Activity For CO Oxidation Research Articles

Revealing pretreatment-induced structure evolution of LaFeO3 supported Au catalyst for CO oxidation reaction

Heterogeneous catalysts play a pivotal role in the chemical industry. Pretreatments in reducing or oxidizing atmospheres have been widely utilized to alter the structure of heterogeneous catalysts, with the aim of enhancing their catalytic performance. However, the pretreatment atmosphere can, at times, trigger unexpected structural changes in catalysts and even lead to catalytic degradation. Hence, the selection of an appropriate pretreatment atmosphere for heterogeneous catalysts is critical and requires a clear understanding of their corresponding dynamic evolution to improve their performance in a targeted manner, particularly relying on in situ observation. In this study, a promising CO oxidation catalyst, LaFeO3 supported Au nanoparticles (Au/LFO) is selected, and the influence of the pretreatments in different atmospheres on Au/LFO is explored by using in situ transmission electron microscopy (TEM) and density functional theory (DFT) calculation. Our findings reveal that the commonly used reducing pretreatment for noble-metal catalysts triggered strong metal-support interactions in Au/LFO, suppressing its CO adsorption performance. In contrast, the oxidizing pretreatment preserves the metallic Au and the metal/support interface as efficient active sites to promote CO oxidation activity and stability simultaneously. This work discloses the structure evolution at the interface between noble metals and perovskite oxide supports in response to different gas phase treatments and clarifies their structure-property relationships.

Effects of Metal Promoters (M = Fe, Co, and Cu) in Pt/M x Zr y O z Catalysts and Influence of CO2 and H2O on the CO Oxidation Activity (PROX): Analysis of Surface Properties After Reaction.

In the present paper, the effects of metal promoters (M = Fe, Co, and Cu) in Pt/M x Zr y O z catalysts and the influence of CO2 and H2O on the CO oxidation activity (PROX) were investigated. To do that, characterizations of catalyst structures and surfaces were performed and reported here. The catalyst Pt/Fe x Zr y O z (PFeZ) was the most active at low temperatures among the analyzed ones. The addition of platinum caused strong interaction with the mixed oxide, affecting the structure and the surface composition, blocking basic sites, and thus preventing catalyst deactivation. Particularly, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results evidenced the formation of carboxylate and carbonate species. Besides, the addition of CO2 and H2O in the gas feed stream affected the observed CO oxidation results, showing that CO2 competes with O2 on metallic sites. Moreover, DRIFTS and temperature-programmed desorption (TPD) analyses suggested the occurrence of OH- oxidation by CO, leading to the formation of highly reactive compounds that can be easily oxidized.

In situ exsolution of Pt nanoparticles on low Pt-substituted A-site deficient perovskite for efficient CO oxidation

Platinum nanoparticles often lose their efficacy in challenging working environments. In this study, we developed a novel approach for the preparation of highly dispersed precious metal catalysts. The method involves the utilization of composite materials consisting of PtOx/(LC)0.9MP, achieved through the exsolution of a low Pt substituted A-site deficient perovskite (La0.97Ce0.03)0.9Mn0.99Pt0.01O3 ((LC)0.9MP). This procedure facilitates the in situ exsolution of Pt nanoparticles from (LC)0.9MP through heat treatment under 10 vol% H2/Ar environment. During this process, PtOx undergoes transformation to Pt0, exhibiting a high CO catalytic oxidation activity, with the T100(CO) decreasing from 213 to 141 °C. This capability primarily stems from the substantial number of oxygen vacancies and alterations in Pt species induced by the catalyst during the redox process. The active Pt nanoparticles are strongly integrated on the surface of (LC)0.9MP, demonstrate excellent CO oxidation activity and stability. This performance is attributed to the specific structure of perovskite. Upon reoxidation, these particles do not undergo direct reincorporation into the lattice structure. Instead, NPs result in the formation of stable, anchored oxide nanoparticles. This strategy can be extended to other metals oxides catalysts, thus may help the rational design of highly efficient transition metal oxide-based catalysts and beyond.

