In situ FTIR studies of the catalytic oxidation of ethanol on Pt(1 1 1) modified by bi-dimensional osmium nanoislands

This paper presents the study of ethanol electrooxidation on Pt(1 1 1) electrode modified by different coverage degrees of a submonolayer of osmium nanoislands, which were obtained by spontaneous deposition. The ethanol oxidation reaction was extensively studied by employing in situ FTIR. Collections of spectra of the ethanol adsorption and oxidation processes were acquired over a series of positive potential steps, in order to determine the intermediate species and the main products that are formed. It was shown that the increase in the catalytic activity of Pt(1 1 1) after osmium deposition for ethanol oxidation is greater than that observed on nonmodified Pt(1 1 1). It was also demonstrated that the mechanistic pathway for this reaction depends directly on the degree of osmium coverage. Thus, for low osmium coverage (θ_Os ≤ 0.28), the formation of CO as an intermediate is favored, and hence the full oxidation of adsorbed ethanol to CO₂ is increased, additionally, the formation of acetaldehyde is also observed in low degrees of osmium coverage. For intermediate osmium coverage (0.28 < θ_Os ≤ 0.40), the oxidation of ethanol to acetaldehyde and then to acetic acid is favored, although on Pt(1 1 1) the formation of acetaldehyde is promoted. For higher degrees of osmium coverage (θ_Os > 0.51), the catalytic activity of the electrode for ethanol oxidation decreases. For an almost complete osmium layer (θ_Os = 0.92), obtained by electrodeposition at 50 mV, catalytic activity for ethanol oxidation shows the lowest value. In addition, the direct oxidation of ethanol to acetic acid at lower potentials is observed.     

Fabrication of novel porous Pd particles and their electroactivity towards ethanol oxidation in alkaline media

Novel porous Pd particles (nanoPd-PEG, nanoPd-PEG-EDTA, nanoPd-HCHO-EDTA, nanoPd-EG, nanoPd-HCHO and nanoPd-EG-EDTA) were synthesized by a hydrothermal method using different reduction agents in the absence and presence of EDTA and investigated as electrocatalysts for ethanol oxidation in alkaline solutions. Results showed that PdCl₂ was hydrothermally reduced to nano-scale palladium particles and a three-dimensional texture was formed for Pd particles. Presence of EDTA was favorable for the formation of Pd nanoparticles with small sizes of ca. 70 nm. Ethanol oxidation on the present Pd catalysts took place at a more negative anodic potential in 1 M NaOH solution. Among the electrocatalysts investigated, the electrocatalytic activity of the nanoPd-HCHO-EDTA was the greatest, which was characterized by the largest anodic peak current density of 151 mA cm⁻² and lowest onset oxidation potential of −0.788 V (vs. SCE) for the positive scan. Very low charge transfer resistances on the nanoPd-HCHO-EDTA in 1 M NaOH containing various concentrations of ethanol were obtained according to the analysis for electrochemical impedance spectra (EIS). The prepared porous Pd catalysts were promising alternatives to Pt electrodes applied in alkaline direct alcohol fuel cells.     

Study on the two dealloying modes in the electrooxidation of Au-Sn alloys by in situ Raman spectroscopy

The electrochemical processes in dealloying of Au-Sn alloys in a solution of 2 mol dm⁻³ HCl have been first investigated in detail by means of in situ potential-dependent and time-resolved Raman spectra. Two dealloying modes were found occurring within different potential regions in the electrooxidation of Au-Sn alloys. One is the mode known as classical dealloying, where Sn is selectively dissolved; and the other a so-called quasi-dealloying mode found here, in which Au re-deposits automatically after simultaneous dissolution with Sn. Meanwhile, nanoporous gold, thin layers of gold nanoparticles stacked on the surface, and colloidal gold in the solution can be prepared from the Au-Sn alloys simply by an electrochemical control of potential. Moreover, the quasi-dealloying manner of Au-Sn alloys has also been grafted onto a pure Au electrode with a tin overlayer by electrodeposition to construct the SERS substrate conveniently.     

