abstract
Amorphous aluminosilicate catalysts have been used industrially on a large scale for almost a century. However, the influence of the pH on the alumination of silica in aqueous solutions has remained largely unclear. Herein, room temperature aluminations of different mesoporous amorphous silicas (fumed silica, dried silica gel, SBA-15, MCM-41, and COK-12) with aqueous solutions of various pH (3-13) are explored. The aqueous solutions are prepared using different aluminum sources (Al(NO3)(3) or NaAlO2) and alkaline additives (NaOH or NH4OH). The decoupling of pH and Al source using alkaline additives results in a vast experimental potential to prepare unique aluminosilicates, whereby an important role is played by the pH development during the treatment. The bulk and surface composition, acidity, aluminum coordination, morphology, hydrothermal stability, and porosity of the obtained materials are characterized. Optimal samples possess large surface areas and superior acidities (up to 50% higher) and outstanding stabilities compared to aluminosilicates prepared with state-of-the-art methods. The obtained materials are evaluated in a series of acid-catalyzed model reactions involving substrates of various chemical reactivity and size, enabling insight in the catalytic functionality of the introduced BrOnsted and Lewis sites. The potential of the obtained materials is emphasized by the similar or superior acidity and catalytic performance compared to several benchmark industrial silica-alumina-based catalysts.
keywords
POST-SYNTHESIS ALUMINATION; FRAMEWORK ALUMINUM CONTENT; SOLID ACID CATALYSTS; LACTIC-ACID; MCM-41; ZEOLITE; ABSORPTION; CONVERSION; DESIGN; SBA-15
subject category
Chemistry
authors
Locus, R; Verboekend, D; d'Halluin, M; Dusselier, M; Liao, YH; Nuttens, N; Jaumann, T; Oswald, S; Mafra, L; Giebeler, L; Sels, B
our authors
Luís Mafra
Principal Researcheracknowledgements
D.V. and M.D. acknowledge support from an FWO post-doctoral fellowship. R.L. acknowledges the IAP. N.N. acknowledges the KU Leuven (FLOF). L.M. thanks CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013 and PTDC/QEQ-QAN/6373/2014), financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. The authors are also grateful to the Portuguese NMR Network (RNRMN).