IR Bands Of CO Research Articles

DRIFTS study of CO adsorption on Pt nanoparticles supported by DFT calculations

Extensive research has been devoted to the assignment of IR bands of CO adsorbed on Pt nanoparticles, which are widely used in heterogeneous and electrocatalysis (e.g. fuel cells). In contrast to single crystal studies, the assignment of CO adsorption to the nanoparticle structure is still controversial. Here we present a case study where we assign CO adsorption bands to the structure of Platinum nanoparticles with a given size distribution. Using a special diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) cell allows to achieve high quality data under in-situ conditions. Temperature dependent CO adsorption spectra are resolved into three bands which depend on the applied flow and pretreatment conditions. Our calculations using Density Functional Theory (DFT) can mimic the experimental findings and link these bands to the particle structure. By explicitly calculating the IR spectra of CO/Pt nanoparticles of different sizes we show that the IR bands are due to a combined size and site effect. For fully covered small nanoparticles the IR bands are attributed to all binding sites. For larger nanoparticles the dominant contribution is related to {111} facets but the other bands are still site independent. Here we provide a tool to assign CO adsorption bands on Platinum nanoparticles with a given size distribution. This can be related to the structure–acitvity relationship which is required for a tailored catalyst design.

Quantification of Silver Sites in Zeolites: Carbon Monoxide Sorption Monitored by IR Spectroscopy

This work was aimed to provide a well-established approach for the quantification of silver sites in zeolites. The experimental procedure based on carbon monoxide sorption in silver exchanged zeolites ZSM-5, Y, and X was monitored by IR spectroscopy. With regard to the Lambert–Beer law the values of the absorption coefficients of the IR bands of CO interacting with exchangeable cations (Ag+) and metallic species (Ag0) were attained. Subsequently, the concentrations of silver species of different kinds were calculated. The values of the absorption coefficients are valid for zeolites of FAU and MFI topologies; thus, they are argued to be used for zeolites of other structures.

Infrared Studies on Bimetallic Copper/Nickel Catalysts Supported on Zirconia and Ceria/Zirconia.

Infrared spectroscopy has been employed for a detailed characterization of ZrO2 and CeO2/ZrO2 supported nickel and copper/nickel catalysts to be utilized for methane decomposition. Adsorption of CO at 303 K was performed in order to determine the surface composition and accessible adsorption sites. Alloy formation occurred during reduction, as indicated by a red-shift of the vibrational band of CO on Ni: by 27 cm−1 on nickel-rich CuNi alloy, by 34 cm−1 on 1:1 Cu:Ni and by 36 cm−1 on copper-rich CuNi alloy. CuNi alloy formation was confirmed by X-ray absorption spectroscopy during reduction revealing a considerably lower reduction temperature of NiO in the bimetallic catalyst compared to the monometallic one. However, hydrogen chemisorption indicated that after reduction at 673 K copper was enriched at the surface of the all bimetallic catalysts, in agreement with IR spectra of adsorbed CO. In situ IR studies of methane decomposition at 773 K demonstrated that the addition of Cu to Ni strongly reduced coking occurring preferentially on nickel, while maintaining methane activation. Modification of the zirconia by ceria did not have much effect on the adsorption and reaction properties. Ceria-zirconia and zirconia supported samples exhibited very similar properties and surface chemistry. The main difference was an additional IR band of CO adsorbed on metallic copper pointing to an interaction of part of the Cu with the ceria.Graphical

Promoting Mechanism of Potassium in the Reforming of Ethanol on Pt/Al2O3 Catalyst

The reaction of ethanol and water has been investigated over K doped 1% Pt/Al2O3 catalysts. The presence of K resulted at room temperature in upward shift of the IR band of CO formed in the ethanol adsorption. At higher temperature the presence of surface acetate species was also detected which, according to the TPD results decomposed above 600 K to form CH4 and CO2. The K destabilized these forms. In the catalytic reaction the H2 selectivities were similar and much higher over all promoted Pt/Al2O3 than on the pure catalyst. In this study it was proved that the K had a destabilizing effect onto the surface acetate groups and thus improved the steam reforming activity of 1% Pt/Al2O3.

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.

