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 seriesof SBA-15-pr-SO3H catalysts with different pore sizes isreported. Elementalanalysis and NMR relaxation/diffusion methods show that changes inpore size have a significant effect on catalyst activity and durability.In particular, the decrease in catalyst activity after catalyst reuseis mainly due to carbonaceous deposition, whereas leaching of sulfonicacid groups is not significant. This effect is more pronounced inthe largest-pore-size catalyst C3, which rapidly deactivatesafter one reaction cycle, whereas catalysts with a relatively mediumand 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 a similar amount of carbonaceous deposition, suggestingthat the increased reusability of the small-pore-size catalyst canbe attributed to the presence of SO3H groups mostly presenton the external surface, as corroborated by results on pore cloggingobtained by NMR relaxation measurements. The increased reusabilityof the C2 catalyst is attributed to a lower amount ofhumin being formed and, at the same time, reduced pore clogging, whichhelps to maintain accessible the internal pore space.

Automated summary

The alcoholysis of furfuryl alcohol in SBA-15-pr-SO3H catalysts with different pore sizes was studied. Results showed that changes in pore size have a significant effect on catalyst activity and durability, with larger-pore-size catalysts deactivating more rapidly. The presence of SO3H groups on the external surface and reduced pore clogging were identified as factors contributing to the increased reusability of smaller-pore-size catalysts.