Unexpected discovery of superoxide radical generation by oxygen vacancies containing biomass derived granular activated carbon

Herein, we discovered and reported oxygen vacancies in silicon oxycarbide containing granular palm shell activated carbon (Si-PSAC) as a photocatalyst under UV irradiation. A strong correlation between the atomic content of Si¹⁺, oxygen vacancies and photocatalytic performance of Si-PSAC was obtained. Based on the electron paramagnetic resonance and photoluminescence analyses, Si-PSAC under UVA₃₆₅ irradiation exhibited a higher donor density, better charge transfer and lower electron-hole recombination than that under the other light sources, leading to a higher O₂^· production efficiency. Si-PSAC exhibited effective removal performance for various anionic dyes and endocrine-disrupting chemicals under UVA₃₆₅ irradiation. Continuous-flow column tests revealed the life span of Si-PSAC under UVA₃₆₅ irradiation was extended by more than 16-fold compared to adsorption column. Since the oxygen vacancies can be created from the naturally present Si in the biomass derived Si-PSAC during the activation, this unexpected discovery of O₂^· production can extend commercially-available Si-PSAC into the full-scale photocatalysis.

Study on the selective oxidation of methane over highly dispersed molybdenum-incorporated KIT-6 catalysts

The isolated MoO_x species contribute to the highly selective formation of formaldehyde.

Partial oxidation of methane to formaldehyde over copper–molybdenum complex oxide catalysts

The Cu₃Mo₂O₉ catalyst forms formaldehyde selectively in the methane oxidation with O₂ in the presence of water.

Direct conversion of methane to formaldehyde and CO on B2O3 catalysts

Direct oxidation of methane to value-added C₁ chemicals (e.g. HCHO and CO) provides a promising way to utilize natural gas sources under relatively mild conditions. Such conversions remain, however, a key selectivity challenge, resulting from the facile formation of undesired fully-oxidized CO₂. Here we show that B₂O₃-based catalysts are selective in the direct conversion of methane to HCHO and CO (~94% selectivity with a HCHO/CO ratio of ~1 at 6% conversion) and highly stable (over 100 hour time-on-stream operation) conducted in a fixed-bed reactor (550 °C, 100 kPa, space velocity 4650 mL g_cat⁻¹ h⁻¹). Combined catalyst characterization, kinetic studies, and isotopic labeling experiments unveil that molecular O₂ bonded to tri-coordinated BO₃ centers on B₂O₃ surfaces acts as a judicious oxidant for methane activation with mitigated CO₂ formation, even at high O₂/CH₄ ratios of the feed. These findings shed light on the great potential of designing innovative catalytic processes for the direct conversion of alkanes to fuels/chemicals.

Partial oxidation of methane to value-added C₁ products remains challenging due to the favorable formation of fully-oxidized CO₂. Here, the authors show supported B₂O₃ catalysts with tri-coordinated BO₃ units as the active site are highly selective in oxidizing methane to HCHO and CO.

(Ag)Pd-Fe3O4 Nanocomposites as Novel Catalysts for Methane Partial Oxidation at Low Temperature

Nanostructured composite materials based on noble mono-(Pd) or bi-metallic (Ag/Pd) particles supported on mixed iron oxides (II/III) with bulk magnetite structure (Fe3O4) have been developed in order to assess their potential for heterogeneous catalysis applications in methane partial oxidation. Advancing the direct transformation of methane into value-added chemicals is consensually accepted as the key to ensuring sustainable development in the forthcoming future. On the one hand, nanosized Fe3O4 particles with spherical morphology were synthesized by an aqueous-based reflux method employing different Fe (II)/Fe (III) molar ratios (2 or 4) and reflux temperatures (80, 95 or 110 °C). The solids obtained from a Fe (II)/Fe (III) nominal molar ratio of 4 showed higher specific surface areas which were also found to increase on lowering the reflux temperature. The starting 80 m2 g-1 was enhanced up to 140 m2 g-1 for the resulting optimized Fe3O4-based solid consisting of nanoparticles with a 15 nm average diameter. On the other hand, Pd or Pd-Ag were incorporated post-synthesis, by impregnation on the highest surface Fe3O4 nanostructured substrate, using 1-3 wt.% metal load range and maintaining a constant Pd:Ag ratio of 8:2 in the bimetallic sample. The prepared nanocomposite materials were investigated by different physicochemical techniques, such as X-ray diffraction, thermogravimetry (TG) in air or H2, as well as several compositions and structural aspects using field emission scanning and scanning transmission electron microscopy techniques coupled to energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic results from a preliminary reactivity study confirmed the potential of magnetite-supported (Ag)Pd catalysts for CH4 partial oxidation into formaldehyde, with low reaction rates, methane conversion starting at 200 °C, far below temperatures reported in the literature up to now; and very high selectivity to formaldehyde, above 95%, for Fe3O4 samples with 3 wt.% metal, either Pd or Pd-Ag.