Evolution of the different types of catalytic sites in aminosilica materials during recycle experiments in aldol chemistry

Aminosilica materials are promising for many applications, including as a catalyst for aldol chemistry. Whereas aminosilica catalysts are known to deactivate overtime, it is unclear how recent revelations about the different types of catalytic sites impact the understanding of the deactivation behavior. In this work, we investigate how the aminosilica catalyst activity decreases and affects the fraction and the type of active sites. After a single catalytic cycle, the catalyst activity decreases, but the fraction of active sites remains constant. The decrease in catalytic activity is consistent with the conversion of medium and high activity sites transfer to low activity sites that lack cooperative interactions. Additional catalytic cycles decrease the fraction of active sites but do not result in aminosilane leaching. The sites are inactive because of accumulation of organic content. Interestingly, the organic can be removed through washing with a dilute sodium carbonate solution. The washed material fully recovers to the catalytic activity of the fresh material. Overall, the catalytic sites evolve after each cycle, but this trend can be reversed, enabling aminosilica materials to be used as sustainable catalysts for aldol chemistry.