Catalytic Oxidation Of CO Research Articles

In situ Observation of Porosity Formation in Porous Single‐crystalline TiO2 Monolith for Enhanced and Stable Catalytic CO Oxidation

AbstractIntroducing pores in single crystals creates a new type of porous materials that incorporate porosity and structural coherence. Herein, we use in situ transmission electron microscopy to disclose the porosity formation by converting KTiOPO4 (KTP) single crystals into porous single‐crystalline (PSC) TiO2 monoliths in a solid‐solid transformation. The isolated crystalline nuclei of TiO2 clusters with identical lattice orientation on KTP surface moves TiO2/KTP interface toward mother phase for growing PSC TiO2 monoliths. The relative density in PSC TiO2 monoliths dominates porosity while the macroscopic dimensions remain unchanged in the transformation. The single‐crystalline nature of porous architecture stabilizes oxygen vacancy to activate lattice oxygen while the three‐dimensional percolation enhances species diffusion. PSC TiO2 monoliths with deposited Pt clusters show enhanced and stable catalytic CO oxidation in air at ∼75 °C for 200 hours of operation.

Effective modeling of coupled reaction and transport inside the catalytic filter wall

A new extension of 1D mathematical model describing diffusion limitation in a catalytic filter wall is proposed. Transport limitations in the flowing gas inside free pores and in the coated catalyst are considered together with a Langmuir–Hinshelwood (LH) reaction kinetics including inhibition effects. Catalytic CO oxidation is investigated as a test reaction both at low and high reactant concentrations. The computed 1D concentration profiles are compared to detailed 3D pore-scale simulations involving the structure of a real filter wall obtained from X-ray tomography (XRT) scans. The best agreement is achieved when both gas-in-pores and intra-catalyst diffusion with LH effectiveness factor are considered in the 1D model. The impact of mass transfer limitations on CO light-off curves is then simulated using a 1D+1D model of the entire monolith filter. The extended model including diffusion limitation in free pores predicts the presence of undesired reactant slip at high flow rates as observed in experiments, which was not possible with the previously published models.

Vacancy Formation Energy as an Effective Descriptor for the Catalytic Oxidation of CO by Au Nanoparticles

Gold nanoparticles (AuNPs) have attracted wide attention in the field of catalysis because of their excellent stability and electrical properties. Herein, an accurate vacancy formation energy model based on nanothermodynamics theory is developed, the intrinsic correlation between vacancy formation energy and CO oxidation activity is investigated in detail, and the relationship between vacancy formation energy and activity-influencing factors such as particle size, temperature, and crystal surface is analyzed. The results show an excellent linear relationship between vacancy formation energy and CO oxidation activity, with an accuracy of up to 95%. In addition, the vacancy formation energy also corresponds well to the influencing factors of size, temperature, and crystal surface, and its correspondence is particularly accurate when the size is below 20 nm and the temperature is below 500 K. It can serve as a normalized expression of the three influencing factors. Moreover, the present research reveals that the essence of the vacancy formation energy descriptor is the chemical bond energy, and gives its correspondence with the coordination number, diffusion activation energy, and adsorption energy (with a decrease in vacancy formation energy, the adsorption effect of AuNPs is stronger), further demonstrating the feasibility and accuracy of the vacancy formation energy as a descriptor. This research not only overcomes the problem that traditional single-influence descriptors are difficult to apply in complex environments but also has considerable potential for defect modulation.

Activity and Thermal Aging Stability of La1-xSrxMnO3 (x = 0.0, 0.3, 0.5, 0.7) and Ir/La1-xSrxMnO3 Catalysts for CO Oxidation with Excess O2.