In situ studies of heterogeneous catalysis: Diffractometric and spectroscopic approaches

Lessons are drawn from the work of molecular biologists who have succeeded in elucidating the mechanisms of many enzymatic processes from X-ray crystallographic analyses of data recorded on the catalyst-reactant system prior to and after catalytic reaction. The use of in situ infrared spectroscopy to clarify the processes of adsorption and catalytic reactions on uniform heterogeneous catalysts is exemplified through a series of studies of the dehydration of the four isomers of butanol over H-ZSM-5.     

Electrochemical and in situ FTIR studies of biferrocene platinum(II) complex

Electron transfer mechanism during redox process of Pt(LSB)₂, a derivative of S-benzyl-N-(ferrocenyl-1-methyl-metylidene)-dithiocarbazate (HLSB), is studied by cyclic voltammetry, differential pulse voltammetry, digitally simulation and in situ FTIR spectroelectrochemistry. Electrochemistry results indicated the redox process of Pt(LSB)₂ involves two consecutive one-electron steps. Coordination of Pt to HLSB resulted in the increase of electron-withdrawing of the dithiocarbazate group, which is demonstrated by the positive shift of redox potentials of Pt(LSB)₂ compared with those of HLSB. The peak-peak separation of 129 mV revealed a strong degree of electronic communication between the two-ferrocene moieties in Pt(LSB)₂. The results of in situ FTIR indicated that electronic communication takes place through the skeleton chain of HLSB due to the extensive electron delocalization in the whole molecule.     

In situ FTIR studies on the electrochemical hydrodechlorination of 3,4,5,6-tetrachloropicolinic acid on Ag cathode

The electrochemical hydrodechlorination reaction from starting material 3,4,5,6-tetrachloropicolinic acid (3,4,5,6-TCP) to the end product 3,6-dichloropicolinic acid (3,6-DCP) was investigated by cyclic voltammetry and in situ Fourier transform infrared spectroscopy (in situ FTIR). Compared with copper and glassy carbon, Ag cathode showed a high electrocatalytic activity for the irreversible reduction process of 3,4,5,6-TCP in NaOH aqueous solution. In situ FTIR results suggested that electrochemical hydrodechlorination took place in the 4- or 5-position of 3,4,5,6-TCP on Ag cathode after receiving an electron to get mixed trichloropicolinic acid free radical, which could receive another electron and give 3,5,6-trichloropicolinic acid (3,5,6-TCP) and 3,4,6-trichloropicolinic acid (3,4,6-TCP) at the potential more positive than −1000 mV afterwards. Finally, 3,5,6-TCP and 3,4,6-TCP were further dechlorinated to produce 3,6-dichloropicolinic acid (3,6-DCP) at the potential more negative than −1000 mV. Further studies of preparative electrolysis experiments by constant current electrolysis were carried out. The results were in good agreement with those from in situ FTIR investigations.     

Electrooxidation of ethanol on a Pt electrode in acid solutions: in situ ATR-SEIRAS study

The electrooxidation of ethanol was investigated on a Pt thin film electrode in a HClO₄ solution using surface enhanced infrared absorption spectroscopy (SEIRAS) with the attenuated total reflection (ATR) technique. The spectra indicate that during this reaction acetate and CO adsorbates are formed. The intensity of symmetric OCO stretching band of adsorbed acetate correlates well with voltammetry in the potential range between −0.1 and 0.85 V. The CO stretching band for adsorbed acetaldehyde and/or acetyl also was observed; these compounds are the reaction intermediates whose oxidation generates CO_ad and acetic acid. We also explored the oxidation behavior of adsorbed residues. The oxidation of acetaldehyde was studied for comparison.     

In situ FTIR study on NO reduction by C3H6 over Pd-based catalysts

The reaction mechanism of the reduction of NO by propene over Pd-based catalysts was studied by FTIR spectroscopy. It was observed that the reaction between NO and propene most probably goes via isocyanate (2256–2230 cm⁻¹), nitrate (1310–1250 cm⁻¹) and acetate (1560 and 1460 cm⁻¹) intermediates formation. Other possible intermediates such as partially oxidized hydrocarbons, NO₂, and formates were also detected. The reaction between nitrates and acetates or carbonates reduced nitrates to N₂ and oxidized carbon compounds to CO₂. In situ DRIFT provides quick and rather easily elucidated data from adsorbed compounds and reaction intermediates on the catalyst surface. The activity experiments were carried out to find out the possible reaction mechanism and furthermore the kinetic equation for NO reduction by propene.     

