CO Oxidation Research Articles

Bismuth Boosts the Preferential oxidation of CO over Pt/Al2O3 by Regulating the Reactant adsorption and reaction route

Bismuth Boosts the Preferential oxidation of CO over Pt/Al2O3 by Regulating the Reactant adsorption and reaction route

Synergistic effect of Cu and Ag on porous (Cu, Ag) co-doped CeO2 nanosheets for low-temperature CO oxidation

Synergistic effect of Cu and Ag on porous (Cu, Ag) co-doped CeO2 nanosheets for low-temperature CO oxidation

Fe-modified Cu/TiO2 catalyst with anti-Pb poisoning performance for the synergistic catalysis of NH3-SCR and CO oxidation

Fe-modified Cu/TiO2 catalyst with anti-Pb poisoning performance for the synergistic catalysis of NH3-SCR and CO oxidation

Poisoning effect of chlorine anions in the catalytic activity of CuO/CeO2/UiO-66 for CO-PROX reaction and strategy for catalyst activation.

UiO-66 was synthesized using ZrOCl2·8H2O as metal precursor, and CuO/CeO2/UiO-66 catalysts were prepared and tested for preferential CO oxidation in H2-rich streams (CO-PROX reaction), a reaction of practical significance in hydrogen purification for fuel cells. The study highlights the detrimental effect of residual chlorine anions from UiO-66 synthesis and DMF washing on the catalytic performance of CuO/CeO2/UiO-66. An activation strategy involving rigorous water washing and thermal treatment at 160 ºC under CO-PROX conditions was developed. Both steps were deemed necessary, as employing only one proved insufficient to reduce chlorine levels to non-poisoning thresholds. This activation procedure does compromise UiO-66 crystallinity and porosity, but it is justified by achieving a fully functional catalyst. TEM images confirm the uniform dispersion of the CuO/CeO2 active phase on the UiO-66 matrix post-activation and after catalytic testing. A 16-hour CO-PROX test at 160 ºC with the CuO/CeO2/UiO-66 catalyst, once activated, demonstrated stable performance throughout the extended long-term experiment. This research provides valuable insights into optimizing CuO/CeO2/UiO-66 catalysts for CO-PROX application.

AuPd/TiO2 Catalysts in the CO Oxidation: Insights into the Synthesis Procedure and In-situ Spectroscopy Studies

Abstract A series of bimetallic AuPd/TiO2 catalysts (Au/Pd = 1) were prepared through either the impregnation or the deposition-precipitation in urea (DPU) approach and tested in the CO oxidation reaction. Among these, the sample synthesized through a sequential impregnation (Pd) followed by DPU (Au), with an intermediate thermal treatment in air, presented a remarkable CO conversion at sub-ambient temperatures and an enhanced catalytic stability, compared to the monometallic samples. The ex-situ characterization revealed that the synthesis procedure led to the formation of well-dispersed bimetallic AuPd nanoparticles over the TiO2 support. The in-situ characterization helped to propose that bimetallic NPs were composed of an intermetallic Au-Pd phase with both atoms available in the surface. Both in-situ FTIR and UV-vis spectroscopies helped to recognize the active sites during the reaction: Au in close interaction with the TiO2 at low temperatures, and step/edges Pd sites at high temperatures. Finally, the pivotal role of the TiO2 reducibility in the CO oxidation reaction, promoted by the bimetallic AuPd NPs, was determined through in-situ Raman spectroscopy.

Modulation of Co spin state at Co3O4 crystalline-amorphous interfaces for CO oxidation and N2O decomposition

Modulation of electronic spin states in cobalt-based catalysts is an effective strategy for molecule activations. Crystalline-amorphous interfaces often exhibit unique catalytic properties due to disruptions of long-range order and alterations in electronic structure. However, the mechanisms of molecule activation and spin states at interfaces remain elusive. Herein, we present a Co3O4 spinel-based catalyst featuring crystalline-amorphous interfaces. Characterization analyses confirm that tetrahedral Co2+ is selectively etched from bulk spinel, forming amorphous CoO islands on the surface. The resultant symmetry breaking in the coordination field induces a reconstruction of the Co3+3 d orbitals, leading to high-spin states. In CO oxidation, the interface serves as novel active sites with a lower energy barrier, facilitated by lattice oxygen activation. In N2O decomposition, the interface promotes reassociation of dissociated oxygen through quantum spin exchange interactions. This work provides a straightforward approach to modulating the spin state of interfaces and elucidates their role in molecule activations.

