Catalytic Hydrogenation of Methyl Orange and Acid Orange 7 Using NaBH₄ over Core-shell Multicomponent Alloys

Azo dyes are common aqueous environmental pollutants in developing countries. Hydrogenation is a highly effective method for decomposition of azo dyes; however, this method requires the use of noble metals as catalysts. In this study, we investigated the use of multi-component alloy catalysts. Eight multi-component alloys (CoFeNiTiCr(800), CoFeNiTiAl(800), CoFeNiTiV(800), Fe40Mn10Cr15Ni25Al5(800), Fe35Mn10Cr20Ni35(800), Fe50Mn27Cr13Ni10(800), Al0.2Co1.5CrFeNi1.5Ti0.5(600), and Al0.2Co1.5CrFeNi1.5Ti0.5(800)), where numbers in brackets represent calcine temperature (°C), were used for hydrogenation of methyl orange and Acid Orange 7 with NaBH4. These multicomponent alloys were prepared from oxide precursors using a nonelectrochemical molten salt synthesis method. The reaction rates increased in the order of Al0.2Co1.5CrFeNi1.5Ti0.5(800) < CoFeNiTiAl(800) < Al0.2Co1.5CrFeNi1.5Ti0.5(600) for hydrogenation of methyl orange. Al0.2Co1.5CrFeNi1.5Ti0.5(600) rapidly decreased the methyl orange concentration to almost zero within 10 min. The reaction rates increased in the order of CoFeNiTiCr(800) < Al0.2Co1.5CrFeNi1.5Ti0.5(600) < CoFeNiTiV(800) for hydrogenation of Acid Orange 7. CoFeNiTiV(800) rapidly decreased the Acid Orange 7 concentration to almost zero within 10 min. This difference in catalytic activity for each azo dye was thought to arise because Acid Orange 7 was insufficiently decomposed by the reducing agent NaBH4, and this affected its interaction with the catalyst.