Pt0.3Mnx/SiO2 nanocubic (nc) micro-/meso-porous 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 eff ect 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. 18 O2 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 Mn 4+ /Mn 3+ redox cycle in Mn2O3 allows for the donation of electrons to the Pt nanoparticles, enhancing the proportion of Pt 0 /Pt 2+ 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.
The development of highly active single-atom catalysts (SACs) and identifying their intrinsic active sites in oxidizing industrial hazardous hydrocarbons are challenging prospects. Tuning the electronic metal-support interactions (EMSIs) is valid for modulating the catalytic performance of SACs. We propose that the modulation of the EMSIs in a Pt 1 À CuO SAC significantly promotes the activity of the catalyst in acetone oxidation. The EMSIs promote charge redistribution through the unified PtÀ OÀ Cu moieties, which modulates the d-band structure of atomic Pt sites, and strengthens the adsorption and activation of reactants. The positively charged Pt atoms are superior for activating acetone at low temperatures, and the stretched CuÀ O bonds facilitate the activation of lattice oxygen atoms to participate in subsequent oxidation. We believe that this work will guide researchers to engineer efficient SACs for application in hydrocarbon oxidation reactions.
Hierarchically micro-mesostructured Pt/K-Al-SiO2 catalysts with regular nanorod (Pt/KA-NRS) and spherical nanoflower-like (Pt/KA-SNFS) morphologies were prepared. The existence of Al atoms generates Brønsted acid sites and reduces silanol groups over the supports, promoting the dispersion of Pt nanoparticles and stability of catalysts. Potassium atoms balance the negative charge of supports and enhance O2 mobility. The Pt/KA-NRS catalysts exhibit unexceptionable low temperature activity, CO2 selectivity, and stability for MEK oxidation. Amongst, 0.27 wt.% Pt/KA-NRS completely converts MEK at just 170 °C (activation energy as low as 37.22 kJ• % mol −1), more than 100 °C lower than other typical Pt/Pd supported catalysts reported in the literature. Diacetyl and 2,3-butandiol are the main intermediates during MEK activation, which convert into H2O and CO2 through aldehydes and acids. The excellent catalytic activity of Pt/KA-NRS is ascribed to their regular morphology, high Pt 0 content and dispersion, excellent MEK adsorption capacity and superior O2/CO2 desorption capability under low temperature.
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