Hydrogen adsorption sites studied by carbon monoxide adsorption to explain the hydrogenation activity of benzene on Pd and Pt catalysts

FT-IR of CO has been employed to study the relations between hydrogen adsorption and benzene hydrogenation on Pd/SiO 2 and Pt/SiO 2 catalysts. Three IR bands of CO stretching: 2085 (L 1 band), 1984 (B 1 band) and 1948 cm −1 (B 2 band), have been observed on Pd/SiO 2. Hydrogenation of benzene is dominated by hydrogen adsorption on B 1 sites (CO band at 1984 cm −1) of Pd/SiO 2, because benzene and/or the benzene ring of acetophenone can preferentially cover on the B 1 sites to hinder hydrogen adsorption, leading to poor catalytic activity for hydrogenation of benzene. When hydrogen is pre-covered on Pd/SiO 2 to occupy the B 1 sites, it will cause intense benzene hydrogenation. Pre-adsorbed acetophenone on Pt/SiO 2 surface presents a surprising phenomenon that adsorbed acetophenone does not impede CO adsorption. We propose that adsorption of hydrogen is independent of the exposure of pre-adsorbed acetophenone, and therefore Pt/SiO 2 catalyst can offer high catalytic activity for hydrogenation of benzene.

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.

In SituSTM Studies of Electrochemical Growth of Nanostructured Ni Films and Their Anomalous IR Properties

We have extended the study of anomalous IR properties, which were initially discovered on nanostructured films of platinum group metals and alloys, to nanostructured films of nickel, a member of the iron group triad, and broadened the fundamental knowledge on this subject. Nanostructured thin films of nickel supported on glassy carbon [nm-Ni/GC(n)] were prepared by electrochemical deposition under cyclic voltammetric conditions, and the thickness of films was altered systematically by varying the number (n) of potential cycling within a defined potential range for electrodeposition. Electrochemical in situ scanning tunneling microscopy (STM) was employed to monitor the electrochemical growth of nanostructured Ni films. These in situ STM images illustrated that, along the increase of the film thickness, Ni films have undergone a transformation from layer structure to island structure and finally to lumpish arris structure. Investigations by in situ FTIR spectroscopy employing adsorbed CO as the probe revealed that these nanostructures of Ni films yield abnormal IR features, Fano-like IR features, and normal IR features, respectively. The IR bands of CO adsorbed on Ni thin films of a layer structure were inverted in their direction and enhanced in their intensity up to 15.5 times on an nm-Ni/GC(4) electrode. The Fano-like IR features, which are defined as a bipolar band with its negative-going peak on the low wavenumber side and its positive-going peak on the high wavenumber side, are observed for the first time on Ni thin films of an island nanostructure, i.e., at the nm-Ni/GC(16) electrode. IR features changed to normal absorption in CO adsorbed on the nm-Ni/GC(25) electrode, i.e., that with lumpish arris nanostructured Ni film of a larger thickness.

Correlation between CO surface coverage and selectivity/kinetics for the preferential CO oxidation over Pt/γ-Al 2O 3 and Au/α-Fe 2O 3: an in-situ DRIFTS study

We present in-situ IR (DRIFTS) measurements on CO adsorption and preferential CO oxidation (PROX) in H 2-rich gas on Pt/γ-Al 2O 3 and Au/α-Fe 2O 3 catalysts at their envisaged operating temperatures of 200°C and 80°C, respectively, which in combination with kinetic data show that the underlying reason for the very different PROX reaction kinetics on these two catalysts is the difference in steady-state CO coverage. Whereas on the platinum catalyst this is always near saturation under reaction conditions, causing a negative reaction order (−0.4) and a p CO-independent selectivity, the amount of adsorbed CO on the gold particles (indicated by an IR band at ∼2110 cm −1) strongly depends on the CO partial pressure. From the position of the IR band of CO adsorbed on Au/α-Fe 2O 3, the steady-state coverages on the Au surface are shown to be significantly below saturation, with an upper limit of approximately θ CO=0.2. Low reactant surface concentrations on Au explain the positive reaction order with respect to p CO (+0.55 at 80°C) as well as the observed decoupling of the CO and H 2 oxidation rates, which results in a loss of selectivity with decreasing p CO.

IR study of the interaction of hydroxyl groups of silica gel with Cr species of Phillips' type catalysts

Spectroscopic evidence for the interaction of hydroxyl groups and chromium ions was obtained using a catalyst prepared from chromyl chloride. A new OH peak, observed at 3705 cm−1 after pumping away CO gas, is attributed to the direct interaction of OH with the low-valent chromium. This peak shifts to 3590 cm−1 on contact with O2 at room temperature and it is assigned to a hydroxyl interacting with the oxidized chromium. New assignments are also proposed for IR bands of CO presorbed on the catalyst. The peak due to CO at 2188 cm−1 decreases as the OH intensity at 3705 cm−1 increases, suggesting that the former peak arises from adsorption on Cr(II) species to which two oxygen atoms are attached.

