CO Oxidation Research Articles

Mining wastes as CO oxidation mesoporous catalysts from the Fe-skarns of Serifos Island, Cyclades, Greece

The Fe-skarns from the Greek Island of Serifos in Cyclades has been utilized only for the exploitation of magnetite ores, while significantly vast amounts of red and yellow hematite ores remained unexploited as mining wastes. This study explores the effective utilization of such mining wastes per se, as active mesoporous catalysts for energy applications, taking CO oxidation as a model reaction. The results of our multi-analytical study have illustrated that the physicochemical characteristics of the hematite materials can be positively influenced by the implementation of a simple calcination step, while the characteristics of magnetite remained unaffected. The calcined yellow and red mineral hematite from Serifos Fe-skarns mining wastes per se, act beneficial in the catalytic activity with respect to calcined magnetite catalyst. The calcinated counterparts of hematite, and especially yellow hematite, can efficiently be used as a support for depositing Au nanoparticles, and thus achieving even higher activity for CO oxidation (90% CO conversion), at much lower temperatures (T ∼62.0 °C). The mining wastes per se of Serifos, mainly of mesoporous hematite, are particularly active for CO oxidation, without any complex pretreatments or activation or functionalization in the context of circular economy.

Active nanointerfaces sites for low-temperature water-gas shift reaction over inverse configuration Nb–CeO2/Cu catalysts

A comparative investigation of inverse Nb–CeO2/Cu catalysts obtained via sol–gel, coprecipitation, hydrothermal, and incipient wetness impregnation methods was performed against a normal configuration for hydrogen production through a water–gas shift reaction. Exposed oxygen-deficient Nb–CeO2 (111) facet sites deposited on Cu (111) facets with enhanced densities of Ce3+, Cu+, and Ov species for high reducibility were confirmed using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Nb–CeO2/Cu catalyst prepared by coprecipitation exhibited the highest activity of 68 % CO conversion, 100 % H2 selectivity at 360 °C, and gas hourly space velocity of 43,535 h−1. The lowest activation energy (39.67 kJ/mol) and high turnover frequency illustrate facilitated water dissociation and CO oxidation in close vicinity across nanointerfaces. For the Nb–CeO2/Cu catalyst prepared by the coprecipitation method, nanosized Nb–CeO2 stabilized over the porous Cu support was optimum for generating interfaces and facilitating catalytic performance. It is to underscore that the catalyst prepared by coprecipitation exhibited constant H2 production under realistic conditions for 102 h, demonstrating the robust structural features of the configuration Nb–CeO2/Cu.

Single atom sites as CO scavenger to allow for crude hydrogen usage in PEMFC

Nanosized Pt catalysts are the catalyst-of-choice for proton exchange membrane fuel cell (PEMFC) anode, but are limited by their extreme sensitivity to CO in parts per million (ppm) level, thereby making the use of ultrapure H2 a prerequisite to ensure acceptable performance. Herein, we confront the CO poisoning issue by bringing the Ir/Rh single atom sites to synergistically working with their metallic counterparts. In presence of 1000 ppm CO, the catalyst represents not only undisturbed H2 oxidation reaction (HOR) catalytic behavior in electrochemical cell, but also unparalleled peak power density at 643 mW cm−2 in single cell, 27-fold in mass activity of the best PtRu/C catalysts available. Pre-poisoning experiments and surface-enhanced Raman scattering spectroscopy (SERS) and calculation results in combine suggest the presence of adjacent Ir/Rh single atom sites (SASs) to the nanoparticles (NPs) as the origin for this prominent catalytic behavior. The single sites not only exhibit superb CO oxidation performance by themselves, but can also scavenge the CO adsorbed on approximated NPs via supplying reactive OH* species. We open up a new route here to conquer the formidable CO poisoning issue through single atom and nanoparticle synergistic catalysis, and pave the way towards a more robust PEMFC future.

