IR Absorption Of CO Research Articles

Matrix isolation studies of carbonyl selenide, OCSe: Evidence of the formation of dimeric species, (OCSe)2

OCSe isolated in solid Ar or N2 at 10K was investigated by FTIR spectroscopy. The IR spectra of OCSe diluted in a 1:1000 proportion with the matrix gases were interpreted in terms of monomeric carbonyl selenide in a single matrix site. The IR spectra of more concentrated matrices revealed several new IR absorptions, which were tentatively assigned to different dimeric structures, aided by the prediction of quantum chemical calculations. The different matrices were exposed to UV–visible broad-band radiation, finding that monomeric OCSe decomposes into CO and Se, as evidenced by the IR absorption of CO perturbed by the presence of a selenium atom in the same matrix cage, while dimeric forms of OCSe decompose giving mainly (CO)2.

CoPt nanoparticles and their catalytic properties in electrooxidation of CO and CH3OH studied by in situ FTIRS

CoPt nanoparticles supported on a glassy carbon electrode (denoted as CoPt/GC) were prepared by galvanic replacement reaction between electrodeposited Co nanoparticles and K(2)PtCl(6) solution. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were both employed to characterize the CoPt nanoparticles. It was shown that the CoPt nanoparticles have irregular shapes and most of them exhibit a core-shell structure with a porous Co core and a shell of Pt tiny particles. The composition of the CoPt nanoparticles was analyzed by energy-dispersive X-ray spectroscopy (EDX), which depicts a Co : Pt ratio of ca. 21 : 79. Studies of cyclic voltammetry (CV) demonstrated that CoPt/GC possesses a much higher catalytic activity towards CO and methanol electrooxidation than a nanoscale Pt thin film electrode. In situ FTIR spectroscopic studies have revealed for the first time, that a CoPt nanoparticles electrode exhibits abnormal IR effects (AIREs) for IR absorption of CO adsorbed on it. In comparison with the IR features of CO adsorbed on a bulk Pt electrode, the direction of the IR bands of CO adsorbed on the CoPt/GC electrode is inverted completely, and the intensity of the IR bands has been enhanced up to 15.4 times. The AIREs is significant in detecting the adsorbed intermediate species involved in electrocatalytic reactions. The results demonstrated a reaction mechanism of CH(3)OH oxidation on CoPt/GC in alkaline solutions through evidencing CO(L), CO(M), HCOO(-), CO(3)(2-), HCO(3)(-) and CO(2) as intermediate and product species by in situ FTIRS.

Electrocatalytic oxidation of carbon monoxide and methanol at Pt nanoparticles confined in SBA-15: voltammetric and in situ infrared spectroscopic studies

Electrocatalytic oxidation of carbon monoxide and methanol at Pt nanoparticles confined in mesoporous molecular sieve SBA-15 was studied by using cyclic voltammetry and in situ FTIR spectroscopy. Cyclic voltammetric studies revealed that the Pt nanoparticles confined in SBA-15 exhibit a high activity in the presence of hydrated phase consisting of SiO2 in the SBA-15. In situ FTIR spectroscopy results discovered that IR absorption of CO adsorbed on Pt nanoparticles confined in SBA-15 has been enhanced 11-fold, and the full-width at half-maximum of the CO band is significantly increased, in comparison with IR feature of CO adsorbed on a bulk Pt electrode. The linearly adsorbed CO species is the only intermediate derived from dissociative adsorption of methanol, which is more readily oxidized to form CO2 in the aid of the active oxide in SBA-15.

Anomalous IR optical properties of aggregates of Pd nanoparticles induced through electrochemical cyclic voltammetry

IR optical properties of Pd nanoparticles with different size and aggregation state were studied in the current paper. The dispersed Pd nanoparticles ( P d n a ) stabilized with poly( N-vinylpyrrolidone) (PVP) were synthesized by the seeding growth method, in which the seeds were formed step by step through reducing H 2PdCl 4 with ethanol. The dispersed Pd nanoparticles of much large size ( P d n b ) were grown from the P d n a by keeping the colloid of P d n a undisturbed for 150 days at room temperature around 20 °C. The aggregates of P d n a ( P d n ag ) were prepared through an agglomeration process induced during a potential cyclic scanning between −0.25 V and 1.25 V for 20 min at a scan rate of 50 mV s −1. Scanning electron microscope (SEM) patterns confirmed such aggregation of P d n a . Fourier transform infrared (FTIR) spectroscopy together with CO adsorption as probe reaction was employed in studies of IR optical properties of the prepared Pd nanoparticles. The results demonstrated that CO adsorbed on P d n a films substrated on CaF 2 IR window or glassy carbon (GC) electrode yielded two strong IR absorption bands around 1970 cm −1 and 1910 cm −1, which were assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. Similar IR bands were observed in spectra of CO adsorbed on P d n b films, except the IR bands were much weak, whereas CO adsorbed on P d n ag film produced an IR absorption band near 1906 cm −1, and an anomalous IR absorption band whose direction has been completely inverted around 1956 cm −1. The direction inversion of the IR band of CO bonded to asymmetric bridge sites on P d n ag was ascribed to the interaction between Pd nanoparticles inside the aggregates. Based on FTIR spectroscopic and cyclic voltammetric results, the aggregation mechanism of Pd nanoparticles from P d n a to P d n ag has been suggested that the agglomeration of Pd nanoparticles was driven by the alteration of electric field across electrode–electrolyte interface, when the PVP stabilizer was stripped via oxidation during cyclic voltammetry.

