Control of Zeta Potential of Hierarchical Mesoporous Zeolite Y via Inorganic Surface Modification without Micropore Blockage and Phase Separation

• Published in: Crystal growth & design Vol. 23; no. 8; pp. 5601 - 5613
• Main Authors: Xu, Le, Okrut, Alexander, Rea, Thomas, Chaudhuri, Kaustav, Han, Jinyi, Kuperman, Alexander, Katz, Alexander
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.08.2023
• Subjects: Chemistry; Crystallography; Materials Science
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.3c00261

We describe a selective postsynthetic surface modification of the interior surface of mesoporous Y zeolite (Meso-Y), which results in a uniform nanoscale silica, alumina, or aluminosilicate coating, without causing significant micropore blockage and without synthesizing a separate bulk alumina-containing phase. The approach relies on CTAB surfactant (required for Meso-Y-as synthesis) acting as a soft template. Our results demonstrate the importance of conducting surface modification under dry conditions at the stage of reacting alkoxide molecular precursors with the Meso-Y-as surface. If this is not performed, it leads to undesired micropore blockage by N2 physisorption at 77 K for thicker silicate overlayers as well as phase separation for alumina overlayers. This separate alumina phase is a consequence of the water sensitivity of the latter and the impenetrability of partially condensed alumina colloids into the Meso-Y particle, and it is visible on the external surface of the Meso-Y particle as a bulk micrometer-scale aggregate via SEM. In contrast, uniform layers with no evidence of either phase separation or zeolite micropore blockage could be achieved for oxide coating synthesized under dry conditions. In the case of alumina surface modification, these layers were imaged by TEM as uniform nanoscale (∼10 nm thick) overcoats, and their uniformity in modifying the internal surface of the Meso-Y particle is demonstrated by a combination of zeta-potential measurements and SEM/EDX data. We demonstrate that our approach for synthesizing uniform oxide coatings on Meso-Y particles can be used to control the surface charge, which is crucial for applications in adsorption and catalysis.