查看更多>>摘要：? 2022 Elsevier B.V.For coke oven flue gases, the simultaneous removal of NOx and CO pollutants is highly demanded but still remains a big challenge. So far there isn't a single efficient catalyst that can simultaneously achieve selective catalytic reduction of NOx by NH3 and the catalytic oxidation of CO to CO2 in the presence of excessive O2 at low temperatures (180–220 °C). Here, we report a bifunctional catalyst Mn2Cu1Al1Ox that possesses dual active sites and is highly active for both NH3-SCR and CO oxidation reactions under the above mentioned conditions. By tuning the redox properties and surface oxygen vacancies, the optimized Mn2Cu1Al1Ox catalyst achieved high conversions of both NOx and CO in the NH3-NO-CO-O2 system, with a NOx conversion of 86.8% and a CO conversion of 100% at 200 °C. The active reaction sites and the interaction principal between NH3-SCR and CO oxidation reactions were thoroughly investigated by well-designed experiments, in-situ DRIFTS and DFT calculations. It was revealed that NH3 and CO competed for the same active sites, which significantly influenced the catalytic performance of Mn3Al1Ox and Cu3Al1Ox for CO oxidation reactions. For the bifunctional Mn2Cu1Al1Ox catalyst, CO is more easily adsorbed on the Cu sites, while NH3 is more inclined to adsorb on the Mn sites, which enables both NH3-SCR and CO oxidation reactions to proceed simultaneously on one catalyst. The improvement of CO oxidation performance on Mn2Cu1Al1Ox catalyst is mainly attributed to the reduced Jahn-Teller effect of Cu atoms by doping into Mn3O4, which leads to the lift of d-band center and finally enhances the CO adsorption.
查看更多>>摘要：? 2022 Elsevier B.V.With mounting concerns over critical element sustainability in future bio-refineries, the conversion of phyto-extracted nickel (from contaminated lands) into an inexpensive and clean catalyst could help to reduce demand for virgin precious metals. Utilizing this green approach, noble metal catalysts, which require substantial downstream processing, could potentially be replaced by a naturally developed non-noble metal catalyst. We report a biologically bound non-noble metal catalyst (Ni-phytocat, 0.1–2.5 wt% Ni) prepared using simple, one-step, energy efficient, microwave-assisted pyrolysis (250℃, 200 W, <10 min). The biologically bound Ni in the plant matrix directs the catalytic hydrogenation of cinnamaldehyde selectively and efficiently (up to 97% conversion and 96% selectivity at T≤120 ℃), Our findings indicate that the presence of bio-carbon matrix around the phyto-extracted Ni enables an efficient suppression of the over-hydrogenation reaction pathway and prevents further dissociation of adsorbed hydrocinnamaldehyde molecules. The simplicity, long-term stability and ease of handling make this catalyst an economically and environmentally attractive alternative to Raney nickel and precious metal–based catalysts.
查看更多>>摘要：? 2022 Elsevier B.V.It is significant to realize the synergistic effect of single-atom sites and its support to obtain excellent performance photocatalysts. Here, single-atom silver (SAAg) is embedded into the hierarchical tremella-like carbon nitride (3DT-CN) by an efficient one-step reduction method. The photo-degradation mechanism of SAAg/3DT-CN for tetracycline (TC) is first proposed. And the synergistic effect to improve photocatalytic activity is also discussed in depth. Density functional theory (DFT) calculations and physicochemical characterizations reveal that the synergistic effect of SAAg and 3DT-CN has improved the absorption capacity of visible light, the binding energy with oxygen, charge transfer behavior and other properties. Electron spin resonance (ESR) and capture experiments validate the active species involved in the reaction. The first-order kinetic constant of TC degradation by SAAg/3DT-CN is 8.4 times and 3.8 times that of 3DT-CN and AgNP/3DT-CN in 75 min, respectively. This work provides a meritorious structure-activity strategy for the removal of refractory antibiotics.
查看更多>>摘要：? 2022 Elsevier B.V.CoFe2O4/g-C3N4 p-n heterojunction photocatalysts have been successfully synthesized. The formation of p-n heterojunction and the unique morphology of g-C3N4 enhanced electron transfer and charge separation, leading to a significant improvement in photocatalytic efficiency. 5-CoFe2O4/CNS not only had a high photocatalytic hydrogen evolution rate of 18.9 mmol·g?1·h?1, but also possessed an efficient photocatalytic fluoroquinolone antibiotics removal efficiency. A smaller band gap in 5-CoFe2O4/CNS photocatalyst promoted more light generated electrons under visible light irradiation. An internal electric field at the contact interface accelerated the accumulation of electrons and holes in the valence band of g-C3N4 and conduction band of CoFe2O4, thereby revealing a higher separation efficiency and noticeable inhibited recombination rate of the photoinduced electrons and holes. Also, improved removal efficiency for fluoroquinolone antibiotics was attained in the self-designed acousto-optic microreactor, which was 7.2 and 30 times higher than quartz glass tube and batch experiment, respectively.
查看更多>>摘要：? 2022 Elsevier B.V.A series of TiO2-supported MOx catalysts (M=V, W, Ce, Cu and S) were investigated for their SCR activity. In situ Raman spectroscopy indicated that the supported MOx phases were completely dispersed as surface sites on the TiO2 support. In situ IR revealed that surface VOx, WOx and SOx sites anchored at both CeOx/CuOx and TiO2 sites. The number of surface Lewis acid sites decreased with the addition of basic (CeOx/CuOx) and acidic (VOx/WOx) sites in all catalysts, and acidic SOx in the unpromoted and Ce-promoted catalysts. The surface VOx, WOx and SOx sites introduced surface Br?nsted acid sites. The redox promoters increased the NO conversion, but SOx impregnation inhibited their effect due to acid (SOx)-base (CeOx/CuOx) interactions. The SCR reaction was shown to efficiently proceed via either surface NH3* or NH4+* species, resolving the long-standing dispute on the involvement of these species in the SCR reaction.