Surface and bulk transformations of Ag2CuMnO4 delafossite during the interaction with CO+O2 mixture

Ternary oxide of silver, copper and manganese (Ag2CuMnO4) with delafossite-type structure demonstrates excellent catalytic activity in the reaction of CO oxidation at room temperature and even below. To prepare delafossite-based catalyst the hydrothermal approach using metal nitrates in alkaline solution with an excess of peroxodisulphate was applied. X-ray diffraction pattern of Ag2CuMnO4 particles was successfully simulated taking into an account crystallite shape anisotropy, particle size distribution, the presence of stacking faults, and the lattice expansion along c axis. As-prepared Ag2CuMnO4 sample was characterized by the presence of Ag1+-, Cu2+- and Mn4+-like surface species predominantly. In situ XRD data revealed the thermal stability of delafossite-type structure in catalytic CO+O2 mixture up to 500 °C, while ex situ XPS showed an evident reorganization of Ag2CuMnO4 surface at markedly lower temperatures (200–250 °C). Heating in CO+O2 medium at 150–400 °C also resulted in significant catalytic activation of Ag2CuMnO4 owing to the Mn enrichment and optimization of manganese and copper electronic exchange. The low-temperature activity of Ag2CuMnO4 catalyst in CO+O2 reaction was proposed to be mainly provided by redox transitions with the participation of Cu1+/Cu2+ and Mn3+/Mn4+ couples, while the catalytic role of silver species is considered as auxiliary only. The innovation point of this work is related to the investigation of the dynamics of surface and bulk structure transformations in connection with the catalytic activation of delafossite particles for the low-temperature oxidation.

Cooperation of Mn and P atoms in graphene for efficiently catalyzing CO oxidation at low temperature

Computational studies show that the co-doping of Mn and P atoms in graphene (MnP4-Gr) can provide high CO oxidation performance at room temperature. Results suggest that the configuration (CO+O2)* can be easily obtained due to the better adsorption of CO on the Mn atom and O2 on the P atom. (CO+O2)* is further found to undergo a fast Langmuir−Hinshelwood (LH) process and then left one atomic oxygen on P which is difficult to remove. Therefore, due to the more favorable adsorption of CO on the Mn atom and O2 on other P atoms, coupled with the speed of the LH process, the configuration (CO+4O)* of one atomic oxygen adsorbed on each P atom and CO on Mn atom is finally obtained. The whole reaction is determined by the atomic oxygen removal in (CO+4O)* with an energy barrier of 0.80 eV. It is predicted that the cooperation of Mn and P atoms is conducive to the fast LH process of MnP4-Gr and also the weaker binding between P and O in MnP4-Gr. Moreover, thermodynamic and kinetics analysis indicates that increasing temperature can accelerate CO oxidation and facilitate reaction in thermodynamics. Therefore, the insights reported in this paper will provide a new catalyst for low-temperature CO oxidation.

Deposited PtGe Clusters as Active and Durable Catalysts for CO Oxidation**

AbstractControl of CO emissions raises serious environmental concerns in the current chemical industry, as well as in nascent technologies based on hydrogen such as electrolyzers and fuel cells. As for now, Pt remains one of the state‐of‐the‐art catalysts for the CO oxidation reaction, but unfortunately, it suffers from CO self‐poisoning. Recently, Pt−Ge alloys were proposed to be an excellent alternative to reduce CO poisoning. This work investigates the impact of Ge content on the CO oxidation kinetics of Pt4Gen subnanoclusters supported on MgO. A Ge concentration dependence of the reaction kinetics is found due to a strong synergy between Pt and Ge. Pt−Ge nanoalloys act as a bifunctional catalyst by displaying dual adsorption sites; i. e., CO is adsorbed on Pt whereas oxygen binds to Ge, forming an alternative oxygen source GeOx. Besides, Ge alloying modifies the electronic structure of Pt (ligand effects) and reduces the affinity to CO. In this way, the competition between CO and O2 adsorption and the overbinding of CO is alleviated, achieving a CO poisoning‐free kinetic regime. Our calculations suggest that Pt4Ge3 is the optimal catalyst, evidencing that alloying composition is a parameter of extreme importance in nanocatalyst design. The work relies on global optimization search techniques to determine the accessibility of multiple structures at different conditions, mechanistic studies and microkinetic modeling.

