Mechanical alloying for green catalyst synthesis

S. Pithakratanayothin, R. Tongsri, T. Chaisuwan, S. Wongkasemjit
Chulalongkorn University,
Thailand

Keywords: mechanical alloying, green catalyst synthesis

Summary:

Over a decade, bimetallic catalyst performed tremendously powerful catalytic activities in many fields of chemistry, especially, hydroxylation of benzene or phenol, and selective hydrogenation in α,β-unsaturated aldehyde due to its versatile properties from the second metal which changed the crystal structure and the polarity on the surface. Unfortunately, the traditional preparation protocol of bimetallic catalysts had been done by chemical deposition, co-precipitation, and incipient wetness impregnation. These processes need a larger amount of solvent, acid, and base, thus, generating waste toxic in a large volume over a year in which affects to environment. Our research group herewith presented mechanical alloying (MA) as an alternative catalyst synthesis pathway since MA is the most practical technique, easy to handle, solvent free, and provides high productivity in both lab and commercial scales. Moreover, it is found that the mechanically alloyed (MAed) technique also results in new phases of intermetallics and produces small grains of materials that exhibit different thermodynamic properties. The prepared catalysts were characterized and confirmed crystal structure of intermetallic catalysts by X-ray diffraction (XRD) and the high resolution transmission electron micrographs (HRTEM) with selected area electron diffraction (SAED). The MAed catalysts of CuaSnb and NiaSnb were tested for the phenol hydroxylation to observe their catalytic activity and the effect of the second metal on tin. The results showed that the mix crystal structure of Cu6Sn5, Cu41Sn11, and Cu3Sn provided the highest catalytic activity, giving conversion of 84% as catechol, hydroquinone, and benzoquinone whereas a single crystal structure of Ni3Sn4 gave less conversion of 42%, however, provided higher selectivity of hydroquinone (100%).