Humin Formation on SBA-15-pr-SO3H Catalysts during the Alcoholysis of Furfuryl Alcohol to Ethyl Levulinate: Effect of Pore Size on Catalyst Stability, Transport, and Adsorption

Herein, the alcoholysis of furfuryl alcohol in a series of SBA-15-pr-SO3H catalysts with different pore size is reported. Elemental analysis and NMR relaxation/diffusion methods show that changes in pore size have a significant effect on catalyst activity and durability. In particular, decrease in catalyst activity after catalyst reuse is mainly due to carbonaceous deposition, whereas leaching of sulfonic acid groups is not significant. This effect is more pronounced in the largest pore size catalyst C3, which rapidly deactivates after one reaction cycle, whereas catalysts with relatively medium and small average pore size (named, respectively, C2 and C1) deactivate after two reaction cycles and to a lesser extent. CHNS elemental analysis showed that C1 and C3 experience the same amount of carbonaceous deposition, suggesting that the increased reusability of the small pore size catalyst can be attributed to the presence of SO3H groups mostly present on the external surface as corroborated by pore clogging evaluated by NMR relaxation measurements. The increased reusability of C2 is attributed to a lower amount of humin formation and, at the same time, reduced pore clogging, which helps to maintain the accessible internal pore space.