IR Spectra Of CO Research Articles

Characterization of a Pt/TiO 2 (rutile) catalyst for water gas shift reaction at low-temperature

Recently, we have reported that the Pt/TiO 2 (R: rutile) catalyst has relatively high activity for the water gas shift reaction at low-temperature (LT-WGS). In this study, Pt catalysts supported on TiO 2 (R), TiO 2 (A: anatase), ZrO 2 and Al 2O 3, were characterized by TEM, XPS, TPD, and FT-IR measurements. These results suggested detailed reasons for the high catalytic activity of the Pt/TiO 2 (R) catalyst. TEM micrographs showed that the Pt dispersion of the Pt/TiO 2 (R) catalyst was lower than those of the Pt/ZrO 2 and Pt/Al 2O 3 catalysts, although Pt/TiO 2 (R) had superior catalytic activity. Furthermore, the Pt/TiO 2 (R) catalyst had larger Pt dispersion than Pt/TiO 2 (A), although Pt/TiO 2 (R) had lower BET surface area than Pt/TiO 2 (A). XPS spectra indicated that the TiO 2 (R and A) supports had a stronger electronic effect with Pt than ZrO 2 and Al 2O 3. In addition, CO-TPD profiles revealed that the strength of Pt–CO bonding on Pt/TiO 2 (R) and Pt/TiO 2 (A) catalysts was weakened due to the interaction between the support and Pt. These results indicated that the catalytic activity of Pt catalysts for LT-WGS is greatly affected by the interaction between the support and Pt, rather than by Pt dispersion, although the difference in catalytic activity between the Pt/TiO 2 (R) and Pt/TiO 2 (A) catalysts can mainly be explained by the degree of Pt dispersion. Finally, IR spectra of CO–H 2O and –D 2O reactions on the Pt catalysts indicated that the high catalytic activity of Pt/TiO 2 (R) could be attributed to the fast formation and decomposition of formate as a reaction intermediate.

Punctual investigation of surface sites of HA and magnesium-HA

Abstract IR spectroscopy of adsorbed CO is used for the first time to characterize surface cationic centres of pure and magnesium doped hydroxyapatite (HA and MHA, respectively). In air, water molecules saturate the coordination sphere of exposed surface cations by a strong coordinative interaction. At first, the materials were outgassed at 300 °C in order to remove water molecules adsorbed on the surface. Following this treatment, surface sites able to adsorb CO are produced. The vibrational frequency of adsorbed CO is sensitive to the features of the adsorbing sites. The IR spectra of CO adsorbed on HA revealed the presence of surface Ca2+ ions differing for the degree of coordinative unsaturation and of P OH groups. On MHA, CO was able to monitor the presence of surface Mg2+ ions, the amount of which increased by aging the material in air.

IR and NMR studies of mesoporous alumina and related aluminosilicates

The synthesis of mesoporous alumina and aluminosilicates of Si/Al from 0.2 to 10 was done, and the status of Si and Al was followed by 29Si and 27Al MAS NMR. The properties of acid sites were studied by following the IR spectra of CO, N 2, pyridine and ammonia adsorbed. The mesoporous alumina contained only surface weak Lewis acid sites, the insertion of Si resulted in loss on such Lewis sites and in the formation of Brønsted sites. The Al OH bands decreased (the Al IV OH band related to tetrahedral Al species diminished the first) and Si OH Al one (IR band at 3605 cm −1)—similar as in the case of zeolites appeared as well as Si OH groups (IR band at 3740 cm −1). The aluminosilicates of higher Si content contained also strong Lewis acid sites formed by the dehydroxylation of Si OH Al groups (process similar as in zeolites), which occurred at the activation. The concentration of both Lewis and Brønsted sites was determined by quantitative IR studies of ammonia and pyridine adsorption. The concentration of Brønsted acid sites increased with Si content due to the formation of acidic Si OH Al, and at high Si/Al, it increases also due to the growing surface area. The concentration of Lewis sites decreased with Si content due to the transformation of surface Al species, which are potential Lewis sites into Si OH Al and also to dilution of the material with Si species. The acid strength of Lewis sites increased with Si content due to increasing contribution of strongly acidic sites produced by dehydroxylation. The mesoporous aluminosilicate (Si/Al = 10) studied in this research showed higher concentration and higher acid strength of Brønsted sites than HMCM-41 of the same Si/Al—it may be an potential catalyst in fine chemistry reactions.

