Kinetic model of CO oxidation on heterophase surface analyzed regarding COads spillover, I. Homotopic method. Effect of temperature and CO pressure

The homotopic method has been used to analyze the kinetic models of CO oxidation on two surface patches conjugated by CO_ads spillover. On each patch reaction proceeds via a three-stage mechanism but with different constants. The stability of steady-states solution has been studied. CO_ads spillover from one patch to another changes substantially the bifurcation picture of steady states and produces islands.     

Kinetic model ofCO oxidation on nonuniform surface analyzed regardingCOads spillover, 2. homotopic method. Effect ofm1 surface portion

The homotopic method has been used to analyze the kinetic model of three-stageCO oxidation on two nonuniform surface patches conjugated byCO ₂ spillover. Diagrams of steady states depending on the portion of surface patchm ₁ at various temperatures and pressure ratiosP(O ₂)/P(CO) have been constructed. The ratios of different type patches corresponding to the maximum overall reaction rate have been found.     

Kinetics of CO oxidation on the surface of heterophase catalysts. Modeling by the Monte Carlo method

The Monte Carlo method has been used to simulate CO oxidation on a lattice consisting of various alternating patches: M1, where s(CO)>s(O₂) and M2, where s(CO)2). The reaction is shown to proceed over all the surface at low temperature as CO_ads spillover from M1 to M2 and backwards.     

COads spillover and low-temperature activity of heterophase catalysts in CO oxidation

The kinetics of CO oxidation on heterophase surfaces composed of two different types of patches M1 and M2 is analyzed. The kinetic conjugation of the patches caused by CO_ads spillover leads to the substantial change in reaction rate temperature dependences, as well as to the appearance of a low-temperature, superadditive activity.     

Experimental study of intermediates and wave phenomena in co oxidation on platinum metal (Pt,Pd) surfaces

The mechanism of catalytic CO oxidation on Pt(100) and Pd(110) single-crystal surfaces and on Pt and Pd sharp tip (～10³ Å) surfaces has been studied experimentally by temperature-programmed reaction, temperature desorption spectroscopy, field electron microscopy, and molecular beam techniques. Using the density functional theory the equilibrium states and stretching vibrations of oxygen atoms adsorbed on the Pt(100) surface have been calculated. The character of the mixed adsorption layer was established by high resolution electron energy loss spectroscopy—molecular adsorption (O_2ads, CO_ads) on Pt(100)-hex and dissociative adsorption (O_ads, CO_ads) on Pt(100)-(1×1). The origin of kinetic self-oscillations for the isothermal oxidation of CO in situ was studied in detail on the Pt and Pd tips by field electron microscopy. The initiating role of the reversible phase transition (hex) ? (1 × 1) of the Pt(100) nanoplane in the generation of regular chemical waves was established. The origination of self-oscillations and waves on the Pt(100) nanoplane was shown to be caused by the spontaneous periodical transition of the metal from the low-active state (hex) to the highly active catalytic state (1 × 1). A relationship between the reactivity of oxygen atoms (O_ads) and the concentration of CO_ads molecules was revealed for the Pd(110) surface. Studies using the isotope label ¹⁸O_ads demonstrated that the low-temperature formation of CO₂ at 150 K is a result of the reaction of CO with the highly reactive state of atomic oxygen (O_ads). The possibility of the low-temperature oxidation of CO via interaction with the so-called “hot” oxygen atoms (O_hot) appearing on the surface at the instant of dissociation of O_2ads molecules was studied by the molecular beam techniques.     

Adsorption of NO and CO and specific features of their interaction on the Pt(100) surface

This article presents an analytical review of the author’s results and the literature concerning the nature of species resulting from NO and CO adsorption on the unreconstructed (1 × 1) and reconstructed hexagonal (hex) Pt(100) surfaces, including specific features of the reactions between these species. At 300 K, both surfaces adsorb NO and CO mainly in their molecular states. When adsorbed on Pt(100)-1 × 1, the NO_ads and CO_ads molecules are uniformly distributed on the surface. Under the same conditions, the hexagonal surface undergoes adsorption-induced reconstruction with the formation of NO_ads/1 × 1 and CO_ads/1 × 1 islands, which are areas of the unreconstructed phase saturated with adsorbed molecules and surrounded with the adsorbate-free hex phase. In adsorption on structurally heterogeneous surfaces containing both hex and 1 × 1 areas, the 1 × 1 and hex phases are occupied in succession, the latter undergoing reconstruction into the 1 × 1 phase. The reaction between NO and CO on the unreconstructed surfaces occurs even at room temperature and results in the formation of N₂ and CO₂ in quantitative yield. On the hexagonal surface, a stable layer of adsorbed molecules as (NO_ads + CO_ads)/1 × 1 mixed islands forms under these conditions. Above 350 K, the reaction in the mixed islands is initiated by the desorption of small amounts of the initial compounds, and this is followed by rapid self-acceleration leading to a surface explosion yielding N₂, CO₂, and N₂O (minor product). These products show themselves as very narrow desorption peaks in the temperature-programmed reaction spectrum.     

