Binding Of CO Molecule Research Articles

In Situ DRIFTS Study of Single-Atom, 2D, and 3D Pt on γ-Al2O3 Nanoflakes and Nanowires for C2H4 Oxidation

Up to now, a great number of catalysts have been reported that are active in the oxidation of volatile organic compounds (VOCs). However, supported noble-metal catalysts (especially Pt-based catalysts) are still the most excellent ones for this reaction. In this study, Pt species supported on γ-Al2O3 and ranging from single-atom sites to clusters (less than 1 nm) and 1–2 nm nanoparticles were prepared and investigated for oxidizing C2H4. The Pt-loaded γ-Al2O3 nanoflakes (PtAl-NF) and Pt-loaded γ-Al2O3 nanowires (PtAl-NW) were successfully prepared. The samples were characterized using XRD, TEM, XPS, HAADF-STEM, and in situ DRIFTS. Based on in situ DRIFTS, a simple surface reaction mechanism was developed. The stable intermediates CO on single-atom Pt, subnanometer Pt particles, and fully exposed Pt clusters could be explained by the strong binding of CO molecule poisoning Pt sites. Moreover, the oxidation of C2H4 was best achieved by Pt particles that were 1–2 nm in size and the catalytic activity of PtAl-NF was better when it had less Pt. Lastly, the most exposed (110) facets of γ-Al2O3 nanoflakes were more resistant to water than the majorly exposed (100) facets of γ-Al2O3 nanowires.

Catalytic CO Oxidation by CO-Saturated Au Nanoparticles Supported on CeO2: Effect of CO Coverage

Understanding the reaction mechanism and the nature of the reactive species of heterogeneous catalysts under reaction conditions is the first step in the design of more consistent, reliable, and practical catalysts. We used density functional theory (DFT) calculations to study the mechanism of CO oxidation catalyzed by CeO2-supported Au nanoparticles (NPs) under reaction conditions by considering the sequential CO adsorption onto and CO saturation of Au NPs. We found that the Au9 NPs supported by CeO2(100) and CeO2(111) bind as many as eight or four CO molecules, respectively. The last-bound CO molecule opens the fast CO oxidation pathway. The CO oxidation pathways constructed on both systems show that the reaction occurs at the Au–CeO2 interface via the Mars–van Krevelen mechanism. We found that the most important O–C–O-type intermediate was spontaneously formed at the Au–CeO2(100) interface upon the sequential binding of CO molecules onto the Au NPs. The reaction pathway therefore becomes relatively sim...

CO oxidation on nanosized Au/Al2O3 by surface hydroxyl groups and in the absence of O2, studied by inverse gas chromatography

In catalysis by gold, the term “decomposition” is used in order to describe CO oxidation by surface hydroxyl groups in the absence of O2, at which carbon dioxide is formed without the deposition of carbon. This process is not only important due to its contribution in the activity of CO oxidation but also because it can offer significant information concerning the mechanism of CO oxidation on gold catalysts. In the present work reversed-flow inverse gas chromatography (RF-IGC) is utilized in order to compare the kinetics of CO oxidation by surface hydroxyl groups, the adsorptive capacity and the nature of the active sites related to CO sorption over bare γ-Al2O3 and Au/γ-Al2O3 catalyst, in a wide temperature range (50–300°C).The rates related to CO surface binding exhibit exactly the same behavior, as the activity of CO oxidation by surface hydroxyl groups does over bare γ-alumina and Au/Al2O3 respectively, indicating that at higher temperatures a much stronger binding of CO molecules over γ-Al2O3 can occur. While, the strong bonding of CO over Au/Al2O3 catalyst, is attributed to CO on active sites of cationic Aux+ near the alumina support, in the case of bare γ-Al2O3 is related to CO insertion in surface Al-hydroxyls, which are inactive at lower temperatures.Rise of temperature affects the topography in a different way resulting in homogeneity in the case of γ-Al2O3 and heterogeneity in that of Au/Al2O3. Gold phase enhances the sorption of bigger amounts of CO over Au/Al2O3 catalyst in comparison to bare γ-Al2O3 support, in agreement with the fact that CO is activated preferably at small particles of metallic Au. Although, a certain amount of CO is stored on the studied solids as inactive spectators of CO oxidation e.g. as carbonate like species during CO adsorption particularly over γ-Al2O3, Au containing catalyst exhibits higher adsorptive capacity towards CO. Slight decrease of the amount of surface CO with rising temperature is observed due to the enhancement of CO oxidation by surface hydroxyl groups over both bare alumina and Au/Al2O3.CO oxidation by surface hydroxyl groups indicates a “periphery” mechanism in which CO molecule activated on metallic gold (Au0…CO) is attacked by an hydroxyl group either on a support cation or on a peripheral AuIII ion, forming an intermediate carboxylate group attached to the latter.

The binding of CO molecule with small Wn(n = 2−9) clusters: a DFT investigation

The hybrid DFT functional has been utilized to investigate CO adsorption on small W n (n = 2−9) clusters. The reactivity-selectivity descriptor Δf(r) is proved to be an appropriate tool for predicting the local adsorption site. Our results indicate that the binding of CO to tungsten cluster prefers terminal adsorption mode except for W3 trimer. The Wiberg bond index can predict the interaction between W atoms and CO molecule to a good accuracy using a linear fit. The dependency on number of adsorbate and charge state of host clusters is also investigated. The high CO coverage seriously weakens the W-CO interaction. The anion cluster reveals the stronger interaction with CO molecule than cation and neutral ones. Moreover, the interesting coverage-dependence is revealed for anion cluster.

Size dependences in the adsorptive properties of the surface of ytterbium nanofilms deposited on silicon: The CO-Yb-Si(111)7 × 7 system

This paper reports on a study of the adsorption of CO molecules on the surface of ytterbium nanofilms of different thicknesses, which were sublimed on Si(111)7 × 7 at room temperature. Dependences of two types were investigated: the surface concentration of adsorbed molecules vs. CO dose expressed in langmuirs and the work function of films vs. CO dose. It was shown that the behavior of these dependences is mediated by size effects and Friedel oscillations generated by the ytterbium-silicon interface. Both effects exert an influence on the binding of CO molecules to the surface. At low molecule concentrations, this binding is effected through lone electron pairs localized at the carbon ends of the molecules. These electrons form a donor-acceptor bond to the vacant 5d level of the metal, with the level dropping below the Fermi level. At high CO molecule concentrations, the pattern becomes more complex; indeed, the enhanced Coulomb interaction gives rise to a partial transfer of electrons from the 5d level to the vacant 2π* orbital of CO molecules.

DFT study of CO adsorption on neutral and charged Pdn(n = 1–7) clusters

Density functional calculations have been performed to investigate CO adsorption on neutral, cationic and anionic Pdn (n=1–7) clusters. From the results, it is observed that the binding of CO molecule to neutral and cationic palladium clusters takes place via 1-, 2- and 3-fold coordination. On the other hand, only terminal adsorption of CO molecule is possible in anionic clusters barring bridging adsorption in Pd7- cluster.

Diffusion and binding of CO on Pt nanowires

The diffusion and binding of CO molecules on self organized Pt nanowires on Ge(0 0 1), have been studied by room temperature scanning tunneling microscopy. CO molecules are found to bind at the bridge position of the Pt dimers. The CO molecules are mobile at room temperature and perform an “unrestricted” one-dimensional random walk in defect-free regions of the Pt nanowires.