Magnetism and catalysis

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Abstract
Catalysts have been characterized through their magnetic properties for many years. Bulk phases, such as metals, oxides, carbides, etc., are easily identified by magnetic transitions and moments. Unique magnetic contributions to catalysis occur in catalyst dispersions and adsorption. Catalysts are prepared as small crystallites upon the surface of a refractory support. These crystallites are in the diameter range of 10 to 200 Å, which means they are superparamagnetic for ferromagnetic metals and superantiferromagnetic for antiferromagnetic oxides. Magnetization measurements lead to crystallite size distributions of dispersed nickel and these have been useful in the investigation of preparational methods, crystallite size effects in adsorption and catalysis and sintering phenomena. Similar results are possible for supported oxides, such as NiO, Fe2O3, etc., but reported applications are not extensive. Adsorption of gases on ferro‐ and paramagnetic catalysts may result in a transfer of electrons, detectable through magnetic changes. This effect has been applied to adsorption intermediates. Current trends in catalysis indicate the importance of molecular clusters of atoms, which will be a promising application for magnetism, both experimental and theoretical.