Heterostructured CeO2-M (M = Co, Cu, Mn, Fe, Ni) Oxide Nanocatalysts for the Visible-Light Photooxidation of Pinene to Aroma Oxygenates

Ni-Based SBA-15 Catalysts Modified with CeMnOx for CO2 Valorization via Dry Reforming of Methane: Effect of Composition on Modulating Activity and H2/CO Ratio

Dry reforming of methane with ratio CH4/CO2 = 1 is studied using supported Ni catalysts on SBA-15 modified by CeMnOx mixed oxides with different Ce/Mn ratios (0.25, 1 and 9). The obtained samples are characterized by wide-angle XRD, SAXS, N2 sorption, TPR-H2, TEM, UV-vis and Raman spectroscopies. The SBA-15 modification with CeMnOx decreases the sizes of NiO nanoparticles and enhances the NiO-support interaction. When Ce/Mn = 9, the NiO forms small particles on the surface of large CeO2 particles and/or interacts with CeO2, forming mixed phases. The best catalytic performance (at 650 °C, CH4 and CO2 conversions are 51 and 69%, respectively) is achieved over the Ni/CeMnOx/SBA-15 (9:1) catalyst. The peculiar CeMnOx composition (Ce/Mn = 9) also improves the catalyst stability: In a 24 h stability test, the CH4 conversion decreases by 18 rel.% as compared to a 30 rel.% decrease for unmodified catalyst. The enhanced catalytic stability of Ni/CeMnOx/SBA-15 (9:1) is attributed to the high concentration of reactive peroxo (O-) and superoxo (O2-) species that significantly lower the amount of coke in comparison with Ni-SBA-15 unmodified catalyst (weight loss of 2.7% vs. 42.2%). Ni-SBA-15 modified with equimolar Ce/Mn ratio or Mn excess is less performing. Ni/CeMnOx/SBA-15 (1:4) with the highest content of manganese shows the minimum conversions of reagents in the entire temperature range (X(CO2) = 4-36%, X(CH4) = 8-58%). This finding is possibly attributed to the presence of manganese oxide, which decorates the Ni particles due to its redistribution at the preparation stage.

Cerium-Bismuth Oxides/Oxynitrates with Low Toxicity for the Removal and Degradation of Organophosphates and Bisphenols

Nanoscale cerium-bismuth oxides/oxynitrates were prepared by a scalable low-temperature method at ambient pressure using water as the sole solvent. Solid solutions were formed up to a 1:1 Ce/Bi molar ratio, while at higher doping levels, bismuth oxynitrate photocatalysts with a pronounced layered structure were formed. Bismuth caused significant changes in the structure and surface properties of nanoceria, such as the formation of defects, oxygen-containing surface groups, and Lewis and Brønsted acid sites. The prepared bifunctional adsorbents/photocatalysts were efficient in the removal of toxic organophosphate (methyl paraoxon) from water by reactive adsorption followed by photocatalytic decomposition of the parent compound and its degradation product (p-nitrophenol). Bi-doped ceria also effectively adsorbed and photodegraded the endocrine disruptors bisphenols A and S and outperformed pure ceria and the P25 photocatalyst in terms of efficiency, durability, and long-term stability. The very low toxicity of Bi-nanoceria to mammalian cells, aquatic organisms, and bacteria has been demonstrated by comprehensive in vivo/in vitro testing, which, in addition to its simple "green" synthesis, high activity, and durability, makes Bi-doped ceria promising for safe use in abatement of toxic chemicals.

Chirally modified cobalt-vanadate grafted on battery waste derived layered reduced graphene oxide for enantioselective photooxidation of 2-naphthol: Asymmetric induction through non-covalent interaction

The cobalt oxide-vanadium oxide (Co₃O₄-V₂O₅) combined with reduced graphene oxide (rGO) having band gap of ∼ 3.3 eV appeared as a suitable photocatalyst for selective oxidation of 2-naphthol to BINOL. C2-symmetric BINOL was achieved with good yield using hydrogen peroxide as the oxidant under UV-light irradiation. The same catalyst was chirally modified with cinchonidine and a newly synthesized chiral Schiff base ligand having a sigma-hole center. The strong interaction of the chiral modifiers with the cobalt-vanadium oxide was truly evident from various spectroscopic studies and DFT calculations. The chirally modified mixed metal oxide transformed the oxidative CC coupling reaction with high enantioselectivity. High enantiomeric excess upto 92 % of R-BINOL was obtained in acetonitrile solvent and hydrogen peroxide as the oxidant. A significant achievement was the formation of S-BINOL in the case of the cinchonidine modified catalyst and R-BINOL with the Schiff base ligand anchored chiral catalyst. The UV-light induced catalytic reaction was found to involve hydroxyl radical as the active reactive species. The spin trapping ESR and fluorescence experiment provided relevant evidence for the formation of such species through photodecomposition of hydrogen peroxide on the catalyst surface. The chiral induction to the resultant product was found to induce through supramolecular interaction like OH…π, H…Br interaction. The presence of sigma hole center was believed to play significant role in naphtholate ion recognition during the catalytic cycle.

Recent advances in non-noble metal-based oxide materials as heterogeneous catalysts for C–H activation

This perspective article summarizes the recent developments of non-noble metal-based oxides, as a new class of catalysts for C−H bond activation, focusing on their essential surface properties.

Visible light assisted production of methanol from CO2 using CdS@CeO2 heterojunction

The production of methanol from CO₂ is highly desirable in present scenario due to the excessive CO₂ emission. Several photocatalytic materials have been developed for reduction of CO₂ into methanol under mild conditions, but things need to be developed soon. In the present work, the solvothermal process had synthesized high surface area CeO₂ supported CdS nanocomposite. The catalytic amount of CdS@CeO₂ heterojunction materials was highly active to produce methanol and CO from CO₂. CdS@CeO₂ heterojunction demonstrated a good formation of methanol (1534 μmol-g^-1) and CO (213 μmol-g^-1) under similar conditions. CdS@CeO₂ heterojunction materials were studied using several characteristic techniques, such as XRD, XPS, HR-TEM, UV-vis, FTIR, PL, and Raman spectroscopy, physisorption and EIS analysis. CdS@CeO₂ nanocomposite demonstrated excellent activity and stability with no leaching of metal content at the end of the sixth run.

Facile synthesis, characterization, mechanism and enhanced visible-light photocatalytic activity of SiW12/α-Fe2O3 nanocomposites

The photocatalytic mechanism of the SiW12/α-Fe2O3 nanohybrid.