Influence of the nature of amino acids on the formation of mesoporous LTA-type zeolite

• Published in: Microporous and mesoporous materials Vol. 252; pp. 79 - 89
• Main Authors: Zhang, Jian, Chen, Zhuwen, Wang, Yanding, Zheng, Guangchao, Zheng, Hairong, Cai, Feiyan, Hong, Mei
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.11.2017
• Subjects: Amino acid; Hydrothermal synthesis; LTA zeolite; Mesoporous zeolite; Mesoporous zeolite; Amino acid; Hydrothermal synthesis; LTA zeolite
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2017.05.036

Hydrothermal crystallization of LTA zeolite has been conducted in the presence of amino acid in order to introduce mesoporosity. Eight different types of proteinogenic amino acids have been employed. The influence of their structure and physicochemical properties on the formation of hierarchically mesoporous LTA (MLTA) zeolite have been investigated. All eight amino acids bearing either basic, or acidic, or polar non-ionizable, or non-polar non-ionizable side chains were able to generate mesopores within LTA crystals. The isoelectric points of amino acids influenced the resulting MLTA's morphology, crystallization kinetics, and impurity content. Pure phase MLTA with controllable shape was obtained. Amino acid with a higher isoelectric point generated smaller and more spherical MLTA in less crystallization time, but induced slightly more impurity FAU phase. The mesopore size generally decreased with hydropathy index so that amino acids with non-polar, non-ionizable side groups generated 14–15 nm mesopores, 5–10 nm smaller than those generated by amino acids in other categories. The hydrophobic moieties in amino acids tended to shrink the mesopores, in contrast with their pore expansion effect in surfactant-mediated mesopore generation route, suggesting a different mesopore formation mechanism. Stability of amino acid during the hydrothermal zeolite synthesis and easy amino acid removal by washing with water was further confirmed. The findings discovered in this study paves a new way for tailoring hierarchical zeolite materials with controlled texture properties. [Display omitted] •Eight different proteinogenic amino acids have been employed as mesopore generating agents to prepare mesoporous zeolite A.•Mesopore formation mechanism mediated by amino acids is different from that by surfactants.•Isoelectric point of amino acids influences zeolite morphology, crystallization kinetics, and impurity content.•Hydropathy index of amino acids inversely affects mesopore size, indicating pore shrinkage effect by hydrophobic moieties.