Hydrodynamic Effects on Mesostructure Ordering and Pore Texture in SBA-15 Synthesis across Reaction Volumes

The synthesis of SBA-15 is one of the most robust procedures to prepare mesoporous silica particles and has therefore gained prominence in adsorption and catalysis studies. Despite its reproducible synthesis and well-established lab-scale parameters, the impact of hydrodynamics-related processing variables on scale-up remains poorly quantified. In this work, we aim to understand the role of stirring rate and reactor size on the morphological, structural, and textural properties of SBA-15. By means of Small Angle X-ray Scattering, nitrogen sorption, and SEM characterization, we show that low stirring rates lead to smaller SBA-15 particles that present lower mesoscopic order and increased disordered porosity due to interparticle voids, while high stirring rates result in larger particles with well-defined hexagonal mesopores that contribute most to the surface area. We demonstrate that even simple changes in stirring or reactor size lead to relevant changes in surface area (15–25%) or dramatic changes in mesopore-derived surface area (up to 400%). These changes are related to phenomena taking place in the early stages of precipitation that lead to nanoparticle formation and evolution. By following the precipitation process through visual inspection combined with in situ SAXS, we find that the stirring rate markedly affects the nucleation and growth of the initial nanoparticles, which are the origin of the observed changes in particle and mesopore size. Increasing reactor volume amplifies the differences between stirring conditions, leading to distinct transformation kinetics of intermediate structures and, ultimately, to different final textures and morphologies. This work provides valuable information to answer both fundamental and applied questions, linking the effect of processing variables on the formation of SBA-15 and the actual textural properties. These findings are relevant in real application problems such as those related to mesopore fine-tuning and reproducibility of mesoporous silica, which is a relevant aspect in the SBA-15 scaling up for industrial purposes.