Catalytic Active Sites Research Articles

Ligin-derived graphene-like ultrathin carbon materials for ORR catalysis

Low-cost nitrogen-doped carbon materials with graphene-like structures were designed and prepared from extensive renewable biomass waste lignin. The obtained carbon materials exhibited well-designed ultrathin two-dimensional structures with high specific area and mesoporous characteristics. Benefiting from the well-designed structures with extensive catalytic active sites and efficient mass transfer and diffusion, as well as the modified electronic characteristics from nitrogen doping, the lignin-derived carbon materials exhibited pronounced ORR catalytic activity and methanol tolerance. Considering these, the lignin-derived carbon materials hold great application potentials as ORR catalysts and catalyst supports.

Mxene quantum dots decorated reduced graphene oxide networks as multifunctional electrocatalyst for advanced lithium–sulfur batteries

Lithium sulfur (Li-S) battery has shown great potential as an attractive rechargeable energy storage devices, but the shuttle behavior and slow conversion kinetics of the intermediate lithium polysulfides (LiPSs) are the main obstacles to the practical application of Li-S battery. Herein, a simple and scalable spray drying strategy was used to construct conductive polar Ti3C2 MXene quantum dots (QDs)-decorated reduced graphene oxide (rGO) microsphere (rGO@Ti3C2 QDs) as efficient electrocatalyst and absorbent for Li-S battery. Firstly, the DFT results show that Ti3C2 QDs can effectively adsorb and catalyze LiPSs conversion. This ability can be attributed to the Ti3C2 QDs can provide a large number of LiPSs catalytic active sites. In addition, the rGO provides physical LiPSs constraint and a flexible substrate to prevent QDs from aggregating. Moreover, both parts are conductive, effectively improving the electron/charge transfer. Therefore, this unique structure and composition show high LiPSs adsorption and catalysis, while allowing rapid Li+/electron transfer. As a result, the S/rGO@Ti3C2 QDs electrode provides high initial capacity (1185 mAh/g at 0.2C), good rate capability (758 mAh/g at 3C), and excellent long-term cyclability (500 cycles at 1C with low attenuation of 0.07% per cycle), as well as an excellent electrochemical performance even at high sulfur loading. Meanwhile, the Li-S pouch cell based on S/rGO@Ti3C2 QDs also achieved a high initial energy density of 230.9 Wh kg−1. This work may provide a promising strategy to obtain better electrochemical performance by introducing quantum dots into Li-S cathodes.

Investigating Potential Cancer Therapeutics: Insight into Histone Deacetylases (HDACs) Inhibitions.

Histone deacetylases (HDACs) are enzymes that remove acetyl groups from ɛ-amino of histone, and their involvement in the development and progression of cancer disorders makes them an interesting therapeutic target. This study seeks to discover new inhibitors that selectively inhibit HDAC enzymes which are linked to deadly disorders like T-cell lymphoma, childhood neuroblastoma, and colon cancer. MOE was used to dock libraries of ZINC database molecules within the catalytic active pocket of target HDACs. The top three hits were submitted to MD simulations ranked on binding affinities and well-occupied interaction mechanisms determined from molecular docking studies. Inside the catalytic active site of HDACs, the two stable inhibitors LIG1 and LIG2 affect the protein flexibility, as evidenced by RMSD, RMSF, Rg, and PCA. MD simulations of HDACs complexes revealed an alteration from extended to bent motional changes within loop regions. The structural deviation following superimposition shows flexibility via a visual inspection of movable loops at different timeframes. According to PCA, the activity of HDACs inhibitors induces structural dynamics that might potentially be utilized to define the nature of protein inhibition. The findings suggest that this study offers solid proof to investigate LIG1 and LIG2 as potential HDAC inhibitors.

