Influence of the Preparation Procedure on the Catalytic Activity of Gold Supported on Diamond Nanoparticles for Phenol Peroxidation

Size-matched polyoxometalate encapsulated in UiO-66(Zr): an extraordinary catalyst with double active sites for the highly efficient ultra-deep oxidative desulfurization of fuel oil

In this study, for the first time, we selected a size-matched polyoxometalate α-Mo8O26, and successfully prepared Mo8-UiO-66(Zr) as a catalyst with double active sites for extractive and catalytic oxidative desulfurization systems (ECODS).

Kinetic and Mechanistic Study of Rhodamine B Degradation by H2O2 and Cu/Al2O3/g-C3N4 Composite

The classic Fenton reaction, which is driven by iron species, has been widely explored for pollutant degradation, but is strictly limited to acidic conditions. In this work, a copper-based Fenton-like catalyst Cu/Al2O3/g-C3N4 was proposed that achieves high degradation efficiencies for Rhodamine B (Rh B) in a wide range of pH 4.9–11.0. The Cu/Al2O3 composite was first prepared via a hydrothermal method followed by a calcination process. The obtained Cu/Al2O3 composite was subsequently stabilized on graphitic carbon nitride (g-C3N4) by the formation of C−O−Cu bonds. The obtained composites were characterized through FT-IR, XRD, TEM, XPS, and N2 adsorption/desorption isotherms, and the immobilized Cu+ was proven to be active sites. The effects of Cu content, g-C3N4 content, H2O2 concentration, and pH on Rh B degradation were systematically investigated. The effect of the catalyst dose was confirmed with a specific reaction rate constant of (5.9 ± 0.07) × 10−9 m·s−1 and the activation energy was calculated to be 71.0 kJ/mol. In 100 min 96.4% of Rh B (initial concentration 20 mg/L, unadjusted pH (4.9)) was removed in the presence of 1 g/L of catalyst and 10 mM of H2O2 at 25 °C, with an observed reaction rate constant of 6.47 × 10−4 s−1. High degradation rates are achieved at neutral and alkaline conditions and a low copper leaching (0.55 mg/L) was observed even after four reaction cycles. Hydroxyl radical (HO·) was identified as the reactive oxygen species by using isopropanol as a radical scavenger and by ESR analysis. HPLC-MS revealed that the degradation of Rh B on Cu/Al2O3/CN composite involves N-de-ethylation, hydroxylation, de-carboxylation, chromophore cleavage, ring opening, and the mineralization process. Based on the results above, a tentative mechanism for the catalytic performance of the Cu/Al2O3/g-C3N4 composite was proposed. In summary, the characteristics of high degradation rate constants, low ion leaching, and the excellent applicability in neutral and alkaline conditions prove the Cu/Al2O3/g-C3N4 composite to be a superior Fenton-like catalyst compared to many conventional ones.

The wet synthesis and quantification of ligand-free sub-nanometric Au clusters in solid matrices

The synthesis of ligand-free sub-nanometric metal clusters on a large scale suffers typically from very low yields (<5% yield) and needs very high dilutions. Here we show that Au clusters can be prepared with ethylene-vinyl alcohol copolymers (EVOH), charcoal, and different metal oxides (CeO₂, Al₂O₃, TiO₂ and ZnO) in >15% yields, as unambiguously determined using a very simple and extremely sensitive analytical reaction test.

Influence of the organic linker substituent on the catalytic activity of MIL-101(Cr) for the oxidative coupling of benzylamines to imines

MIL-101(Cr) having substituents at the terephthalate linker (X = H, NO₂, SO₃H, Cl, CH₃ and NH₂) promotes the aerobic oxidation of benzylamines to the corresponding N-benzylidene benzylamines at different rates.

{[Cu3Lu2(ODA)6(H2O)6]·10H2O}n: the first heterometallic framework based on copper(ii)/lutetium(iii) for the catalytic oxidation of olefins and aromatic benzylic substrates

The catalytic performance of the novel framework {[Cu₃Lu₂(ODA)₆(H₂O)₆]·10H₂O}_n was tested in the oxidation of alkenes and benzylic hydrocarbons, using tert-butyl hydroperoxide (TBHP) and molecular oxygen (O₂) as oxidants.