Revealing the CO Tolerance Mechanism in Acidic Hydrogen Oxidation Reactions on Platinum‐Based Catalyst Surfaces

AbstractThe presence of trace CO impurity gas in hydrogen fuel can rapidly deactivate platinum‐based hydrogen oxidation reaction (HOR) catalysts due to poisoning effects, yet the precise CO tolerance mechanism remains debated. Our designed Au@PtX bifunctional core–shell nanocatalysts exhibit excellent performance of CO tolerance in acidic solution during HOR and possess exceptional Raman spectroscopy enhancement. Through capturing and analyzing in situ Raman spectroscopy evidences on *OH, metal‐O species and *CO evolution under 0.3 V, we confirm that oxygen‐containing species on PtRu and PtSn catalysts promote the oxidation and desorption of *CO. While Ru enhances *CO adsorption on Pt, the primary CO tolerance performance of PtRu arises from *CO oxidation via a bifunctional pathway. Additionally, electronic structure of Sn reduces *CO adsorption on Pt sites, complementing the bifunctional mechanism to further enhance the CO tolerance performance of PtSn. These discoveries significantly deepen our understanding of the anti‐poisoning mechanism of Pt‐based catalysts in the HOR process and offer valuable insights for rational catalyst design.

Asymmetric Pt1O4-Ov Dual Active Sites Induced by NbOx Clusters Promotes CO Synergistical Oxidation.

Pt/CeO2 single-atom catalysts are attractive materials for CO oxidation but normally show poor activity below 150 °C mainly due to the unicity of the originally symmetric Pt1O4 structure. In this work, a highly active and stable Pt1/CeO2 single-site catalyst with only 0.1 wt % Pt loading, achieving a satisfied complete conversion of CO at 150 °C, can be obtained through fabricating asymmetric Pt1O4-oxygen vacancies (Ov) dual-active sites induced by well-dispersed NbOx clusters. Specifically, the formation of new Ce-O-Nb interactions weakened the strength of the original Pt-O-Ce bond, thus transferring the originally near-perfect square-planar Pt1O4 into the distorted square-planar one, along with forming abundant Ov around the Pt site. Hence, the promoted CO activation on the asymmetric Pt1O4 structure and the facilitated dissociation of the O2 on the neighboring Ov site synergistically improved the CO catalytic oxidation performance. The fabrication of such asymmetric Pt1O4-Ov double-active sites was also active for the oxidation of other typical hydrocarbons pollutants such as C7H8 and C3H6 from exhaust gases, shedding light on engineering high-efficiency Pt-based oxidation catalysts for low-temperature environmental catalysis.

Unravelling the Cu and Ce Effects in MnO2-Based Catalysts for Low-Temperature CO Oxidation

Cu-containing and Ce-modified OMS-2 catalysts were prepared at various calcination temperatures using the hydrothermal method and tested for low-temperature CO oxidation. The structure, chemical compositions, and physical–chemical properties of the catalysts were characterized using XRD, N2 physisorption, XRF, Raman spectroscopy, SEM, high-resolution TEM with EDX, TPR-H2, and XPS. The incorporation of Cu into the Ce-OMS-2 sample facilitated the transformation of pyrolusite into cryptomelane, as confirmed by Raman spectroscopy data. In the light-off mode, the Cu/Ce-OMS-2-300 and Cu/OMS-2 samples exhibited higher activity in low-temperature CO oxidation (T90 = 115 and 121 °C, respectively) compared to sample Cu/Ce-OMS-2-450. After a long-run stability test, the Cu/Ce-OMS-X samples demonstrated excellent performance: the T80 increased by 16% and 7% for the samples calcined at 300 °C and 450 °C, respectively, while the T80 for the Cu/OMS-2 increased by 40%. The Cu/OMS-2 and Cu/Ce-OMS-2-300 samples were found to have an increased content of nanodispersed copper sites on their surfaces. These copper sites contributed to the formation of the Cu2+-O-Mn4+ interface, which is responsible for the CO oxidation. The presence of Ce3+ in the catalyst was found to increase its stability in the presence of water vapor due to the higher reoxidation ability in comparison with Ce-free sample Cu/OMS-2.

Enhancing CO oxidation performance by controlling the interconnected pore structure in porous three-way catalyst particles.

Highly ordered porous structured particles comprising three-way catalyst (TWC) nanoparticles have attracted attention because of their remarkable catalytic performance. However, the conditions for controlling their pore arrangement to form interconnected pore structures remain unclear. In particular, the correlation between framework thickness (distance between pores) or macroporosity and the diffusion of gaseous reactants to achieve a high catalytic performance has not been extensively discussed. Here, the interconnected pore structure was successfully controlled by adjusting the precursor components (i.e., template particle concentration) via a template-assisted spray process. A cross-sectional image analysis was conducted to comprehensively examine the internal structure and porous properties (framework thickness and macroporosity) of the porous TWC particles. In addition, we propose mathematical equations to predict the framework thickness and macroporosity, as well as determine the critical conditions that caused the formation of interconnected pores and broken structures in the porous TWC particles. The evaluation of CO oxidation performance revealed that porous TWC particles with an interconnected pore structure, thin framework, and high macroporosity exhibited a high catalytic performance owing to the effective diffusion and utilization of their internal parts. The study findings provide valuable insights into the design of porous TWC particles with interconnected pore structures to enhance exhaust gas emission control in real-world applications.