Infrared studies of the effect of acetylene, hydrogen, and oxygen on CO adsorption on platinum hydrosols

Infrared spectra of CO-treated platinum hydrosols subsequently treated with acetylene, hydrogen, and oxygen reveal that v(CO)_ads decreases from 2070 cm⁻¹ with increasing gas-treatment time. This has been attributed to a reduction in the coverage of adsorbed CO. In Pt sol/CO/C₂H₂ systems, v(CO)_ads decreases to a limiting value of ca. 2060 cm⁻¹ after exposure to acetylene. In the Pt sol/CO/H₂ systems, v(CO)_ads decreases to ca. 2050 cm⁻¹ after exposure to hydrogen gas. The lower frequency in the Pt sol/CO/H₂ system has been attributed to CO adsorption on more active metal sites formed from the reduction of surface platinum oxides. Exposure of the CO-treated platinum hydrosols to O₂ gas was found to cause the eventual disappearance of the v(CO)_ads band in infrared spectra, which was attributed to oxidation of adsorbed CO to CO₂ by weakly bound surface layers of platinum oxides formed by the oxygen treatment.     

Transients of the Open-Circuit Potential during Carbon Monoxide Interaction with Oxygen Preliminarily Adsorbed on Smooth and Platinized Platinum Electrodes

Variations of potential E in time , observed during the carbon monoxide interaction with preliminarily-adsorbed oxygen O_ads on smooth and platinized platinum electrodes under open-circuit conditions (supporting electrolyte 0.5 M H₂SO₄), are measured. The potential decay rate on smooth Pt is more than ten times that on Pt/Pt; there are some differences in the transients as well. The obtained data suggest that CO interacts with O_ads on smooth Pt and Pt/Pt via different mechanisms. Two models for the process on smooth platinum are considered. In one model, the interaction of O_ads with CO from solution is accepted as the rate-determining step; in the other, the interaction of O_ads with CO_ads. A comparison of theoretical E vs. dependences with experimental data using the MathCad program suggests that CO interacts with O_ads via both mechanisms.     

Spectroelectrochemical studies of poly-o-phenylenediamine Part 2. In situ UV—vis subtractive reflectance spectroscopy

In our previous paper, the phenazine-like structure of the poly-o-phenylenediamine (PoPD) and its three steady redox states have been revealed mainly by using in situ resonance Raman spectroscopy. It has also been shown that the semi-oxidized state of PoPD is the most stable state of PoPD, while the totally-oxidized state of PoPD is chemically unstable and can exist only at certain electrode potentials. In the present work, the more detailed reaction mechanism of a PoPD film in strong acid solution has been studied by using in situ UV—vis substractive reflectance spectroscopy. The semi-oxidized state and the totally-oxidized state of PoPD have electronic absorption bands around 300 nm, 430 nm, 500 nm and 300 nm, 450 nm, 530 nm, 735 nm respectively in the in situ steady state UV—vis subtractive reflectance spectra with respect to the reduced state of PoPD, which verifies once again that three redox states of PoPD exist in the redox process of PoPD. Moreover, the relative intensity between two oxidized states of PoPD at the maximum absorption wavelength (λ_max) reveals that only about one third of the semi-oxidized state of PoPD can be oxidized to the totally-oxidized state of PoPD. The in situ resonance Raman spectra and the cyclic voltammograms of PoPD display the same quantitative relationship. New absorption bands were observed in the in situ time-resolved UV—vis subtractive reflectance spectra with appropriate time resolutions, which illustrate the dynamic structure changes of PoPD in its redox process. These intermediate states of PoPD are more unstable than its three redox states.     

