酸处理对斜发沸石结构影响的研究

The effect of acid treatment on the structure of clinoptilolite

采用不同浓度硝酸对斜发沸石(HEU)进行改性处理,结合元素分析(ICP-AES)、N_2物理吸附、X射线粉末衍射(XRD)、魔角旋转固体核磁(MAS NMR)等测试手段及DFT理论计算,研究了酸处理对斜发沸石结构的影响。结果表明,硝酸处理对不同平衡阳离子的HEU(Na-K-HEU、NH_4-HEU、H-HEU)具有不同的脱铝效果。酸处理后Na-K-HEU和NH_4-HEU的硅铝比、比表面积均显著升高。随硝酸浓度增大两个沸石样品的脱铝程度逐渐增加,同时骨架结构也逐渐破坏,硝酸浓度达到4 mol/L时其相对结晶度已低于50%。而H-HEU样品的骨架结构稳定,随硝酸浓度的增大铝含量轻微降低,硝酸浓度达到6 mol/L时相对结晶度仍高达94.8%。阳离子反交换实验结果证明,平衡阳离子的类型不是影响HEU骨架稳定性的主要因素。Na-K-HEU和经硝酸铵交换后的NH_4-HEU中铝都以骨架铝的形式存在,而在后者焙烧成为H-HEU时出现部分非骨架铝,伴随了骨架的稳定化过程。

The influence of nitric acid treatment on the composition and structure of clinoptilolite（ HEU） was analyzed by various characterization techniques,such as element analysis（ ICP-AES）,N2 physical adsorption,X-ray powder diffraction（ XRD）,^27 Al/^29 Si MAS NMR and DFT calculation. The Si/Al ratio and BET surface area of Na-K-HEU and NH4-HEU were significantly increased after nitric acid treatment,and meanwhile,their relative crystallinity decreased to below50% when the concentration of nitric acid reached 4 mol/L,illustrating the severe distortion of zeolite framework. However,the structure of H-HEU was more stable and it could maintain a high relative crystallinity of 94.8% even the concentration of nitric acid reached 6 mol/L. The results of27 Al/29 Si MAS NMR indicated that some extra-framework aluminum species appeared in H-HEU and they could protect the framework aluminum from further distortion,whereas this protective effect did not exist on NaK-HEU and NH4-HEU,as they have little extra-framework aluminum species. It can be further proved that through back-exchanging the H-HEU to Na-HEU and K-HEU,their resistance to nitric acid treatment could be markedly improved.