Activating low-temperature diesel oxidation by single-atom Pt on TiO2 nanowire array

We report herein a new sulfur-functionalized MXene Ti2C (Ti2CS2)-supported osmium-metal single-atom catalyst (SAC) Os1/Ti2CS2 with high low-temperature catalytic activity for CO oxidation. Using periodic density functional theory calculations, the most stable SAC, Os1/Ti2CS2, has been screened from a series of group 8–11 transition metal SACs M1/Ti2CS2 (M = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir, Pt, Au). The calculations show that it is favorable for O2 and CO to be coadsorbed on the Os1 single atom (SA) of Os1/Ti2CS2 and the adsorption energy of the first O2 molecule is slightly higher than that of CO. Moreover, the termolecular co-adsorption of O2 + 2CO on Os1 SA is also possible, which is favorable for CO oxidation on Os1 SA through a novel three-molecule reaction mechanism. Accordingly, four different catalytic mechanisms, the Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R), termolecular Langmuir-Hinshelwood-A (TLH-A) and termolecular Langmuir-Hinshelwood-B (TLH-B), are systematically studied for CO oxidation by O2 on Os1/Ti2CS2. The theoretical studies indicate that the TLH-B mechanism is the most feasible for CO oxidation with the reaction barrier energy of only 0.74 eV, which is far lower than for L-H, E-R and TLH-A with barrier energies of 1.06, 1.09 and 1.47 eV, respectively. The results provide fundamental understanding to the surface chemistry of MXene and designing new sulfur-functionalized two-dimensional MXene catalytic nanomaterials.

Structure evolution of nanocrystalline Ce1−xPdxO2−y mixed oxide in oxidizing and reducing atmosphere: Reduction-induced activity in low-temperature CO oxidation

A commercial cordierite sample showed a small catalytic activity in iso-propanol conversion carried out at 150-350 °C and no measurable activity in CO oxidation by O2. On the other hand, supporting NiO on Al2O3–modified cordierite resulted in the formation of an active solid that having good catalytic activity in iso-propanol conversion and CO oxidation by O2. These two reactions were carried out at 150-350 and 200 °C, respectively. The results revealed that the catalyst containing 5wt (percent) NiO showed the biggest activity in the alcohol conversion and acted as selective dehydration catalyst. The catalyst sample containing 20wt (percent) NiO exhibited a good activity in CO oxidation by O2 which decreased progressively by increasing its calcination temperature within 350-600 °C. Al2O3–treated cordierite dissolved a portion of NiO in its lattice which increased by increasing the calcination temperature within 350-600 °C.

The alteration of the performance of field-aged Pd-based TWCs towards CO and C3H6 oxidation

Synthesis of nanosized Ce0.85M0.1Ru0.05O2−δ (M = Si, Fe) solid solution exhibiting high CO oxidation and water gas shift activity

Single atom catalysts (SACs) are highly desirable for the effort to maximize the efficiency of metal atom use. However, the synthesis of SACs is a major challenge that largely depends on finding an appropriate supporting substrate to achieve a well-defined and highly dispersed single atom. This work demonstrates that, based on the density functional theory (DFT) calculation, graphyne is a good substrate for single Fe atom catalysts. The Fe atom can be tightly embedded in a graphyne sheet with a high binding energy of ∼4.99 eV and a high diffusion energy barrier of ∼1.0 eV. The graphyne-supported Fe (Fe-graphyne) SAC shows high catalytic activity towards CO oxidation, which is often regarded as a prototype reaction for designing atomic-scale catalysts. We studied the adsorption characteristics of CO and O2 on Fe-graphyne SACs, and simulated the reaction mechanism of CO oxidation involving Fe-graphyne. The simulation results indicate that O2 binding on Fe-graphyne is much stronger than that of CO, and the adsorbed O2 prior to occupy the Fe atoms as the co-existence of O2 and CO. The reaction of CO oxidation by adsorbed O2 on Fe-graphyne SACs favors to proceed via the Eley-Rideal (ER) mechanism with the energy barrier of as low as ∼0.21 eV in the rate-limiting step. Calculation of the electronic density of states (DOS) of each reaction step demonstrates that the strong interaction of the O2 and Fe adatom promotes the CO oxidation on Fe-graphyne SACs. The results presented here suggest that graphyne could provide a unique platform to synthesize SACs, and the Fe-graphyne SACs could find potential use in solving the growing environmental problems caused by CO emission from automobiles and industrial processes, in removing CO contamination from vehicle exhaust and in fuel cells.

The MnOх-ZrO2-CeO2 oxide catalysts were synthesized by co-precipitation method with varying (1) Zr/Zr + Ce molar ratio at constant manganese content of 0.3; (2) manganese content at constant Zr/Ce molar ratio of 1; (3) Mn/Mn + Zr molar ratio at constant Ce content of 0.5. Catalysts are characterized by XRD, N2 adsorption, TPR, and XPS. The catalytic activity of all the series was tested in the CO and propane oxidation reactions. In contrast to the variation of the manganese content, the Zr/Zr + Ce molar ratio does not significantly affect the catalytic properties. The dependence of the catalytic activity in CO oxidation on the manganese content has a «volcano» shape, and the best catalytic performance is exhibited by the catalyst with Mn/(Zr + Ce) = 1. In the case of propane oxidation reaction, there is «sigma» like dependence, activity increases with increase of Mn/(Mn + Zr + Ce) molar ratio up to 0.3, stabilizing with a further increase in the manganese content. XRD and XPS have shown that with an increase of the Mn concentration in the MnOx-ZrO2-CeO2 catalysts, the amount of crystalline manganese oxides such as Mn2O3 and Mn3O4, as well as the surface concentration of Mn cations, increases. While the content of MnxZryCe1-x-yO2 solid solution decreases, the concentration of manganese cations (x) in volume of MnxZryCe1-x-yO2 mixed oxide grows. The maximum activity in CO oxidation corresponds to the balance between the amount of the solid solution and the concentration of manganese cations in the volume of mixed oxide. The propane oxidation reaction is less sensitive to the state of manganese ion rather than to its amount. In this case, a decrease in the content of the MnxZryCe1-x-yO2 solid solution with increase in manganese amount in catalyst is compensated by an increase in content of crystalline manganese oxides and the surface concentration of manganese.