The catalytic oxidation of CO is probably the most investigated reaction in the literature, for decades, because of its extended environmental and fundamental importance. In this paper, the oxidation of CO on La1-xSrxMnO3 perovskites (LSMx), either unloaded or loaded with dispersed Ir nanoparticles (Ir/LSMx), was studied in the temperature range 100-450 °C under excess O2 conditions (1% CO + 5% O2). The perovskites, of the type La1-xSrxMnO3 (x = 0.0, 0.3, 0.5 and 0.7), were prepared by the coprecipitation method. The physicochemical and structural properties of both the LSMx and the homologous Ir/LSMx catalysts were evaluated by various techniques (XRD, N2 sorption-desorption by BET-BJH, H2-TPR and H2-Chem), in order to better understand the structure-activity-stability correlations. The effect of preoxidation/prereduction/aging of the catalysts on their activity and stability was also investigated. Results revealed that both LSMx and Ir/LSMx are effective for CO oxidation, with the latter being superior to the former. In both series of materials, increasing the substitution of La by Sr in the composition of the perovskite resulted to a gradual suppression of their CO oxidation activity when these were prereduced; the opposite was true for preoxidized samples. Inverse hysteresis phenomena in activity were observed during heating/cooling cycles on the prereduced Ir/LSMx catalysts with the loop amplitude narrowing with increasing Sr-content in LSMx. Oxidative thermal sintering experiments at high temperatures revealed excellent antisintering behavior of Ir nanoparticles supported on LSMx, resulting from perovskite's favorable antisintering properties of high oxygen storage capacity and surface oxygen vacancies.

Boosting CO Catalytic Oxidation Performance via Highly Dispersed Copper Atomic Clusters: Regulated Electron Interaction and Reaction Pathways.

Copper-loaded ceria (Cu/CeO2) catalysts have become promising for the catalytic oxidation of industrial CO emissions. Since their superior redox property mainly arises from the synergistic effect between Cu and the CeO2 support, the dispersion state of Cu species may dominate the catalytic performance of Cu/CeO2 catalysts: the extremely high or low dispersity is disadvantageous for the catalytic performance. The nanoparticle catalysts usually present few contact sites, while the single-atom catalysts tend to be passivated due to their relatively single valence state. To achieve a suitable dispersion state, we synthesized a superior Cu/CeO2 catalyst with Cu atomic clusters, realizing high atomic exposure and unit atomic activity simultaneously via favorable electron interaction and an anchoring effect. The catalyst reaches a 90% CO conversion at 130 °C, comparable to noble-metal catalysts. According to combined in situ spectroscopy and density functional theory calculations, the superior CO oxidation performance of the Cu atomic cluster catalyst results from the joint efforts of effective adsorption of CO at the electrophilic sites, the CO spillover phenomenon, and the efficient bicarbonate pathway triggered by hydroxyl. By providing a superior atomic cluster catalyst and uncovering the catalytic oxidation mechanism of Cu-Ce dual-active sites, our work may enlighten future research on industrial gaseous pollutant removal.

CO oxidation with Pt catalysts supported on different supports: A comparison of their sulfur tolerance properties

Insights into the CO oxidation and sulfur tolerance over supported Pt catalysts were carried out. The nominal 1 wt% Pt was loaded onto Al2O3, TiO2, SiO2, and SnO2 by the incipient wetness impregnation method. Results showed that the presence of H2O would promote the catalytic oxidation of CO, and Pt/TiO2 and Pt/SnO2 catalysts showed superior catalytic activity. In combination with a series of characterizations, it was concluded that excellent catalytic activity was dependent on higher dispersion and strong metal support interaction (SMSI) whether water is present or not. In the coexistence of H2O and SO2, the sulfation of the support will lead to the deactivation of the catalyst. Sulfur resistance can be improved over TiO2 with low sulfate decomposition temperature. While for Pt/SnO2 catalyst, its superior sulfur-tolerance was strongly associated with its special core-shell structure. It provides guidelines for the development of catalysts with excellent CO catalytic activity and sulfur tolerance.