Effect of cobalt on CeO2 nanorod supported Pt catalyst: Structure, performance, kinetics and reaction mechanism in CO oxidation

Catalytic oxidation represents a highly efficient and extensively employed approach for the elimination of CO in exhaust gas. Rationally designing and preparing catalysts with exceptional activity and stability in the presence of H2O and SO2 at low temperatures represent crucial avenues for future advancements. In this work, a series of Pt catalysts supported on CeO2 nanorods incorporated with varying amounts of Cobalt (Co/CeO2 ratio ranging from 0 to 10 %) were prepared and evaluated for their catalytic activity in CO oxidation under both dry and wet conditions. The ultrahigh dispersion of Pt, outstanding redox properties, and abundant oxygen vacancies on the surface of Co-doped CeO2 nanorod supported Pt catalysts were revealed by XRD, TEM, Raman spectroscopy and H2-TPR techniques. The catalytic activity for CO oxidation strongly depends on the Co content and reaction conditions. Among them, Pt/Co-CeO2-5 % exhibits the highest CO oxidation performance with a T90 (the temperature to achieve 90 % conversion of CO) of 170 °C under dry conditions, which is significantly lower by 140 °C compared to T90 of Pt/CeO2. Pt/Co-CeO2-1 % demonstrates superior CO oxidation performance with a T90 of 195 °C under wet conditions, exhibiting a reduction in temperature by 65 °C compared to the T90 of Pt/CeO2. Moreover, Pt/Co-CeO2 exhibits excellent resistance to SO2 compared to Pt/CeO2. Kinetic studies, in situ DRIFT analysis and isotopic experiments demonstrated direct participation of H2O in the reaction. On the catalysts with a low Co/Ce ratio (Co/Ce < 0.03), CO readily reacts with hydroxyl groups dissociated from H2O to form carboxyl intermediates, which subsequently undergo rapid decomposition into CO2, resulting in an enhanced reaction rate of CO oxidation at low temperature.

Synthesis of thin-film CuMn2O4 for low-temperature CO oxidation

Thin films, 0.5- and 1.0-nm thick, of CuMn2O4 were synthesized on γ-Al2O3 using Atomic Layer Deposition (ALD); and their catalytic activities for CO oxidation were measured and compared to that of bulk CuMn2O4. For bulk CuMn2O4, the surface area decreased dramatically when the sample was calcined at 1073 K; but the area-specific rates for CO oxidation were the same for bulk samples calcined at 473 K and 1073 K. For thin films of CuMn2O4 on γ-Al2O3, both the surface area and spinel structure were maintained following oxidation at 1073 K or reduction at 973 K. Area-specific, CO-oxidation rates on the ALD-prepared catalysts were somewhat lower than those found on bulk CuMn2O4; however, adding an additional ALD cycle of Cu on the CuMn2O4/γ-Al2O3 increased the rates to the same level as that of the bulk CuMn2O4.

Advantages and disadvantages of barium oxide addition to bimetallic Pd-Rh three-way catalysts supported on zirconia-doped alumina

Due to enhanced high-temperature stability, zirconia-stabilized alumina is widely used as a support of three-way catalysts. The addition of barium oxide is known to improve the catalytic performance of the composition. In order to go in-depth about the effects of BaO addition, a series of samples was prepared using nitrates and complex salts as a precursor. The interaction of BaO with alumina was found to change dramatically the metal-support interaction of the latter with metals. Thus, the presence of BaO resulted in the sintering of Pd with the formation of agglomerated Pd0 species, which explains a lower activity in CO oxidation of the BaO-doped samples after thermal treatment. Contrarily, the addition of barium nitrate showed a positive effect, inhibiting the collapse of the porous structure of the support, which was the most crucial and accompanied by the formation of the α-Al2O3 phase when no barium nitrate was added.

