IR Spectra Of CO Research Articles

Comment on “surface characterization of cerium oxide catalysts using deep learning with infrared spectroscopy of CO”

We demonstrate that the predicted distribution of ceria facets in CeO2 nanorods, derived from the analysis of the measured IR spectrum of CO by fitting it using experimentally or DFT(HSE) calculated CO vibrational frequencies collected on all three low-index ceria surfaces, does not align with that derived using deep learning methods [1]. The latter utilizes a dataset based on extensive DFT(PBE) + U calculations, which are erroneous and have thus been scaled to the experimental values.

Retraction Note to: Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports

Retraction Note to: Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports

RETRACTED ARTICLE: Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports

Gold surfaces and nanoparticles have commonly been investigated by IR spectroscopy using carbon monoxide as a molecular probe. An evolution of the IR spectra with time under CO was reported in some cases and tentatively assigned to geometrical effects (e.g. surface reconstruction or particle restructuring) or electronic effects, e.g. gold becoming negatively charged following support reduction. We report here an investigation of the evolution of the IR spectrum of CO adsorbed at 50 °C in the case of Au nanoparticles supported on non-reducible silica and alumina supports. The evolution of the carbonyl IR band signal, proposed to arise mostly from Au particle restructuring, was clearly observed. In addition, the formation of hydrogenocarbonates species on the alumina reemphasized that Au nanoparticles are somewhat active for CO dissociation via Boudouard reaction near room temperature, leading to some deposition of carbon. Water could not prevent restructuring, while O2 prevented irreversibly the reconstruction, which could even be reversed when O2 was introduced on an already restructured sample. It is hypothesized that the role of O2 would be to remove the deposited elemental carbon that otherwise stabilize reconstructed Au. These results emphasize the complexity of the parameters affecting the restructuration of Au surfaces induced by CO and the difficulty in interpreting IR spectra of CO adsorption on Au-based materials.

Two dimensional infrared spectroscopic investigations of protein and enzyme dynamics

Ultra fast two dimensional infrared (2D IR) spectroscopy is used to measure dynamics and interactions in complex materials in the ground electronic state under thermal equilibrium conditions. Two observables, ultra fast chemical exchange and spectral diffusion, will be discussed. In a 2D IR experiment, three variably time delayed IR excitation pulses, tuned to the vibrational transition of interest, give rise to a fourth vibrational echo pulse, the signal in the experiment. The first two pulses in the sequence label the vibrations with their initial frequencies. After a waiting period, Tw, the third pulse induces the vibrational echo, which reads out the final vibrational frequencies. Structural changes of the system cause the vibrational frequencies to change. Therefore, measuring the time evolution of the vibrational frequencies reports on the time evolution of the structure. Folded proteins can exist in multiple conformational substates. Each substate reflects a local minimum on the free‐energy landscape with a distinct structure. Using 2D‐IR chemical exchange spectroscopy, conformational switching between two well defined substates of two myoglobin mutants were observed on the ~50 ps time scale. The conformational dynamics were measured through the growth of off‐diagonal peaks in the 2D IR spectra of CO bound to the heme. The conformational switching likely involves motion of the distal histidine/E helix that changes the position of the histidine's imidazole side group. These results demonstrate that interconversion between protein conformational substates can occur on very fast time scales. Detailed MD simulations are able to capture some of the observed behavior, but not quantitatively. Cytochrome (cyt) P450s hydroxylate a variety of substrates that can differ widely in their chemical structure. The importance of these enzymes in drug metabolism and other biological processes has motivated the study of the factors that enable their activity on diverse classes of molecules. 2D IR spectroscopy was used to measure the dynamics of cyt P450cam from Pseudomonas putida using CO bound at the active site as the vibrational probe. The experiments measure spectral diffusion, the time evolution of the CO vibrational frequencies within the in homogeneously broadened vibrational absorption line. The time evolution of the frequencies is caused by the time evolution of the enzyme structure. The enzyme bound to both its natural substrate, camphor, and a series of related substrates were investigated to explicate the role of dynamics in molecular recognition in cyt P450cam and to delineate how the motions may contribute to hydroxylation specificity. Correlations in the observed dynamics with the specificity of hydroxylation of the substrates, the binding affinity, and the substrates' molecular volume suggest that motions on the hundreds of picosecond time scale contribute to the variation in activity of cyt P450cam toward different substrates.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Reaction of thiosemicarbazide with some divalent ions: Synthesis, characterization, molecular modeling, and evaluation of the catalytic and biological activity of the complexes