查看更多>>摘要：? 2022 Elsevier B.V.Designing heterojunctions with a feasible charge transfer pathway is a promising strategy for establishing highly efficient artificial photosystems. The step-scheme (S-scheme) heterojunction has shown considerable potential in enhancing redox ability and charge transfer of photocatalysts. Herein, a hierarchical heterojunction involving vacancy-defect TiO2 quantum dots (QDs) and 2D g-C3N4 nanosheets was constructed using a multi-step assembly strategy. Computational and experimental studies show that the vacancy-defect TiO2 QDs can induce an S-scheme charge transfer pathway in the 0D/2D heterojunction under visible-light irradiation, which greatly improved the redox ability of charge carriers, enhanced the charge transfer and separation at interfaces, and facilitated the H2O adsorption and dissociation. This results in over 10-fold increase in hydrogen evolution reaction (HER) of photocatalytic water splitting for a wide range of carbon nitrides. The values achieved compare favorably with the best carbon nitride photocatalysts developed to date.
查看更多>>摘要：? 2022 Elsevier B.V.Persistent radical covalent organic frameworks (COFs) have exhibited great application potential in the fields of photocatalysis, magnetism, and biology. However, there is still a lack of a simple, green, and effective way to produce persistent radical COFs. Here, we synthesized two sp2 carbon-covalent organic frameworks (sp2C-COFs) with persistent triphenylamine radical cation (TPA+?), which can be generated by simple light irradiation since the effective donor–acceptor heterojunction is formed in ordered skeleton. The number of persistent TPA+? will increase with the intensity of light irradiation and the photogenerated electrons generated simultaneously can be consumed by O2 to form reactive oxygen species, which can be then used to carry out the oxidative organic transformations under visible light. In addition, femtosecond-transient absorption spectra prove that the difference in the structure of the two radical cation sp2C-COFs will significantly influence the charge recombination rate, so that the materials show different catalytic efficiency.
查看更多>>摘要：? 2022 Elsevier B.V.Copper-based catalysts are widely used to adjust the activity and selectivity of CO2 electroreduction reactions (CO2RR). In this article, we choose to use hollow mesoporous carbon spheres (HMCS) to confine and protect Cu clusters to achieve high C2 selectivity. The electrocatalytic results show that when the amount of Cu clusters confined by HMCS reaches 20% (Cu/HMCS5-20%), the selectivity of C2 products reach 88.7% at ? 1.0 V vs. RHE. In situ Fourier transform infrared spectroscopy (FTIRS) shows that Cu clusters confined and protected by HMCS is beneficial to the conversion of *CO to *CHO, while the nanocavities formed by HMCS can effectively confine the in situ formed *CHO carbon intermediates, which facilitates the C-C bond coupling to form C2H4 and C2H5OH. We proposes a method to improve the C2 selectivity of CO2RR and reduce the amount of Cu in CO2RR by using the confinement effect of HMCS.
查看更多>>摘要：? 2022 Elsevier B.V.Reducing the usage of noble metals, such as platinum-based catalysts for oxygen reduction reaction (ORR) is pressingly demanded towards the practical applications of proton-exchange membrane fuel cells. One promising way is to develop Pt single atom catalysts (SACs), which, however, are plagued by their preference toward two-electron ORR pathway as well as stability issue. Herein, a single-atom alloy (SAA) catalyst with platinum-cobalt (Pt-Co) dual sites encapsulated in nitrogen-doped graphitized carbon nanotubes (Pt1Co100/N-GCNT) consisting of isolated Pt atoms decorated on the surface of Co nanoparticles was reported. Based on complementary spectroscopic characterizations and first-principle calculations, we propose that the unique Pt-Co dual sites in SAA facilitates the adsorption and dissociation of oxygen, particularly for the immobilization of OOH* intermediate and the dissociation of OH* intermediate, and thus result in high-efficiency four-electron ORR pathway. Consequently, the Pt1Co100/N-GCNT SAA catalyst achieves a mass activity of 0.81 A mg–1Pt at 0.90 V (versus the reversible hydrogen electrode) in 0.1 M HClO4 electrolyte, outperform commercial Pt/C catalyst for 5.4 times. The superior stability of the SAA catalyst was reflected by the results from the 30,000 potential-scanning cycles combined with the post characterization of the catalyst.
查看更多>>摘要：? 2022 Elsevier B.V.Transition metal- and nitrogen-doped mesoporous carbons are prepared, characterised, and used as oxygen reduction reaction (ORR) electrocatalysts in an anion exchange membrane fuel cell (AEMFC). Novel mesoporous carbon (MPC) based engineered catalyst support is doped using high-temperature pyrolysis in the presence of metal acetate(s) and 1,10-phenanthroline (nitrogen source). Three transition metals are used to prepare materials with the following metal compositions: Fe, Co, CoFe, FeMn, and CoMn. Physico-chemical characterisation shows the success of doping with similar morphology and textural properties of all materials. The rotating ring-disc electrode experiments in alkaline solution show that all five catalysts exhibit good electrocatalytic activity towards the ORR, with Fe-N-MPC, CoFe-N-MPC and FeMn-N-MPC being best-performing materials with excellent stability. The HO2– yield depends on the metal composition with Fe-N-MPC and FeMn-N-MPC giving the lowest percentage. The latter two are employed in the AEMFC and reach power densities of 473 and 474 mW cm–2, respectively.
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