On explosion limits of hydrogen–oxygen mixtures with a catalytic platinum surface

Abstract

In this study, we computationally investigated the explosion limits of hydrogen–oxygen (H₂-O₂) mixtures with a catalytic platinum (Pt) surface. As a classical problem in combustion kinetics, the explosion limits of H₂-O₂ mixtures show the non-monotonic, Z-shaped response. Current results show that the explosion limits over Pt still retain the Z-shaped response, but become more explosive. The transition is explained by the responses of the kinetic parameters describing the gaseous and catalytic reactions competition. For the surface species, hydrogen oxidation is characterized mainly by the desorption of H(S) from the surface to allow the numbers of Pt(S), O(S), OH(S), and H₂O(S) sites to increase. Results further show that the site density, residence time, catalytic area, and reactor volume show different effects on the explosion limits. The more intriguing result is that, with increasing equivalence ratio, the H₂-O₂ explosion limit curve in the pressure–temperature space rotates counterclockwise around a point on the third limit, which is determined by the different reactivities of gaseous and catalytic reactions for low- and high-pressure conditions. In addition, catalytic and wall termination effects on the limits are compared. The result provides useful insights into the surface reaction kinetics of the H₂-O₂ explosion limits over Pt, which is closely related to the efficient utilization as well as the assessment of safety issues for hydrogen.