ABSTRACTNew metal complexes of Co(II) and Cu(I) have been synthetized by reaction of metal salts with thiosemicarbazide (TSC: HL1) and urea (U). The metal complexes were characterized on the basis of elemental analyses, molar conductance, spectral (IR, 1H NMR) studies, as well as thermogravimetric analysis. The spectral data show that in the complexes, only TSC is coordinated to the metal. The IR spectra of Co(II) and Cu(I) complexes are different. In addition to the bands of TSC, a new intense band at 2100 cm−1 is assigned to the thiocyanate fragment produced in situ by the cleavage of the TSC C–N bond. On the basis of spectral studies, a N3O3 high-spin environment was assigned to [Co(II)(L1)(SCN)(H2O)3] complex and a dimeric form geometry for Cu(I) complex of general formula [Cu(I)(HL1)(SCN)(H2O)]. In order to gain a better insight into the molecular structure and the reactivity of the ligand and its complexes, quantum chemical calculations were also performed to determine some electronic properties and geometric parameters of the ligand and Cu(I) and Co(II) complexes. The metal complexes have been tested for catalase-like activity in order to assess their catalytic properties. The results seem encouraging. The biological activity of the ligand and its metal complexes is evaluated as well.

On the role of triethylene glycol in the preparation of highly active Ni-Mo/Al2O3 hydrodesulfurization catalysts: A spectroscopic study

The interaction of triethylene glycol (TEG) with alumina and its role in preparing improved NiMo/Al2O3 hydrodesulfurization catalysts was investigated by spectroscopic methods. The FT-IR study shows that TEG is mainly adsorbed on the corners and edges of the alumina microcrystals where the strongest Lewis sites and the higher νOH frequency hydroxyl groups are mainly located. It is also observed that the MoO stretching vibration of surface molybdenyl groups in the oxide catalyst precursor is shifted down in the presence of TEG, indicating a lower interaction with the alumina surface. The IR spectra of CO adsorbed on the reduced/sulfided NiMo/Al2O3 catalysts confirm that the amount of promoted phase (NiMoS sites) increases in the samples prepared with TEG. Accordingly, the activity measurements in the HDS of 4,6-dimethyldibenzothiophene show that the catalyst prepared with TEG is more active than the one prepared without it. It is proposed that TEG and its decomposition products, formed upon heating (mainly acetates) occupy preferably the strongly interacting edge and corner sites of the alumina crystals, forcing the Mo and Ni species to migrate mainly to the less reactive plane faces. This weakens the metal-support interaction allowing a better sulfidation and, at the same time, favoring the Ni–Mo interaction and the formation of the promoted NiMoS phase.

Novel complexes of Co2+, Ni2+, and Cu2+ with N-(phosphonomethyl)aminosuccinic acid

Complexes of Co2+, Ni2+, and Cu2+ with N-(phosphonomethyl)aminosuccinic acid (H4PMAS) of general formula Na2MPMAS·nH2O [M=Co(II), Ni(II), Cu(II), n—number of water molecules] were synthesized. Based on interpretation of diffusion reflectance spectroscopy, structure of all complexes is based on distorted octahedral. Analysis of IR spectra of Co(II), Ni(II), and Cu(II) N-(phosphonomethyl)aminosuccinates demonstrated that metal ions are coordinated to the ligand through nitrogen atom of the imino group, oxygen atoms of the α- and β-carboxyl groups as well as oxygen atom of the phosphonic group of the H4PMAS. We demonstrated that thermal stability of complexes increases in sequence Cu(II) < Ni(II) < Co(II), obviously as a result of change over from the dimeric to polymeric character of the initial complex. Complete decomposition of ligand occurs at these temperatures and is accompanied by release of H2O, CO2, and NO2. The final products of thermal decomposition of the complexes are mixtures of oxides and phosphates of respective metals.