The Study of Nitric Oxide Adsorption and the Mechanism of Surface “Explosions” in the Reaction of CO + NO on Pt(100) and Pd(110) Single Crystal Surfaces

High resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) were used to study NO adsorption and the reactivity of CO_ads and NO_ads molecules on Pd(110) and Pt(100) single crystal surfaces. Compared to the Pt(100)-(1 × 1) surface, the unreconstructed Pt(100)-hex surface is chemically inert toward NO dissociation into N_ads and O_ads atoms. When a mixed adsorbed CO_ads + NO_ads layer is heated, a so-called surface explosion is observed when the reaction products (N₂, CO₂, and N₂O) synchronously desorb in the form of sharp peaks with a half-width of 7-20 K. The shape specificity of TPR spectra suggests that the vacancy mechanism consists of the autocatalytic character of the reaction initiated by the formation an initial concentration of active sites due to partial desorption of molecules from the CO_ads + NO_ads layer upon heating to high temperatures. Kinetic experiments carried out on the Pd(110) surface at a constant reaction pressure and a linear increase in the temperature confirm the explosive mechanism of the reaction NO + CO.     

Analysis of autooscillations during co oxidation on a non-uniform surface consisting of two types of sites coupled by coads diffusion

Areas of occurrence and character of autooscillations during CO oxidation on a non-uniform surface consisting of different sites M₁ and M₂, the reaction on which is kinetically connected by the diffusion of adsorbed CO (CO_ads), has been analyzed using numerical integration of an independent system and search of stationary solutions by the homotopy method.     

Density functional study of H2 molecule and H atom adsorption on α‐U(001) surface

Density functional theory method has been employed to investigate the adsorption of H₂ molecule and H atom on α‐U(001) surface. There exist four initial sites [top (A), triangle‐center (B), long‐bridge (C), and short‐bridge (D)] for H₂ and H atom adsorptions on α‐U(001) surface. The E_ads (adsorption energy) values on the top sites of H₂‐U(001) configurations are around ?0.666 eV, and H₂ molecule has been elongated but not broken into H atoms. For the other three sites, the E_ads values are around ?1.521 eV. The long‐bridge site is the most reactive site for H₂ decomposing. For the H‐U(001) configurations, the E_ads are around ?2.904 eV. Top site and short‐bridge site are the most reactive sites for the H atom react on the α‐U(001) surface. Our work reveals that the different reactive sites play discrepant effects on hydrogenation process. Geometric deformations, diffusion paths, and partial density of states of H₂‐U(001) and H‐U(001) configurations have also been analyzed. Copyright © 2016 John Wiley & Sons, Ltd.     

Mathematical modeling of wave phenomena in the oxidation of CO on the Pt(l00) surface

CO oxidation on Pt(l00) is studied by the Monte Carlo method using a model that accounts for the phase transition (lxl) ai (hex). The influence of surface diffusion of CO_ads on the velocity of wave propagation of O_ads and CO_ads and the distribution of the species in the reaction zone is studied Deceased.     

水在C12-EOx-C12•2Br/正己醇/正庚烷W/O微乳中的状态

以FT-IR方法研究了水/C₁₂-EO_x-C₁₂•2Br/正己醇/正庚烷形成的W/O微乳中水的状态. 结果表明, 其中的水存在4种状态, 分别为阳离子头基结合水、反离子结合水、类似本体的水以及束缚在微乳栅栏层中的水. 由解卷积技术分解FT-IR谱图, 进而获得每个表面活性剂分子对应于这4种状态水分子的数目n_N＋, n_Br-, n_b和n_f. 随着水含量(W₀)增加, n_b急剧增大, n_N＋少许上升, 而n_f和n_Br-维持不变, 这说明微乳水核逐渐长大, 且在所考察W₀范围内, 表面活性剂头基解离度保持不变.     