Characterization of the Cu + sites in MFI zeolites: combined computational and experimental study

The site-specificity of the CO probe molecule interaction with the Cu +/MFI system is investigated by a combination of experimental and theoretical techniques. Three Cu + site types differing in CO adsorption energies ( E ads) were identified. Based on a very good agreement of experimental and calculated E ads, the detail information about the structure and localization of Cu + sites in MFI, including information about the localization of framework Al atom can be obtained. The IR spectra of CO adsorbed on the same Cu +/MFI samples clearly shows that the CO stretching frequencies are not site-specific in Cu +/MFI system. This conclusion is supported by calculated CO frequencies that do not depend on the Cu + site type.

Correlation between acidic properties of nickel catalysts and catalytic activities for ethylene dimerization and butene isomerization

Catalytic activities of NiO–SiO2 for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maxima in activities. The variations in catalytic activities are closely correlated to the acidity of NiO–SiO2 catalysts. Catalytic activities of NiO–TiO2 catalysts modified with H2SO4, H3PO4, H3BO3, and H2SeO4 for ethylene dimerization and butene isomerization were examined. The order of catalytic activities for both reactions was found to be NiO–TiO2/SO42- >> NiO–TiO2/PO43-NiO–TiO2/BO33- > NiO–TiO2/SeO42-> NiO–TiO2, showing clear dependence of catalytic activity upon acid strength. The high catalytic activity of supported nickel sulfate for ethylene dimerization was related to the increase of acidity and acid strength due to the addition of NiSO4. The asymmetric stretching frequency of the S=O bonds for supported NiSO4 catalysts was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. For NiSO4/Al2O3–ZrO2 catalyst, the addition of Al2O3 up to 5 mol% enhanced catalytic activity for ethylene dimerzation and strong acidity gradually due to the formation of Al–O–Zr bond. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni+, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO4/γ -Al2O3 and Ni 2p XPS.

Calculations of the site specific stretching frequencies of CO adsorbed on Li+/ZSM-5

Interaction of the CO molecule with Li+ within ZSM-5 was investigated by means of the combined quantum mechanics/interaction potential function method. Both, C-on and O-on species were considered. The scaling method based on the linear correlation between CO bond length and stretching frequency has been applied to calculate CO frequencies in CO(OC)–Li+/ZSM-5 adsorption complexes. Three types of C-on adsorption complexes with different r(CO) bond lengths, ν(CO) frequencies, and CO binding energies were identified. The calculated IR spectra of CO adsorbed on the Li+/ZSM-5 system show three distinctive bands at about 2194 cm−1, 2187 cm−1 and 2183 cm−1 for C-on complexes and at about 2116 cm−1, 2114 cm−1 and 2104 cm−1 for O-on complexes, in excellent agreement with experimental data. Calculated adsorption energies and CO stretching frequencies were used for the simulation of the IR spectra at various CO coverages.

The roles of active sites of nickel sulfate supported on γ-Al 2O 3 for ethylene dimerization

A series of catalysts, NiSO 4/γ-Al 2O 3, for ethylene dimerization were prepared by the impregnation method using an aqueous solution of nickel sulfate. Nickel sulfate supported on γ-Al 2O 3 was found to be very active even at room temperature, giving a maximum in both activity and acidity when catalyst containing 20% NiSO 4 was calcined and evacuated at 600 °C. The high catalytic activity of NiSO 4/γ-Al 2O 3 was related to the increase of acidity and acid strength due to the addition of NiSO 4. The asymmetric stretching frequency of the SO bonds for NiSO 4/γ-Al 2O 3 samples was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni +, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO 4/γ-Al 2O 3 and Ni 2p XPS.

Characterization of Nickel Sulfate Supported on γ-Al2O3 for Ethylene Dimerization and Its Relationship to Acidic Properties

Nickel sulfate supported on γ-Al2O3 was found to be very active even at room temperature, giving a maximum in both activity and acidity when catalyst containing 20% NiSO4 was calcined and evacuated at 600°C. The high catalytic activity of NiSO4/γ-Al2O3 was related to the increase of acidity and acid strength due to the addition of NiSO4. The asymmetric stretching frequency of the SO bonds for NiSO4/γ-Al2O3 samples was related to the acidic properties and catalytic activity. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni+, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO4/γ-Al2O3 and Ni 2P XPS.