Enhancing the CO Oxidation Performance of Copper by Alloying with Immiscible Tantalum.

Copper-tantalum (Cu-Ta) immiscible alloy nanoparticles (NPs) have been the subject of extensive research in the field of structural materials, due to their exceptional nanostructural stability and high-temperature creep properties. However, Cu is also a highly active oxidation catalyst due to its abundant valence changes. In this study, we have for the first time obtained homogeneous CuxTa1-x (x = 0.5, 0.7, 0.9, 1) nanoparticles by wet coreduction with an average particle size of approximately 30 nm. Testing verified all the CuxTa1-x/TiO2 (x = 0.5, 0.7, 0.9) showed higher CO oxidation activity than Cu/TiO2, with Cu0.7Ta0.3/TiO2 exhibiting the most promising performance. The temperature-programmed reduction with hydrogen demonstrated that Cu0.7Ta0.3/TiO2 exhibits enhanced redox properties. While kinetic studies indicated that the reaction of the Cu0.7Ta0.3/TiO2 catalyst followed the Langmuir-Hinshelwood mechanism, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) verified the introduction of Ta induced the generation of bicarbonate as an intermediate product and increased the adsorption capacity of Cu+ on CO in the catalyst, which facilitated the reaction of surface adsorbed CO with oxygen and led to the enhanced CO oxidation activity.

Revealing the CO Tolerance Mechanism in Acidic Hydrogen Oxidation Reactions on Platinum-Based Catalyst Surfaces.

The presence of trace CO impurity gas in hydrogen fuel can rapidly deactivate platinum-based hydrogen oxidation reaction (HOR) catalysts due to poisoning effects, yet the precise CO tolerance mechanism remains debated. Our designed Au@PtX bifunctional core-shell nanocatalysts exhibit excellent performance of CO tolerance in acidic solution during HOR and possess exceptional Raman spectroscopy enhancement. Through capturing and analyzing in situ Raman spectroscopy evidences on *OH, metal-O species and *CO evolution under 0.3 V, we confirm that oxygen-containing species on PtRu and PtSn catalysts promote the oxidation and desorption of *CO. While Ru enhances *CO adsorption on Pt, the primary CO tolerance performance of PtRu arises from *CO oxidation via a bifunctional pathway. Additionally, electronic structure of Sn reduces *CO adsorption on Pt sites, complementing the bifunctional mechanism to further enhance the CO tolerance performance of PtSn. These discoveries significantly deepen our understanding of the anti-poisoning mechanism of Pt-based catalysts in the HOR process and offer valuable insights for rational catalyst design.

Exhaust Treatment for Engines Operated with the Synthetic Diesel Fuel OME: Low‐Temperature Oxidation of Formaldehyde and CO by Pt/Ceria Catalysts

AbstractC1‐based synthetic fuels like oxymethylene ether (OME) are sulfur‐free, and their combustion forms negligible amounts of soot. This results in reduced ageing requirements and can enable the development of cost‐efficient catalyst technologies. This work focuses on the catalytic oxidation of formaldehyde (HCHO), which is increasingly formed during the combustion of C1‐based fuels such as OME, methanol, or CH4. The oxidation of HCHO on Pt/Al2O3 is inhibited by CO, so that in real exhaust containing CO and NO, full conversion of HCHO is only observed at ∼200 °C. The main discovery of this paper is that on Pt/ceria the oxidation of HCHO is not inhibited by CO, so that full conversion of HCHO is achieved already at ∼100 °C even in the presence of CO. To demonstrate the performance of the new catalyst under realistic operating conditions, a dynamic HCHO dosing unit was developed, allowing to reproduce transient vehicle driving cycles on a lab‐scale test rig. Using this novel setup, the Pt/ceria catalyst shows virtually full conversion of HCHO (99,8%) and CO (98,5%) over an OME cold‐start driving cycle, where the conventional Pt/Al2O3 oxidation catalyst with four‐times higher Pt loading shows only 81% and 62% conversion, respectively.

