Understanding the Promotional Effect of Mn₂O₃ on Micro-/Mesoporous Hybrid Silica Nanocubic-Supported Pt Catalysts for the Low-Temperature Destruction of Methyl Ethyl Ketone: An Experimental and Theoretical Study

Pt_0.3Mn_<i>x</i>/SiO₂ nanocubic (nc) micro-/mesoporous composite catalysts with varied Mn contents were synthesized and tested for the oxidation of methyl ethyl ketone (MEK). Results show that MEK can be efficiently decomposed over synthesized Pt_0.3Mn_<i>x</i>/SiO₂-nc materials with a reaction rate and turnover frequency respectively higher than 12.7 mmol g_Pt^–1 s^–1 and 4.7 s^–1 at 100 °C. Among these materials, the Pt_0.3Mn₅/SiO₂-nc catalyst can completely oxidize MEK at just 163 °C under a high space velocity of 42600 mL g^–1 h^–1. The remarkable performance of these catalysts is attributed to a synergistic effect between the Pt nanoparticles and Mn₂O₃. NH₃-TPD and NH₃-FT-IR experiments revealed that exposed Mn₂O₃ (222) facets enhance the quantity of Brønsted acid sites in the catalyst, which are considered to be responsible for promoting the desorption of surface-adsorbed O₂ and CO₂. It is suggested that the desorption of these species liberates active sites for MEK molecules to adsorb and react. ¹⁸O₂ isotopic labeling experiments revealed that the presence of a Pt–O–Mn moiety weakens the Mn–O bonding interactions, which ultimately promotes the mobility of lattice oxygen in the Mn₂O₃ system. It was determined that the Mn⁴⁺/Mn³⁺ redox cycle in Mn₂O₃ allows for the donation of electrons to the Pt nanoparticles, enhancing the proportion of Pt⁰/Pt²⁺ and in turn increasing the activity and stability of catalyst. In situ DRIFTS, online FT-IR, and DFT studies revealed that acetone and acetaldehyde are the main intermediate species formed during the activation of MEK over the Pt_0.3Mn₅/SiO₂-nc catalyst. Both intermediates were found to partake in sequential reactions resulting in the formation of H₂O and CO₂ via formaldehyde