FTIR Spectra Of CO Research Articles

Cu/SiO2 and Cu/SiO2–TiO2 Catalysts: I. TEM, DR UV-Vis-NIR, and FTIR Characterisation

Three 8 wt% copper catalysts supported on SiO2 and on two SiO2/TiO2 powders with different TiO2 content have been prepared by a “chemisorption–hydrolysis” method. Transmission electron microscopy indicated that after calcination the three catalysts contain supported particles which are small and quite homogeneous in size (mean diameter, dm=3.0 nm). These particles slightly increase in size after reduction in H2 up to 773 K (dm=3.5 nm). On the basis of the diffuse reflectance UV-Vis-NIR spectra CuO and Cu2O were found to be present after calcination, while the electronic spectra were dominated by the features due to metallic Cu particles already after a mild reduction in H2 at 523 K. FTIR spectra of CO adsorbed onto the three catalysts reduced at 523 K appeared very similar. By a spectral fitting procedure, four different carbonylic species were evidenced, three assigned to carbonylic adducts on different types of microfacets exposed at the surface of three-dimensional Cu particles and one related to CO molecules adsorbed on plate-like two-dimensional copper particles. By increasing the reduction temperature an overall decrease in intensity of the bands due to CO adsorbed on copper supported on silica–titania carriers was observed, probably because of the formation of titanium suboxides that can cover a fraction of the copper sites. Furthermore, the CO–O2 and CO–NO reactions were studied by FTIR spectroscopy of the adsorbed species and quadrupole mass analysis of the gas phase over the catalysts. This allows the elucidation of the nature of the surface sites involved in the activation of these molecules and the nature of the intermediates present at the surface of the catalysts during the reactions. The role played in these reactions by the uncoordinated copper surface atoms exposed at the surface of the two different types of Cu particles will be discussed.

Influence of Cesium in Pt/NaCsβ on the Physico-Chemical and Catalytic Properties of the Pt Clusters in the Aromatization ofn-Hexane

Various Pt/NaCsβ catalysts with decreasing Na/Cs ratios and a Pt/KL sample taken as a reference catalyst for aromatization ofn-hexane, have been prepared by exchange of NaCsβ and KL zeolites in a Pt tetraammine solution then calcination and reduction. The increase of the Cs content in the NaCsβ zeolitic support results in a decrease of the cyclohexane adsorption and Pt exchange capacities. The Pt/Csβ and Pt/KL samples show similar behaviors which strongly differ from those of the Na-containing Pt/NaCsβ samples in terms of (i) reducibility of the Pt ions after calcination, (ii) shape of the FTIR spectra of CO adsorbed on the Pt clusters after reduction, and (iii) catalytic activity of these clusters in the conversion ofn-hexane. In particular, the selectivity to aromatization is much higher on the Pt/Csβ and Pt/KL catalysts than on the Na-containing Pt/NaCsβ ones. The reasons for the specific behaviors of the Pt/Csβ and Pt/KL samples are discussed.

Influence of the support on CO 2 methanation over Ru catalysts: an FT-IR study

The hydrogenation of CO2 to methane has been investigated over Ru catalysts supported on zeolite (H-ZSM-5) and on silica. Supported Ru catalysts were very active for the hydrogenation of CO2. Ru/ZSM-5 was more selective to methane than Ru/SiO2. On the basis of FT-IR spectra of CO and CO2 adsorbed on the catalysts, it has been suggested that this behaviour can be related to a higher positive polarization of ruthenium on the zeolite. This leads to a weaker Ru–CO bond on the H-ZSM-5-supported sample with a corresponding increase of the hydrogen surface coverage that favours the transformation of the intermediate CO to methane.

Optimum geometry of CO dimer and FT-IR spectra of CO in solid argon

To gain insight into the optimum geometry of the CO dimer, conventional ab initio and density functional calculations have been carried out. The potential energy surface of the CO dimer appeared to be very flat. Nonetheless, the planar distorted T-shaped structure was computed to be the most stable structure. The slipped antiparallel structure was also computed to be a local minimum. Both the linear and the nonplanar crossed structures seemed unstable. The slipped parallel structure was calculated to correspond to a saddle point. In addition to computing the optimum geometry of (CO) 2, the matrix isolated infrared spectra were taken for CO dispersed in solid argon. Three peaks were identified at 2136.4, 2138.4, and 2139.9 cm −1. The most distinct peak at 2138.4 cm −1 could be assigned to monomeric CO. The other two peaks were attributed to distorted T-shaped dimeric CO species, the 2136.4 cm −1 peak due to (CO) 2 bound through the CO…OC interaction and the 2139.9 cm −1 peak due to (CO) 2 bound through the OC…CO interaction.

