Homogeneous Boroaluminate Xerogels: Synthesis, Characterization, and Catalysis

Boroaluminates are promising materials for various catalytic applications, particularly due to their tunable acidity and textural properties, having not reached their full potential yet. Developing synthetic routes that yield mesoporous structures with high surface areas is crucial for maximizing their performance. Traditional preparation methods (including hydrolytic sol-gel) often struggle to produce highly mesoporous, high-surface-area boroaluminates without the use of templating agents and can lead to heterogeneous elemental distribution. Furthermore, direct comparisons of different non-hydrolytic sol-gel (NHSG) approaches for these materials are limited. In this work, we present an NHSG preparation method for mesoporous boroaluminates, utilizing the alkyl-halide condensation reaction between Al(OiPr)3 and BCl3, with a 1:1 boron/aluminum precursor ratio. This approach resulted in amorphous xerogels featuring a homogeneous distribution of boron and aluminum atoms within the structure. Our method successfully produced mixed boria-alumina xerogels with high surface areas, reaching up to 600 m2 g−1 without the need for any templating agent. We characterized these materials using 11B and 27Al MAS NMR spectroscopy, SEM and STEM-EDS microscopy, N2 porosimetry, thermogravimetry, ICP-OES and XPS elemental analysis and ammonia-TPD. Additionally, we provide a comparative analysis with boroaluminates prepared by other non-hydrolytic sol-gel reactions and demonstrate their practical utility in catalysis through the ethanol dehydration (with >83 % ethanol conversion at 275 °C), producing both ethylene and diethyl ether. This work offers a promising route for synthesizing mesoporous boroaluminates for catalytic applications.