Influence of support texture and reaction conditions on the accumulation and activity in the gas-phase aldol condensation of n-pentanal on porous silica

In this work, the continuous gas-phase aldol condensation reaction of n-pentanal was investigated on silica supports. Since high aldol formation can lead to deactivation by pore blocking, the reaction is important to improve continuous gas-phase hydroformylation processes. Aldehyde conversion was monitored depending on the surface acidity. The spent catalysts were analyzed by thermogravimetric analysis (TGA) to evaluate the accumulation of substrate and product inside the pores. The pore size was altered using hydrothermal treatment. The obtained supports were analyzed using N2-sorption, mercury pore intrusion/extrusion, point-of-zero-charge measurements, temperature programmed desorption measurements (CO2 and NH3), and 29Si MAS NMR. A variation of reaction duration, pressure, and temperature was carried out. The influence of the silica texture on activity and accumulation was investigated using different particle size fractions and median pore diameters. In larger pores, the total volume-based accumulation was lower compared to the one in smaller pores. At the same time, the aldol was enriched compared to n-pentanal in the condensed liquid inside the pore network.