Workflow-driven catalytic modulation from single-atom catalysts to Au–alloy clusters on graphene

Gold-based (Au) nanostructures are efficient catalysts for CO oxidation, hydrogen evolution (HER), and oxygen evolution (OER) reactions, but stabilizing them on graphene (Gr) is challenging due to weak affinity from delocalized carbon orbitals. This study investigates forming metal alloys to enhance stability and catalytic performance of Au-based nanocatalysts. Using ab initio density functional theory, we characterize sub-nanoclusters (M = Ni, Pd, Pt, Cu, and Ag) with atomicities , both in gas-phase and supported on Gr. We find that M atoms act as “anchors,” enhancing binding to Gr and modulating catalytic efficiency. Notably, /Gr shows improved stability, with segregation tendencies mitigated upon adsorption on Gr. The d-band center () model indicates catalytic potential, correlating an optimal range of eV for HER and OER catalysts. Incorporating Au into adjusts closer to the Fermi level, especially for Group-10 alloys, offering designs with improved stability and efficiency comparable to pure Au nanocatalysts. Our methodology leveraged SimStack, a workflow framework enabling modeling and analysis, enhancing reproducibility, and accelerating discovery. This work demonstrates SimStack’s pivotal role in advancing the understanding of composition-dependent stability and catalytic properties of Au-alloy clusters, providing a systematic approach to optimize metal-support interactions in catalytic applications.

Non-Stoichiometric BaxMn0.7Cu0.3O3 Perovskites as Catalysts for CO Oxidation: Optimizing the Ba Content.

In this work, a series of BaxMn0.7Cu0.3O3 samples (x: 1, 0.9, 0.8, and 0.7, BxMC) was synthesized, characterized, and used as catalysts for CO oxidation reaction. All formulations were active for CO oxidation in the tested conditions. A correlation between the electrical conductivity, obtained by impedance spectroscopy, and the reducibility of the samples, obtained by H2-TPR, was observed. The Ba0.8Mn0.7Cu0.3O3 composition (B0.8MC) showed the best catalytic performance (comparable to that of the 1% Pt/Al2O3 reference sample) during tests conducted under conditions similar to those found in the exhaust gases of current gasoline engines. The characterization data suggest the simultaneous presence of a high Mn(IV)/Mn(III) surface ratio, oxygen vacancies, and reduced copper species, these two latter being key properties for ensuring a high CO conversion percentage as both are active sites for CO oxidation. The reaction temperature and the reactant atmosphere composition seem to be the most important factors for achieving a good catalytic performance, as they strongly determine the location and stability of the reduced copper species.

Mechanisms of CO oxidation on high entropy spinels.

The CO oxidation reaction on (Co,Mg,Mn,Ni,Zn)(Al,Co,Cr,Fe,Mn)2O4 and (Cr,Mn,Fe,Co,Ni)3O4 high entropy spinel oxides was studied for what concerns its mechanism by means of operando soft X-ray absorption spectroscopy. In the (Cr,Mn,Fe,Co,Ni)3O4 high entropy spinel, CO oxidation starts at ca. 150 °C, and complete conversion to CO2 is obtained at ca. 300 °C. For the (Co,Mg,Mn,Ni,Zn)(Al,Co,Cr,Fe,Mn)2O4 spinel oxides, in contrast, the reaction starts at ca. 200 °C, and complete conversion needs temperatures of the order of 350 °C. Concerning the reaction mechanism, we found that, in both cases, Mn is the active metal, via the Mn(II)/Mn(III) redox couple. CO is found to adsorb on surface Mn(III) sites and reduces them to Mn(II). The Mn(III) oxidation state is recovered by O2, yielding CO2. All the other transition metals are found to be inactive and act just as spectators. These findings are discussed in the framework of the present knowledge on high entropy oxides.

Tuning support morphology to control alloy over PtCo/γ-Al2O3 for the preferential oxidation of CO

Tuning support morphology to control alloy over PtCo/γ-Al2O3 for the preferential oxidation of CO

Investigation on catalytic oxidation of CO over Mo-Sn catalysts

Investigation on catalytic oxidation of CO over Mo-Sn catalysts

Abundant surface adsorbed oxygen species originated from defect/vacancy sites during preferential CO oxidation

Abundant surface adsorbed oxygen species originated from defect/vacancy sites during preferential CO oxidation

Optimizing CO preferential oxidation pathways via active-site engineering: A case study on MgO nano-sheets supported ultrasmall PtNi alloys

Active-sites play a pivotal role in catalyzing reactions at surfaces, yet engineering these active sites still remains a significant challenge. In this work, hydroxylated MgO nanosheets supported ultrasmall PtNi alloys approximately 2.6(1) nm (xPt-yNi/MgOhydr) has been investigated via active-site engineering. Experimental results and DFT calculations reveal that electron transfers from Ni to Pt and from hydroxyl groups to Pt 5d-orbitals generate active sites NiPt-(OH)x. In the preferential CO oxidation (CO-PROX) reaction, these active sites on xPt-yNi/MgOhydr switch the bicarbonates reaction pathway depending on temperature range. Consequently, the optimal catalyst, 5%Pt-0.5%Ni/MgOhydr, achieves 100% CO conversion at 100 °C, demonstrating a broad temperature operation window (100–200 °C) and excellent durability. The active site engineering approach presented in this study can promote the discovery of more excellent catalysts with the optimal reaction route for various applications.