A Unique Amorphous Porous BiSbOx Nanotube with Abundant Unsaturated Sb‐Stabilized BiO8−x Sites for Efficient CO2 Electroreduction in a Wide Potential Window

AbstractThe CO2 electroreduction reaction using sustainable electricity emerges as a viable strategy to produce high‐value‐added and profitable chemicals. The achievement of superior activity at a lower overpotential and higher selectivity in a wide potential window is vitally important for large‐scale industrial applications. Herein, a carbon‐composite amorphous porous BiSbOx nanotube with abundant unsaturated sites is reported to boost the conversion of CO2 to formate, exhibiting a formate selectivity of >90% in an extremely broad range of potentials from −0.5 to −1.4 V versus reversible hydrogen electrode (RHE) and a maximal energy conversion efficiency of 77.1%. Importantly, pure formic acid solution is directly obtained in a solid‐electrolyte cell for industrial‐scale applications. The porous tubular structure can expose more catalytic active sites, accelerate the mass transfer, and show fast surface charge transfer. Moreover, the unique coordination‐unsaturated Sb‐stabilized BiO8−x site can not only enhance the adsorption and activation of CO2 but also reasonably balance the stabilization and hydrogenation of *OCHO intermediate, thus leading to its obviously higher catalytic performance. As a result, a novel amorphous porous BiSbOx nanotube is successfully designed for efficient CO2 electroreduction, which may shed new light on developing many more amorphous composite metal oxide catalysts for conversion of inert small molecules.

Macroporous NiFe-LDH accelerating highly-selective electrosynthesis of benzaldehyde accompanied with hydrogen production

Alkaline overall water splitting (OWS) is a potential technology for hydrogen (H2) production, however, the sluggish oxygen evolution reaction (OER) with high overpotential has limited its large-scale application. Herein, we successfully prepared the macroporous NiFe layered hydroxide (M-NiFe-LDH) on self-supported carbon cloth (CC) as electrocatalyst to drive an energy-saving device for both H2 production and benzyl alcohol (BA) oxidation to synthesize benzaldehyde (BAD). By utilizing the polystyrene (PS) microsphere templates and electrodeposition technology, CC@M-NiFe-LDH can be easily obtained after removing the PS templates. Due to the synergistic effect of bimetallic NiFe-LDH and macropores arrays which can expose more catalytic active sites, CC@M-NiFe-LDH electrocatalyst only needs a low potential of 1.31 VRHE to reach the current density of 10 mA cm−2 with a high BAD selectivity (∼99 %). Consequently, an energy-saving two-electrode device with both BAD electrosynthesis and H2 production can be assembled, which needs a low cell voltage of 1.648 V and electricity consumption of 3.60 kW h per cubic meter of H2, lower than that of OWS (1.826 V and 3.99 kW h).

Intrinsic pentagon defect engineering in multiple spatial-scale carbon frameworks for efficient triiodide reduction

Intrinsic topological defect engineering has been proven as a promising strategy to elevate the electrocatalytic activity of carbon materials. However, the controllable construction of high-density and specific topological defects in carbon frameworks to reveal the relationship between reactivity and defect structure remains a challenging task. Herein, the intrinsic pentagon carbon sites that can favor electron overflow and enhance their binding affinity towards the intermediates of catalytic reaction are firstly presented by the work function and the p-band center calculations. To experimentally verify this, the cage-opening reaction of fullerene is proposed and utilized for synthesizing carbon quantum dots with specific pentagon configuration (CQDs-P), subsequently utilizing CQDs-P to modulate the micro-scale defect density of three-dimensional reduced graphene oxide (rGO) via π-π interactions. The multiple spatial-scale rGO-conjugated CQDs-P structure simultaneously possesses abundant pentagon and edge defects as catalytic active sites and long-range-ordered π electron delocalization system as conductive network. The defects-rich CQDs-P/rGO-4 all-carbon-based catalyst exhibits superb catalytic activity for triiodide reduction reaction with a high photoelectric conversion efficiency of 8.40%, superior to the Pt reference (7.97%). Theoretical calculations suggest that pentagon defects in the carbon frameworks can promote charge transfer and modulate the adsorption/dissociation behavior of the reaction intermediates, thus enhancing the electrocatalytic activity of the catalyst. This work confirms the role of intrinsic pentagon defects in catalytic reactions and provides a new insight into the synthesis of defects-rich carbon catalysts.

