SO2对三效催化剂载体的毒化作用研究

根据三效催化剂的工况，分别于400℃和760℃，在不同气氛下对其载体的主要组分γ-Al2O3和CeO2用SO2进行硫化处理，采用红外、XRD、扫描电镜等方法对SO2处理前后的γ-Al2O3和CeO2结构进行表征。结果表明，对于γ-Al2O3而言，在氧化气氛下SO2可与γ-Al2O3反应生成硫酸盐，而还原气氛下则未检测到硫酸盐；与400℃、氧化气氛相比，760℃、氧化气氛下SO2更容易与γ-Al2O3。反应生成硫酸盐。SO2与γ-Al2O3反应生成硫酸盐，使γ-Al2O3的比表面积下降，孔结构被破坏。对于CeO2而言，在氧化气氛和还原气氛下SO2均可与CeO2反应生成硫酸盐；氧化气氛下，400℃时SO2比760℃时更容易与CeO2反应生成硫酸盐。CeO2与SO2反应生成硫酸盐后，其催化CO氧化的能力显著下降。     

NaY分子筛中苯分子吸附和扩散行为的分子模拟

In the article the Grand Canonical Monte Carlo (GCMC), molecular dynamics (MD), and kinetic Monte Carlo (KMC) simulations with particular focus on ascertaining the loading dependence of benzene diffusion in the zeolite were performed. First, a realistic representation of the structure of the sorbate-sorbent system was obtained based on GCMC simulation. The simulation clearly shows the characteristics of the adsorption sites of the benzene-NaY system, from which two kinds of preferably adsorbing sites for benzene molecules, called SII and W sites, are identified. The structure thus obtained was then used as a basis for KMC and MD simulations. A compara-tive study by introducing and comparing two different mechanisms underlying jump diffusion in the zeolite of in-terest shows that the MS diffusivity values predicted by the KMC and MD methods are fairly close to each other, leading to the conclusion that for benzene diffusion in NaY, the SII→W→SII jumps of benzene molecules are dominated, while the W→W jumps do not exist in the process. These findings provide further support to our previous conclusion about the absence of the W→W jumps in the process of benzene diffusion in NaY. Finally, two relations for predicting the self- and MS diffusivities were derived and found to be in fair agreement with the KMC and MD simulations.     

活化扩散和支撑层阻力对MFI沸石膜分离正丁烷和异丁烷的影响

采用Maxwell-Stefan方程描述MFI沸石膜及支撑层内的表面扩散、气相活化MFI扩散、分子扩散和努森扩散,预测正丁烷和异丁烷在MFI沸石膜中单、双组分的扩散特性。预测结果表明,考虑支撑层阻力时,在MFI沸石膜层中,正丁烷和异丁烷活化扩散的活化能分别为(12.7±0.1)kJ/mol和(20.8±0.4)kJ/mol,活化扩散通量均随温度的升高而增大,异丁烷扩散主要受活化扩散控制;支撑层阻力对正丁烷和异丁烷混合物的扩散通量有显著影响;400K以下时,混合物中异丁烷活化扩散通量较小,正丁烷选择性高,有利于分离;400K以上时,异丁烷活化扩散通量增长显著,正丁烷选择性减小。     

载体预处理对催化剂涂层结构的影响

汽车尾气净化催化剂的净化转化效果及耐久性,与催化剂涂层和载体的结合强度密切相关。选用堇青石蜂窝载体经改性预处理后涂覆催化剂,涂层表面无明显龟裂现象,且不易剥落;经4次冲蚀后,涂层中催化剂量的损失小于5％。     

硅-铝催化剂酸中心失活与再生的分析

含 Si、Al 元素的固体酸催化剂,其活性来源于其酸性,催化剂的失活与再生一定程度上是其酸性中心的失活与再生。L酸中心具有吸引孤对电子的空轨道,空轨道是L酸中心的活性中心;B酸中心能提供 H⁺,H⁺是B酸中心的活性中心。L酸中心的空轨道被孤对电子占据后,L酸中心失去活性,B酸中心给出 H⁺后也会失去活性。烯烃在L酸中心作用下生成了环正碳离子,环正碳离子从失活的L酸中心获取H^-生成了环烷烃,而失活的L酸中心在给出 H^-的同时,占据活性中心的1对电子被去掉,变成为空轨道,这样L酸中心又具有吸引孤对电子的能力,又恢复了活性。如果环正碳离子提供 H⁺给失活的B酸中心,C⁺与相邻的提供 H⁺的C原子各自的2个sp³轨道相互作用形成-C=C-双键,即生成了环烯烃,使失活的B酸中心再次获得 H⁺后其活性也得到了恢复。