Catalytically activated isotope exchange in multicomponent systems gas–solid: statistical theory and its application on example of proton-conducting oxides

Abstract

This study aims to develop a comprehensive theory of the kinetics of catalytically activated isotope exchange in closed heterogeneous systems, grounded in the ideal statistical laws governing isotope distribution. Based on this theory, all systems exhibiting isotope exchange are categorised into three groups: one-component, two-component, and multicomponent, according to isotope behaviour. It is demonstrated that any mechanism of catalytically activated isotope exchange can be represented through subtypes of exchange characterised by atom transfer quasireactions, which mediate transitions between distinct types of isotope distribution within the components. An algorithm for describing experimental data within this theoretical framework was formulated and applied to a range of literature data concerning H/D exchange in ethylene, methane, methane–hydrogen, ethane–hydrogen, and methanol–hydrogen mixtures over metal and oxide-supported catalysts. Employing the theory, the mechanism of catalytically activated isotope exchange in pure methane and methane–hydrogen mixtures over BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3−α, a promising proton-conducting catalyst, was investigated, revealing catalytic heterogeneity of active sites and H₂-induced kinetic isotope effects.