Selective oxidation of CO over CuO-CeO2 catalyst: effect of calcination temperature

A Facile Approach of Fabricating Bifunctional Catalysts for Redox Applications by Uniformly Immobilized Metallic Nanoparticles on NiCr LDH

This study discloses the development of NiCr LDH, Ag@NiCr LDH, and Pd@NiCr LDH bifunction catalysts using a hydrothermal coprecipitation method followed by sol immobilization of metallic nanoparticles. The structures and morphologies of the synthesized nanocomposites were analyzed using FTIR, XRD, XPS, BET, FESEM-EDX, and HRTEM. The catalytic effectiveness of the samples was evaluated by tracking the progression of NaBH₄-mediated nitrobenzene (NB) reduction to aniline and CO oxidation using UV-visible spectrophotometry and an infrared gas analyzer, respectively. Pd@NiCr LDH displayed much higher performance for both reactions than the bare NiCr LDH. The catalyst Pd@NiCr LDH showed robust catalytic activity in both the oxidation of carbon monoxide (T_50% (136.1 °C) and T_100% (200.2 °C)) and NaBH₄-mediated nitrobenzene reduction (98.7% conversion and 0.365 min^-1 rate constant). The results disclose that the Ni²⁺@ Cr³⁺/Cr⁶⁺ @Pd° ion pairs inside the LDH act as a charge transfer center and hence significantly enhance the catalytic performance. As a result, this research offers the novel NiCr LDH catalyst as a bifunctional catalyst for air depollution control and the organic transformation process.

Decomposition of Copper Formate Clusters: Insight into Elementary Steps of Calcination and Carbon Dioxide Activation

The decomposition of copper formate clusters is investigated in the gas phase by infrared multiple photon dissociation of Cu(II) n (HCO2)2n+1 -, n≤8. In combination with quantum chemical calculations and reactivity measurements using oxygen, elementary steps of the decomposition of copper formate are characterized, which play a key role during calcination as well as for the function of copper hydride based catalysts. The decomposition of larger clusters (n >2) takes place exclusively by the sequential loss of neutral copper formate units Cu(II)(HCO2)2 or Cu(II)2(HCO2)4, leading to clusters with n=1 or n=2. Only for these small clusters, redox reactions are observed as discussed in detail previously, including the formation of formic acid or loss of hydrogen atoms, leading to a variety of Cu(I) complexes. The stoichiometric monovalent copper formate clusters Cu(I) m (HCO2) m+1 -, (m=1,2) decompose exclusively by decarboxylation, leading towards copper hydrides in oxidation state +I. Copper oxide centers are obtained via reactions of molecular oxygen with copper hydride centers, species containing carbon dioxide radical anions as ligands or a Cu(0) center. However, stoichiometric copper(I) and copper(II) formate Cu(I)(HCO2)2 - and Cu(II)(HCO2)3 -, respectively, is unreactive towards oxygen.

An atomic-level insight into the basic mechanism responsible for the enhancement of the catalytic oxidation of carbon monoxide on a Cu/CeO2 surface

Reaction mechanism of CO molecules onto a Cu/CeO₂ surface and morphological changes.

The absence of a gap state and enhancement of the Mars-van Krevelen reaction on oxygen defective Cu/CeO2 surfaces

We report a detailed first-principles analysis of the electronic structures of oxygen defective CeO2 and Cu/CeO2 surfaces aimed at elucidating the disappearance of the gap state of defective CeO2 when a Cu atom is added at the surface. The top of the valence band of Cu/CeO2 originates from the O 2p states around this Cu atom. We show that this redistribution of electronic states at the defective Cu/CeO2 surface enhances the reactivity of the surface O atoms. Indeed, dynamical simulations show an acceleration of catalytic NO oxidation occurring via the Mars-van Krevelen mechanism mediated by these highly reactive oxygens.

Room-temperature synthesis of mesoporous CuO and its catalytic activity for cyclohexene oxidation

CuO nanoleaves with a mesoporous structure have been synthesized in the presence of triethylamine at room temperature. The mesoporous CuO nanoleaves exhibit excellent catalytic activity for solvent-free cyclohexene oxidation with oxygen.

Low-temperature CO oxidation on CuO/CeO2catalysts: the significant effect of copper precursor and calcination temperature

The performance of CuO/CeO₂catalysts for CO oxidation strongly depends on the type of copper precursor and the calcination temperature.