Strong Pyramidal Growth of Metal Films Studied with IR Transmittance and Surface Enhanced IR Absorption of CO

Metal-film surfaces show well ordered facets if grown at sufficiently high temperature and at relatively small deposition rate. Such films may grow as pyramids that become increasingly steep with more coverage. On MgO(001) at about 400 °C iron forms nanoparticles with a shape like cuboids. These cuboids avoid coalesce with further deposition, and therefore they are an interesting system for effects that involve field enhancement, like for example surface enhanced infrared absorption of adsorbate vibrations. In this work we show that for such films the percolation is extended over a broad coverage range. Surface enhanced infrared absorption of CO adsorbed on the film shows the asymmetry of the C−O stretch line, which is typical for films near the percolation threshold. Both the line shape and the line intensity do not change remarkably above a certain average film thickness.

Special IR properties of palladium nanoparticles and their aggregations in CO molecular probe infrared spectroscopy

Dispersed Pd nanoparticles (Pdπ) have been synthesized by reducing H2PdCl4 with ethanol, and stabilized using poly(vinylpyrrolidone) (PVP). The Pdπ is applied to the glassy carbon substrate to form a thin film, and then the potential cyclic scanning at 50 mV-s−1 from -0.25 to 1.25 V was carried out for about 30 min to form the aggregations of Pdπ (Pdagπ). FTIR spectroscopy of both transmission and reflection modes was employed to study CO adsorption on Pdπ and Pdagπ in both solid|liquid and solid|gas interfaces. It has been revealed that CO adsorption on Pdπ film yields two IR bands near 1964 and 1906 cm−1, which are assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. In contrast to the IR properties of CO adsorbed on Pdπ, only species of CO bonded on asymmetric bridge sites was determined on Pdagπ, and the direction of the IR band near 1963 cm−1 is completely inverted. The full width at half-maximum (FWHM) of the COasinB band near 1964 cm−1 is measured to be 14 cm−1 on Pdπ film, while it is 24 cm−1 on Pdagπ film. The results of the present study demonstrated that the inverting of the IR band direction is a general phenomenon that is closely related to the interaction between nanoparticles in aggregation of Pdπ.

Enhanced IR absorption of CO adsorbed on Pd nanoparticles embedded in the mesoporous molecular sieve SBA-15

Enhanced IR absorption (EIRA) of CO adsorbed on Pd nanoparticles embedded in the mesoporous molecular sieve SBA-15 was discovered in the current paper. Palladium ions (Pd 2+) were introduced into the mesoporous molecular sieve SBA-15 through impregnation of the sieve into palladium chloride solution followed by calcinations. The Pd 2+ ions embedded in SBA-15 were reduced firstly to small primary Pd particles (Pd 0) by cyclic potential scans between 0.00 and −0.40 V (SCE). Pd nanoparticles (Pd 0 n ) were formed ultimately by adsorption and desorption of CO on Pd 0-embedded SBA-15, in which CO served to induce migration and coalescence of the Pd 0. Cyclic voltammograms of electrodes of both Pd 0 and Pd 0 n display characteristic features of surface processes of hydrogen adsorption–desorption, which are different from those of a bulk Pd electrode showing mainly bulk processes of hydrogen absorption. Cyclic voltammetric studies demonstrated that electrochemical reactions might be carried out easily in SBA-15 that is composed of an orderly arrangement of hexagonal channels of size 10 nm, ascribed to a small resistance of ion diffusion and electron transition in the Pd 0 n -embedded SBA-15 system. In situ FTIR results revealed that IR absorption of CO adsorbed on Pd nanoparticles embedded in the SBA-15 has been enhanced 11-fold, and the full-width at half-maximum of the CO bands is significantly increased. Nevertheless, the Stark tuning rate of the IR band of bridge bonded CO is determined to be only 24 cm −1 V −1, which is much smaller than the value (42 cm −1 V −1) measured for the same species on a bulk Pd electrode. The present study is of importance to reveal the particular IR optical properties of metal nanoparticles confined in molecular sieves.

