Mechanical alloying for green catalyst synthesis S. Pithakratanayothin * , R. Tongsri ** , T. Chaisuwan * , and S. Wongkasemjit * * The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, THAILAND, dsujitra@chula.ac.th ** Powder Metallurgy Research and Development Unit (PM_RDU), National Metal and Materials Technology Center, Pathum Thani 12120, THAILAND ABSTRACT This work herewith presents mechanical alloying (MA) as an alternative catalyst synthesis pathway and the most practical technique, which is 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 and the high resolution transmission electron micrographs with selected area electron diffraction. The MAed catalysts of Cu a Sn b and Ni a Sn b 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 Cu 6 Sn 5 , Cu 41 Sn 11 , and Cu 3 Sn provided the highest catalytic activity, giving conversion of 84% as catechol, hydroquinone, and benzoquinone whereas a single crystal structure of Ni 3 Sn 4 gave less conversion of 42%, however, provided only hydroquinone (100%). Keywords: Cu-Sn intermetallic, Ni-Sn intermetallic, Mechanical alloying, Phenol hydroxylation, strong acid sites 1 INTRODUCTION Generally, the catalyst preparation was done by using a large number of solvents, base, acid, and many other organic compounds. Those chemicals are toxic to environment and need specific methodes for treatment. Nowadays, the bimetallic catalysts were studied and showed the interestingly catalytic activity in many fields of chemistry (i.e. hydroxyaltion of benzen and phenol, selective hydrogenation of α,β-unsaturated aldehyde, hydrogenation of hydrocarbon, upgrading bio-oil, and partial oxidation) [1-4]. Bimetallic catalysts do not only reveal the combination of the properties related to the presence of two individual metals, but also generate new and distinctive properties due to synergetic effects between the two metals presence. However, their final structure strongly depends upon the composition, their synthesis method and conditions. Evidently, the key factor for fabricating bimetallic catalyst was the energy which helped the second metal diffuse into the one another metal and create metal-metal bond to form bimetallic. The nature of the Ma process consists of fracturing and welding [5], contributing to surface diffusion mechanism and resulting in the formation of more free surfaces and grain boundaries, surface diffusion which was driven by the reduction in surface area and radius of the crack tip [6-7]. For formation of a new crystal structure containing two different elements, the smaller diameter atoms penetrate to the interstitial site of the other to form solid solution, resulting in alloys or intermetallics. The diffusion process is very rapidly during mechanical alloying [8]. In this work, the catalysts were prepared by MA technique and studied their catalytic activity in phenol hydroxylation. The metal targets were tin (Sn), copper (Cu), nickel (Ni). Unfortunately, pure Cu and Ni did not give the satisfied results, showing over-oxidation to tar when using Cu [9] and low conversion when using Ni due to less hydroxyl radical generated [10]. Sn was revealed that it could enhance the hydrogen peroxide efficiency and prevent over oxidation of desired products [11]. The objective of this study was to provide a short review on series of Cu-Sn and Ni-Sn intermetallic catalysts synthesized by MA technique and their catalytic activity. 2 EXPERIMENTAL 2.1 Materials Nickel (Ni, 99.99 %wt), Copper (Cu, 99.99 %wt) and tin (Sn, 99.99 % wt) powders were produced using gas atomization, as detailed in elsewhere [12]. Methanol (CH 3 OH, 99.99%) was purchased from Labscan, Thailand; catechol (CAT, 99%), hydroquinone (HQ, 99%), 1,4- benzoquinone (BQ, 98%) from Sigma-Aldrich, USA; phenol detached crystals and hydrogen peroxide (H 2 O 2 , 30 %w/v) from Fisher Scientific, UK. All chemicals were used without purification. 2.2 Synthesis of Cu a Sn b and Ni a Sn b intermetallic catalysts Ni (32 ≤ um), Cu (32 ≤ um), and Sn (32 ≤ um) were used to prepare Cu a Sn b and Ni a Sn b nanoparticles, following Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2017 29