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
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Abstract
Pt0.3Mnx/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 Pt0.3Mnx/SiO2-nc materials with a reaction rate and turnover frequency respectively higher than 12.7 mmol gPt–1 s–1 and 4.7 s–1 at 100 °C. Among these materials, the Pt0.3Mn5/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 Pt0.3Mn5/SiO2-nc catalyst. Both intermediates were found to partake in sequential reactions resulting in the formation of H2O and CO2 via formaldehyde.
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