A novel Fe-Co double-atom catalyst with high low-temperature activity and strong water-resistant for O3 decomposition: A theoretical exploration

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2- and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

DFT study of mercury adsorption on Al2O3 with presence of HCl

mercury emission control from flue gas is a crucial issue for environment protection. Alumina is an important alkali metal oxide for mercury adsorption in particulate, meanwhile is the potential adsorbent for mercury removal. The cognition on mercury heterogeneous reaction mechanism with alumina in presence of hydrogen chloride is inadequate. In this work, the DFT calculation was applied to detect mercury's chlorides adsorption on α-Al2O3 (001) surface, the Bader charge analysis was used to estimate electron transfer and the transition state theory was used to clarify reaction pathway and energy barrier, besides, the kinetic analysis based on Gibbs free energy was conducted to study the impact of temperature on chemical reaction. The results show that Hg can be captured by weak chemisorption on α-Al2O3 (001) surface with the adsorption energy of -56.37 kJ/mol, HgCl, HgCl2 are intensively bonded on surface with adsorption energies of -276.90 kJ/mol and -231.87 kJ/mol, the surface unsaturated Al and O atoms are the active sites. Charge transfer and PDOS analysis prove that the forming of covalent bonding is responsible for Hg species adsorption. Two possible reaction pathways of Hg oxidization to HgCl2 are discussed, in which a smaller energy barrier of 0.1 eV implies the dominant pathway 1 via Eley-Rideal mechanism: two adsorbed HCl molecules dissociate on surface and then react with one Hg atom. High temperature can promote the reaction rate constants of pathway 1 and 2, but is only favorable for reducing energy barrier of pathway 2.

Effects of intermetal distance on the electrochemistry-induced surface coverage of M-N-C dual-atom catalysts

The often-overlooked electrocatalytic bridge-site poisoning of the emerging dual-atom catalysts (DACs) has aroused broad concerns very recently. Herein, based on surface Pourbaix analysis, we identified a significant change in the electrochemistry-induced surface coverages of DACs upon changing the intermetal distance. We found a pronounced effect of the intermetal distance on the electrochemical potential window and the type of pre-covered adsorbate, suggesting an interesting avenue to tune the electrocatalytic function of DACs.

α-Fe2O3-supported Co3O4 nanoparticles to construct highly active interfacial oxygen vacancies for ozone decomposition

Ozone pollution has become one of the most concerned environmental issue. Developing low-cost and efficient catalysts is a promising alternative for ozone decomposition. This work presents a creative strategy that using α-Fe₂O₃-supported Co₃O₄ nanoparticles for constructing interfacial oxygen vacancies (Vo) to remove ozone. The efficiency of Co₃O₄/α-Fe₂O₃ was superior to that of pure α-Fe₂O₃ by nearly two times for 200-ppm ozone removal after 6-h reaction at 25 °C, which is ascribed to the highly active interfacial Vo. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy suggest that the Fe³⁺-Vo-Co²⁺ was formed when Co₃O₄ was loaded in α-Fe₂O₃. Furthermore, the density functional theory (DFT) calculations reveal the desorption and electron transfer ability of intermediate peroxide (O₂^2-) on Fe³⁺-Vo-Co²⁺ are higher than the Vo from other regions. In situ diffuse reflectance Fourier transform (DRIFT) spectroscopy also demonstrate the higher conversion rate of O₂^2- on Co₃O₄/α-Fe₂O₃. Base on the intermediates detected, we propose a recycle mechanism of interfacial Vo for ozone removal: O₂^2- is quickly converted to O₂^- and transformed into O₂ on interfacial Vo. Moreover, O₂-temperature-programmed desorption (TPD), H₂-temperature-programmed reduction (TPR), and electrochemical impedance spectroscopy (EIS) reveal that the oxygen mobility, reducibility, and conductivity of Co₃O₄/α-Fe₂O₃ are greatly superior to those of α-Fe₂O₃, which is contributed to the conversion of O₂^2-. Consequently, our proposed strategy effectively enhances the activity and stability of the bimetallic transition oxides for ozone decomposition.

