Should we still be using HCl in the synthesis of SBA-15 and Al-SBA-15?

• Published in: Microporous and mesoporous materials Vol. 378; p. 113222
• Main Authors: Iga, Gustavo D., Vieira, José Lucas, Santos, Érick A., Albuquerque, Jonas S., Urquieta-González, Ernesto A., Bueno, José Maria C., Gallo, Jean Marcel R.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2024
• Subjects: Acid-effect; Al-SBA-15; Counterion; Hofmeister; SBA-15; Hofmeister; Al-SBA-15; SBA-15; Counterion; Acid-effect
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2024.113222

HCl is not always the best option for synthesizing SBA-15 and Al-SBA-15, and using different acids can bring beneficial structural and surface properties. While SBA-15-HCl and SBA-15-H2SO4 exhibited similar structural and textural characteristics, SBA-15-H2SO4 showed significantly lower contamination of the acid counterion in the final material, making it advantageous in catalytic applications where Cl− poisoning is a concern. On the other hand, SBA-15-HBr demonstrated a narrower pore size distribution. Notably, no residual Br− was detected in the final material for SBA-15-HBr. SBA-15-HNO3 and SBA-15-HBr displayed the highest concentration of 29Si MAS-NMR Q2 species, which can benefit grafting applications. The high degree of silica condensation in SBA-15-HCl and SBA-15-H2SO4 provides superior hydrothermal stability for these samples. From a fundamental perspective, a linear correlation was also identified between the Gibbs Free Energy of Hydration (ΔGhyd) of the anions and the SBA-15 mesopore sizes. Additionally, the study extended to preparing Al-SBA-15, and a facile methodology based on the pH-adjusting method was proposed. The samples displayed a Brønsted/Lewis ratio higher than typically reported, suggesting an efficient incorporation of Al as Brønsted acid sites. [Display omitted] •HCl is not always the optimal acid for synthesizing SBA-15 and Al-SBA-15.•Acid-conjugated base affects mesopore sizes in agreement with the Hofmeister series.•SBA-15 prepared with HCl and H2SO4 have higher hydrothermal stability.•SBA-15 prepared with HBr and H2SO4 have narrower pores and lower anion contamination.•Improved direct synthesis of Al-SBA-15 leads to a high Brønsted/Lewis acid ratio.