Particles Morphology and Surface Properties As Investigated by HRTEM, FTIR, and Periodic DFT Calculations: From Pyrogenic TiO2(P25) to Nanoanatase

By combining electron microscopy, FTIR spectroscopy of different CO isotopic mixtures, and DFT calculations, a complete assignment of the IR spectrum of CO adsorbed on P25 (a mixture of 85% anatase and 15% rutile) at various dehydration states, on its pure rutile component, and on nanoanatase was obtained. It is shown that the measurements at 60 K provide IR spectra of unprecedented quality and that the spectroscopic method is extremely powerful not only to study the surface Lewis and Bronsted acidity but also to investigate the particles morphology. Indeed, as CO adsorbed on different faces is characterized by different stretching frequencies, the IR spectrum contains information on the exposed faces and hence on particles morphology. This information, combined with the study of the IR spectrum of CO adsorbed on defects, of dipole–dipole interactions between parallel oscillators adsorbed on extended faces and with HRTEM results allowed us to fully explore the relations between particles morphology and su...

The roles of CeyZr1−yO2 in propane dehydrogenation: Enhancing catalytic stability and decreasing coke combustion temperature

The influence of CeyZr1−yO2 content (0<y<1) in Pt-Sn/xCeZr-Al catalysts, where x was the weight percentage of (Ce+Zr) and calculated as [mass of (Ce+Zr)]×100/[mass of (Ce+Zr+Al2O3)], on stability and regeneration temperature in propane dehydrogenation was studied using a fixed-bed reactor at 600°C and 1bar of pressure. The XRD data revealed that CeyZr1−yO2 phases were formed over xCeZr-Al (x≠0) supports and the concentration of Zr4+ ions in these phases increased when the CeyZr1−yO2 content was increased. The band of oxygen vacancies characterized by Raman spectra at ca. 620–645cm−1 was strongly dependent on catalyst processing; introduction of metal (Pt, Sn) and/or re-calcination created more oxygen vacancies in the catalysts. The XRD patterns and XPS data of the reduced Pt-Sn/xCeZr-Al catalysts did not indicate the formation of Pt-Sn alloys. The XPS and CO-IR spectra demonstrated that Pt became more electron deficient with increasing CeyZr1−yO2 content. The higher catalytic stability and lower coke combustion temperature (regeneration temperature) were obtained with a higher CeyZr1−yO2 content in Pt-Sn/xCeZr-Al catalysts.

Macroscopic and Molecular Insights from CO Adsorption on NaY Zeolite: A Combined FTIR and Manometric Study

This survey combines both quantitative and IR molecular descriptions and aims to provide new insights for the description of CO adsorption on NaY zeolite at 77 K. Quantitative measurements of the number of CO molecules trapped in the microporous super cage are compared to the corresponding IR spectra of CO as adsorbed species. We demonstrate that polycarbonyls formed during the completion of the accessible SII Na+ coordinative vacancies result in the formation of mono-, di- and tricarbonyls but not consecutively. Quantitative analysis and measurements of the CO molecules that are adsorbed prove that polycarbonyls coexist with different proportions over the adsorption step in line with previous theoretical prediction.(1) Moreover, we establish that polycarbonyl formation settles rapidly and stops, although the completion of the SII Na+ coordinative vacancies has not been fully achieved. The formation of CO in the pseudoliquid phase causes this adsorption limitation, and distinction within adsorbed species must be made between species that are truly Na+-coordinated and those that are adsorbed in a condensed state in the confined micropores. As a result, this combined analysis reveals that the sole manometric measurements resulting in the macroscopic CO isotherm overestimate the number of “true” coordinated species.