Catalytic Oxidation of Propane and Carbon Monoxide by Pd Nanoparticles on Mn/TiO2 Catalysts

The present work shows experimental results on the catalytic oxidation of C3H8 and CO by Pd nanoparticles supported on MnOx/TiO2 synthesized by the sol–gel method. The results show a strong interaction between Pd and MnOx/TiO2; likewise, the annealing temperature of the TiO2 support modified the catalytic properties of the Pd–MnOx/TiO2 catalyst. In this line, the catalysts with 1 and 2 wt% of Pd loading supported on MnOx/TiO2 showed outstanding catalytic activity oxidizing C3H8 and CO within two temperature intervals: 200–400 °C and 25–200 °C, respectively. The Pd–MnOx/TiO2 catalyst also displayed very high stability during long-term tests and the addition of Pd nanoparticles reduced greatly the oxidation temperature of MnOx/TiO2. The outcomes revealed that the Pd–Mn interaction promoted the formation of new Pd0/Pd2+ active sites as well as the formation of oxygen vacancies and reduced Ti4+ to Ti3+ species, which led to the improvement of the Mn3+ and Mn4+ redox features, thus boosting the catalytic oxidation capacity of the Pd–MnOx/TiO2 catalyst.Graphical

Probing gas phase catalysis by atomic metal cations with flow tube mass spectrometry.

The evolution and applications of flow tube mass spectrometry in the study of catalysis promoted by atomic metal ions are tracked from the pioneering days in Boulder, Colorado, to the construction and application of the ICP/SIFT/QqQ and ESI/qQ/SIFT/QqQ instruments at York University and the VISTA-SIFT instrument at the Air Force Research Laboratory. The physical separation of various sources of atomic metal ions from the flow tube in the latter instruments facilitates the spatial resolution of redox reactions and allows the separate measurement of the kinetics of both legs of a two-step catalytic cycle, while also allowing a view of the catalytic cycle in progress downstream in the reaction region of the flow tube. We focus on measurements on O-atom transfer and bond activation catalysis as first identified in Boulder and emphasize fundamental aspects such as the thermodynamic window of opportunity for catalysis, catalytic efficiency, and computed energy landscapes for atomic metal cation catalysis. Gas-phase applications include: the catalytic oxidation of CO to CO2 , of H2 to H2 O, and of C2 H4 to CH3 CHO all with N2 O as the source of oxygen; the catalytic oxidation of CH4 to CH3 OH with O3 ; the catalytic oxidation of C6 H6 with O2 . We also address the environmentally important catalytic reduction of NO2 and NO to N2 with CO and H2 by catalytic coupling of two-step catalytic cycles in a multistep cycle. Overall, the power of atomic metal cations in catalysis, and the use of flow tube mass spectrometry in revealing this power, is clearly demonstrated.

Catalytic Activity of LaFe0.4Ni0.6O3/CeO2 Composites in CO and CH4 Oxidation Depending on Their Preparation Conditions.

LaFe0.4Ni0.6O3/CeO2 (1:1) two-phase composite materials were prepared by mechanochemical (MC) and Pechini routes. The catalytic properties of the composites in methane and CO oxidation reactions strongly depend on their preparation conditions. In low-temperature (<600 °C) catalytic CO oxidation the composites demonstrate a higher activity compared with LaFe0.4Ni0.6O3 perovskite. The highest activity was observed for the composite prepared by mechanical treatment of perovskite and fluorite precursors. There is a correlation between activity and the content of weakly bound surface oxygen species. Catalytic activity in high-temperature (>750 °C) catalytic methane oxidation correlates with the reducibility of samples. The highest activity was observed for the composite prepared by the one-pot Pechini route with higher reducibility of the sample up to 600 °C.

Humidity tuning CO oxidation on Ti decorated V2CO2 monolayer (MXene) catalyst: A density functional calculation study

Considering the high efficiency and low cost, original single-atom catalyst Ti/V2CO2 is used for CO catalytic oxidation in this work. Besides, density functional theory (DFT) calculations are adopted to explore H2O effects on performance and mechanisms of CO catalytic oxidation. Finally, the single atom of Ti is proven to be evenly distributed on V2CO2 monolayer. Also, it is discovered that CO oxidation cannot occur on Ti/V2CO2 in dry conditions. While, in humid conditions, water molecule is responsible for transferring charge to Ti atom, thus weakening O2 adsorption and causing lower activation energy of 0.71 eV. Rather than directly participating in CO oxidation by generating -OH groups with O2, it prefers to act as a co-catalyst with Ti/V2CO2. Consequently, the energy barrier of rate-limiting step based on Eley-Rideal (ER) mechanism is remarkably reduced from 1.79 to 0.57 eV, due to CO catalytic oxidation with the help of H2O in accelerating the interaction between single O atom and CO molecule. According to our findings, the existence of water can promote Ti/V2CO2 to be an effective single-atom catalyst for catalytic oxidation of CO in a humid environment.