The catalytic effects of various third molecules on reaction channels of weakly bound complex CO2HF systems in the vapor phase

In this investigation, reaction channels of weakly bound complexes CO₂HF, CO₂HFH₂O, CO₂HFNH₃, CO₂HFCH₃OH, CO₂HFNH₂CH₃, CO₂HFNH(CH₃)₂ and CO₂HFN(CH₃)₃ systems were studied at the B3LYP/6-311++G(3df,2pd) level. The conformers of syn-fluoroformic acid or syn-fluoroformic acid plus a third molecule (H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃) were found to be more stable than the conformers of the related anti-fluoroformic acid or anti-fluoroformic acid plus a third molecule (H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃). However, the weakly bound complexes were found to be more stable than either the related syn- and anti- type fluoroformic acid or the acid plus third molecule (H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃) conformers. They decomposed into CO₂+HF, CO₂+H₃OF, CO₂+NH₄F, CO₂+(CH₃)OH₂F, CO₂+NH₃(CH₃)F, CO₂+NH₂(CH₃)₂F, or CO₂+NH(CH₃)₃F combined molecular systems. The weakly bound complexes have seven reaction channels, each of which includes weakly bound complexes and their related systems. Moreover, each reaction channel includes two transition state structures. The transition state between the weakly bound complex and anti-fluoroformic acid type structure (T₁₃) is significantly higher than that of internal rotation (T₂₃) between the syn- and anti-FCO₂H (or FCO₂HH₂O, FCO₂HNH₃, FCO₂HCH₃OH, FCO₂HNH₂CH₃, FCO₂HNH(CH₃)₂, or FCO₂HN(CH₃)₃) structures. However, adding the third molecule H₂O, NH₃, CH₃OH, NH₂CH₃, NH(CH₃)₂ or N(CH₃)₃ can significantly reduce the activation energy of T₁₃. The catalytic strengths of the third molecules are predicted to follow the order H₂O<NH₃<CH₃OH<.NH₂CH₃<NH(CH₃)₂<N(CH₃)₃.     

Insights into the role of D-A-π-A type pro-aromatic organic dyes with thieno[3,4-b]pyrazine as A acceptor group into dye-sensitized solar-cells. A TD-DFT/periodic DFT study

Time-dependent density functional theory (TD-DFT)/periodic DFT calculations were performed to determine the role of pro-aromatic organic D-A -π -A type dyes (the NL1-NL17 family) with Thieno[3,4-b]pyrazine (Tpy) as A acceptor group into dye-sensitized solar-cells (DSSC). This work presents a discussion of the ground and excited states of these dyes along with the aromaticity analysis and the electron injection step using a dye@(TiO₂)₇₂ model. The results suggest that the pro-aromatic behavior increases from the thiophene ring to the pyrazine when an acceptor π-bridge such as phenyl is used. This strong pro-aromaticity is also reflected in the electron injection step, studied using a 3x2 3 layer (TiO₂)₇₂ slab model. The resulting adsorption energies (ΔE_ads and ΔG_ads) and the electron injection (ΔG_inject) in the stablest coordination mode, Bid_CN_COOH, indicate that the redox reaction (Dye* ➔ Dye⁺ + e⁻) is stronger and more spon than the adsorption reaction (Dye⁺ + TiO₂ [+e⁻] ➔ Dye@TiO₂) in the electron injection. In this way, the highest efficiency of NL6 and NL12 is a consequence of the more significant pro-aromatic characteristics and the more spontaneous redox process. Finally, these NL dyes are promising in the molecular engineering of D-A -π -A metal-free types dyes.     

Oxidation of carbon monoxide and formic acid on bulk and nanosized Pt–Co alloys

Bulk Pt₃Co and nanosized Pt₃Co and PtCo alloys supported on high area carbon were investigated as the electrocatalysts for the CO_ads and HCOOH oxidation. Pt₃Co alloy with Co electrochemically leached from the surface (Pt skeleton) was employed to separate electronic from ensemble and bifunctional effects of Co. Cyclic voltammetry in 0.1 M HClO₄ showed reduced amount of adsorbed hydrogen on Pt sites on Pt₃Co alloy compared to pure Pt. However, no significant difference in hydrogen adsorption/desorption and Pt-oxide reduction features between Pt₃Co with Pt skeleton structure and bulk Pt was observed. The oxidation of CO_ads on Pt₃Co alloy commenced earlier than on Pt, but this effect on Pt₃Co with Pt skeleton structure was minor indicating that bifunctional mechanism is stronger than the electronic modification of Pt by Co. The HCOOH oxidation rate on Pt₃Co alloy was about seven times higher than on bulk Pt when the reaction rates were compared at 0.4 V, i.e., in the middle of the potential range for the HCOOH oxidation. Like in the case of CO_ads oxidation, Pt skeleton showed similar activity as bulk Pt indicating that the ensemble effect is responsible for the enhanced activity of Pt₃Co alloy toward HCOOH oxidation. The comparison of CO_ads and HCOOH oxidation on Pt₃Co/C and PtCo/C with the same reaction on Pt/C were qualitatively the same as on bulk materials.     