Composition-tunable Co3-xFexSe4 as efficient electrocatalysts for the oxygen evolution reaction

In the oxygen evolution reaction (OER), the selection of highly active catalysts is fundamental to curtail overpotentials and to enhance the typically sluggish kinetics characteristic of the reaction. Cobalt selenide (Co3Se4), with its optimally configured electronic structure of cobalt ions, is consistently hailed as a prospective electrocatalyst for the OER, making it highly efficient in facilitating the reaction.Despite the persistent challenges of the exposure of catalytic active sites and the limited electronic conductivity, our study unveils a breakthrough solution. We introduce a highly efficient Fe-doped Co3Se4 electrocatalyst for the OER, addressing these long-standing issues, and it has desirable compositional flexibility, formed Co3-xFexSe4 (0 ≤ x ≤ 3) selenides, by introducing Fe doping, the electronic structure of Co3Se4 is effectively regulated, resulting in a remarkable reduction in the overpotential of the OER under alkaline conditions.Simultaneously, the introduction of Fe induces the formation of highly active Co–O sites, ultimately establishing a highly active and stable catalytic surface for oxygen evolution. Consequently, this leads to a significant improvement in the activity of the oxygen evolution reaction (OER). The synthesized Co2.5Fe0.5Se4 catalyst exhibits lower overpotential (η10 = 220 mV) and Tafel slope (41.2 mV dec−1), which is superior to the general commercial RuO2 benchmark. In addition, Co2.5Fe0.5Se4 also exhibits exceptional structural integrity and sustained operational longevity, with a durability of up to 280 h at 100 mA cmgeo−2. Impressively, the Pt/C∥Co2.5Fe0.5Se4 water electrolysis cell only requires a battery voltage of 1.67 V to provide a current density of 100 mA cmgeo−2 and has excellent long-term stability.

Iron oxide-based catalyst of (Fe1-xMgx)O·Fe2O3 with well-dispersed active sites favoring carbon nanotubes growth for high-performance microwave absorption

Traditional catalysts for carbon nanotubes growth require specific substrates to prevent catalyst aggregation, then designing environmentally friendly and efficient catalysts remains enormous challenges. Herein, we developed an iron oxide-based catalyst of (Fe1-xMgx)O·Fe2O3 with catalytic active sites for the low-cost growing of carbon nanotubes (CNT) in chemical vapor deposition (CVD) system. This (Fe1-xMgx)O·Fe2O3 was prepared by solid-phase sintering of iron oxide and magnesium oxide uniformly mixed in mass ratio of 3%∼20 wt% MgO at 1400 °C. The introduction of magnesium oxide possesses some advantages of reducing the decomposition temperature of iron oxide and hindering the aggregation of as-formed Fe catalyst during CVD process. Furthermore, the in-situ growing CNT wrapped up the magnetic (Fe1-xMgx)O·Fe2O3 catalyst to form the 3D CNT/(Fe1-xMgx)O·Fe2O3 with the high-performance of microwave absorption. The maximum absorption of the three-dimensional carbon nanocomposites at 11.8 GHz with a thickness of 2.0 mm is −37.3 dB. The coupling of dielectric loss of CNTs and magnetic loss of (Fe1-xMgx)O·Fe2O3 results in the enhancement of microwave absorption. Therefore, this study provides a low-cost and green route to design the efficient catalyst for carbon nanotubes as well as high-performance absorbing materials.

Dipole increase synergistic frustrated Lewis pairs induced by Sn dopant boosts ultrathin layered bismuth oxychloride for CO2 photoreduction

Photocatalytic conversion of CO2 into valued chemicals is limited by the CO2 adsorption and activation capability on catalyst surface. In this work, Sn element was successfully doped in ultrathin BiOCl with oxygen vacancies. The dipole moment of catalyst efficient increased due to the Sn doping, leading to a stronger internal electric field. In addition, the surface frustrated Lewis pairs were simultaneously constructed near the oxygen vacancies due to Sn dopant. The formed region of frustrated Lewis pairs-oxygen vacancies as active sites enable an improved CO2 adsorption, and the enhanced internal electric field intensity promoted the charge carrier separation and transfer, leading to the enhanced CO2 reduction performances. This work provides light on enhancing internal electric field by increasing dipole moment and presents feasible tunability of catalytic active sites at atom-scale, providing fundamental insights for understanding of mechanism of element doping in catalyst for improving CO2 photoreduction performance.