NOx adsorption on MnO2/NaY composite: an in situ FTIR and EPR study

The NO, NO/O₂, and NO/O₂/H₂O adsorption on MnO₂/NaY (5 and 15 wt.% MnO₂) composite catalyst and NaY has been studied by means of in situ FTIR and EPR spectroscopy at elevated temperatures and during heating under reaction-like conditions. NO adsorption and co-adsorption of NO and O₂ on NaY and MnO₂/NaY proceeds via oxidation of NO forming NO₂⁻ and NO₃⁻ species. Whereas the manganese dioxide preferably acts as oxidising agent, the zeolite stores the NO_x species as nitrite and nitrate ions in the solid. In the presence of oxygen, the nitrate formation is enhanced due to additional oxidation of NO through gaseous oxygen leading to NO₂. Dimerisation of NO₂ to N₂O₄ and following disproportionation of the latter causes the formation of NO⁺ and NO₃⁻ species which are associated with nucleophilic zeolitic oxygen and especially alkali cations of the zeolite, respectively. The presence of oxygen facilitates reoxidation of Mn²⁺ which keeps more Mn ions in the active state. Pre-adsorbed water and higher amounts of water vapour in the feed hinder the NO adsorption by blocking the adsorption sites and shift the nitrate formation to higher temperatures. The quantities and thermal stability of the nitrates formed during NO and NO/O₂ adsorption differs which points to a different mechanism of nitrate formation. In the absence of gaseous oxygen, nitrates are formed by participation of only lattice oxygen. In the presence of oxygen, nitrate formation by dimerisation and disproportionation reactions of NO₂ dominates. The manganese component of the composite catalyst supports the oxidation of NO to nitrite and subsequently to nitrate. During this process Mn⁴⁺ is reduced to Mn²⁺ as evidenced by in situ EPR measurements.     

In situ FT-IR spectroelectrochemical study of electrooxidation of pyridoxol on a gold electrode

The electrochemical oxidation of pyridoxol (PN) on a polycrystalline gold electrode was investigated by cyclic voltammetry and in situ Fourier transform infrared spectroscopy (FTIRS). In 0.1 M aqueous NaOH solution, the gold electrode showed a high catalytic activity for the irreversible oxidation process of PN. The individual ionic species and the major tautomeric equilibria of PN molecules in aqueous solutions were evidenced well from the pH-dependent attenuated total reflectance (ATR) spectra, and the results were in good agreement with the voltammetric observations. In situ single potential alteration infrared reflectance spectroscopy (SPAIRS) demonstrated that a lactone form of PN, rather than pyridoxal aldehyde, was likely formed, which was subsequently diffused into the thin layer solution and underwent hydrolysis slowly to pyridoxic acid (PA) as the final product. In addition, the adsorption of PN at Au electrode was characterized by in situ subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy (SNIFTIRS) method, which revealed that the adsorption of deprotonated PN, via nitrogen atom in vertical configuration on electrode surface, occurred from −0.5 V versus Ag?AgCl?KCl(sat), which was much lower than the potential of PN electrooxidation observed from ca. 0 V.     

In situ fluorescence spectroscopic studies of polymerization of anaerobic adhesives

Anaerobic adhesives cured by a redox initiated free radical mechanism contain acrylate monomers, stabilizers, accelerators, a nonreactive fluorophore used as an inspection aid, and various nonreactive ingredients to modify polymer properties and rheology. Fluorescence spectroscopy has shown that collisional quenching of the fluorophore due to an amine cure‐accelerator is reduced by rising viscosity during polymerization, thus resulting in an increase in fluorescence intensity. By monitoring the changes in fluorescence intensity with an in situ fiber‐optic method, room temperature polymerizations have been characterized both in a model formulation containing only reactive ingredients as well as in a real commercial formulation containing many nonreactive ingredients. The results from this fluorescence method on polymerization monitoring show excellent correlation with the FTIR results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Thermosetting mechanism study of silicon-containing polyarylacetylene via in situ FTIR and solid-state NMR spectroscopy

