Nanoporous catalysts for sustainable chemical process

Abstract

The development of advanced solid acid catalysts is essential for sustainable chemical manufacturing. This thesis presents an integrated strategy for designing nanostructured acid catalysts with enhanced Brønsted acidity, hierarchical porosity, and stability for biomass valorisation and petrochemical transformations. Three studies demonstrate rational synthesis from renewable feedstocks and novel processing methods alongside key acidity–structure–function insights. First, hierarchical ZSM-5 zeolites were synthesized from rice husk ash via polyol pre-treatment, producing reactive silica that crystallized into mesoporous ZSM-5. XRD, N₂ adsorption, HRTEM, and ssNMR confirmed dual micro–mesoporosity and strong Brønsted sites. These catalysts showed superior glycerol dehydration activity and stability due to improved diffusion and reduced coking. Second, the surface acidity of amorphous silica–alumina (ASA) was tuned via flame spray pyrolysis by varying oxygen flow, generating materials with controlled aluminum coordination. Solid-state NMR and XANES revealed increased penta-coordinated Al near silanols, forming pseudo-bridging Brønsted sites that delivered high activity and selectivity in arene benzylation. Finally, AlV-rich Al₂O₃ nanosheets modified with silica were developed to achieve zeolite-like superacidity. Their nanosheet morphology and incorporated silanols created distorted AlV–SiOH environments, with 31P-TMPO NMR shifts confirming superacidic Brønsted sites. These materials outperformed ZSM-5 in glycerol dehydration while offering greater accessibility and coke resistance. Overall, this work demonstrates the sustainable design of nanoporous solid acids through renewable precursors, scalable synthesis, and advanced spectroscopy, providing principles for next-generation catalysts in biomass conversion and petrochemical processes.