Dip coating of ceria–manganese mixed oxides on cordierite and its CO oxidation activity

Dip coating of ceria–manganese mixed oxides on cordierite and its CO oxidation activity

Impact of mild hydrothermal aging on kinetics of NH[formula omitted], NO, SO[formula omitted] and CO oxidation reactions on Cu/SSZ-13 catalyst

Cu/SSZ-13 is a catalyst commonly used for selective catalytic reduction (SCR) of nitrogen oxides (NOx) in diesel engine exhaust. Standard configurations are based on SCR preceded by an oxidation catalyst, however, a close-coupled SCR configuration appears relevant for upcoming regulations addressing cold-start emissions. Two often discussed ion-exchanged Cu sites in Cu/SSZ-13 are denoted ZCuOH and Z2Cu, where Z represents an Al atom in the zeolite framework. Mild hydrothermal aging (HTA) causes Cu redistribution within the catalyst; ZCuOH sites transform into more stable Z2Cu species. In this work, the effect of mild HTA on NH3, NO, SO2, and CO oxidation is studied on a commercial Cu/SSZ-13 sample. Temperature-programmed reaction experiments, performed in a lab reactor, and previously published catalyst characterization data using H2-TPR, NH3-TPD, and DRIFTS were used to build and validate a mathematical model. It couples the kinetics of the oxidation reactions with ZCuOH and Z2Cu concentration evolution during mild HTA. The model uses two distinct rate coefficients for ZCuOH and Z2Cu sites, allowing prediction of the catalyst activity during aging. The results suggest that the rate coefficients for the studied reactions on Z2Cu are effectively nil, so the observed activity in NH3, NO, SO2, and CO oxidation can be attributed solely to ZCuOH sites.

Unique role of silica in MOF-Derived High-Loading Palladium-on-Ceria single atom catalysts with excellent efficiency and durability

In most cases, the sintering tendency of supported metal single atoms could be attributed to the unstable structural characteristics of supports in demanding operating conditions, particularly for high-loading single-atom catalysts (SACs), ultimately resulting in deactivation. To address this issue, SiO2 is employed to enhance the structural stability of both supports and the supported Pd single atoms. SiO2 serves not only to prevent the collapse of support structures but also to promote the activation of surface oxygen species by facilitating electron transfer with the supports. This, in turn, establishes strong metal-support interactions (MSIs) to stabilize and activate atomically dispersed Pd species. Additionally, the electrons donated from Ce-O and Si-O to Pd atoms further catalyze the formation of oxygen vacancies, ultimately leading to significantly improved activity and durability in CO oxidation. Without SiO2, the instability of support structure, coupled with the weak MSIs, promotes the aggregation of Pd atoms, resulting in relatively lower catalytic activity and durability.

Effects of Synthesis Method on Catalytic Activities of Ag/TiO2 Catalyst in CO Oxidation Reaction

Supported silver catalysts on titanium dioxide have been synthesized by three different methods to compare catalytic activity in CO oxidation. The catalysts were prepared by the wet impregnation method with 10 mole% of silver. In the first method, the silver catalysts were impregnated on the titanium dioxide nanoparticles (Ag/TNP), while in the second method, the silver catalysts were impregnated on the titanium dioxide nanotubes (Ag/TNT). The third method, the silver catalysts were impregnated on the titanium dioxide nanoparticles before the nanotube process (Ag/TNP-TNT). The Ag/TNP and Ag/TNT catalysts showed highly dispersed silver nanoparticles with an average particle size of less than 5 nm on the surface of titanium dioxide, whereas the Ag/TNP-TNT catalyst exhibited much lower dispersion of silver nanoparticles. The highly dispersed silver on the titanium dioxide resulted in a large number of surface active sites (Ag0). The catalytic activity test found that the Ag/TNT catalysts with the highest number of active sites (2.20 × 1020 atom/g-catalyst) exhibited higher CO oxidation activity than the Ag/TNP and Ag/TNT catalysts with 100% CO conversion at 125°C.