Silicon-containing polyarylacetylene (abbreviated as PSA) resins, which contain Si-(R₁, R₂) (R₁ and R₂ represent methyl or phenyl groups) and —CC—, exhibits high thermal stability upon curing up to 250 °C. The structure and thermosetting mechanism of PSA were characterized using FTIR, in situ FTIR, ¹³C and ²⁹Si CP-MAS spectroscopy, and thermogravimetric analysis. From the experimental results we can conclude that: (1) biphenyl and naphthalene rings are formed via a Diels–Alder reaction between the Ph—CC and CC groups at 210 °C, (2) the terminal alkyne mainly transforms into ethylenic bonds at 170 and 210 °C, and (3) an oxidation reaction occurs to give the oxide structure (Si—O—Si) and carbon dioxide at 250 °C. A new curing procedure has been proposed to maximize the T_d5 up to 635.2 °C on that basis. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47301.     

Studies on electrochemical hydrodebromination mechanism of 2,5-dibromobenzoic acid on Ag electrode by in situ FTIR spectroscopy

Cyclic voltammetry and in situ FTIR were employed to study the electrochemical hydrodebromination (EHB) mechanism of 2,5-dibromobenzoic acid (2,5-DBBA) in NaOH solution. Compared with titanium and graphite electrodes, silver electrode exhibited a high electrocatalytic activity for the hydrodebromination reaction of 2,5-DBBA. On the basis of in situ FTIR data, EHB reaction of 2,5-DBBA on Ag cathode might be represented as a sequence of electron additions and bromine expulsions. Firstly, from potential at approximately −1100 mV, 2,5-DBBA received an electron to form 2,5-DBBA radical anion, which lost a bromine ion in the 2-position to form 3-bromobenzoic acid (3-BBA) free radical. Then the free radical received a proton to give 3-BBA. Finally, 3-BBA further took off another bromine ion to produce benzoic acid free radical and the end product benzoic acid was obtained by receiving another electron and a proton with the potential shifting to more negative values.     

Mechanistic study of partial oxidation of methane to synthesis gas over supported rhodium and ruthenium catalysts using in situ time-resolved FTIR spectroscopy

In situ time-resolved FTIR spectroscopy was used to study the reaction mechanism of partial oxidation of methane to synthesis gas and the interaction of CH₄/O₂/He (2/1/45) gas mixture with adsorbed CO species over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts at 500–600°C. It was found that CO is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over H₂ reduced and working state Rh/SiO₂ catalyst. Direct oxidation of methane is the main pathway of synthesis gas formation over Rh/SiO₂ catalyst. CO₂ is the primary product for the reaction of CH₄/O₂/He (2/1/45) gas mixture over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts. The dominant reaction pathway of CO formation over Ru/γ-Al₂O₃ and Ru/SiO₂ catalysts is via the reforming reactions of CH₄ with CO₂ and H₂O. The effect of space velocity on the partial oxidation of methane over SiO₂ and γ-Al₂O₃ supported Rh and Ru catalysts is consistent with the above mechanisms. It is also found that consecutive oxidation of surface CO species is an important pathway of CO₂ formation during the partial oxidation of methane to synthesis gas over Rh/SiO₂ and Ru/γ-Al₂O₃ catalysts.     

乙醇发酵原位分离产物耦合方法研究进展

乙醇发酵过程存在明显的产物抑制现象,严重制约了乙醇产率的提高。乙醇发酵与产物分离的耦合可有效解决这一难题,目前乙醇发酵耦合产物分离的方法主要有乙醇气提发酵、乙醇真空发酵、乙醇吸附发酵、乙醇萃取发酵、乙醇膜分离发酵等。作者主要概述了各种乙醇发酵耦合产物分离方法的研究进展,并对今后乙醇发酵耦合产物分离研究开发提出了展望。     

In situ FTIR experimental results in the silylation of low-k films with hexamethyldisilazane dissolved in supercritical carbon dioxide

In situ Fourier Transform Infrared Spectroscopy measurements were performed using an innovative equipment to study the surface modification reaction between a functionalized porous MSQ-film and hexamethyldisilazane (HMDS) dissolved in CO₂ at supercritical conditions (scCO₂). scCO₂ was used in the heterogeneous reaction due to enhancing properties, ideal for porous materials. Different infrared signatures, from the gas and solid phases, were observed and identified, implying gas–gas and solid–gas phase reactions. Among the different component signatures observed in the gas phase, carbonic acid was observed as a possible silylating gas phase nucleophilic component, while in the solid phase the predominant reaction mechanism proceeded by forming SiOSi bonds and Trimethylaminosilane (as gas phase product).     

