Mikrokinetisk

Mikrokinetisk modeling, or microkinetic modeling, is a detailed approach to describing chemical reactions on catalytic surfaces by explicitly considering the elementary steps that make up a reaction network. Rather than using broad, aggregated rate laws, mikrokinetisk modeling enumerates individual processes such as adsorption, surface diffusion, surface reactions, and desorption, each with its own rate constant. The method aims to connect molecular-level events with observable macroscopic rates.

A typical mikrokinetisk model specifies a network of species and reactions, including gas-phase and surface-bound intermediates. Rate expressions are derived from Arrhenius or transition state theory for each elementary step. The resulting set of coupled differential equations tracks the time evolution of surface coverages and gas-phase concentrations, subject to a site balance that constrains total surface occupancy. Parameters are often obtained from density functional theory calculations, complemented by experimental data. Sensitivity analysis helps identify rate-determining steps and informs catalyst design and optimization.

Applications span heterogeneous catalysis, such as hydrocarbon reforming, ammonia synthesis, methanol production, and various fuel-cell and electrocatalytic processes. The approach provides mechanistic insight into selectivity and turnover frequencies and supports catalyst screening and process optimization. Benefits include predictive capability and the ability to interpret experimental observations in terms of elementary steps. Limitations arise from the need for reliable, detailed kinetic data, potential surface heterogeneity, and computational complexity, as well as simplifications like neglecting diffusion limitations or strong adsorbate–adsorbate interactions.