Effects of structural defects and alloying on the FTIR spectra of CO adsorbed on [formula omitted

The curve fitting analysis of the FTIR spectra of two differently pretreated Pt ZnO dispersed samples is discussed. Carbon monoxide adsorbed on a photodeposited Pt ZnO sample mildly reduced in a 0.5% H 2 N 2 mixture at 493 K shows a main band at 2100 cm −1, shifting to the red and reducing its intensity by decreasing the surface coverage. All the spectra are well fitted by the addition of five Lorentzian bands. Looking at the literature, the five components, on the basis of their spectroscopic features can be assigned to Pt x+ sites, Pt 0(111) terrace sites with coordination number 9, Pt 0(100) terrace sites with coordination number 8, and Pt 0 step sites with coordination number 7. The spectra of CO adsorbed on the same Pt ZnO sample reduced in pure H 2 at 523 K exhibit a main band at ≈ 2070 cm −1, at lower frequency, significantly less intense and further red-shifting by decreasing the coverage. In this case the band appears as the superposition of two bands, not completely well fitted by Lorentzian bands. The maximum of these bands appears related to Pt atoms with coordination numbers 6 and 5. It must be stressed that by increasing the temperature of reduction in the case of Pt supported on refractory oxides, usually prepared by ionic exchange, a sintering and clustering occurs; these processes convert almost isolated low coordinated metal sites into terrace sites and induce a blue-shift of the absorption band. Our mildly reduced samples, as a consequence of the photoreductive method, are made of well crystallized Pt small particles. By increasing the reduction temperature, the alloying of Pt with Zn atoms coming from the support occurs; the opposite frequency shift observed and the change in the shape of the band can be ascribed to the chemical effect of the alloying of platinum with zinc. This hypothesis is confirmed by the analysis of isotopic mixtures experiments.

Adsorption potentials and spectral shifts of CO adsorbed on C60

Adsorption potentials and IR spectral shifts of CO physically adsorbed on high surface area C60 films were calculated and compared with results obtained with other carbon allotropes, graphite and diamond. The potentials were calculated as a sum of dispersion and repulsion interactions of the adsorbed molecule with each atom of the adsorbent using the Buckingham-Corner and Lennard-Jones potentials. The calculations were performed for different sites on the (100) and (111) surface planes of two C60 structures, fcc and hcp. The lowest potentials were obtained for CO adsorbed in voids between the C60 molecules. Spectral shifts (Δν) from the CO gas frequency were calculated by means of the perturbation method. The Δν values calculated for sites between four and two C60 molecules were in good agreement with previously reported FTIR spectra of CO adsorbed on C60 where two absorption bands shifted by −15 and −8 cm−1 were obtained. The two bands were assigned to CO adsorbed on sites differing in energy.

Polarized FTIR - Spectra of C 60 layers and adsorbates of CO and CO 2 on C 60

Thin films of buckminsterfullerene C 60 were deposited on KBr(100) at 78 K that were prepared by cleaving in UHV. The thickness of the film was monitored by recording the IR spectrum of C 60 at different polarizations. For the first time FTIR spectra of CO and CO 2 adsorbed on C 60 film were measured under UHV conditions. At pressures <10 −9 mbar the transmission spectra of CO 2 adsorbed on the C 60 film at temperatures below 90 K show a single ν 3 absorption peak at 2328 cm −1 with a linewidth (FWHM) of 5 cm −1. At higher CO 2 pressures the coverage grows and the linewidth and intensity of the absorption peak increase. A second absorption peak at 2331 ± 1 cm −1 was detected. At still higher pressures multilayer adsorption takes place with absorptions at 2344 and 2380 cm −1 at p-polarization and 2344 cm −1 at s-polarization. A single absorption peak of CO adsorbed on C 60 was recorded in transmission at 2134 cm −1 with a linewidth of 5 cm −1 at temperatures below 40 K. With increasing CO pressure a peak shift to 2138 cm −1 and an enhancement of the linewidth to 10 cm −1 was observed. Still higher pressures lead to multilayer adsorption with absorptions at 2142 and 2139 cm −1 at p-polarization and 2139 cm −1 at s-polarization. All absorptions detected, including the C 60 spectra, possess higher intensities at s-polarization than at p-polarization. At an angle of incidence of 45° the ratio of the integrated absorption (A s/A p) at s-polarization and p-polarization respectively is 1.3.

IR spectroscopic study of Pt/Kl zeolites using adsorption of CO as a molecular probe

FTIR spectra of CO adsorbed on Pt/KL catalysts show that the relative band intensities and the total dispersion markedly depend on the catalyst preparation method (ion exchange, incipient wetness impregnation or co-impregnation with KCl). The CO stretching frequency of the dominant band for linear CO is shifted to higher wavenumbers, parallel with the proton concentration in the reduced catalyst, which is derived independently from the intensity of the IR bands of the OH groups. The results are in accordance with the model that electron-deficient platinum particles are platinum-proton adducts.