Transition metal and Pr co-doping induced oxygen vacancy in Pd/CeO2 catalyst boosts low-temperature CO oxidation

Cerium oxide-based materials have wide application prospects in catalytic oxidation reactions. Doping valence metals in CeO2 is an effective strategy to increase the content of oxygen vacancy of CeO2 and regulate the surface and interface structure of CeO2 supported metal catalysts. In this work, transition metal (M = Fe, Co and Mn) and Pr co-doped CeO2 nanorod were prepared by hydrothermal method and used to support Pd, which significantly improved the activity of CO catalytic oxidation. Under dry and wet condition, the T99 (temperature to achieve 99% conversion of CO) decreased from 190 °C and 165 °C for single-doped Pd/Pr-CeO2 catalyst (Pd content of 0.2 wt%) to 125 °C and 107 °C for co-doped Pd/FePr-CeO2 catalyst under reaction condition with GHSV (gas hourly space velocity) of 70, 000 mL gcat.-1h−1, respectively. Moreover, the Pd/FePr-CeO2 catalyst showed an excellent stability and kept its activity more than 2400 min. The systematic characterizations revealed that the outstanding CO catalytic performance is attributed to the co-doping of Pr and Fe, which increases the oxygen vacancy content on the catalyst surface, promotes the activation of lattice oxygen in the support, and strengthens the interaction and electron transport ability between Pd and the support. This work opens promising perspectives to enhance the activity of supported metal catalysts in oxidation reactions by co-doping of valence metals in oxide supports.

The development of carbon monoxide oxidation reactor for multi-chamber furnaces for baking electrode blanks

The article highlights the development of cheap affordable highly efficient catalytic oxidation system of harmful components of industrial flue gases of carbon graphite enterprises, its design features according to the parameters of furnace equipment, which will significantly improve the environmental safety of metallurgical and machine-building enterprises. The presented calculation and design solutions, in addition to carbon production, can be used in environmental protection technologies at other environmentally hazardous facilities to neutralize toxic emissions.&#x0D; The paper presents the calculation of the catalytic CO oxidation reactor made for the real flow rate of flue gases with temperature range 270−390 ºC, which come out of the combustion chamber of the Riedhammer "first fire" kiln, heated by the flue gases. For such medium exothermic processes, mass and heat transfer between gas flow and the outer surface of the catalyst grains is sufficient intense. In this case for description of the catalytic process in the reactor is sufficient to use quasi-homogeneous single-phase model.&#x0D; The model of plug-flow reactor with a fixed bed of catalyst was used to calculate the flow parameters of the gas mixture through a reactor loaded with a composite zeolite-based manganese-oxide catalyst in the process of catalytic CO oxidation. The calculation results obtained using the software CHEMCAD 7.1.5 were almost identical to the previously made calculation. The peculiarity of the suggested solution was the use of the designed catalytic reactor for treatment of large volume of flue gases with low concentrations of CO at the companies of electrode carbon graphite production

Distinct Roles of Additives in the Improved Sensitivity to CO of Ag- and Pd-Modified Nanosized LaFeO3