Computational Study on Interactions between CO2 and (TiO2)n Clusters at Specific Sites

The energetic pathways of adsorption and activation of carbon dioxide (CO₂) on low-lying compact (TiO₂)_n clusters are systematically investigated by using electronic structure calculations based on density-functional theory (DFT). Our calculated results show that CO₂ is adsorbed preferably on the bridge O atom of the clusters, forming a "chemisorption" carbonate complex, while the CO is adsorbed preferably to the Ti atom of terminal Ti-O. The computed carbonate vibrational frequency values are in good agreement with the results obtained experimentally, which suggests that CO₂ in the complex is distorted slightly from its undeviating linear configuration. In addition, the analyses of electronic parameters, electronic density, ionization potential, HOMO-LUMO gap, and density of states (DOS) confirm the charge transfer and interaction between CO₂ and the cluster. From the predicted energy profiles, CO₂ can be easily adsorbed and activated, while the activation of CO₂ on (TiO₂)_n clusters are structure-dependent and energetically more favorable than that on the bulk TiO₂. Overall, this study critically highlights how the small (TiO₂)_n clusters can influence the CO₂ adsorption and activation which are the critical steps for CO₂ reduction the surface of a catalyst and subsequent conversion into industrially relevant chemicals and fuels.     

Density functional theory study of CO2 capture and storage promotion using manipulation of graphyne by 3d and 4d transition metals

In this work, the electronic and structural properties of 3d and 4d transition metal (TM)-decorated graphyne (GY) (TM-GY) toward CO₂ adsorption were studied using the D3-corrected density functional theory (DFT-D3) method. Then, CO₂ capture and storage (CCS) of the most stable structures were investigated. Results show that the most stable site for all TM decoration is the center of the 12-membered ring with various distances from carbon plane, and GY decorated with Ni and Zn from 3d and Zr and Cd from 4d TMs are also the most and the least stable, energetically with E_b of −5.834, −0.467, −6.181, and −0.963 eV, respectively. Evaluation of the adsorption behavior of CO₂ on TM-GY reveals that the strongest adsorption energies belong to Cr and Mo-GY (−1.502 and −1.117 eV, respectively), and for all 3d and 4d TMs, the horizontal direction of CO₂ is more stable, energetically. Increasing CO₂ molecules, step by step, on Cr and Mo-GY shows that they can hold 13 and 18 CO₂ molecules with average E_ads of −0.374 and −0.330 eV/CO₂ and corresponding CO₂ storage capacities of 47.66 and 54.10 wt%, respectively. These findings show that Cr and Mo-GY can be used in the future as suitable candidates for CCS applications.     

ZrCdOx/SAPO-18双功能催化剂催化CO2加氢合成低碳烯烃性能

采用并流共沉淀法制备了不同Zr/Cd原子比(n_Zr/n_Cd)的ZrCdO_x金属氧化物,并与水热法制备的不同硅铝比(n_{SiO_(2})/n_{Al_(2}O₃))的片状SAPO-18分子筛物理混合制得ZrCdO_x/SAPO-18双功能催化剂,研究了其催化CO₂加氢直接合成低碳烯烃性能。采用透射电子显微镜(TEM)、X射线衍射(XRD)、N2吸附-脱附、CO₂程序升温脱附(CO₂-TPD)、NH3程序升温脱附(NH3-TPD)和X射线光电子能谱(XPS)对催化剂进行了分析。与单一ZrO2相比,引入CdO使得ZrCdO_x比表面积下降,当n_Zr/n_Cd=8时制备的Zr8Cd1氧化物呈现出无定形小颗粒状,Zr与Cd之间较强的协同作用使得Zr Cd Ox氧化物产生了更多的氧空位,有利于CO₂的吸附活化。通过对Zr8Cd1金属氧化物与SAPO-18(硅铝比0.1)的质量比、工艺反应温度、压力和空速对催化性能影响的考察,获得了最佳反应条件。研究还发现,当SAPO-18的硅铝比从0.1降为0.01时,Br?nsted酸含量降低,产物中烯烃/烷烃物质的量之比从18.6提高至37.2,但副产物CO含量迅速增加,低碳烯烃时空收率明显下降。