Bimetallic promotion of alcohol production in CO hydrogenation and olefin hydroformylation on RhFe, PtFe, PdFe, and IrFe cluster-derived catalysts

Iron-containing bimetallic catalysts were prepared from carbonyl clusters as precursors deposited on SiO 2. FeRh 4 and Fe 2Rh 4 cluster-derived catalysts showed high activity and selectivity for formation of ethanol and methanol in CO hydrogenation. Fe 3Pt 3, Fe 6Pd 6 and FeIr 4 cluster catalysts gave methanol in high selectivity, while Fe-rich Fe 4Pt and Fe 4Pd were not selective catalysts. The RhFe cluster catalysts showed improved activity in hydroformylation of olefins; C 4-alcohols were substantially obtained from C 3 + CO + H 2. Mössbauer and EXAFS studies on the Fe 2Rh 4/SiO 2 catalyst show that highly dispersed RhFe bimetallic particles are located on the SiO 2 surface, where Fe atoms exist preferentially in the state of Fe 3+ even after H 2 reduction. FTIR spectra of CO chemisorbed on Fe 2Rh 4/SiO 2 exhibit a low-frequency band possibly due to the G and O-bonded CO on Rh-Fe 3+ sites. Bimetallic promotion of alcohol production in CO hydrogenation and olefin hydroformylation is proposed to originate from the two-site interaction of Rh-Fe 3+ (or Pt-Fe 3+, Pd-Fe 3+, IrFe 3+) sites with CO to enhance migratory CO insertion.

Modified chromium/silica gel catalysts: impregnation of the silica gel with aluminium acetylacetonate and comparison with chromium on alumina (Alon-C) and SiO2

Al2O3 supported on silica gel was prepared by impregnating silica gel with aluminium acetylacetonate/ethanol with different Al content (0.2, 0.4, 1 and 2 mmol Al/g SiO2) and investigated in comparison with silica gel and alumina (Alon-C). It was found that the aluminium oxide is highly dispersed. However, at higher Al concentration not all aluminium is present as surface cations. Polymerization measurements with ethene showed that chromium/Al2O3 silica gel catalysts have, after reduction with CO, similar (0.2 and 2 mmol Al) or different catalytic activity by a factor of two (0.4 and 1 mmol Al). Owing to a small increase of the chromium(III) concentration, a faster decrease of the polymerization activity was observed. This was also seen in FTIR spectra of CO adsorbed at low temperature. From low-temperature IR spectra of CO it is concluded, that in contrast to silica gel and Al2O3/silica gel, where surface dichromate is stabilised in the activated catalysts, alumina (Alon-C) stabilises only surface monochromate. The surface monochromate on alumina is reduced with CO to mononuclear chromium(II) surface species, while surface dichromate on silica gel is reduced mainly to dinuclear chromium(II) surface compounds.

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.

Ship-in-a-bottle formation of Pd13(CO) x clusters in zeolite NaY

FTIR spectra of CO adsorbed on gently reduced Pd/NaY show very sharp bands and are markedly different from the familiar broad band CO/Pd/support spectra. New bands are formed when part of the CO is removed. It is proposed that Pd13(CO)x clusters are formed with singly and multiply bonded CO, including a butterfly configuration. Very similar spectra are obtained, if Pd ions are initially located in the sodalite cages or in the supercages.

2143. Stimulated Brillouin scattering of CO 2 laser radiation from underdense plasma : A A Offenberger et al,J Appl Phys,47 (4), 1976, 1451–1458

Thin films of buckminsterfullerene C60 were deposited on KBr(100) at 78 K that were prepared by cleaving in UHV. The thickness of the film was monitored by recording the IR spectrum of C60 at different polarizations. For the first time FTIR spectra of CO and CO2 adsorbed on C60 film were measured under UHV conditions. At pressures <10−9 mbar the transmission spectra of CO2 adsorbed on the C60 film at temperatures below 90 K show a single ν3 absorption peak at 2328 cm−1 with a linewidth (FWHM) of 5 cm−1. At higher CO2 pressures the coverage grows and the linewidth and intensity of the absorption peak increase. A second absorption peak at 2331 ± 1 cm−1 was detected. At still higher pressures multilayer adsorption takes place with absorptions at 2344 and 2380 cm−1 at p-polarization and 2344 cm−1 at s-polarization. A single absorption peak of CO adsorbed on C60 was recorded in transmission at 2134 cm−1 with a linewidth of 5 cm−1 at temperatures below 40 K. With increasing CO pressure a peak shift to 2138 cm−1 and an enhancement of the linewidth to 10 cm−1 was observed. Still higher pressures lead to multilayer adsorption with absorptions at 2142 and 2139 cm−1 at p-polarization and 2139 cm−1 at s-polarization. All absorptions detected, including the C60 spectra, possess higher intensities at s-polarization than at p-polarization. At an angle of incidence of 45° the ratio of the integrated absorption (As/Ap) at s-polarization and p-polarization respectively is 1.3.

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.

X-ray diffraction study of nickel ion migration in Y-zeolite

FTIR spectra of CO adsorbed on reduced Ni-containing USY zeolites with Si/Al = 30 besides weak H-bond with bridged hydroxyls and silanol groups and bonding to Ni2+ cations reveal formation of mono-, di- and tricarbonyls with Ni+ sites. The bands of adsorbed CO species are very narrow, with FWMH˜1–1.5 cm−1. The spectra of isotopically mixed nickel dicarbonyl species reveal the splitting, which shows that two CO molecules occupy non-equivalent positions, so that the species exist in two isomeric forms, despite the similarity of sites, following from the spectra of monocarbonyls. Possible explanations of this phenomenon are discussed.