Perovskite-type mixed-metal oxides are of particular interest as semiconductor gas sensors due to the variability in the material composition and the stability of sensing parameters. LaFeO3 is a p-type semiconductor with relatively high conductivity and gas sensitivity. However, less is known about the sensitivity and sensing mechanisms of LaFeO3 modified by catalytic noble metals. In this work, we used a microwave-assisted sol–gel method to synthesize perovskite LaFeO3 nanoparticles with an average size of 20–30 nm and a specific surface area of 6–8 m2/g. LaFeO3 was modified by 2–5 wt.% Ag and Pd nanoparticles via the impregnation route. Using X-ray photoelectron spectroscopy, the additives were observed in the partially oxidized states Ag2O/Ag and PdO/Pd, respectively. Electric conduction and sensitivity to noxious gases were characterized by electrophysical measurements. It was shown that LaFeO3 modified by Ag and Pd had improved sensitivity and selectivity to CO, and the sensing behavior persisted in a wide range of relative humidity. Pristine and Ag-modified LaFeO3 had the maximum sensitivity to CO at a temperature of 200 °C, while modification with Pd resulted in a decreased optimal operating temperature of 150 °C. In situ infrared spectroscopy revealed that supported Pd nanoparticles specifically catalyzed CO oxidation at the surface of LaFeO3 at room temperature, which was the likely reason for the improved sensitivity and decreased optimal operating temperature of LaFeO3/Pd sensors. On the other hand, Ag nanoparticles were deduced to activate CO oxidation by lattice oxygen at the surface of LaFeO3, providing enhanced CO sensitivity at a higher temperature.

In situ study of catalytic CO oxidation on ultrathin MgO film supported Pd nanoparticles by sum frequency generation: size and site effects.

Controlling the reactive sites of nanoparticles (NPs) is crucial to improve catalyst efficiency. In this work, sum-frequency generation is used to probe CO vibrational spectra on MgO(100) ultrathin film/Ag(100) supported Pd nanoparticles ranging from 3 to 6 nm in diameter and compared to those of coalesced Pd NPs and Pd(100) single crystals. We aim to demonstrate in situ the role played by active adsorption sites in the catalytic CO oxidation reactivity trends varying with the NP size. From ultrahigh vacuum to the mbar range and temperatures from 293 K to 340 K, our observations suggest that bridge sites are the main active sites for CO adsorption and catalytic oxidation. On Pd(100) single crystals at 293 K, CO oxidation predominates over CO poisoning at a pressure ratio of O2/CO greater than 300; on Pd NPs, both the site coordination due to NP geometry and MgO-induced Pd-Pd interatomic distance change impact the reactivity trend varying with size in different ways. Edge sites with low coordination are more reactive than facet sites, while facet sites with a smaller Pd-Pd atomic length are more reactive than that with a larger length. The interplay of both site and size effects gives rise to a non-monotonic reactivity trend of CO on the MgO(100) ultrathin film supported Pd NPs: the reactivity of Pd NPs increases for the smaller NP size side due to a higher edge/facet ratio and meanwhile increases for the larger NP size side due to the terrace facet with a smaller Pd-Pd atomic length at the NP surface and a lower diffusion barrier.

Promoted catalytic activity of CO oxidation at low temperatures by tuning ZnO morphology for optimized CuO/ZnO catalysts

Catalytic oxidation of CO is an effective route to eliminate the pollution of automobile exhaust. Tuning the fraction of exposed polar and non-polar crystal facets in ZnO provides an effective strategy to tailor metal-oxide interfacial active sites. Herein, the morphology of ZnO support was tuned to alter the fraction of exposed (002) polar/(100), (101) non-polar facets. ZnO nanodisks and nanorods were prepared, followed by deposition of ∼3.1 ± 0.9 nm CuO nanoparticles. The impact of the ZnO morphology upon CuO deposition and catalytic activity towards CO oxidation were investigated. The CuO/ZnO derived from ZnO nanodisks (NDs) with the most exposed (002) polar plane exhibited more than 2 folds higher catalytic activity at 150 °C than that over CuO/ZnO with commercial ZnO support (CuO/ZnO-C), highlighting the morphology influence of ZnO. For its enhanced catalytic activity and cyclic stability, the CuO/ZnO-NDs could be a promising catalyst for CO oxidation.

Ultralow reaction barriers for CO oxidation in Cu-Au nanoclusters.