Changes in soil microbial functions involved in the carbon cycle response to conventional and biodegradable microplastics

Biodegradable mulch film has become an encouraging alternative to conventional petroleum–based plastic, but it is likely to generate more microplastics (MPs) than conventional films with lower resistance and thus profoundly affects the soil environment. However, the effects of biodegradable (BMPs) and conventional polyethylene MPs (PE–MPs) on soil microbial carbon (C) cycle remain unclear. Here, metagenomic sequencing was used to investigate microbial functional and relative taxonomic traits in response to PE–MP and BMP addition (5 % w/w) via a soil microcosm experiment. The results showed that the presence of BMPs, rather than PE–MPs, significantly changed soil microbial C cycling patterns at the functional and taxonomic levels. In soils, BMP addition significantly increased the abundances of genes regulating aerobic respiration, C decomposition (intracellular), C fixation, fermentation and CO oxidation pathways compared to those in the control and PE–MP added soils. Specifically, BMPs promoted soil starch and PHA (liable C) degradation, acetate and ethanol fermentation, Calvin–Benson–Bassham (CBB) cycle and 3–hydroxypropionate/4–hydroxybutyrate (3HP/4HB) associated with C fixation. Most of these C cycling pathways were further strengthened in the microplastisphere of BMPs. Furthermore, MPs selectively enriched specific taxa on their surface and subsequently increased their abundance in soils; Bradyrhizobium, Ramlibacter and Variovorax (enriched by BMPs) positively regulated labile C degradation, and Amycolatopsis and Nocardia (enriched by PE–MPs) promoted recalcitrant C degradation. Moreover, Pseudonocardia and Variovorax that were enriched by BMPs improved C dissimilation and assimilation by regulating fermentation and C fixation processes, respectively. Taken together, these results improve the understanding of the influence of conventional and biodegradable MPs on soil C cycling pathways and related microbial communities, highlighting that the presence of BMPs rather than PE–MPs accelerates soil C turnover.

Exploring the role of oxygen species on β- and γ-MnO2 catalyst under in-plasma catalysis configuration at different temperature in CO oxidation using operando TPR-DRIFTS-MS

Catalyst surface active oxygen species have an important influence on plasma catalytic oxidation. However, the reaction process of CO and O3 migration and transformation on the catalyst surface during discharge at different temperature is still unclear. In this study, β- and γ-MnO2 are selected to unveil the roles of different oxygen species under in-plasma catalysis configuration at different temperature in CO oxidation. Operando TPR-DRIFTS-MS is used to reveal CO and O3 oxidation pathways. The results show that O3 can react with CO at room temperature, and O3 is also converted to other reactive oxygen species on the catalyst surface. As the temperature increases, the oxygen species of the catalyst itself (MnO and Mn-O-Mn) can react with CO to form oxygen vacancies (Mn-□-Mn and Mn=□). Mn-□-Mn are beneficial for O2 decomposition and promotes the regeneration of MnO and Mn-O-Mn. The carbonate covered on the surface of the catalyst is the rate-determining step of CO oxidation. It is hoped that Mn-based catalysts with more reactive oxygen species and oxygen defects will be prepared to facilitate low-temperature CO oxidation under plasma conditions.

Efficient CO Oxidation by Co/Ta2O5 Prepared by Deposition–Precipitation with Urea

Efficient CO Oxidation by Co/Ta2O5 Prepared by Deposition–Precipitation with Urea

Investigating NH3-SCR coupled with CO oxidation reaction mechanisms on titanium nanotube-loaded CuMnFe composite metal catalysts