Structural changes of the Cu surface of a Cu/ZnO/Al 2O 3 catalyst, resulting from oxidation and reduction, probed by CO infrared spectroscopy

The morphology of the Cu surface of a Cu/ZnO/Al 2O 3 (60:30:10) catalyst, produced by reduction of the copper oxide component of the catalyst either with H 2 or CO, has been probed by measuring the IR spectra of CO adsorbed on these surfaces. Pre-reduction in H 2 produces a Cu surface, which contains the (110) and (211) faces and which is active in CO 2 decomposition. Re-reduction of the CO 2-oxidised Cu surface in CO results in a twofold increase in the Cu(211) surface. Re-reduction of the CO 2-oxidised Cu surface in H 2 results in the restoration of the original Cu morphology, i.e. in a decrease in the Cu(211) surface population. Initial reduction of the copper oxide component of the Cu/ZnO/Al 2O 3 catalyst by CO produces a surface, which is inactive in the decomposition of CO 2.

CoMo/alumina prepared from carbonyl precursors: DRIFT, TPR and HDS studies

Mo(CO) 6 was deposited on alumina by gas phase adsorption in a fluidised bed reactor. Samples were heated gradually to determine the thermal behaviour of the surface species of molybdenum carbonyls. Mo(CO) 3(ads) was identified as the most stable species, evidently appearing as two adsorption sites of different thermal stability. The IR spectrum recorded after deposition of Co 2(CO) 8 on Mo/alumina was the same as the IR spectrum of Co 2(CO) 8 on alumina. After decarbonylation at 200°C, the ν(CO) bands due to the less stable of the Mo(CO) 3(ads) species were better resolved when Mo(CO) 6 was deposited after decarbonylation of Co 2(CO) 8 on alumina, than when it was directly deposited on alumina. Temperature-programmed reduction demonstrated interactions between alumina supported molybdenum and cobalt species. Activity of the samples was tested in hydrodesulphurisation of thiophene using a batch reactor. n-Butane was the main product, and the thiophene conversion was found to depend on the deposition order of the metals when the concentrations of the metals were similar.

Density Functional Studies of Alkali-Exchanged Zeolites. Cation Location at Six-Rings of Different Aluminum Content

The interaction of a sodium cation and six-rings of a zeolite framework with different numbers of aluminum atoms was studied with the aid of a density functional method and cluster models. The cation preferentially interacts with the oxygen atoms connected to aluminum at shortest distances of about 220 pm. For six-rings with two or three aluminum atoms, sodium positions on each side of the rings were identified. At both locations Na+ interacts mainly with the oxygen atoms directed toward the inside of the six-ring. From a comparison of calculated Na−O distances with crystallographic data and vibrational frequencies with the IR spectra of CO on NaY zeolite, it is deduced that the crystallographic SII site in faujasites may actually consist of two cation positions. The sodium location in a ring with one aluminum atom differs from that in the other clusters; it is almost in the plane of the T atoms. The sodium cation was calculated to experience a very low-energy barrier for crossing the six-ring (ca. 10 kJ/...

Origin of the infrared reflectance increase produced by the adsorption of CO on particulate metals deposited on moderately reflecting substrates

Potential-difference IR spectra of CO chemisorbed on noble metal electrodes have, if the two potentials are within the stability range of chemisorbed CO, a bipolar shape, since the frequency of the absorption maximum of the CO stretching band increases with increasing electrode potential. Therefore, in an IR spectrum with the reference at the lower potential the higher frequency lobe of the bipolar band is negative. An anomalous bipolar band with the opposite shape was first reported in 1994 for CO chemisorbed on Pt particles deposited on a basal plane graphite disc, and the anomaly was attributed to a reversible potential-induced migration of the chemisorbed CO molecules from Pt terraces to edge or kink sites. Anomalous bipolar bands were later found for other metals deposited on glassy carbon, and it was observed that the anomalous shape was due to the fact that the adsorbed CO produced an increase, instead of a decrease, of the IR reflectance at the frequency of the absorption maximum. On the basis of our observation of the band also with s-polarized radiation, which shows that the metals surface selection rule cannot be applied to glassy carbon, it is shown that this reflectance increase is due simply to the use of a glassy carbon substrate, which absorbs moderately, and therefore reflects IR radiation only moderately. Consequently, adsorption of a strong IR absorber, such as CO, will increase the reflectivity of glassy carbon.

