Quasicrystals, materials with unique atomic structures that exhibit symmetry axes forbidden in classical crystallography, have attracted considerable attention in catalysis. Their use as catalyst modifiers opens up new horizons in controlling the selectivity and activity of reactions.
One of the methods of applying quasi-crystals to a catalyst is the impregnation method. The essence lies in dissolving precursors of the quasi-crystalline phase in a solvent with subsequent impregnation of the carrier (for example, aluminum oxide). After drying and calcination, a quasi-crystalline coating is formed on the surface of the catalyst.
Another approach is magnetron sputtering. In a vacuum chamber, argon ions bombard a quasi-crystalline target, knocking out atoms that settle on the catalyst surface to form a thin film. This method allows control over the thickness and composition of the coating.
Mechanochemical synthesis is also used to apply quasicrystals. In a ball mill, the mixture of precursors and the carrier is intensively mixed and ground, resulting in the formation of a quasicrystalline phase directly on the catalyst surface.
The choice of the deposition method depends on the required catalyst characteristics, the size and composition of the quasicrystals, and economic feasibility. Steam reforming of methanol (CH3OH + H2O → 3H2 + CO2) was carried out using a stable quasicrystalline material AlCuFe. It was found that AlCuFe exhibits increased catalytic activity after leaching treatment. The hydrogen productivity of 235 l/kg min at 553 K was achieved. Quasicrystals have two key advantages: brittleness, which facilitates their grinding, and heat resistance, which allows them to be used as a catalyst support at high temperatures. In addition, the catalytic properties of Al–Cu–Fe alloys of different compositions were investigated. It was found that the Al63Cu25Fe12 alloy exhibits the highest specific activity among the studied Al–Cu–Fe alloys.
Icosahedral quasicrystals, first discovered in 1984, are characterized by forbidden fivefold symmetry in diffraction patterns, showing sharp diffraction peaks indicating long-range order similar to crystals. This discovery stimulated interactions between physics and materials science. Over the past decade, alloy synthesis, structure, and physical properties have been intensively studied. More than 100 binary, ternary, and quaternary alloy systems containing a quasicrystalline phase have been discovered.
Author: M Yoshimura, AP Tsai
Institute: Corporate Research Laboratory, Mitsubishi Gas Chemical Company, 22 Wadai, Tsukuba, Ibaraki 300-4247, Japan, National Institute of Materials Science, Tsukuba 305-0047, Japan