Systematic structure prediction of CunAum nanoclusters was carried out for a wide compositional area (n + m ≤ 15) using the evolutionary algorithm USPEX and DFT calculations. The obtained structural data allowed us to assess the local stability of clusters and their suitability for catalysis of CO oxidation. Using these two criteria, we selected several most promising clusters for an accurate study of their catalytic properties. The adsorption energies of reagents, reaction paths, and activation energies were calculated. We found several cases with low activation energies and explained these cases using the patterns of structural change at the moment of CO2 desorption. The unique case is the Cu7Au6 cluster, which has extremely low activation energies for all transition states (below 0.05 eV). We thus showed that higher flexibility due to the binary nature of nanoclusters makes it possible to achieve the maximum catalytic activity. Considering the lower price of copper, Cu-Au nanoparticles are a promising new family of catalysts.

A layer by layer strategy for the TiO2/CuxO/CeO2hierarchical structure supported on carbon cloth as a photocarrier-assisted photothermal catalyst with fast visible light response

CC/TiO2/CuxO/CeO2hierarchical structures show fast visible light response with light irradiation playing a controllable switch role, completing photocarrier-assisted photothermal catalytic CO oxidation.

Gas-phase reactions driven by polarized metal-metal bonding in atomic clusters.

Multimetallic catalysts exhibit great potential in the activation and catalytic transformation of small molecules. The polarized metal-metal bonds have been gradually recognized to account for the reactivity of multimetallic catalysts due to the synergistic effect of different metal centers. Gas-phase reactions on atomic clusters that compositionally resemble the active sites on related condensed-phase catalysts provide a widely accepted strategy to clarify the nature of polarized metal-metal bonds and the mechanistic details of elementary steps involved in the catalysis driven by this unique chemical bonding. This perspective review concerns the progress in the fundamental understanding of industrially and environmentally important reactions that are closely related to the polarized metal-metal bonds in clusters at a strictly molecular level. The following topics have been summarized and discussed: (1) catalytic CO oxidation with O2, H2O, and NO as oxidants (2) and the activation of other inert molecules (e.g., CH4, CO2, and N2) mediated with clusters featuring polarized metal-metal bonding. It turns out that the findings in the gas phase parallel the catalytic behaviors of condensed-phase catalysts and the knowledge can prove to be essential in inspiring future design of promising catalysts.

Structural evolution after oxidative pretreatment and CO oxidation of Au nanoclusters with different ligand shell composition: a view on the Au core.

The reactivity of supported monolayer protected Au nanoclusters is directly affected by their structural dynamics under pretreatment and reaction conditions. The effect of different types of ligands of Au clusters supported on CeO2 on their core structure evolution, under oxidative pretreatment and CO oxidation reaction, was investigated. X-ray absorption and X-ray photoelectron spectroscopy studies revealed that the clusters evolve to a similar core structure above 250 °C in all the cases, indicating the active role of the ligand-support interaction in the reaction.

Robust 2 nm-sized gold nanoclusters on Co3O4 for CO oxidation.

In this study, gold nanoparticles were dispersed on Co3O4 nanoplates, forming a specific Au-Co3O4 interface. Upon calcination at 300 °C in air, aberration-corrected STEM images evidenced that the gold nanoclusters (NCs) on Co3O4{111} were maintained at ca. 2.2 nm, which is similar to the size of the parent Au colloidal particles, demonstrating the stronger metal-support interaction (SMSI) on Co3O4{111}. Au/Co3O4{111} showed good catalytic activity (a full CO conversion achieved at 80 °C) and durability (over 10 hours) in CO oxidation, which was mainly due to the promotion by the surface oxygen vacancies and intrinsic defects of Co3O4{111} for activating O2 and by Au0, Auδ+, and Au+ species on the surface of gold NCs for CO activation, as evidenced by Raman and Fourier-transform infrared (FT-IR) spectroscopy analysis. Au/Co3O4 catalyzed CO oxidation obeyed the Langmuir-Hinshelwood mechanism at low temperatures.