Nano-Fe3O4/polymerize aniline/carbon cathode based microbial fuel cell for efficient power generation and uranium separation

Microbial fuel cells (MFCs) have gained increasing attention in the field of uranium-containing wastewater (UCW) treatment as a self-powered bioelectrochemical system (BES) due to its advantages of recovering uranium resources and generating electricity. However, the lack of catalytic active sites on the carbon fiber cathode significantly hinders the reaction performance of surface electrons with uranium ions in solution, thereby limiting the application of MFC. In this study, we propose a carbon brush (CB) cathode modification process that utilizes cyclic voltammetry synthesis technique (CVS) to polymerize aniline (PA) on the surface of carbon fibers and uniformly load nano-Fe3O4 particles (nFe3O4). The loading of PA/nFe3O4 not only significantly improve the catalytic active sites but also enhance the synergistic effect of adsorption and conductivity of CB cathode. Consequently, the nFe3O4/PA/CB-MFC showed excellent ability to continuous power generation and uranium separation. Over eight cycles of uranium separation, the nFe3O4/PA/CB-MFC exhibited an average maximum power density of 15.17 mW/m2 and a uranium separation efficiency of 95.52 %, showcasing substantial enhancements by 2.10-fold and 1.44-fold compared to the CB-MFC, respectively. Our study presents an efficient approach to enhance the efficiency of uranium separation and boost power density of MFC by increase catalytic active sites on carbon-based cathode.

Facile Fabrication of an SnSx‐SnO2‐Decorated Cobalt Sulfide Film as an Effective Counter Electrode for Dye‐Sensitized Solar Cells

AbstractMetal sulfide stands out as one of the novel and promising platinum‐free counter electrode (CE) materials for dye‐sensitized solar cells (DSSCs). In this work, SnSx‐SnO2‐decorated CoSx films were designed and synthesized by a low‐temperature fabrication process. The small clusters of nanoparticles create a large amount of catalytic active sites, resulting in superior electrocatalytic activity for triiodide reduction. The DSSC with SnSx‐SnO2‐decorated CoSx film has achieved an impressive power conversion efficiency of 4.57 %, which is close to the efficiency of the DSSC with platinum CE (4.82 %). Furthermore, regarding the attenuation of the photovoltaic performance for the DSSC with SnSx‐SnO2‐decorated CoSx film, negligible change was observed after a prolonged storage under ambient condition for five days. Therefore, it is worthwhile to expect the explorations of novel fabricate technique for synthesizing cost‐effective metal sulfide films with long‐term stability in DSSCs.

Fe3C-modified porous carbon as anode electrocatalyst for improving extracellular electron transfer and removing Cr(VI) in microbial fuel cells

The anode, as a host site for electricigens, is regarded as an important determinant of the power generation of microbial fuel cells (MFCs), which is confined by the sluggish extracellular electron transfer (EET) at the electricigens/anode interface. In this study, a novel spindle-shaped material, Fe-modified porous carbon (Fe3C/PC), was rationally designed to boost the efficiency of EET. As expected, the MFCs equipped with the as-synthesized Fe3C/PC@CF anode exhibited excellent electrocatalytic activity for charge transfer and achieved much higher power density (1425 mW m−2). Ultimately, mature MFCs would be used to treat real effluent and Cr(VI) sewage. The excellent performance of MFCs was due to the active surface area provided by the porous carbon in Fe3C/PC@CF, which was conducive to electricigens adhesion, and the Fe3C doping provided abundant catalytic active sites for the anode. This work provides a new concept for the design of high performance anode electrocatalysts for MFCs and wastewater treatment.

Enhanced hydrogen evolution and tetracycline degradation by a Z-scheme g-C3N4 nanosheets loaded CeO2 photocatalyst under visible light irradiation

In the quest to enhance photocatalytic performance, structural regulation and interface engineering stand out as effective strategies for amplifying active sites and fostering the separation of photogenerated electron-hole pairs. In this study, a pioneering approach was employed, utilizing a straightforward two-step calcination method to prepare a novel photocatalyst: porous graphite carbon nitride (g-C3N4, CN) nanosheets (NS) loaded with mesoporous cerium oxide (CeO2/CNNS). The distinctive architecture of CeO2/CNNS not only elevates the specific surface area and catalytic active sites but also facilitates efficient mass transfer. Experimental results and density functional theory (DFT) calculations corroborate the existence of an internal electric field (IEF) within the Z-scheme heterojunction formed by uniformly dispersed CeO2 and CNNS. This IEF proves pivotal in promoting charge separation and migration, thereby maintaining robust redox capabilities. Under visible light irradiation, CeO2/CNNS demonstrates an impressive 4.2-fold increase in the hydrogen production rate compared to bulk g-C3N4 (BCN), coupled with a 48.5% boost in the photocatalytic degradation rate constant (k) of tetracycline (TC). This study not only unveils the innovative design of CeO2/CNNS but also paves the way for a fresh perspective on the design and preparation of multifunctional photocatalysts.