A novel copper(ii)–lanthanum(iii) metal organic framework as a selective catalyst for the aerobic oxidation of benzylic hydrocarbons and cycloalkenes

The synthesis and catalytic activity of a novel heteronuclear Cu^II and La^III metal organic framework (MOF) having pyridinedicarboxylic acid (CuLa-MOF) is reported.

Copper nanoparticles supported on diamond nanoparticles as a cost-effective and efficient catalyst for natural sunlight assisted Fenton reaction

A series of catalysts consisting of Cu nanoparticles (NPs) supported on diamond nanoparticles (D) were obtained by polyol reduction of Cu(NO₃)₂ in the presence of D.

Influence of hydrogen annealing on the photocatalytic activity of diamond-supported gold catalysts

Fenton-treated diamond nanoparticles have been submitted to hydrogen reduction at 500 °C with the purpose of modifying the nature of the functional groups present on the diamond surface. The nature of the functional groups on the diamond samples was characterized by a combination of spectroscopic and analytical techniques. In particular, Fourier-transformed infrared spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS) show the decrease in the population of carboxylic acids, esters, and anhydrides after hydrogen treatment. XPS also shows a decrease on the oxygen content after the hydrogen treatment of the diamond nanoparticles and lower electronegativity of the carbons as assessed by the lower binding energy values. Although Fenton-treated diamond colloids in water changes the zeta potential from positive to negative values as a function of the pH, hydrogen annealing and the disappearance of the carboxyl groups determines that the zeta potential of the resulting sample remains positive in the complete pH range. Deposition of gold nanoparticles was carried out by the polyol method consisting on the reduction of HAuCl4 by hot ethylene glycol in the presence of the support. TEM analysis shows a variation of the average gold nanoparticle size that decreases after hydrogen reduction of carboxylic groups and becomes smaller for low gold loadings. The catalytic activity of the diamond supported gold nanoparticles as a function of the surface annealing treatment and gold loading was evaluated for the natural sunlight-assisted peroxidation of phenol by H2O2. It was observed that the most efficient sample was the one having lower gold nanoparticle size that was obtained for diamond samples reduced by hydrogen at 500 °C after the Fenton treatment and having low gold loading (0.05 wt %). Turnover frequencies above 2400 and 940 h(-1) were obtained for phenol degradation and H2O2 decomposition, respectively.

Metal nanoparticles as heterogeneous Fenton catalysts

The Fenton reaction (the generation of hydroxyl radicals from hydrogen peroxide) is the most useful method for degradation of organic pollutants in aqueous solution at moderate concentrations. In this Review we summarize the use of metal nanoparticles, either unsupported or deposited on large-surface-area solids, as Fenton catalysts. The Review complements two other reviews in the field of heterogeneous Fenton catalysis using aluminosilicates and carbonaceous materials. Herein, particular emphasis is given to the reaction conditions in which these catalysts are used, highlighting the operating mechanism and the relative efficiency of the materials. Aspects such as leaching of the metal to the solution, reusability, and the concentration of hydrogen peroxide used are analyzed in detail. Besides a critical description of the present status of the field, future trends and the need to establishing valid comparisons to assess the relative efficiencies of the materials are commented on.

Heterogeneous fenton catalysts based on activated carbon and related materials

The Fenton reaction is widely used for remediation of waste water and for the degradation of organic pollutants in water. Currently, there is considerable interest to convert the classical Fenton reaction, which consumes stoichiometric amounts of iron(II) salts, into a catalytic process that is promoted by a solid. This review describes the work that has used carbonaceous materials either directly as catalysts or, more frequently, as a large-area support for catalytically activated transition metals or metal-oxide nanoparticles. The interest in this type of catalyst derives from the wide use of carbon in conventional water treatments and the wide applicability of the Fenton reaction. After two general sections that illustrate the scope and background of Fenton chemistry, the review describes the activity of activated carbon in the absence or presence of metal-containing particles. The last sections of the review focus on different types of carbonaceous materials, such as carbon nanotubes and diamond nanoparticles. The review concludes with a section that anticipates future developments in this area, which are aimed at overcoming the current limitations of low activity and occurrence of metal leaching.