Kinetics of the isomerization of α-pinene epoxide over Fe supported MCM-41 and SBA-15 materials

Abstract

A kinetic study for the isomerization of α-pinene epoxide over Fe/SBA-15 and Fe/MCM-41 catalysts was developed using a pseudo-homogeneous (polynomial law) and heterogeneous (LHHW formalism with one and two actives sites) models. TEM analysis of Fe/SBA-15 and Fe/MCM-41 showed that the materials have the typical hexagonal organization; FTIR adsorption–desorption of pyridine revealed the presence of Lewis acidity in both Fe/SBA-15 and Fe/MCM-41 catalysts. The presence of Fe3+ and Fe2+ species was concluded from XPS analysis; however, active site for α-pinene epoxide isomerization was attributed to Fe3+. With toluene as solvent, it was found that in both catalysts, the more adequate kinetic model was the unimolecular LHHW model with two active sites of the same type. Apparently, α-pinene epoxide isomerization is much faster over Fe/MCM-41 (5.78 L h−1 gFe−1) than over Fe/SBA-15 (1.14 L h−1 gFe−1). The activation energy for both Fe catalysts was evaluated using solvents of different polarity. In the case of Fe/MCM-41, the less energetic barrier was observed with toluene (30.99 kJ mol−1), while tert-butanol (13.76 kJ mol−1) was more favorable in the case of Fe/SBA-15 catalyst. Fe/MCM-41 is a very robust catalyst because it can be used up to four times without a significant loss of catalytic activity in comparison with Fe/SBA-15 that only can be used two times. Finally, a reaction mechanism was proposed for the isomerization of α-pinene epoxide over both Fe/SBA-15 and Fe/MCM-41 catalysts.