Time-dependent fifth-order bands in nominally third-order 2D IR vibrational echo spectra.

Progress in the field of 2D IR vibrational spectroscopy has been bolstered by the production of intense mid-IR laser pulses. As higher-energy pulses are employed, a concomitant increase occurs in the likelihood of fifth-order contributions to the 2D IR spectra. We report the appearance of fifth-order signals in 2D IR spectra of CO bound to the active site of the enzyme cytochrome P450(cam) with the substrate norcamphor. Two bands with novel time dependences, one on the diagonal and one off-diagonal, are not accounted for by normal third-order interactions. These bands are associated with a ν = 1-2 vibrational transition frequency. Both bands decay to 0 and then grow back in with opposite sign. The diagonal band is positive at short time, decays to 0, reappears with negative sign, before eventually decaying to 0. The off-diagonal band is negative at short time, decays to 0, reappears positive, and then decays to 0. The appearance and time dependence of these bands are characterized. Understanding these fifth-order bands is useful because they may be misidentified with time-dependent bands that arise from other processes, such as chemical exchange, vibrational coupling, or energy transfer. The presence and unusual time dependences of the fifth-order bands are reproduced with model calculations that account for the fact that vibrational relaxation from the ν = 2 to 1 level is approximately a factor of 2 faster than that from the ν = 1 to 0 level.

Cooperative Cation Migrations upon CO Addition in CuI- and Alkali-Exchanged Faujasite: A DFT Study

CO adsorption in Al-rich faujasite zeolite containing copper and alkali cations has been investigated using DFT methods in order to determine how CO interacts and may modify the original position of the cations. Whether a cluster or a periodic model is used, addition of CO induces the formation of stable complexes labeled DI(CO) in which CO interacts by both its C-end and its O-end, resulting from a cooperative rearrangement of cations. In addition to a CuI migration from site II to the supercage, a migration of alkali from site III′ to site III may occur. DI(CO) also induces a downshift of the νCO mode in comparison with the complex containing CO interacting with a single cation, SI(CO). These results suggest a new assignment of the IR spectra of CO adsorbed in YCuI and YNa+: for YCuI, the upshifted signal at ca. 2160 cm−1 in comparison with νCOgas at 2143 cm−1 could be assigned to a SI(CO) structure, whereas the downshifted signal at ca. 2140 cm−1 could be assigned to a DI(CO) complex. For YNa+, the upshifted signal at ca. 2170 cm−1 could be assigned to SI(CO) NaSII···CO and/or to DI(CO) NaSII···OC···NaSIII′, whereas the downshifted signal at ca. 2122 cm−1 could be assigned to DI(CO) complex NaSII···CO···NaSIII′. This study shows that the DI(CO) interaction is a key ingredient for understanding the metal-exchanged zeolite properties.

First-principles calculation of monitoring spin states of small magnetic nanostructures with IR spectrum of CO

A fully ab initio controlled ultrafast magnetooptical switching mechanism in small magnetic clusters is achieved through exploiting spin-orbit-coupling enabled Λ processes. The idea is that in the magnetic molecules a fast transition between two almost degenerate states with different spins can be triggered by a laser pulse, which leads to an electron excitation from one of the degenerate states to a highly spin-mixed state and a deexcitation to the state of opposite spin. In this paper a CO molecule is attached to one magnetic center of the clusters, which serves as an experimental marker to map the laser-induced spin manipulation to the IR spectrum of CO. The predicted spin-state-dependent CO frequencies can facilitate experimental monitoring of the processes. We show that spin flip in magnetic atoms can be achieved in structurally optimized magnetic clusters in a subpicosecond regime with linearly polarized light.

