(689f) Cooperative Catalytic Site Evolution upon Catalyst Recycling for Heterogeneous Aminosilica Materials in the Aldol Reaction and Condensation

Sustainable production of chemicals will require creating highly active catalysts for upgrading biomass using key reactions, including Aldol chemistry. Traditionally, Aldol chemistry is catalyzed by enzymes that use acid-base cooperativity to form C-C bonds. These cooperative interactions can be translated to heterogeneous aminosilica SBA-15, which are promising candidates for these reactions.

Unfortunately, there is a limited understanding of structure-function behavior for these aminosilica catalysts, preventing further optimization for this chemistry. In this work, site quantification experiments are used to establish structure-function relationships for negligible-micropore (NMP) SBA-15. In contrast to widely accepted assumptions that these sites have equal contributions, we have discovered that three different types of sites exist with different catalytic contributions. Furthermore, the relative amount of each type of site may be tuned to optimize SBA-15 for Aldol chemistry. To improve the viability of NMP-SBA-15 for industrial applications, recycling tests are performed to assess how the catalytic sites and capabilities change upon catalyst reuse. It is demonstrated that high-activity sites are transformed to low-activity sites after initial use, resulting in decreased catalytic performance for subsequent use. To combat this, three possible reactivation methods were investigated and proposed: (1) toluene pre-treatment, (2) potassium carbonate solution treatment, and (3) water treatment. Preliminary results of the second reactivation show that the intermediates on the catalyst surface might be removed. Overall, this work demonstrates the importance of a molecular understanding of cooperative interactions at catalytic sites to improve catalyst performance and stability.