An investigation on catalytic performance and reaction mechanism of RuMn/meso-TiO2 derived from RuMn intermetallic compounds for methyl ethyl ketone oxidation

In this work, we first used the oil-phase co-reduction strategy to synthesize the RuxMny (Mn/Ru molar ratio (y/x) = 7 : 20, 21 : 25, and 17 : 10) intermetallic compounds, then used the KIT-6-templeting method to prepare mesoporous titania (meso-TiO2), and finally used the impregnation method to generate the RuxMny/meso-TiO2 (Ru loading = 0.60–0.79 wt%) catalysts. Various techniques were used to measure physicochemical properties of the samples, and their catalytic performance was determined for methyl ethyl ketone (MEK) oxidation. It is found that the RuxMny/meso-TiO2 samples possessed a three-dimensionally ordered mesoporous structure, a surface area of 71–173 m2/g, and a uniform RuxMny particle size of 2.3–2.9 nm. Among all of the samples, Ru25Mn21/meso-TiO2 exhibited the best catalytic performance and good hydrothermal stability: the temperatures at MEK conversions of 10, 50, and 90 % were 131, 226, and 248 °C at a space velocity of 20,000 mL/(g h), with the apparent activation energy, specific reaction rate at 160 °C, and turnover frequency (TOF) at 160 °C being 73 kJ/mol, 41.73 mmol/(gRu s), and 4.20 s−1, respectively. In addition, introduction of 5 vol% moisture to the reaction system exerted a positive effect on catalytic activity of Ru/meso-TiO2 or Ru25Mn21/meso-TiO2 at higher temperatures. Such good performance of the Ru25Mn21/meso-TiO2 sample was related to its well dispersed Ru25Mn21 nanoparticles, high adsorbed oxygen species concentration, active surface lattice oxygen, high MEK adsorption capacity, good redox ability, and strong interaction between Ru25Mn21 and meso-TiO2. We propose that MEK might be oxidized by the adsorbed oxygen and/or surface lattice oxygen species via in turn formation of 2,3-butanedione, acetaldehyde, acetic acid, formaldehyde, and formic acid, all of which were finally converted to water and carbon dioxide.