Controlled engineering of high-purity pseudo-boehmite with large pore volume by aluminum alkoxide hydrolysis: Mechanistic understanding and reforming catalysis

Abstract

The mechanistic understanding of the pore formation during aluminum alkoxide hydrolysis is of crucial importance for the controlled engineering of large pore volume pseudo-boehmite. The time-dependent structure evolution during n-hexanol-aluminum hydrolysis and the DFT calculations were performed to monitor the changes in the aluminum coordination. The results show that the hydrolysis, oxolation and alcoxolation reactions dominate the pore construction in turn with the continuous addition of water. The aluminum coordination undergoes aggregation from Al tetra-coordinates to Al hexa-coordinates and further stable Al3hexa-coordinates as repeating units for linear growth. The rate and amount of water injection is critical for the retention of at least one OR (R = -C6H13) group, which acts as a directed pore-forming group to promote the large cyclization growth of the Al3hexa-coordinates. Consequently, 1.44 cm3/g pore volume of high-purity pseudo-boehmite was obtained, and the prepared PtSn-Al2O3 catalyst exhibits a > 80 % of toluene selectivity for n-heptane reforming.