Scalable Synthesis of Uniform Mesoporous Aluminosilicate Microspheres with Controllable Size and Morphology and High Hydrothermal Stability for Efficient Acid Catalysis

Abstract

Mesoporous aluminosilicates are promising solid acid catalysts. They are also excellent supports for transition metal catalysts for various catalytic applications. Synthesis of mesoporous aluminosilicates with controllable particle size, morphology, and structure, as well as adjustable acidity and high hydrothermal stability, is very desirable. In this work, we demonstrate the scalable synthesis of Al-SBA-15 microspheres with controllable physicochemical properties by using the microfluidic jet-spray-drying technology. The productivity is up to ∼30 g of dried particles per nozzle per hour. The Al-SBA-15 microspheres possess uniform controllable micron sizes (27.5-70.2 μm), variable surface morphologies, excellent hydrothermal stability (in pure steam at 800 °C), high surface areas (385-464 m2/g), ordered mesopore sizes (5.4-5.8 nm), and desirable acid properties. The dependence of various properties, including particle size, morphology, porosity, pore size, acidity, and hydrothermal stability, of the obtained Al-SBA-15 microspheres on experimental parameters including precursor composition (Si/Al ratio and solid content) and processing conditions (drying and calcination temperatures) is established. A unique morphology transition from smooth to wrinkled microsphere triggered by control of the Si/Al ratio and solid content is observed. The particle formation and morphology-evolution mechanism are discussed. The Al-SBA-15 microspheres exhibit high acid catalytic performance for aldol-condensation reaction between benzaldehyde and ethyl alcohol with a high benzaldehyde conversion (∼56.3%), a fast pseudo-first-order reaction rate (∼0.1344 h-1), and a high cyclic stability, superior to the commercial zeolite acid (H-ZSM-5). Several influencing factors on the catalytic performance of the obtained Al-SBA-15 microspheres are also studied.