Novel phenomenon of enhancement of IR absorption of CO adsorbed on nanoparticles of Pd confined in supercages of Y-zeolite

Nanoparticles of palladium were synthesized by a `ship-in-a-bottle' technique in supercages of Y-zeolite. The ions of Pd 2+ were introduced into the zeolite by ion-exchange between PdCl 2 and NaY zeolite. They were then reduced by an electrochemical method and assembled to form nanoparticals by admission and release of CO. The electrode of palladium-loading zeolite film was characterized by cyclic voltammetry, and the adsorption of carbon monoxide on the electrode was studied using in situ electrochemical FTIR reflection spectroscopy. A novel phenomenon of enhanced IR absorption (EIRA) was observed for the first time. In comparison with CO adsorbed on a massive Pd electrode, the IR absorption of CO adsorbed on nanoparticles of Pd confined in supercages of Y-zeolite has been enhanced to about 51 times.

In situ FTIR spectroscopic studies of CO adsorption on electrodes with nanometer-scale thin films of ruthenium in sulfuric acid solutions

A nanometer-scale thin film of ruthenium supported on glassy carbon (nm-Ru/GC) was prepared by electrochemical deposition under cyclic voltammetric conditions. Scanning tunneling microscopy (STM) was used to investigate the structure and to measure the thickness of the thin film. It has been found that the Ru thin film is composed of layered Ru crystallites that appear in a hexagonal form with dimensions of about 250 nm and thickness around 30 nm. In situ FTIR spectroscopic studies demonstrated that such a nanostructured Ru thin film exhibits abnormal infrared effects (AIREs) for CO adsorption (G.Q. Lu et al., Langmuir 16 (2000) 778). In comparison with CO adsorbed on a massive Pt electrode, the IR absorption of COad on nm-Ru/GC was significantly enhanced. Moreover, the direction of COad bands is inverted and the full width at half maximum of COad bands is increased. It has been revealed that the enhancement factor of IR absorption of CO adsorbed on nm-Ru/GC electrodes depends strongly on the thickness of the Ru film. An asymmetrical volcano relationship between the enhancement factor and the thickness of the Ru film has been obtained. The maximum value of the enhancement factor was measured as 25.5 on a nm-Ru/GC electrode of Ru film thickness around 86 nm. The present study has contributed to exploration of the particular properties of nanostructured Ru film material and to the origin of the abnormal infrared effects.

Infrared Absorption Enhancement for CO Adsorbed on Au Films in Perchloric Acid Solutions and Effects of Surface Structure Studied by Cyclic Voltammetry, Scanning Tunneling Microscopy, and Surface-Enhanced IR Spectroscopy

The adsorption of CO on Au thin film electrodes vacuum-deposited on silicon substrate has been studied in 0.1 M perchloric acid solution by surface-enhanced infrared absorption spectroscopy (SEIRAS) with the Kretschmann attenuated-total-reflection configuration. Scanning tunneling microscopy (STM) was used to investigate the surface structures of the Au films subjected to different treatments. The IR absorption of CO adsorbed on the Au film electrodes is 20 times larger than that of CO adsorbed on bulk Au electrodes measured by reflection−absorption spectroscopy. When the Au film is subjected to flame annealing, which reorients the crystallites of the Au film and results in a highly ordered (111) surface, the enhancement factor is increased further to ca. 40. Cyclic voltammetric studies demonstrated that the highly ordered Au(111) films possess a higher electrocatalytic activity toward CO oxidation than polycrystalline Au films without flame annealing. Two different linearly bonded CO species, COL and COL...

On the SF6-sensitized IR photodecomposition of Fe(CO)5: 5 μm transient absorption measurements and absorption energy measurements

Abstract The 5 μm transient absorption and absorption energy were measured in the SF 6 -sensitized IR photodecomposition of Fe(CO) 5 using a transversely excited atmospheric (TEA) CO 2 laser. The time-resolved IR absorption of CO and vibrationally excited Fe(CO) 5 and the depletion of the parent Fe(CO) 5 were measured in the range 1975–2080 cm −1 using a tunable diode laser. In a mixture of 1.0 Torr (133.322 Pa) SF 6 and 1.0 Torr Fe(CO) 5 irradiated with a laser fluence of 0.15 J cm −2 , the formation of CO (ν=0) and the depletion of vibrationally cold Fe(CO) 5 occur with rate constants of 8.5 × 10 −14 cm 3 molecule −1 s −1 or greater (rise time of 364 μs Torr or less) and 4.7 × 10 −13 cm 3 molecule −1 s −1 (67 μs Torr) respectively. More than 95% of the dissociated CO is formed in the vibrational ground state. In contrast, IR absorption of vibrationally hot Fe(CO) 5 observed in the 1977–2003 cm −1 region shows a fast rise time of 5.4 μs Torr under the same experimental conditions. The slow formation of CO indicates that the decomposition occurs thermally in spite of the fast vibrational—vibrational (V—V) energy transfer between SF 6 and Fe(CO) 5 . The thermochemical aspects of the decomposition were determined on the basis of the rate constant of CO formation and the reaction temperature in the irradiated volume, calculated from the average number of photons absorbed by the SF 6 molecule at various laser fluences.