Effects of Catalyst Synthesis Methods on the Physicochemical Properties of Silica-Supported Au-Ru Bimetallic Catalysts and their Influence on the Oxidation of Phenols with H2O2.

Herein, silica-supported Au-Ru catalysts with 5% loading for each metal were prepared by microwave-assisted loading (MW) and deposition (DP) methods. Au-Ru nanoparticles are obtained on MW-5Au5Ru while short Au-Ru nanochains are obtained on DP-5Au5Ru. The performance of the catalysts is tested through the oxidation of 2,3,5-trimethylhydroquinone (TMHQ) and 4-methoxy-1-naphthol (MNL) with H₂O₂, in which 2,3,5-trimethyl-1,4-benzoquinone (TMBQ) and 4,4'-dimethoxy-2,2'-binaphthalenylidene-1,1'-dione (BNP) are produced as main products, respectively. Catalytic data obtained for the oxidation of TMHQ demonstrate that the structures of the catalysts, type of solvent, and reaction temperatures used have a significant influence on the activities and selectivities of the catalysts. When MeOH and MeNO₂ are used at room temperature (RT) in the oxidation of TMHQ on MW-5Au5Ru catalyst, 58.2% and 100% conversions of TMHQ are achieved, respectively. Both MW and DP-synthesized catalysts are highly active in the oxidation of TMHQ. Similar to TMHQ, the catalytic outcomes on the oxidative coupling of MNL highly depend on the temperature and structure of the catalyst. For example, 34% and 96% conversions of MNL are achieved at RT and 60 °C, respectively, over MW-5Au5Ru catalyst in MeOH. However, MNL conversion of 82% is achieved on DP-5Au5Ru catalyst in MeOH at RT.