NOx and CO are the primary air pollutants emitted from sintering flue gas, and their effective treatment is crucial. However, achieving good N2 selectivity with the CuMnFe composite metal oxide catalyst alone is challenging due to its oxidizing nature. Hence, in this study, titanium dioxide nanotubes were employed as carriers for the catalyst. CuMnFe composite metal oxide catalysts supported on titanium dioxide nanotubes were prepared using the co-precipitation method. The optimized catalysts demonstrated excellent performance, maintaining over 90% conversion of NOx and CO at low temperatures ranging from 120 to 200 ℃. Furthermore, significant improvement in N2 selectivity was achieved using these catalysts. Characterization results revealed several positive effects of incorporating titanium dioxide nanotube carriers into the catalyst. Firstly, it efficiently reduced the mobility of adsorbed oxygen on the catalyst surface, thus decreasing its oxidation capacity. Secondly, the addition of carriers helped balance the acidity on the catalyst surface, leading to an increase in Lewis acid sites. These modifications in the catalyst's surface properties proved advantageous for the selective catalytic reduction reaction. Moreover, the mechanisms of NH3-SCR and CO oxidation over the catalysts were extensively studied using DRIFTS. The results demonstrated that the CO oxidation reaction followed the Mars-van Krevelen mechanism, with a competitive adsorption relationship observed between O2 and CO at the active sites. On the other hand, the NH3-SCR reaction primarily followed the Eley-Rideal mechanism, with minimal occurrence of the Langmuir-Hinshelwood mechanism in the SCR reaction. The presence of NH3 inhibits CO adsorption at the active site, resulting in decreased CO oxidation performance in the NH3-SCR-coupled CO oxidation reaction at low temperatures. Nevertheless, NH3-SCR can enhance NO conversion by utilizing some of the latent heat generated from the exothermic CO oxidation.

Engineering the CuO/MnO2 interface with multivalent conversion for low-temperature and efficient CO oxidation

A novel interface of MnO2 with CuO with multivalent conversion is fabricated by the deposition-precipitation method for low-temperature and efficient CO oxidation. It is found that the temperature for CO thermal-catalytic oxidation to reach a complete conversion significantly decreases to 105 °C for the CuO/MnO2. A combination of experimental and theoretical studies demonstrates the successful formation of the CuO/MnO2 interface, inducing a pronounced effect that promotes CO oxidation. The CuO/MnO2 interface leads to the formation of Cu-O-Mn, a superior redox system with multivalent conversion (Cu+ + Mn4+ ↔ Cu2+ + Mn3+, Cu+ + Mn3+ ↔ Cu2+ + Mn2+), abundant active sites, excellent ability to activate O2, the rapid oxygen transfer, and more suitable adsorption energy for O2, CO, and CO2. These characteristics are advantageous to CuxO-MnxOy for achieving a 100 % removal of CO at a lower temperature. Furthermore, the computational study reveals that the CO oxidation process follows two mechanistic pathways (Eley-Rideal (E-R) and Mars-van Krevelen (M-K)), indicating that there is no competitive adsorption of CO and O2 on the CuO/MnO2. This study shows that the interface created between suitable metal oxides can improve the catalytic performance and provides new perspective for catalyst design and performance enhancement mechanisms.

Novel Nanostructured Pd/Co-Alumina Materials for the Catalytic Oxidation of Atmospheric Pollutants.

Cobalt-doped alumina catalysts were prepared using different methods, either conventional wet impregnation (WI) and/or advanced spray impregnation (SI), and they were evaluated as novel oxidation catalysts for CO and MeOH oxidation. The spray impregnation technique was used with the aim of achieving the synthesis of core-shell catalytic nanostructures to secure the chemical/thermal stability of active sites on the catalyst carrier. The catalysts were further promoted with a low Pd content (0.5 wt.%) incorporated via either incipient wetness impregnation (DI) or spray impregnation. The results revealed the superior performance of the spray-impregnated catalysts (Co/γ-Al2O3-SI) for both reactions. The deposition of Co oxide on the outer surface of the alumina particle (SEM images) and the availability of the active Co phase resulted in the enhancement of the Co/γ-Al2O3 catalysts' oxidation activity. Pd incorporation increased the catalysts' reducibility (TPR-H2) and improved the catalysts' performance for both reactions. However, the Pd incorporation method affected the catalytic performance; with the SI method, the active phase of Co3O4 was probably covered with PdO and was not available for the oxidation reactions. On the contrary, the incorporation of Pd with the DI method resulted in a better dispersion of PdO all over the Co/Al catalyst surface, maintaining available Co active sites and a better Pd-Co interaction. MeOH desorption studies revealed the methanol oxidation mechanism: the Co/Al catalysts promoted the partial oxidation of MeOH to formaldehyde (HCHO) and dehydration to dimethyl ether (DME), while the Pd-based Co/Al catalysts enhanced the complete oxidation of methanol to CO2 and H2O.

