(580b) Impact of Microporosity on the Catalytic Performance of Micro-Mesoporous Aminosilica Materials for the Knoevenagel Condensation

Porous silica materials are thermally stable and robust with tunable pore architecture. These materials are widely used as supports for functionalizing catalysts. Many such materials have dual porosity in the form of micropores (< 2 nm) and mesopores (2 – 50 nm). The dual porosity in their structure provides a high surface area that enables a wide range of catalyst densities (catalyst moles nm^-2 silica) to be achieved on their surface. The relationship between density of catalysts on support surface and their corresponding catalytic activity has previously been elucidated for different chemical reactions. Indeed, such studies aid in rational design of heterogeneous catalysts. While this is insightful, the impact of support pore architecture on the relationship between catalyst density and catalyst activity is yet not clearly understood. As proof of concept, the current work examines the effect of tuning pore architecture of micro-mesoporous silica supports through elimination of microporosity. This is done using “regular micropore” Santa Barbara Amorphous-15 (REG SBA-15) as the model micro-mesoporous silica support. An updated synthesis technique is utilized to eliminate microporosity and obtain “no micropore” SBA-15 (NMP SBA-15). Hence, the impact of micropore elimination is elucidated using the Knoevenagel condensation as the test chemical reaction, and tertiary amines functionalized on SBA-15 with their density ranging from 0.1-1.6 N nm^-2 SBA-15 as the test catalysts. Based on the initial turnover frequency (TOF₀) vs amine density plot obtained, the confinement effect of micropores is indeed seen to cause the density-activity relationship of REG materials to differ from that of NMP materials. At similar surface densities, the NMP materials consistently show a higher TOF₀ than their REG counterparts. Hence, the current work provides experimental insight on the impact of support pore architecture on catalyst activity and contributes to the design of lucrative supported catalysts with improved performance.