In situ FTIR spectroscopy on rhodium-exchanged NaX zeolite with different metal dispersion during syngas reaction

In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol.     

Dehydration and rehydration of mesolite: An in situ FTIR study

The dehydration and rehydration processes of mesolite belonging to NAT group of zeolites were investigated using in situ Fourier Transform Infrared spectroscopy (FTIR). The thermal induced variations of the water molecule bending (ν₂), the stretching (ν₃ and ν₁) modes and the corresponding second order modes in the wavenumber region 4000–8000 cm⁻¹ were followed as indicative of the dehydration process. Observed spectral variations were well correlated with thermogravimetric studies and indicate that the mesolite dehydrates in three stages (470; 510 and 650 K). Anomalous spectral variations of 4600 cm⁻¹ at first stage indicate that the dehydration is triggered by the expulsion of water coordinating AlO₄ tetrahedron. Partial rehydration (up to 85%) at second stage indicates disordering of natrolite and scolecite layers. During the third stage mesolite completely dehydrates, causing the destruction of framework.     

Electrocatalytic oxidation of ethanol on Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript>(<Emphasis Type="Italic">x</Emphasis>)</Subscript>O<Subscript>2</Subscript> electrodes in acid medium

The electrochemical oxidation of ethanol at Sn_(1−x)Ir _x O₂ electrodes (with x = 0.01, 0.05, 0.1 and 0.3) was studied in 0.1 mol L⁻¹ HClO₄ solution. Electrolysis experiments were carried out and the reaction products were analyzed by Liquid Chromatography. It was found that the amounts of the reaction products depended on the composition of the electrode. In situ infrared reflectance spectroscopy measurements were performed to identify the adsorbed intermediates and to postulate a reaction mechanism for ethanol electrooxidation on these electrode materials. As evidence, acetaldehyde and acetic acid were formed through a successive reaction process. Carbon dioxide was also identified as the end product, showing that the cleavage of the carbon–carbon bond occurred. These results indicate that the synthesized catalysts are able to lead to the total combustion of organic compounds. Analysis of the water bending band at different potentials illustrated its role at the electrode interface.     

In situ FTIR study on reaction pathways in Ni(CO)4/CH3OK catalytic system for low-temperature methanol synthesis in a liquid medium

An in situ infrared spectroscopic study was conducted to elucidate the reaction pathways for low-temperature methanol synthesis in a catalytic system composed of Ni(CO)₄ and CH₃OK (denoted as Ni(CO)₄/CH₃OK). The reaction was conducted in a liquid medium at 313–333 K with an initial pressure of 3.0 MPa. When CH₃OK was added to Ni(CO)₄ solution at 293 K, different carbonylnickelates, [Ni₅(CO)₁₂]²⁻, [Ni₆(CO)₁₂]²⁻ and [Ni(CO)₃(COOCH₃)]⁻, were immediately formed from Ni(CO)₄. The species and the composition of the carbonylnickel complexes varied with temperature. The variations in concentrations of methanol (MeOH) and methyl formate (MF) during the run, which were determined from their IR absorptions, indicated a pattern characteristic of consecutive reactions with MF as an intermediate. Thus, it was shown that methanol was produced through the carbonylation of MeOH to MF and the subsequent hydrogenation of MF to MeOH. Stable hydridocarbonylnickel anions, [HNi(CO)₃]⁻ and/or [HNi₂(CO)₆]⁻, were observed together with a small amount of Ni(CO)₄ throughout the methanol synthesis. Since Ni(CO)₄ alone showed no activity for the hydrogenation of MF, the hydridocarbonylnickel anions generated in the presence of CH₃OK must be responsible for the reaction. The dual role of CH₃OK in the catalytic system was stated.