Ytkatalysen

Ytkatalysen, or surface catalysis, refers to the acceleration of chemical reactions by a catalyst that operates at an interface, typically a solid surface in contact with gas or liquid reactants. In heterogeneous catalysis the catalyst presents discrete active sites on the surface where reactants adsorb, react, and desorb as products. The overall rate depends on adsorption, surface coverage, and the kinetics of surface steps.

Most surface reactions proceed through adsorption, surface transformation, and desorption. Common mechanisms include Langmuir-Hinshelwood, where two adsorbed species react on the surface; Eley-Rideal, where a gas-phase molecule reacts with an adsorbed species; and the Mars-van Krevelen mechanism, typical for oxide catalysts, which uses lattice oxygen in the reaction.

Catalysts are usually metals, metal oxides, or combinations, often supported on high-surface-area materials. The activity and selectivity depend on the nature of active sites, which are influenced by facet, defects, particle size, and metal–support interactions. Well-known examples include Pt-, Pd-, Ni-, and Fe-based systems and supports such as TiO2, Al2O3, and SiO2.

Characterization of surface catalysis employs chemisorption measurements, temperature-programmed desorption, in-situ spectroscopy, and microscopy to identify active sites and reaction pathways. Deactivation by poisoning, sintering, or coking is a major challenge, prompting design strategies that control composition, support, and nanostructure.

Ytkatalysen underpins many industrial processes, including ammonia synthesis on iron catalysts, hydrocarbon reforming and hydrogenation on noble metals, and oxidation reactions in catalytic converters. Ongoing advances in single-atom and nanoscale catalysts, along with computational design, seek higher efficiency and lower precious-metal use by revealing surface reactions at the atomic level.