Incorporation of the substrate structure into kinetics on heterogeneous acid catalysis through application of linear free-energy relationships

• Application of linear free energy relationship to complex reactions on nanoporous acid catalysts. • The general treatment for micro/mesoporous materials with different types of pores. • The two-step sequence, Eley-Rideal and Langmuir-Hinshelwood mechanisms are considered. • The acid site density is incorporated for reactions in the nanoconfined space. • Temperature dependence of Taft parameters in alkyllevulinates hydrogenation was modelled. Linear free energy relationships imply a linear relation between energy of activation or Gibbs activation energy with respectively enthalpy or the Gibbs energy of the reaction. Typically for reactions catalysed by mineral acids the Hammett or the semi-empirical Taft equations are used for calculating the rate constants of elementary reactions depending on the substituents present respectively in the aromatic or aliphatic compounds. These equations mainly utilize additivity of various interactions such as polar, resonance and steric. The current treatment is based on the application of the linear free energy relationship connecting the Gibbs free energy of a reaction with the Gibbs activation energy for complex reactions on the surface of nanoporous acid catalysts. The general treatment was developed for micro/mesoporous materials with different types of pores considering also reactions on the outer surface of the crystals. The methodology has been applied for the two-step sequence, along with Eley-Rideal and Langmuir-Hinshelwood mechanisms. The temperature dependence of the rates for cyclization of various esters of 4-hydroxypentanoic acid to γ-valerolactone on a mildly acidic carbon was used to illustrate how the developed methodology can be applied to describe the experimental data.