Nanoporous gold with microporous structure prepared by sodium dodecyl sulfate-mediated electrochemical dealloying

Nanoporous gold (NPG) is a promising catalytic material for the oxidation of CO and methanol applications. However, NPGs are prone to extensive macroscopic cracking that often decrease mechanic properties of NPGs and depresses their catalytic action. To produce crack-free NPG with an ultra-finer porosity in room temperature, the anionic surfactant sodium dodecyl sulfate (SDS) was added in electrochemical dealloying process. SDS has the effect of reducing the surface diffusion of gold which hinder the initial coarsening of ligaments and prevents interior silver atoms from being exposed and dissolved. As a result, the pore and ligment size are finer, but higher residual silver of NPG samples. NPG with pore size down to 2 nm and the ligament 4.0 nm was successfully fabricated with 13.32 mM SDS in perchloric acid solution. The surface diffusion coefficient of Au atoms was 1.6 × 10−24 m2·s−1, nearly 3 orders of magnitude smaller than that of Au atoms in the absence of SDS (2.8 × 10−21 m2·s−1). Nanoindentation results demonstrated that high residual silver content made NPG samples harder and stiffer，the specific surface areas of NPG with 6.66 mM SDS was 190 m2 g−1 by BET. This work provided very important clues on how to control the crack free ultrafine nanoporous structure of other materials.

Novel insights for simultaneous NOx and CO Removal: Cu+-Sm3+-Ov-Ti4+ asymmetric active site promoting NH3-SCR coupled with CO oxidation reaction

Ammonia selective catalytic reduction (NH3-SCR) coupled with CO oxidation is a promising approach for simultaneous removal of NOx and CO. However, finding a bifunctional catalyst that can effectively facilitate both reactions remains a significant challenge. This study investigates the enhancing effect of Cu+-Sm3+-Ov-Ti4+ asymmetric active sites on the oxidation reaction of NH3-SCR coupled with CO oxidation. The traditional Cu/TiO2 catalyst can achieve a maximum NOx conversion of 75 % at 225 °C, while the CuSmOTi catalyst can achieve 100 % NOx conversion at 200 °C. The successful construction of the asymmetric active site leads to an increase in Cu+ content, producing abundant oxygen vacancies, accelerating the redox cycle in the reaction process, and improving the adsorption capacity of CO. Additionally, compared with the 8.4 % Cu dispersion on the Cu/TiO2 catalyst, the Cu dispersion on the SmCuOTi catalyst is as high as 75.0 %, which improves the reduction performance of the catalyst. A large number of Lewis acid sites optimize the activation and adsorption of the catalyst to the reactants. In-situ DRIFTS analysis indicates that the NH3-SCR reaction on the CuSmOTi catalyst primarily follows the (E-R) mechanism, while CO oxidation follows the (MvK) mechanism. Moreover, the formation of a significant number of amide intermediates during the reaction process enhances the N2 selectivity. These findings present a novel concept of utilizing asymmetric active sites in NH3-SCR coupled with CO oxidation reactions, provides valuable insights for achieving the complete removal of nitrogen oxides and carbon monoxide in the case of “0″ by-products.

Ru/Ir nanojunctions supported on CNTs as active and ultrastable catalysts for CO preferential oxidation toward hydrogen purification

Hydrogen purification is animportanttechnological step for proton exchange membrane fuel cells (PEMFCs), which can promote the service life of batteries. The preferential oxidation of CO (PROX) in hydrogen is a promising solution for hydrogen purification to avoid poisoning of catalysts by the trace amount of CO present in thehydrogen-richfeedgas. Herein, we demonstrate an interface engineering strategy to prepare Ru/Ir-CNTs nanojunctionswith remarkablecatalyticactivity for CO oxidation. The as-prepared catalyst shows thetotal COconversionin awidetemperaturerange of 50-200℃ under a high feeding gas flow velocity of 72000 mL g-1h−1 and remains stable after 48 h of continuous working. The catalyst also exhibits 100 % CO conversion in temperature from 80 to 100℃ under a much higher feeding gas flow velocity of 108000 mL g-1h−1. Moreover, the CO conversion remains 100 % after intermittent performance testing over a one-week time period. Theoretical calculations reveal that the interface of Ru/Ir can weaken the adsorption of *CO2, thus greatly increasing the temperature range of the complete transformation of CO. Compared to oxide supports, CNTs are more difficult to combine with CO2, which makes the catalyst completely convert CO for a long time within the operating temperature range.

