Coverage-Dependent Microkinetics in Heterogeneous Catalysis Powered by the Maximum Rate Analysis

Microkinetic analysis plays an important role in catalyst design. Although Langmuirian microkinetics is widely used, surface kinetics is actually non-Langmuirian, which depends on the surface nonuniformity caused by either the adsorbate-adsorbate interactions or various types of active sites exposed on the surfaces. Herein we proposed an approach based on the maximum rate analysis for an accurate and efficient analysis of surface kinetics, where the details of the surface nonuniformity were incorporated into the apparent rate coefficients. The present approach was verified by using the water-gas shift reaction on Cu(111) surfaces as a case study. Furthermore, a formulation of free energy landscape (FEL) was proposed to provide a general and intuitive picture of the catalytic reaction network, which was used to understand how surface coverages could affect the values of the macroscopic measurables. Our results demonstrated that even a mild coverage effect, which changed the overall rate only slightly, could significantly change the values of the macroscopic measurables, such as the reaction orders and the apparent activation energies. These were mainly due to the fact that even a mild coverage effect could change the rate-determining steps and weaken the binding strength of some key intermediates. Our results highlight the importance of the coverage-dependent microkinetic analysis aided by the present formulation FEL, which offers a useful tool to bridge theory and experiment and to reveal the in situ nature of the active sites, the rate-determining steps, and the key intermediates, which in turn are beneficial to the rational design of catalysts.

Automated summary

Microkinetic analysis is crucial in catalyst design, where surface kinetics, affected by surface nonuniformity, can be accurately and efficiently analyzed using maximum rate analysis. The formulation of free energy landscape provides a general picture to understand how surface coverages impact macroscopic measurables.