La/Mn molar ratio tuning the activity of La–Mn perovskites for CO and propane oxidation

A series of non-stoichiometric LaxMnO3 with La/Mn molar ratio x in the range of 0.80–1.2 have been prepared by a glycine combustion method and calcinated at 700 °C. The Mn-rich (x < 1) and La-rich (x > 1) catalysts presented higher and lower activity for CO and propane oxidation than the stoichiometric LaMnO3, respectively. The LaxMnO3 presented pure perovskite phase without La- or Mn-related phases detected even calcinated at 1000 °C. Notably, the 50% conversion temperature for CO and propane oxidation on the best La0·84MnO3 were around 70 and 35 °C lower than those on the stoichiometric LaMnO3, whereas which on the worst La1·15MnO3 were around 60 and 50 °C higher. The La0·84MnO3 possessing higher activity for CO and propane oxidation was predominately attributed to more Mn4+ cations, thus achieving abundant surface Mn4+–O bridge site as redox sites and surface Mn4+ sites as Lewis acidic sites, while the La1·15MnO3 owning lower activity for the reactions was primarily ascribed to less Mn4+ cations, and the lower reducibility of Mn4+ cations and surface adsorbed oxygens.

Identifying Active Sites of Pt‐NiFe LDH Catalysts for CO Oxidation Using In‐Situ DRIFTS with Multiple Microscopy and Spectroscopy Techniques

AbstractLayered double hydroxide (LDH) nanostructures are commonly used to study the interfacial effects of Pt‐based catalysts in CO oxidation. However, the specific role and detailed intermediates involved in CO oxidation remain unclear. Density functional theory (DFT) predicted that NiFe LDH loaded with single Pt atoms would exhibit satisfactory CO oxidation activity. On this basis, we prepared Pt1NiFe LDH catalysts with various Fe : Ni ratios by using the one‐pot method and achieved favorable dispersion of single Pt atoms. Pt1/FN‐1, which had the optimal Fe : Ni ratio (1 : 1), exhibited satisfactory catalytic performance for CO oxidation and a high turnover frequency, as determined through DFT calculations and experimental characterization. In‐situ diffuse reflectance infrared Fourier transform spectroscopy confirmed that CO directly reacted with Pt1/FN‐1 to produce CO2 and that introduced O2 formed bicarbonate species to produce CO2 together with the adsorbed CO on Pt1 sites. Overall, our work provides new insights into the catalytic mechanism of the well‐known Pt1NiFe LDH catalysts in CO oxidation.

A Ce/hopcalite catalyst for low-temperature oxidation of CO:Preparation, performance and mechanism

The utilization of atomic-scale doping in catalysts has been recognized as an effective strategy for enhancing CO oxidation catalytic activity. This work adjusted the lattice structure of hopcalite (CuMnOx) catalysts via Ce-doping. Ce species was uniformly dispersed on the surface of amorphous porous catalysts, which built abundant interfaces along with many active sites. The lattice distortion degree can be regulated by changing Ce dosage. The modified catalysts with 7.5 wt%Ce-doping exhibited the optimal intrinsic activity for CO oxidation. Compared with the original sample, the CO conversion increased by 50 % at room temperature, and the reaction rate was eight-fold faster, superior to most reported hopcalite catalysts. Integrating with the various characterizations, the enhancing of low-temperature activity mainly originates from the weakened binding of oxygen atoms by lattice distortions. Moreover, the experiments and characterization results revealed that the reactivity of both adsorbed and lattice oxygen is enhanced on Ce-modified samples at low temperature. This work provides new insights into the rational modulation of reactive oxygen species and reinforces the utility of hopcalite catalysts for oxidizing CO at low temperature.

Comparative Study of Exsolved and Impregnated Ni Nanoparticles Supported on Nanoporous Perovskites for Low-Temperature CO Oxidation.

This study investigated the redox exsolution of Ni nanoparticles from a nanoporous La0.52Sr0.28Ti0.94Ni0.06O3 perovskite. The characteristics of exsolved Ni nanoparticles including their size, population, and surface concentration were deeply analyzed by environmental scanning electron microscopy (ESEM), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) mapping, and hydrogen temperature-programmed reduction (H2-TPR). Ni exsolution was triggered in hydrogen as early as 400 °C, with the highest catalytic activity for low-temperature CO oxidation achieved after a reduction step at 500 °C, despite only a 10% fraction of Ni exsolved. The activity and stability of exsolved nanoparticles were compared with their impregnated counterparts on a perovskite material with a similar chemical composition (La0.65Sr0.35TiO3) and a comparable specific surface area and Ni loading. After an aging step at 800 °C, the catalytic activity of exsolved Ni nanoparticles at 300 °C was found to be 10 times higher than that of impregnated ones, emphasizing the thermal stability of Ni nanoparticles prepared by redox exsolution.

Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity.

Exfoliated M-Al layered double hydroxide (M-Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO2 and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO2 coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO2. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co-Al MMO-coated Au/SiO2. In contrast, the deposition of CoAlOx on Au/SiO2 by impregnation or the deposition of Au on Co-Al MMO-coated SiO2 resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co-Al MMO overlayer on Au/SiO2 possessed abundant oxygen vacancies, which would play an important role in O2 activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO2, and the obtained Co-Al MMO-coated Pt/SiO2 also exhibited a much improved catalytic activity for CO oxidation.

Manufacturing AAl2O4 (A=Cu, Co, Ni, Zn) Spinel Catalysts for Toluene Combustion: Elucidating the A‐site Replacement Effect on the Reactivity

AbstractTo decode the A‐site substitution effect on the reactivity of Al‐based spinel complex oxides, a series of AAl2O4 (A=Cu, Co, Ni, Zn) compounds were manufactured and tested by toluene combustion. It was confirmed that a pure spinel crystalline phase has been successfully synthesized for all the catalysts. The toluene and CO oxidation activity are sequenced as CuAl2O4&gt;CoAl2O4&gt;NiAl2O4&gt;ZnAl2O4. As discovered, both active surface O2− and acid sites are the two critical factors to determine the reactivity, which can adsorb and activate the reactants effectively to form active intermediates, possibly following a Mars‐van‐Krevelen pathway. The activity improves positively with the amount increasing of these two kinds of active sites, thus showing an evident A‐site replacement effect. CuAl2O4 owns the biggest numbers of these two kinds of active sites, thereby exhibiting the optimal catalytic activity. Moreover, it also shows good stability in a dry feed, and considerable ability to resist water vapor and sulfur poisoning. In‐situ DRIFTS results have indicated that benzyl, benzoate, benzaldehyde and benzoquinone might be the major reaction intermediates.

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.

Functionalisation of alkali-resistant nanoporous glass via Au nanoparticle decoration using alkaline impregnation: catalytic activity for CO removal.

The concerted use of nano-metal particles with catalytic functions and nanoporous materials holds promise for effective air purification and gas sensing; however, only a few studies have used porous glasses as supports for Au nanoparticles. Furthermore, Au/nanoporous glasses with activities comparable to that of Au/TiO2, which is a typical Au catalyst, have not been reported to date. This study demonstrates that a nanoporous glass, which is highly acid- and alkali-resistant and chemically stable, can be decorated with Au nanoparticles using an alkali impregnation method. The resulting composite exhibits high catalytic activity in CO oxidation. The catalysts reported herein are as active as Au/TiO2 catalysts per active site. Further optimisation of the pore properties of the glass and sizes of the Au nanoparticles is expected to result in excellent catalytic systems for CO removal and sensing.

Catalytic activity of CeO2@TiO2 for environmental protection

Core–shell nanoparticles can be used as catalysts. CeO2@TiO2 catalysts with a higher proportion of rutile have better activity in CO oxidation. Dyes oxidation proceeds most efficiently on Fe-composites with a higher proportion of anatase and brookite.

A molecular beam study of CO oxidation on Pd clusters supported on alumina: the effect of cluster size.

The activity in CO oxidation of regular arrays of Pd clusters, in the size range of 5-180 atoms, supported on alumina has been studied by using a molecular beam method. The Pd clusters are grown on a nanostructured ultrathin alumina film on Ni3Al(111) providing a hexagonal array of clusters with a narrow size distribution. The steady state turnover frequency (TOF) is measured as a function of the mean cluster size. On average the TOF increases with size. Below about 20 atoms, the TOF increases rapidly and for larger clusters it grows slowly and reaches a value close to those obtained on bulk single crystals at 180 atoms. The size effect is explained by the smaller activity of Pd atoms in contact with the alumina support.