IR investigations of CO 2 adsorption on chromia surfaces: Cr 2O 3 (0001)/Cr(110) versus polycrystalline α-Cr 2O 3

The adsorption of carbon dioxide has been studied on a single-crystalline Cr 2O 3(0001) film as well as on samples of polycrystalline α-Cr 2O 3. The Cr 2O 3(0001) film has been grown on the (110) surface of a chromium single crystal. Upon CO 2 dosage, two chemisorbed and two weakly bound adsorption states are identified. We associate the strongly bound carbon dioxide with carboxylates, bent CO δ− 2 species adsorbed on top of the chromium ions of the ‘polar’ (0001) surface. An assignment to surface carbonate formed upon adsorption on surface oxygen ions is not compatible with the vibrational data. The IR spectra of CO 2 chemisorbed on polycrystalline α-Cr 2O 3 differ substantially from the IRAS spectra of the CO 2/Cr 2O 3(0001)/Cr(110) system. As the faces of the microcrystals show mainly non-(0001) termination, we consider different modes of coordination of the CO 2 chemisorbates. In particular, bidentate carbonate species are discussed.

Properties of Si-modified Pd catalyst for selective hydrogenation of acetylene

Supported Pd catalysts have been modified with Si deposited on them by silane decomposition. When used in acetylene hydrogenation, the Si-modified catalysts show higher selectivity for ethylene and produce less amount of green oil than the unmodified Pd catalysts. IR and XPS analyses of the catalysts suggest that Si covers the Pd surface as Si or SiO 2 patches. The Pd surface is diluted with the deposited Si as observed by IR spectra of CO adsorbed on the surface. However, the electronic property of the Pd surface seems to be unaffected by the Si species because such a modification is not observed in XPS nor acetylene-TPD analysis. Accordingly, we conclude that improved performance of the Si-modified catalysts comes mostly from geometric modification of the Pd surface by Si.

IR spectral shifts and adsorption potentials of CO and N2 adsorbed on LiF and LiCl

Abstract Following our recent work on IR spectra of molecules adsorbed on C 60 embedded in LiF and LiCl films, adsorption potentials of CO and N 2 adsorbed on LiF (100) and LiCl (100) were calculated. For CO on LiF, a value of 2.0 kcal mol −1 was obtained, close to that calculated for CO adsorbed on a single C 60 molecule. The calculated value for CO on LiCl is much higher, 6.8 kcal mol −1 . It is therefore concluded that in the case of CO adsorbed on mixed LiF/C 60 films, the adsorbed CO molecules are distributed almost evenly on the LiF and C 60 single molecules, whereas in the case of CO adsorbed on mixed LiCl/C 60 films the salt is greatly preferred as the adsorption site. Adsorption potential calculations for a similar system, N 2 on LiF and LiCl, gave values of 1.5 and 4.4 kcal mol −1 , respectively. In this case, a much too large value was found for the adsorption potential on the LiCl surface. IR spectra of CO on the two substrates showed two strong absorptions for each of them. With N 2 induced spectra were obtained. Spectral shifts have been calculated for the above systems and were all toward higher frequencies, in agreement with experimental findings.

Surface and bulk properties of Cu–ZSM-5 and Cu/Al 2O 3 solids during redox treatments. Correlation with the selective reduction of nitric oxide by hydrocarbons

This paper deals with the redox properties of Cu ions implanted in ZSM-5 and supported on Al 2O 3, catalysts active in the selective reduction of NO by hydrocarbons such as propane. Data on the reducibility of the Cu systems in various atmospheres (vacuum, CO, H 2, O 2) and on their DeNO x activity are presented. The methods used to obtain informations on the surface and bulk transformations (and their link with catalytic behaviour) are complementary: UV–visible diffuse reflectance spectroscopy being useful to detect the presence of Cu 2+ and Cu 0, while Cu + is detected indirectly by the analysis of the IR spectrum of CO bound selectively to this cation. The main contributions to the previous knowledge are the following: it is possible to distinguish CO bound to isolated and non-isolated Cu + ions; the isolated Cu 2+ ions are reducible under vacuum without participation of organic impurities; the more active solids for the NO reduction into N 2 are characterized by the presence of isolated Cu n+ ions beside the additional influence of the zeolitic framework; after the formation of Cu + ions the redox cycles are reversible but, after the formation of Cu 0, the reversibility or irreversibility of the redox cycles and the restoration of the SCR activity are function of the copper content; the activity decreases after agglomeration into bulk oxides; there is no formation of bulk CuO during the reaction and, with reducing and moderate oxidizing mixtures, part of the copper remains as cuprous ions.

