Theoretical Analysis of Activation Energy of Hydrocarbon Oxidation Reaction Using Supported Pt Catalyst

Abstract

We theoretically investigated the relationship between the activity of the supported Pt catalyst and the oxide support type. The activation energies (E_a) of the propylene (C₃H₆) oxidation reaction with Pt catalysts using different oxide supports were estimated by an Arrhenius plot. The minimum and maximum E_a values were 99 kJ/mol for Pt/TiO₂ and 121 kJ/mol for Pt/La₂O₃, respectively. The chemical potentials of the oxide support (μ_MOx) were estimated by the density functional theory (DFT) calculations. The calculation results showed that the μ_MOx values varied depending on the thickness of the oxide support, but they were not strongly dependent on the crystal structure of the oxide. It was found that E_a can be expressed by the quadratic equation of μ_MOx, and E_a assumes the minimum value when μ_MOx is close to the chemical potential of the O₂ molecule (approx. −6 eV). We succeeded in expressing E_a as a quadratic expression of μ_MOx by theoretical consideration using the Brønsted–Evans–Polanyi (BEP) principle and the hard–soft-acid-base (HSAB) concept, i.e., the E_a value for the C₃H₆ oxidation reaction depends on the binding energy of the catalyst and oxygen. It was also determined that the μ_MOx value is one of the descriptors affecting the activity of the supported Pt catalyst.