Electron Donation from Boron Suboxides via Strong p-d Orbital Hybridization Boosts Molecular O2 Activation on Ru/TiO2 for Low-Temperature Dibromomethane Oxidation

Low-temperature catalytic oxidation is of significance to the degradation of halogenated volatile organic compounds (HVOCs) to avoid hazardous byproducts with low energy consumption. Efficient molecular oxygen (O2) activation is pivotal to it but usually limited by the insufficient electron cloud density at the metal center. Herein, Ru-B catalysts with enhanced electron density around Ru were designed to achieve efficient O2 activation, realizing dibromomethane (DBM) degradation T90 at 182 °C on RuB1/TiO2 (about 30 °C lower than pristine Ru/TiO2) with a TOFRu value of 0.055 s-1 (over 8 times that of Ru/TiO2). Compared to the limited electron transfer (0.02 e) on pristine Ru/TiO2, the Ru center gained sufficient negative charges (0.31 e) from BOx via strong p-d orbital hybridization. The Ru-B site then acted as the electron donor complexing with the 2π* antibonding orbital of O2 to realize the O2 dissociative activation. The reactive oxygen species formed thereby could initiate a fast conversion and oxidation of formate intermediates, thus eventually boosting the low-temperature catalytic activity. Furthermore, we found that the Ru-B sites for O2 activation have adaptation for pollutant removal and multiple metal availability. Our study shed light on robust O2 activation catalyst design based on electron density adjustment by boron.

Roles of Oxygen Species in Low-Temperature Catalytic o-Xylene Oxidation on MOF-Derived Bouquetlike CeO2

To realize efficient low-temperature catalytic o-xylene oxidation, MOF-derived CeO₂-X catalysts were prepared via the pyrolysis of MOF precursors with different ratios of cerium nitrate to trimesic acid. Among the synthesized catalysts, the bouquet like CeO₂-1 exhibited the best activity with T₅₀ and T₉₀ of 156 and 198 °C and the lowest activation energy of 60.67 kJ·mol^-1 (WHSV= 48 000 mL·g^-1·h^-1, o-xylene concentration = 500 ppm). o-Xylene was completely mineralized, and no change in conversion efficiency or CO₂ yield was found at 5 vol % H₂O for over 50 h. The rich active oxygen species (XPS: O_sur/O_latt = 0.69) and abundant oxygen vacancies (Raman: I_D/I_F2g = 0.036) of CeO₂-1 made crucial contribution to its superior catalytic activity. The O₂-TPD and H₂-TPR results confirmed that CeO₂-1 had more surface active oxygen and better mobility of bulk oxygen. Moreover, the reaction routes under different atmospheres were probed through in situ DRIFTS, in which oxygen vacancy played a key role in promoting the adsorption and activation of molecular oxygen and facilitating the migration of the bulk lattice oxygen.

Elimination or Removal of Ethylene for Fruit and Vegetable Storage via Low-Temperature Catalytic Oxidation

Ethylene acts as an important hormone to trigger the ripening and senescence of fruits and vegetables (F&V). Thus, it is essential to eliminate trace ethylene and prevent F&V losses effectively. There are several technologies currently applying to control the ethylene concentration in the storage and transportation environment, including adsorption, gene modification, oxidation, etc. These protocols will be compared, and special attention will be paid to the low-temperature catalytic oxidation that has already been applied to practical production in this review. The active sites, supports, and reaction and deactivation mechanism of the catalysts for the low-temperature ethylene oxidation will be discussed and evaluated systematically to provide new insights for the development of effective catalysts, along with the suggestion of some perspectives for future research on this important catalytic system for F&V preservation.

Crystal Facet Induced Single-Atom Pd/Cox Oy on a Tunable Metal-Support Interface for Low Temperature Catalytic Oxidation

Atomic dispersed metal sites in single-atom catalysts are highly mobile and easily sintered to form large particles, which deteriorates the catalytic performance severely. Moreover, lack of criterion concerning the role of the metal-support interface prevents more efficient and wide application. Here, a general strategy is reported to synthesize stable single atom catalysts by crafting on a variety of cobalt-based nanoarrays with precisely controlled architectures and compositions. The highly uniform, well-aligned, and densely packed nanoarrays provide abundant oxygen vacancies (17.48%) for trapping Pd single atoms and lead to the creation of 3D configured catalysts, which exhibit very competitive activity toward low temperature CO oxidation (100% conversion at 90 °C) and prominent long-term stability (continuous conversion at 60 °C for 118 h). Theoretical calculations show that O vacancies at high-index {112} facet of Co_x O_y nanocrystallite are preferential sites for trapping single atoms, which guarantee strong interface adhesion of Pd species to cobalt-based support and play a pivotal role in preventing the decrement of activity, even under moisture-rich conditions (≈2% water vapor). The progress presents a promising opportunity for tailoring catalytic properties consistent with the specific demand on target process, beyond a facile design with a tunable metal-support interface.

Effect of ball milling on the catalytic activity of cryptomelane for VOC oxidation

Cryptomelane-type manganese oxides prepared by a solvent-free method were evaluated as catalysts for the oxidation of ethyl acetate, ethanol and toluene. The original catalyst (K-OMS-2) presented high catalytic activity for ethyl acetate and ethanol oxidation, achieving 90% conversion into CO₂ around 200°C for both pollutants. Toluene was much harder to oxidize, requiring a temperature near 270°C for the same conversion. The original catalyst was mechanically treated in a ball mill at different intensities, in order to decrease the particle size for subsequent impregnation onto structured supports, as small particle sizes are usually recommended. The catalytic activity of the materials decreases with the increase in the severity of this treatment, which is related to the decrease of the surface area of the catalysts, since the other properties (phase purity, thermal stability, surface oxygen, average oxidation state and reactivity of the oxygen species) are similar among the catalysts with different ball milling treatments. For comparison, a platinum-based catalyst (1%-Pt/Al₂O₃) was also tested, which exhibited a high activity for toluene, but much lower activities for the two other volatile organic compounds tested. A long-term experiment, using ethanol as model pollutant, showed that the cryptomelane catalyst was stable for more than 100 h.