Fe-doped C3N monolayer as a promising SAC for CO oxidation with low temperature and high reactivity

Catalytic activity of thermal CO oxidation was studied for monatomic-layered platinum cluster disks, Pt30, bonded to the (111) surface of a silicon substrate. Temperature-programmed desorption (TPD) measurements were repeated for a given cluster sample with a systematic change in the reactant amounts supplied, and the peaks observed in the TPD spectra were deconvoluted so as to obtain probabilities of individual reactions. It was concluded that this system possesses an ability of low-temperature reductive activation of oxygen molecules, which is one of the critical steps in the CO oxidation. This high performance is explained in terms of negative charges accumulated at a sub-nano interface between the cluster disk and the silicon substrate surface as a result of their strong electronic interaction.

Oxidation of CO over Ru containing perovskite type oxides

The inherent trade-off between activity and stability in platinum single-atom catalysts (SACs) poses a significant challenge for catalytic oxidation reactions. High-coordination Pt sites have good stability, but their overoxidation often passivates activity. In contrast, metastable low-coordination Pt structures typically display high activity but are prone to oxidation and aggregation under harsh conditions. Herein, we propose a defect-engineering strategy to address this dilemma by anchoring oxidized Pt single atoms onto vacancy LaFeO3 (v-LaFeO3) perovskite. The introduced La-vacancy substantially reduces the oxygen vacancy formation energy of LaFeO3, enhancing lattice oxygen mobility while preserving structural integrity. Pt single-atom sites with a high oxidation state (Pt4+) are anchored on the support, and their coordination environments are optimized. The catalyst exhibits high and stable activity for CO oxidation without reduction pretreatment. The structural characterization and in situ experiments indicate that vacancies in LaFeO3 positively regulate the electronic structure between the Pt and v-LaFeO3 interface. The longer Pt-O bonds activate interface oxygen species, accelerate O2 activation, and promote the cycling of CO oxidation. The oxidized Pt atoms and high coordination number enable its stability in long-term and high-temperature oxidation reactions. DFT calculations further verify the structure and reaction mechanism. This work demonstrates that precise control of support defects can concurrently optimize the electronic states and stability of SACs, offering a generalized paradigm for designing robust oxidation catalysts.

Supported gold cluster catalysts prepared by solid grinding using a non-volatile organogold complex for low-temperature CO oxidation and the effect of potassium on gold particle size

Single-atom catalysts (SACs) exhibit distinct catalytic behavior compared with nano-catalysts because of their unique atomic coordination environment without the direct bonding between identical metal centers. How these single atom sites interact with each other and influence the catalytic performance remains unveiled as designing densely populated but stable SACs is still an enormous challenge to date. Here, a fabrication strategy for embedding high areal density single-atom Pt sites via a defect engineering approach is demonstrated. Similar to the synergistic mechanism in binuclear homogeneous catalysts, from both experimental and theoretical results, it is proved that electrons would redistribute between the two oxo-bridged paired Pt sites after hydrogen adsorption on one site, which enables the other Pt site to have high CO oxidation activity at mild-temperature. The dynamic electronic interaction between neighboring Pt sites is found to be distance dependent. These new SACs with abundant Pt-O-Pt paired structures can improve the efficiency of CO chemical purification.

The Front Cover presents a surface-science approach to understanding and steering the catalytic properties of heterogeneous single-atom catalysts (SACs) aiming to step them up for industrial applications. In their Research Article, A. M. Abdel-Mageed et al. show that the CO oxidation activity of Cu/CeO2-TiO2 SACs can be fine-tuned by modulating the Ce/Ti ratio. The catalytic activity obeys a volcano-shaped dependence of Ce/Ti molar ratio. Insights from operando spectroscopy and several other characterizations correlated the highest activity to the highest dispersion and reducibility of CeO2 nanoparticles which culminates around a Ce/Ti ratio of 0.18. Together with the atomically dispersed Cu species, the highly dispersed ceria nanoparticles constitute the catalytically active redox species (Cu2+−O−Ce4+− ⇆ −Cu1+−□−Ce3+−). This study highlights the synergism between the rational design of catalytic materials and the power of operando spectroscopy. More information can be found in the Research Article by A. M. Abdel-Mageed et al..

Three different CeO2 sphere nanomaterials (hollow sphere, flowerlike sphere, spherical cluster) were controllably synthesized by carbon sphere template method, hydrothermal and solvothermal method respectively. Then 2.5 wt% Au was doped on the supports by the deposition precipitation method and Au/CeO2 catalysts with three different morphologies were obtained. Composition, morphology and structure of these catalysts were characterized by the techniques of XRD, Raman, TPR, SEM and TEM, and the activity for CO oxidation of the catalysts was investigated. The catalytic test results indicated that the addition of Au could remarkably improve catalytic performance on CO oxidation. The activities of the three catalysts differ largely, the flowerlike Au/CeO2 catalyst had the highest activity for CO oxidation and its T100% was 29°C. The mechanism for the different activity of the catalysts was investigated. H2-TPR result indicated flowerlike had a more intensive peak at 125°C than others and it implied more reducible Au species in this case, that plays a vital role in the CO oxidation.