Expression of concern: Palladium supported on mixed-metal-organic framework (Co-Mn-MOF-74) for efficient catalytic oxidation of CO.

Expression of Concern for 'Palladium supported on mixed-metal-organic framework (Co-Mn-MOF-74) for efficient catalytic oxidation of CO' by Reda S. Salama et al., RSC Adv., 2021, 11, 4318-4326, https://doi.org/10.1039/D0RA09970H.

Correction and removal of expression of concern: Palladium supported on mixed-metal-organic framework (Co-Mn-MOF-74) for efficient catalytic oxidation of CO.

[This corrects the article DOI: 10.1039/D0RA09970H.].

The confined surface C2N/Pt(111) as a highly efficient catalyst for CO oxidation.

The problem of poisoning on the surface of catalysts used in CO oxidation reactions, such as Pt, needs to be solved. In this work, we constructed lattice-matched C2N/Pt(111) catalysts with different configurations (top/fcc/hcp) and found that, within the confined space between the cover and the substrate, the adsorption energy of CO is reduced by 0.35 eV to 0.43 eV, while the adsorption of other reactants O/O2 is strengthened and the adsorption energy of the product CO2 is positive, indicating that the constraint effect produced by C2N and Pt(111) is beneficial to CO oxidation, when compared to the pure Pt(111). Our work suggests that the C2N cover not only protects the Pt surface under harsh conditions but also allows gaseous molecules CO and O2 to approach the Pt surface through a facile intercalation process, with enhanced surface reactivity for CO oxidation and reduced catalyst poisoning.

CO oxidation reactions on 3-d single metal atom catalysts/MgO(100).

The present work deals with a comprehensive computational theoretical study of the molecular CO and O2 adsorption on 3d single atoms (M/MgO(100)). The study is based on the chemical elements of the 3d row, as they represent an economic advantage compared with the so-called noble metals. The present study has been performed employing density functional theory calculations. Through the representation of the metastable states, we perform a synergetic analysis of the CO oxidation reaction to find trends that suggest the possible use of new candidates such as Ni/MgO(100) or Cu/MgO(100) single-atom catalysts, for this type of redox reaction. We found that Ni and Cu produce energetically viable CO to CO2 reactions. Ni and Cu atoms show the greatest diffusion barrier and are the best candidates due to their low sintering capability. The energetic and electronic properties of the single Cu and Ni atoms on MgO (100) give them the best characteristics to help in the CO oxidation process.

Time-resolved surface reaction kinetics in the pressure gap.

We extend the use of our recently developed Near-Ambient Pressure Velocity Map Imaging (NAP-VMI) technique to study the kinetics and dynamics of catalytic reactions in the pressure gap. As an example, we show that NAP-VMI combined with molecular beam surface scattering allows the direct measurement of time- and velocity-resolved kinetics of the scattering and oxidation of CO on the Pd(110) surface with oxygen pressures at the surface up to 1 × 10-5 mbar, where different metastable surface structures form. Our results show that the c(2 × 4) oxide structure formed at low O2 pressure is highly active for CO oxidation. The velocity distribution of the CO2 products shows the presence of two reaction channels, which we attribute to reactions starting from two distinct but rapidly interconverting CO binding sites. The effective CO oxidation reaction activation energy is Er = (1.0 ± 0.13) eV. The CO2 production is suppressed at higher O2 pressure due to the number of antiphase domain boundaries increasing, and the missing row sites are filled by O-atoms at O2 pressures approaching 1 × 10-6 mbar. Filling of these sites by O-atoms reduces the CO surface lifetime, meaning the surface oxide is inactive for CO oxidation. We briefly outline further developments planned for the NAP-VMI and its application to other types of experiments.