Effect of the Al-MCM-41 properties on the catalytic liquid phase rearrangement of 1,2-epoxyoctane

Abstract

Abstract Liquid phase rearrangement of 1,2-epoxyoctane has been investigated over Al-MCM-41 type mesostructured materials prepared by a sol–gel route with different Si/Al molar ratios. The main reaction product is the corresponding aldehyde, although other rearrangement products, mainly allylic alcohols and diol, are also obtained. The pore size and acidic properties of the Al-MCM-41 catalysts strongly depend on the aluminium content, which affects both the extent and selectivity of 1,2-epoxyoctane rearrangement reaction. A clear lowering of the epoxide conversion with the increase of aluminium content is observed. This fact arises probably from the change from mesoporous to microporus materials as the molar Si/Al ratio of Al-MCM-41 decreases, which leads to diffusional limitations. However, the increase of aluminium content yields high selectivities towards valuable products (octaldehyde and octen-ols) with a low formation of 1,2-octanediol. Catalysts having a Si/Al molar ratio around 40 combine the best catalytic performance in regards to substrate conversion and a valuable product selectivity. TG analyzes of used catalysts indicate that the occupation degree of the pores by occluded organic molecules increases with the aluminium content, as a consequence of the increase in the number of acid sites and the decrease in the pore size of these materials. This fact is in agreement with the lower activity exhibited by the samples having high aluminium contents as it may enhance the diffusional limitations and favour the catalyst deactivation. Nevertheless, the catalytic performance of Al-MCM-41 materials is completely recovered after thermal treatment of the used catalysts.