Synergistic effect of atomically dispersed Fe-Ni pair sites for electrocatalytic reactions to remove chlorinated organic compounds

Electrocatalysis is a promising and environmentally friendly technology for the removal of refractory organics. Diatomic catalysts with an increased number of active sites have emerged with further expansion of the field of atomic catalysts. Here, a metal diatomic FeNi supported graphene (FeNi/N-rGO) catalyst is successfully synthesized. The atomically dispersed Fe and Ni species on graphene is verified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy. The pollutant degradation efficiencies for the cathode and anode are found to reach 97.6% and 95.8%, respectively, within 90 min in the diatomic catalytic system. According to DFT theoretical calculations, FeNi diatomic catalysts have a lower free energy (ΔG = -0.2 eV), and the higher adsorption energy for the active substance H* is -0.412 eV. This work presents a method for the preparation of high-performance diatomic catalysts and promotes their application in the electrochemical degradation of chlorinated organic pollutants.

Influence of water molecule on active sites of manganese oxide-based catalysts for ozone decomposition

Developing an efficient approach to decompose ground-level O₃ in humidity is crucial for preventing O₃ pollution in practical application scenes. In this study, MnO_x, CuO, and Cu/MnO_x were synthesized to investigate the influence of H₂O on the variation of active sites during O₃ decomposition. The structural characterizations of the as-synthetic catalysts were measured by N2 physisorption, XRD, SEM, O₂-TPD, H₂-TPR, TG, and FT-IR analyses. In dry conditions, the elimination rate of O₃ followed the sequence of MnO_x > Cu/MnO_x > CuO. The introduction of Cu to MnO_x enhanced the surface area and pore volume of Cu/MnO_x, accordingly diminishing the amounts of surface defects and the participation of sub-surface lattice oxygen for catalytic cycle, indicating that surface defects and oxygen vacancies (V_O) determined the catalytic activity for O₃ decomposition. In humid conditions, the elimination rate of O₃ changed to the sequence of Cu/MnO_x > MnO_x > CuO, with a variation rate compared to dry conditions of -62.9% for MnO_x, 14.2% for CuO, and 27.7% for Cu/MnO_x. The decrease of participant sub-surface lattice oxygen and the accumulation of intermediates in humidity diminished the decomposition of O₃ on MnO_x, while the active species such as superoxide radicals generating from the reaction of H₂O and Cu/MnO_x facilitated the participation of V_O and the desorption of O₂ from the occupied active sites, accelerating the catalytic cycle on Cu/MnO_x. This work developed a deeper understanding of the influence of H₂O on catalytic activity, promoting the performance of MnO_x-based catalysts for practical O₃ decomposition.

High performance ozone decomposition over MnAl-based mixed oxide catalysts derived from layered double hydroxides

Mesoporous and dispersed MnAl-based mixed metal oxide catalysts (Mn_xAlO) were fabricated via the calcination of layered double hydroxide (LDH) precursors prepared by the coprecipitation method. Their physiochemical properties were characterized and their catalytic activities for ozone decomposition were evaluated. The results indicate that the prepared Mn_xAlO catalysts have excellent catalytic activity owing to their large specific surface area, abundant surface oxygen vacancies and lower average Mn oxidation states. The Mn/Al atomic ratio and calcination temperature are found to significantly affect the textural properties and catalytic activity for ozone decomposition. The Mn₂AlO-400 catalyst (Mn/Al = 2, calcined at 400 °C) exhibited 84.8% ozone conversion after 8 h reaction under an initial ozone concentration of 45 ± 2 ppm, 30 ± 1 °C, a relative humidity of 50% ± 3%, and a space velocity of 550 000 h⁻¹. The results also show that the catalytic activity of Mn₂AlO-400, which was deactivated owing to the accumulation of oxygen-related intermediates, was recovered by calcination at 400 °C under a N₂ atmosphere for 1 h. A possible reason for catalyst deactivation and regeneration is proposed. This work provides a facile method for fabricating Mn_xAlO catalysts with excellent characteristics to achieve better catalytic activity, which are promising candidates for practical ozone decomposition.

Mesoporous and highly dispersed MnAl-based mixed metal oxide catalysts (Mn_xAlO) were fabricated via the calcination of layered double hydroxides (LDHs), which presented excellent catalytic activity for ozone decomposition.

Effect of local coordination on catalytic activities and selectivities of Fe-based catalysts for N2 reduction

Electrochemical reduction of nitrogen is considered as a promising route for achieving green and sustainable ammonia synthesis at ambient conditions. Transition metal atom loaded on N-doped graphene is commonly used...