Ultrafast Interconversion between Protein Conformational Substates: Directly Observed by 2D IR Vibrational Echo Spectroscopy

Conformational dynamics of flexible biomolecules play an important role in the function and stability of proteins. Folded proteins can exist in multiple conformational substates, where each substate has a distinct structure and corresponds to a local minimum on the free energy landscape. Transitions from one minimum to another correspond to dynamical changes in the structure of the protein. By using 2D IR spectroscopy, conformational interconversion between these well defined substates of a myoglobin double mutant is observed on picoseconds timescale. The conformational dynamics are directly measured through the evolution of cross peaks in the 2D IR spectra of CO bound to the heme active site. The conformational switching changes the CO frequency, as detected by the waiting time dependence of the 2D IR vibrational echo spectrum. This result is an example where conformational switching between protein substates occurs on very fast time scales. Moreover, this myoglobin mutant shows enzymatic activity upon substrate binding, which makes it an excellent system to study the influence of substrate binding on structural dynamics.

Active sites on Pt containing sulfated zirconia

The influence of the Pt and sulfate concentration on the activity of Pt containing sulfated zirconia for n-heptane conversion was investigated. Pt was deposited on the support by impregnation and by photocatalytic deposition. The amount deposited was 2.5 and 0.4 wt% respectively. For comparison a hybrid catalyst consisting of sulfated zirconia and Pt on SiO2 was prepared. As supports a commercial sulfated zirconia with a fixed sulfate concentration, a commercial and self synthesized Zr(OH)4 were used. The sulfate content varied between 20 and 60% of a monolayer. The shifts to higher frequency in the IR spectra of CO adsorbed on Pt correlate with the increasing amounts of sulfates on zirconia and are attributable to the changes in the electron density of the supported metal, i.e. the electron deficiency of Pt increases with increasing concentration of acid sites. After activation in air and reduction in hydrogen two SO2 peaks were detected by a temperature programmed heating procedure (TPE—temperature programmed evolution). The lower the desorption temperature of the first SO2 peak, the higher the activity. The shift to lower temperature is connected with a higher Pt and sulfate concentration, furthermore with the proximity of the metal to acid sites. The catalysts with a low sulfate concentration possess only Lewis acid sites and are inactive for n-heptane conversion. At higher sulfate concentration, Bronsted acid sites are present and the catalysts are active. The concentration of these acid sites is related to the concentration of sulfates, which desorb at lower temperature.

Catalytic reduction of N2O by H2 over well-characterized Pt surfaces

A 0.65% Pt/SiO2 catalyst has been prepared using an ion exchange technique and extensively characterized prior to being used for continuous catalytic N2O reduction by H2 at very low temperatures, such as 363 K. The supported Pt with a high dispersion of 92% gave no presence of O atoms remaining on an H-covered Pts, based on in situ DRIFTS spectra of CO adsorbed on Pts after either N2O decomposition at 363 K or subsequent exposure to H2 for more than 1 h; thus the residual uptake gravimetrically observed even after the hydrogen titration on an O-covered surface is associated with H2O produced by introducing H2 at 363 K onto the oxidized Pts. Dissociative N2O adsorption at 363 K on Pts was not inhibited by the H2O(ad) on the silica surface but not on Pts, as acquired by IR peaks at 3,437 and 1,641 cm−1, in very consistent with the same hydrogen coverage, established via H2-N2O titration on a reduced Pts, as that revealed upon the titration reaction with a fully wet surface on which all bands and their position in IR spectra for CO are very similar to that obtained after H2 titration on a reduced Pts. Based on the characterization using chemisorption and in situ DRIFTS and TPD measurements, the complete loss in the rate of N2O decomposition at 363 K after a certain on-stream hour, depending significantly on N2O concentrations used, is due to self-poisoning by the strong chemisorption of O atoms on Pts, while the presence of H2 as a reductant could readily catalyze continuous N2O reduction at 363 K that is a greatly lower temperature than that reported earlier in the literature.