IR spectroscopy of a Pd-carbonyl surface compound

Pd is deposited onto a model alumina surface in the presence of a CO atmosphere of 3 × 10 −6 mbar at liquid nitrogen temperatures. According to the IR spectra the palladium carbonyl compound formed contains weakly bound terminal and more strongly bound bridging CO molecules, the spectra being similar to the IR spectra of colloidal metal particles in solution and the IR spectra of CO adsorbed on small deposited Pd particles. In line with thermal desorption studies of the stability of the compound, the IR spectra reveal the transition from the compound to a situation where CO is adsorbed on larger compact metal aggregates upon heating to room temperature.

Surface Heterogeneity of C60 As Studied by Infrared Spectroscopy of Adsorbed CO and Adsorption Potential Calculations

In our recent investigation of the IR spectrum of CO physically adsorbed on C60 films, two well-resolved absorption bands at 2135 and 2128 cm-1 were found, suggesting that the molecule is adsorbed on two different sites. To determine the nature of these adsorption sites, calculations of adsorption potentials and spectral shifts for the CO/C60 system were performed. The calculations were done for the fcc (100), fcc (111) hcp (001), and hcp (111) surface planes. In the calculations the 6-exponential and the Lennard-Jones potentials were used. A number of adsorption sites were chosen. These included the void space between four, three, and two neighboring C60 molecules and the center of the hexagon and the pentagon on the C60 surface. The calculated potentials and spectral shifts clearly indicate that adsorption sites in the voids between the C60 molecules are energetically preferred over sites on top of single C60 molecules. Comparison is made between results obtained with the two potentials and with results obtained previously with the two other carbon allotropes: graphite and diamond.

IR spectra of CO adsorbed on mixed films of [formula omitted] and [formula omitted

In the present work, IR spectra of CO adsorbed on mixed alkali halide C 60 high surface-area films were investigated. The mixed films were prepared either by simultaneous or by subsequent operation of two evaporation sources and condensing the vapors on a CsBr window cooled to 77 K. The IR spectrum of CO adsorbed on LiF C 60 films prepared by simultaneous deposition showed three absorptions of comparable intensities at 2175, 2162-2153 (depending on coverage) and 2130 cm −1. The first two bands are identical to absorption of CO on pure LiF. The band at 2130 cm −1 is assigned to CO on single C 60 molecules dispersed in the LiF. With LiF C 60 films prepared by subsequent deposition of the two substrates, four bands appeared in the spectrum, at frequencies closely resembling the frequencies obtained with CO adsorbed on the separate films. With mixed NaCl C 60 films absorption bands due only to CO on NaCl were seen. No absorptions were seen for CO on C 60 except at high surface coverages, where a very faint band at 2130 cm −1 appeared. Spectroscopic measurements of the isosteric heats of adsorption of CO on C 60 and LiF and adsorption potential calculations were performed.

Surface and Catalytic Properties of Lanthanum-PromotedNi/Sepiolite Catalysts for Styrene Hydrogenation

The catalytic behavior for styrene hydrogenation of two seriesof La-promoted nickel/sepiolite catalysts (xLaNi and NixLa) isreported. Both series were prepared by two-step impregnations,but lanthanum was incorporated first and nickel afterward inNixLa series and the order was reversed inxLaNi samples. Thecatalysts were characterized by temperature-programmed reduction(TPR), kinetics of reduction by hydrogen, photoelectronspectroscopy (XPS), and infrared spectroscopy of adsorbed CO toobtain information on the nature and distribution of nickel andlanthanum in the oxidic and reduced samples. The kinetics ofreduction and XPS data indicate clearly that Ni2+ions interactstrongly with the sepiolite substrate inxLaNi samples and to alesser extent in NixLa series. The IR spectra of CO adsorbed onthe reduced catalysts demonstrate that the promotion ofNi/sepiolite catalyst with lanthana results in a change in thedistribution of CO-adsorbed structures. It appears thatreconstruction of bridge-bonded species occurs via formation ofNi(100) surfaces. Moreover, CO can be adsorbed in a linear formon Ni atoms which are in contact with oxidic phase. The decreaseof the bridged form and relative higher concentration ofunreduced nickel species gives an indication that lanthanum isdeposited on the nickel particles, leading to a decrease in theprobability to have adjacent nickel atoms on the surface. Theobserved stable maximum in activity for the Ni7.1La catalyst iscaused not only by covering by La a larger fraction of thesilicate substrate but also by isolating Ni atomson the surface of Ni crystallites by La2O3patches deposited on it.