CO Fourier-transform infrared study of metallocenes on silica gel and AlPO4

Metallocenes of vanadium, manganese, cobalt, iron and nickel have been reacted with silica gel and AlPO4. The samples were studied with CO FTIR spectroscopy. Vanadocene on AlPO4 gave a band at 1869 cm–1, interpreted as VCp2CO, and two bands from a more stable species at 2046 and 1992 cm–1, which are due to a [VCp2(CO)2]+ surface compound. Manganocene produced small amounts of a manganese carbonyl compound only after heating to 200 °C.Ferrocene reacted with the AlPO4 surface only at elevated temperatures (300 °C) giving weak CO IR bands at 2065 and 2023 cm–1. These are interpreted as due to a [FeCp(CO)2]+ species. Cobaltocene reacted similarly on both SiO2 and AlPO4. CO IR bands [from CoCp(CO)2] were observed at 2032 and 1964 cm–1(SiO2) and at 2018 and 1950 cm–1(AlPO4).Nickelocene reacted very easily with the surface of both supports. It decomposed at room temperature forming C10H12 and Ni0. At low temperatures (–80 °C) a band at 2103 (AlPO4) or 2094 cm–1(SiO2) was the main absorption band found, which is interpreted as arising from [CpNiCO]+, bonded to the surface via P—O– groups. At room temperature Ni(CO)4(CO IR band at 2056 cm–1) was formed. Only NiCp2 and FeCp2 of the metallocenes studied reacted similarly to chromocene with the two different supports. Ferrocene on the AlPO4 surface gave much weaker CO IR bands and nickelocene on the supports was less stable at room temperature than chromocene.

Modified chromium/silica gel catalysts: impregnation of the silica gel with titanylacetylacetonate and comparison with chromium on SiO2 and TiO2

TiO2 supported on silica gel was prepared by impregnating silica gel with titanylacetylacetonate—ethanol with different Ti content (0.2, 0.4, 1 and 2 mmol Ti/g SiO2). These samples were investigated and compared with silica gel and titania (P 25). At low concentration the titanium is highly dispersed, and at the highest titanium concentration some 30% of the titanium is present as anatase crystallites. Polymerization measurements showed a lower catalytic activity with titanium present. FTIR spectra of CO adsorbed on chromium(II) at room and low temperature showed that for chromium/titanium/silica gel catalysts the chromium(II)-C surface species (characteristic CO IR bands at 2190 and 2120, 2100, 2045 cm–1) is dominant over the chromium(II)-C surface species (characteristic CO IR bands at 2180, 2185 and 2120, 2100, 2035 cm–1), while for normal chromium/silica gel catalysts the chromium(II)-A species is the major one. This effect is more clearly observed for higher chromium concentrations (0.5% Cr as opposed to 0.074% Cr).

On the active site of the Phillips catalyst for ethylene polymerization

The FTIR spectra of CO adsorbed on the chromium(II)-A surface compound (the active site of the Phillips catalyst) before and after short polymerization with ethylene have been reexamined. No difference in the CO spectra of the room temperature triplet at 2190, 2185, and 2179 cm −1 was found for that part of chromium which reacts with ethylene compared to the CO spectra of the unreacted surface compound. The same result was observed with the low temperature CO IR triplet at 2120, 2100, and 2035 cm −1. After low temperature polymerization with ethylene a new CO IR band at 2176.82 cm −1 was observed. After high temperature reaction with ethylene a symmetrical and rather sharp CO IR band at 2171.52 cm −1 was noted at room temperature instead. It is concluded that in both cases rather well-structured chromium surface compounds are formed. The CO IR bands of the room temperature triplet shifted from 2190.79, 2184.74 and 2178.69 cm −1 to 2192.28, 2185.03, and 2180.76 cm −1 after seven oxidation (800 °C, O 2)/reduction (350 °C, CO) cycles. The CO IR bands of the low temperature triplet (−145 °C) separated into two triplets with higher (2121.12, 2102.06, and 2040.37 cm −1) and lower (2117.12, 2098.47 and 2031.34 cm −1) positions than the original one. It is concluded that the surface structure of the support has a rather large influence on the electronic density of the chromium(II) surface ions.