A Combined Electron Paramagnetic Resonance and Fourier Transform Infrared Study of the Co(C6H6)1,2 Complexes Isolated in Neat Benzene or in Cryogenic Matrixes

The products obtained in the reaction of cobalt atoms in neat benzene or in a benzene/argon mixture at low temperature have been reinvestigated. At least three cobalt-containing species were detected by IR, namely, Co(C(6)H(6)), Co(C(6)H(6))(2), and Co(x)(C(6)H(6)), x>1. The IR bands were assigned to these complexes by monitoring their behavior as a function of (a) Co and C(6)H(6) concentration, (b) isotopic substitution, and (c) photoirradiation. We were able to analyze the sample in neat benzene by both electron paramagnetic resonance (EPR) and IR spectroscopy and to determine the magnetic parameters (g tensor and Co hyperfine interaction) for the Co(C(6)H(6))(2) sandwich compound. The large number of fundamental bands observed in the IR spectrum of Co(C(6)H(6))(2), the absorption pattern observed in the Co-ring stretching region of the IR spectrum of the mixed complex, Co(C(6)H(6))(C(6)D(6)) and the orthorhombic g-values extracted from the EPR spectrum are most consistent with nonequivalent benzene ligands in Co(C(6)H(6))(2), i.e., C(s) symmetry. A bonding scheme consistent with both the EPR and IR data for Co(C(6)H(6))(2) is discussed.

Theoretical investigation of site-specific characteristics of CO adsorption complexes in the Li +-FER zeolite

The coordination of extraframework Li + cations in FER and the formation of mono- and dicarbonyl complexes in the Li +-FER zeolite were investigated using a periodic density function theory (DFT) model. The Li + cations strongly prefer the coordination on top of five- or six-member rings on the channel wall. The Li + cation is always coordinated to at least three framework oxygen atoms. Calculated CO stretching frequencies are in excellent agreement with experimental results [Microporous Mesoporous Mater. 34 (2000) 67]; thus, the interpretation of experimental data at the atomic scale level is proposed. The dicarbonyl complexes can be readily formed on Li + cations coordinated in the eight-member ring entrance window of perpendicular channel. The differences in IR spectra of CO adsorbed on Li +-FER and Li +-MFI zeolites can be understood based on the theoretical investigation. The IR band at 2193 cm −1 observed for CO/Li +-MFI system but missing in the IR spectra of CO/Li +-FER is due to the Li + sites on the channel intersection where Li + is coordinated only to two oxygen atoms of AlO 4 tetrahedron. While such sites are populated in Li +-MFI they are not significantly populated in Li +-FER. Therefore, the differences in vibrational dynamics of CO adsorbed on Li + in FER and MFI are due to the differences in Li + coordination in these frameworks.

When the Reporter Induces the Effect: Unusual IR spectra of CO on Au1/MgO(001)/Mo(001)

Innocence lost: The IR spectra of Au/CO complexes adsorbed on of a MgO(001) film differ from the corresponding neutral Au clusters. Calculations indicate this shift of 200–250 cm−1 can be associated with a negative charge on the Au/CO complex. For Au/CO complexes on so-called color centers a charge transfer is expected, however Au atoms on terrace sites are neutral. Thus, CO in fact induces the charge transfer instead of reporting the charge state of the adsorbed Au atoms.

Activation of Pt/TiO2 Catalysts by Structural Transformation of Pt-Sites

Superior activation of on 1 wt% Pt/TiO2 catalysts for the oxidation of CO was attained by loading a large amount of Fe-oxide (100 wt%) and TiO2. In situ IR spectra of CO proved that the structural transformation is brought about on the Pt-sites by loading of Fe-oxide, where predominant Pt-sites giving linear CO change to highly reactive bridge CO Pt-sites. In contrast, no transformation of the linear CO sites to the bridge CO sites takes place by loading of TiO2 but the environment of Pt-sites for linear CO is changed.