Formaldehyde Oxidation over Co@N-Doped Carbon at Room Temperature: Tunable Co Size and Intensified Surface Electron Density

Abstract

Developing transition-metal nanocatalysts with precious-metal-like ability is essential for complete mineralization of formaldehyde (HCHO) at room temperature. Herein, a series of N-doped carbon encased metallic Co (Co@NC-x) nanocatalysts have been fabricated to explore the effect of the Co particle size on HCHO oxidation for the first time. High-angle annular dark-field scanning transmission electron microscopy displayed the small-sized and highly dispersed Co nanoparticles that were formed in Co@NC-0.25, which exhibited the highest specific catalytic activity (0.594 μmolCO2 ·gCo –1·s–1) compared with its counterparts. Zero-valence cobalt was dominant in Co nanoparticles as revealed by X-ray photoelectron spectroscopy. Density functional theory calculations demonstrated an evident charge transfer occurring from the metallic Co core to the carbon layer. Moreover, O2 binds to the carbon site adjacent to the nitrogen atom in an end-on fashion, and the length of the O–O bond is elongated. These results revealed that the special Co@NC structure could supply an electron-rich surface, facilitating adsorption and activation of O2. Based on the identification of reaction intermediates and the microstructure of Co@NC-x, the conversion mechanism of HCHO over the as-prepared Co@NC-x was proposed. This study provides a new insight into indoor HCHO purification using transition-metal nanocatalysts with a similar efficiency as precious metals.

Construction of a Novel Closed-Loop Livestock Waste Valorization Paradigm: Bridging Manure and Ammonia Gas via Phosphate-Doped Hydrochar

“…A large number of electrons were selectively gathered around O and C atoms instead of P atoms, considering the different electron affinities of C, O, and P atoms, for P-containing groups. The P atom functioned as a linker between the O and C atoms and cooperated with the O atom to regulate the charge distribution of the C atom, hence polarized the graphene surface. , The nature of oxygen species was responsible for the NH 3 interaction (Figure S8). NH 3 could act as both the H-bond acceptor and the donor.…”

“…The P atom functioned as a linker between the O and C atoms and cooperated with the O atom to regulate the charge distribution of the C atom, hence polarized the graphene surface. 11,61 The nature of oxygen species was responsible for the NH 3 interaction (Figure S8). NH 3 could act as both the H-bond acceptor and the donor.…”

Zn, Co, and Fe Tridoped N–C Core–Shell Nanocages as the High-Efficiency Oxygen Reduction Reaction Electrocatalyst in Zinc–Air Batteries

“…The Co 2p XPS spectrum indicates two pairs of peaks centered at around 780.7/796.2 and 786/803 eV, which were assigned to the oxidation states of Co 2+ and accompanied with satellite peaks. 21 Unlike the ZnCoFe−N−C sample, all other cobaltcontaining catalysts present a pair of binding energy peaks at 778.4 and 793.46 eV, which were assigned to the elemental cobalt of Co 0 (Figure S4c). This reflects that the cobalt element in the ZnCoFe−N−C catalyst mainly forms Co−N x active sites by bonding nitrogen.…”

“…Zn–N x had been proven to be an effective ORR catalytic site in a previous study. The Co 2p XPS spectrum indicates two pairs of peaks centered at around 780.7/796.2 and 786/803 eV, which were assigned to the oxidation states of Co 2+ and accompanied with satellite peaks . Unlike the ZnCoFe–N–C sample, all other cobalt-containing catalysts present a pair of binding energy peaks at 778.4 and 793.46 eV, which were assigned to the elemental cobalt of Co 0 (Figure S4c).…”

Ultrathin MnO2-Coated FeOOH Catalyst for Indoor Formaldehyde Oxidation at Ambient Temperature: New Insight into Surface Reactive Oxygen Species and In-Field Testing in an Air Cleaner

“…The consumed ROS could be continuously replenished by molecular O 2 or water vapor. , Recently, ROS generated from Fenton-like O 2 activation over Fe-MOF catalysts, including superoxide radicals ( • O 2 – ), hydroxyl radicals ( • OH), and singlet oxygen ( 1 O 2 ), were confirmed as active for HCHO oxidation . However, the specific role and contribution of the oxygen-free radical species in HCHO oxidation over Mn-based catalysts are still unidentified. − Although the role of ROS in HCHO oxidation is under debate, the performance of catalysts can be promoted by increasing the amount of ROS via the introduction of surface oxygen vacancies. The surface oxygen vacancies act as adsorption and active sites to facilitate the dissociation of molecular O 2 into ROS.…”