Recommendations for improving rigor and reproducibility in site specific characterization

Heterogeneous catalysis is driven by the interaction of reactant molecules and the catalyst surface. The locus of this interaction as well as the surrounding ensemble of atoms is referred to as the catalyst active site. Active site characterization attempts to distinguish active catalytic sites from inactive surface sites, to elucidate the structural and chemical nature of active sites, and to quantify active site concentration. Numerous techniques have been demonstrated to provide compositional and structural information about the active sites within a catalyst. However, each technique has its own limitations and experimental pitfalls that can lead to data misinterpretation or irreproducible results. This work aims to provide an overview of the types of data that can be collected, to outline common experimental challenges and how to avoid them, and to assemble relevant references for the most used active site characterization techniques. More broadly, we aim to outline best practices for researchers to collect, interpret, and report active site characterization data in a way that provides the most benefit to the broader catalysis community. Increasing the rigor and reproducibility of active site characterization offers a strategy to better link properties with catalytic performance and to enable the community to develop consensus concerning these relationships.

Utilizing high entropy oxide (Ni0.2Co0.2Ca0.2Cu0.2Mg0.2)Fe2O4 in chemical looping process for highly efficient and stable hydrogen production

Chemical looping reforming coupled with water splitting (CLR-WS) offers a way for negative carbon H2 production when using bio-waste as raw materials. Iron-based oxides are highly anticipated as oxygen carriers (OCs), while the commercial application is hampered by the harsh conditions and low stability. High entropy materials (HEMs), including high entropy oxides (HEOs) and high entropy alloys (HEAs), have displayed multiple active catalytic sites with excellent stability in the field of electrochemistry and photochemistry. However, the family has rarely been studied in CLR-WS before. Herein, (Ni0.2Co0.2Ca0.2Cu0.2Mg0.2)Fe2O4 was synthesized and the H2 yield of 12.66 mmol/g OC with the purity of 99.1 % was exhibited at 700 °C, proved to be at the forefront of the existing literatures. This study first creates a sustainable loop between HEO and HEA and achieves highly efficient and stable H2 production, paving an avenue for the large-scale application of HEM in thermochemical process.

Enhanced electrochemical performance of MoSe2 nanosheets on CoAl- layered double hydroxide for oxygen evolution reaction

The design of high-efficiency electrocatalysts for water electrolysis has attracted much attention. A crucial half-reaction in electrochemical water splitting is the oxygen evolution reaction (OER), which suffers from sluggish reaction kinetics due to the high-energy barrier of the complex electron transfer process. This study presents a MoSe2@CoAl-layered double hydroxide (LDH) hybrid nanostructure prepared using the facile hydrothermal method and investigated as a potential OER electrocatalyst. Morphological analysis indicated that the MoSe2 formed in very thin nanosheet structures containing multiple defects on the LDH platelets, increasing the number of catalytic active sites. Compared with pristine MoSe2 and CoAl-LDH, the obtained MoSe2@CoAl-LDH catalyst exhibited enhanced electrocatalytic activity for the OER in an alkaline solution. The MoSe2@CoAl-LDH electrocatalyst showed an overpotential of 360 mV at a current density of 10 mA cm−2 and a small Tafel slope of 53 mV dec−1. In addition, it demonstrated good electrochemical stability. The MoSe2@CoAl-LDH exhibited a lower Tafel slope than commercial RuO2, indicating faster electron transfer on the MoSe2@CoAl-LDH electrode.

Covalent synthesis of Ti-MOF for enhanced photocatalytic CO2 reduction

Ti based Metal-organic frameworks materials, with their high surface area, visible light responsiveness, and abundant catalytic active sites, have emerged as efficient photocatalysts. However, the number of reports on titanium-based MOFs is limited, mainly due to the challenges associated with their synthesis. In this study, based on the covalent strategy of imine condensation, a novel Ti-MOF was designed and synthesized by rational selection of aldehyde ligands. The photocatalytic CO2 reduction performance of the Ti-MOF was evaluated, and it exhibited a remarkable generation rate of formate ions at 46.0 μmol g−1 h−1, which is more than 6 times higher than that of MOF-902 constructed with the same titanium cluster. The rational selection of aldehyde ligands resulted in a relatively superior band structure for the Ti-MOF, characterized by a narrowed bandgap and a significantly negative shift of the conduction band, leading to enhanced photocatalytic ability.

