(119a) Enhancing Acid-Base Cooperative Catalytic Activity of Aminosilica Materials through Tuning the Micropore Volume
Creating powerful catalytic materials can be achieved through identifying beneficial structure-function relationships that increase catalytic activity. This is particularly challenging for heterogeneous catalytic materials that are known to have a distribution of catalytic sites. While several structure-function relationships have been identified by tuning the structure of the amine [1â4] of aminosilica materials, the silica support can also be modified. Here we will demonstrate that the catalytic activity of aminosilica materials for the aldol reaction and condensation can be more than doubled by reducing the micropore volume. Relative to conventionally synthesized SBA-15, materials with reduced micropore volume are demonstrated with poisoning experiments to have twice the number of accessible catalytic sites. From these experiments, the active sites appear to be in the mesopores of SBA-15 and inaccessible sites are located in the micropores. This observation is supported by advanced NMR experiments examining the mobility of the amines in the materials. Amines in micropores are shown to have low mobility while amines in mesopores are mobile. This is corroborated by computational modeling that shows amines in micropores limit substrate diffusion. Overall, these results demonstrate the importance of micropores in affecting catalytic activity.
(1) Brunelli, N. A.; Didas, S. A.; Venkatasubbaiah, K.; Jones, C. W. J. Am. Chem. Soc. 2012, 134, 13950.
(2) Brunelli, N. A.; Jones, C. W. J. Catal. 2013, 308, 60.
(3) Deshpande, N.; Pattanaik, L.; Whitaker, M. R.; Yang, C.-T.; Lin, L.-C.; Brunelli, N. A. J. Catal. 2017, 353, 205.
(4) Deshpande, N.; Cho, E. H.; Spanos, A. P.; Lin, L.-C.; Brunelli, N. A. J. Catal. 2019, 372, 119.