On the polymerization mechanism of the Chromium(III) and Chromium(II)‐B Silica Gel Catalysts

AbstractFTIR spectra of the chromium(III)/silica gel catalyst after short polymerization with ethylene show weak bands at 2 685 and 1 447 cm−1 from the stretching and the deformation vibration of the methylene group, which binds the growing polymer to the active chromium(III) site. The band at 2 685 cm−1 is reversibly removed by CO adsorption at low temperatures (−145°C). This adsorbed CO shows a broad band at 2 184 cm−1. From the intensity of CO IR bands on unchanged chromium(III) before and after polymerization it was calculated that 12% of the chromium(III) is catalytically active, which is in good agreement with previous measurements by an entirely different determination method (11%). The chromium(II)‐B catalyst showed also a weak band at 2 685 cm−1 and it is therefore concluded that in this case the chromium(II) is oxidised by the ligating surface silanol group (in cooperation with an ethylene molecule). The band at 2 685 cm−1 is discussed in relation to that from normal methylene groups at 2 925 and 2 855 cm−1 and to that from the chromium(II)‐A catalyst at 2 750 cm−1. Evidence for the existence of a mononuclear chromium(II)‐A species is found. This one is, in contrast to the dinuclear chromium(II)‐A species, not polymerization active.

Über die Reaktion von Chromocen mit einem Co/Kieselgel-Träger / On the Reaction of Chromocene with a Co/Silica Gel Support

Abstract The IR spectra of the modified chromocene/Co/silica gel catalyst show a band at 3118 cm" 1 of the cyclopentadienyl ligand, which is shifted by -1-20 cm' 1 compared to the unmodified chromocene/silica gel catalyst. The comparably slow CO adsorption yields two bands at low Cr concentration (-0.1% Cr) at 2065 and 2022 cm" 1 and two more at higher Cr concentration (-1% Cr) at 2028 and 1961 cm -1 . Both band pairs are significantly different from that observed with the "normal" chromocene/silica gel catalyst at 2046 and 1974 cm -1 . No CO IR bands at low wavenumbers were observed with the modified catalyst. Polymerisation measurements showed a slightly lower concentration of catalytically active sites (35% of Cr) for the modified catalyst compared to the unmodified one (50%), while the poly-merisation activity decreased by a factor of four (Cr concentration: 0.083%). It was concluded that the surrounding of the dimeric surface site is changed by Co on the silica gel surface of the chromocen catalyst and that this change is important for the CO adsorption and the polymerisation activity.

Intensities of the ?CO IR bands for isotopic H(D)-carboxylic acid complexes

Intensities of the ?CO IR bands for isotopic H(D)-carboxylic acid complexes

2184. Excitation of high-frequency oscillations in a plasma with accelerating Hall layer: V I Arefev and K P Kirdyashev,Zh Tekh Fiz,45 (3), 19s75, 527–535 ( in Russian)

The FTIR spectra of CO adsorbed on the chromium(II)-A surface compound (the active site of the Phillips catalyst) before and after short polymerization with ethylene have been reexamined. No difference in the CO spectra of the room temperature triplet at 2190, 2185, and 2179 cm−1 was found for that part of chromium which reacts with ethylene compared to the CO spectra of the unreacted surface compound. The same result was observed with the low temperature CO IR triplet at 2120, 2100, and 2035 cm−1. After low temperature polymerization with ethylene a new CO IR band at 2176.82 cm−1 was observed. After high temperature reaction with ethylene a symmetrical and rather sharp CO IR band at 2171.52 cm−1 was noted at room temperature instead. It is concluded that in both cases rather well-structured chromium surface compounds are formed. The CO IR bands of the room temperature triplet shifted from 2190.79, 2184.74 and 2178.69 cm−1 to 2192.28, 2185.03, and 2180.76 cm−1 after seven oxidation (800 °C, O2)/reduction (350 °C, CO) cycles. The CO IR bands of the low temperature triplet (−145 °C) separated into two triplets with higher (2121.12, 2102.06, and 2040.37 cm−1) and lower (2117.12, 2098.47 and 2031.34 cm−1) positions than the original one. It is concluded that the surface structure of the support has a rather large influence on the electronic density of the chromium(II) surface ions.