Co–P/Fe3O4 composite film on nickel foam prepared by one-step electrodeposition for efficient overall water splitting

The design and construction of heterogeneous interface is an effective strategy to enhance the performance of non-precious metal catalysts for electrolytic water splitting. Herein, a facile nanostructure of porous cobalt phosphide/ferroferric oxide (Co–P/Fe3O4) composite film on nickel foam (Co–P/Fe3O4@NF) is designed and prepared by a one-step electrodeposition. The abundant heterogeneous interface of Co–P/Fe3O4 produces and exposes highly active catalytic sites. Meanwhile, the appropriate interaction between cobalt phosphide and Fe3O4 and the close contact between Co–P/Fe3O4 film and NF promote rapid electron transfer in catalytic process. Due to the catalyst being well-designed, the self-supported Co–P/Fe3O4@NF bifunctional electrodes exhibit outstanding performances with only needing overpotentials of 132.8 mV and 343.0 mV for hydrogen evolution reaction and oxygen evolution reaction, respectively, to drive 20 mA cm−2 in 1.0 M KOH. Additionally, the alkaline electrolyzer assembled by Co–P/Fe3O4@NF can achieve 10 mA cm−2 at a low cell voltage of 1.686 V. Even better, the electrolyzer can operate continuously over 40 h with nearly 100% Faraday efficiency and can also be powered by commercial solar cells in general outdoor environments.

Tuning the catalytic active sites of TiO2/CeO2 interactions to improve oxygen vacancy and lattice parameters for CO2 conversion to green fuel additive

In recent years, the conversion of carbon dioxide (CO2) to value-added products has become an area of great interest, both from an industrial and environmental perspective. Here we have successfully synthesized TiO2/CeO2-based catalysts by exo- and endo-template and use for direct conversion of CO2 to dimethyl carbonate (DMC). It was found that the catalytic activity of TiO2/CeO2 catalysts depends on the acidic and basic sites present in the catalyst. The study also investigated the optimization of reaction conditions in a batch reactor. It was found that the catalytic activity of TiO2/CeO2-based catalysts significantly enhances the CO2 conversion and achieves a high DMC yield compared to the performance of pure CeO2 and TiO2. The reusability of the TiO2/CeO2 catalysts was examined as well. Additionally, the heat of the reaction and Gibbs free energy were calculated using chemical equilibrium models. The experimental response data was validated using artificial neural networks (ANN). The R2 values between the expected and experimental results for DMC yield and CO2 conversion were 0.9953 and 0.9969, respectively. The developed ANN model successfully predicts the percentage of CO2 conversion and DMC yield under the given reaction conditions, with prediction accuracy MSE of 0.0013 and 0.0008, respectively.

Understanding the Reverse Water Gas Shift Reaction over Mo2C MXene Catalyst: A Holistic Computational Analysis

AbstractPristine Mo2C MXene has been proposed as an heterogeneous catalysis of the reverse water gas shift (RWGS) reaction. The present computational study aims at understanding its catalytic performance and reaction mechanisms tackling its thermodynamics, kinetics, and surface dynamic effects, combining Gibbs free energy profiles gained by density functional theory (DFT), mean‐field kinetics by microkinetic modeling, and rare‐event steps by kinetic Monte Carlo (kMC). The RWGS endergonicity goes for the use of high temperatures and reactants partial pressures to make the reaction exergonic. Gibbs free energy profiles show a preference for redox mechanism, whereas microkinetic simulations favor a low‐temperature preference of formate mechanism. The kMC reveals simultaneous operating redox and formate pathways, where surface coverage disfavors redox favoring the formate pathway. A peak performance is found at 700 K, in line with reported experiments, where the formation of surface O2* is found to be key, acting as a reservoir for O* adatoms while freeing surface sites upon O2* formation. Even though high turnover frequencies are predicted, the system could benefit from swing operando conditions, alternating CO production steps with H2 reduction regeneration steps, and/or ways to reduce the surface O2* and so to have more active catalytic sites.