With the growing interest in alternative energy sources, steam methanol reforming (SMR) has attracted considerable attention as a promising method for hydrogen production. The efficiency of this process is directly dependent on catalysts, and quasi-crystalline materials have recently shown promising results as catalytic components.
In this paper, we investigate the possibility of using a quasicrystalline Al-Cu-Fe alloy as a catalyst for PRM. Quasicrystals, which have a unique atomic structure with an aperiodic order, can offer specific active centers that are unattainable for traditional crystalline materials. The catalyst was synthesized by rapid melt solidification followed by heat treatment to form a quasicrystalline phase.
Methanol steam reforming (CH3OH + H2O → 3H2 + CO2) was carried out for the first time using a stable AlCuFe quasicrystal. It was found that AlCuFe subjected to leaching treatment exhibits outstanding catalytic activity. At a temperature of 573 K, the hydrogen productivity in the methanol steam reforming reaction reaches 235 l/kg min. This activity is due to the presence of copper nanoparticles on the surface of the quasicrystal grains formed during the leaching process. Quasicrystals have two important advantages: firstly, their fragility allows for efficient grinding, and secondly, the presence of iron prevents the agglomeration of copper particles.
Icosahedral quasicrystals, discovered in 1984, are characterized by forbidden fivefold symmetry in the diffraction pattern and exhibit sharp diffraction peaks indicating a long-range order similar to crystals. This discovery triggered an active interaction between physics and materials science. During the last decade, the issues of alloy synthesis, structure and physical properties have been intensively investigated. More than one hundred binary, ternary and quaternary alloy systems containing quasicrystal phases have been discovered. The lack of periodicity in the structure of most quasicrystals causes a number of common characteristics, such as exceptionally high resistivity reaching several thousand μOhm cm, comparable to semiconductors; hardness in the range of 800–1000 Hv, comparable to the hardness of silica; and a low coefficient of friction close to that of diamond. Currently, quasicrystals are used in various fields, and new products based on them are being developed.
One of the promising areas is the use of quasicrystals in catalysis. Due to their thermodynamic stability and high-temperature stability, quasicrystals can be used as catalysts under high-temperature conditions. Previously, the catalytic behavior of quasicrystalline Al-Pd-Mn was studied in comparison with crystalline Al-Pd, pure Pd, and pure Cu. It was shown that in the methanol decomposition reaction, the quasicrystalline catalyst provides the greatest amount of released hydrogen and the lowest reaction onset temperature.
The results show that the obtained Al-Cu-Fe quasi-crystalline catalyst exhibits high activity in the SRM reaction at relatively low temperatures. Transmission electron microscopy (TEM) studies revealed the presence of nano-sized copper particles on the catalyst surface, which probably play a key role in the catalytic process.
Further studies are aimed at optimizing the composition and structure of the quasi-crystalline catalyst to achieve even higher activity and stability in the PRM process. Modification of the catalyst surface by applying additional promoters, such as metal oxides, can improve the dispersion of active sites and increase the resistance to catalyst poisoning.
Author: A.PTsai, M Yoshimura
Institute: National Metals Research Institute, Tsukuba 305-0047, Japan, Mitsubishi Gas Chemical Co., Corporate Research Laboratory, 22 Wadai, Tsukuba, Ibaraki 300-4247, Japan