FTIR adsorption

Adsorption of sulfate species at pc-Au electrode has been studied [35] in HF—KF buffer of pFi = 2.8 applying Fourier transform infrared spectroscopy (FTIR). Adsorption of sulfate starts at 0.4 V versus Pd/H2 (which is about 0.28 V more positive than the zero charge potential). Adsorption reaches a maximum at 1.2 V. At any potential applied, a band between 1165 and 1193 cm was observed. It was ascribed to the adsorbed S04 . Adsorption... 

Diffuse reflectance FTIR adsorption of probe molecules (pyridine, carbon monoxide, and so forth, monitored by FTIR)... 

Bordiga S, Regli L, Lamberti C, Zecchina A, Bjprgen M, Lillerud KP. FTIR adsorption studies of H O and CH3OH in the isostructural H-SSZ-13 and H-SAPO-34 Formation of H-bonded adducts and protonated clusters. J Phys Chem B 2005 109 7724-32. 

The acid monolayers adsorb via physical forces [30] however, the interactions between the head group and the surface are very strong [29]. While chemisorption controls the SAMs created from alkylthiols or silanes, it is often preceded by a physical adsorption step [42]. This has been shown quantitatively by FTIR for siloxane polymers chemisorbing to alumina illustrated in Fig. XI-2. The fact that irreversible chemisorption is preceded by physical adsorption explains the utility of equilibrium adsorption models for these processes. 

The crystalline mineral silicates have been well characterized and their diversity of stmcture thoroughly presented (2). The stmctures of siHcate glasses and solutions can be investigated through potentiometric and dye adsorption studies, chemical derivatization and gas chromatography, and laser Raman, infrared (ftir), and Si Fourier transform nuclear magnetic resonance ( Si ft-nmr) spectroscopy. References 3—6 contain reviews of the general chemical and physical properties of siHcate materials. 

FTIR SPECTROSCOPIC EVIDENCE FOR THE BASICITY INDUCED BY ADSORPTION... 

FTIR can be used to screen membranes for fouling tendencies prior to the first ultrafiltration experiment. Screening can be done by means of a simple static adsorption test. Membranes showing greater static adsorption are expected to foul more during ultrafiltration and are disfavored. Figure 8 illustrates the FTIR results... 

Figure 8. Example of FTIR analysis of Polysulfone (PS) ultrafilter static adsorption test.

According to experimental data,208,209 the SNIFTIR technique can be used to probe the electrical properties of the electrical double layer even in more concentrated solutions where cyclic voltammetry (cv), impedance, chronocoulometry, and other techniques are not applicable. Iwasita and Xia210 have used FTIR reflection-adsorption spectra to identify the potential at which the orientation of water molecules changes from hydrogen down to oxygen down. 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

The samples were submitted to the sulfidation procedure described above, followed by 2 h of heating at 673 K, under vacuum (about 2x10 3 Pa). After cooling under vacuum, pyridine was adsorbed at room temperature for 30 minutes. The samples were then outgassed in three steps of 1 h the first one at room temperature and the others at 423 K and 523 K. Spectra were taken before pyridine adsorption and after each outgassing step, with a FTIR spectrometer Bruker IFS-88 (spectral resolution set at 1 cm ). Each spectrum represented the average of at least 50 scans. 

For the studied catechol methylation reaction the catalyst structure and surface properties can explain the catalytic behaviour As mentioned above, the reaction at 260-350°C has to be performed over the acid catalysts. Porchet et al. [2] have shown, by FTIR experiments, the strong adsorption of catechol on Lewis acid/basic sites of the Y-AI2O3 surface. These sites control the reaction mechanism. 

The catalyst for the in situ FTIR-transmission measurements was pressed into a self-supporting wafer (diameter 3 cm, weight 10 mg). The wafer was placed at the center of the quartz-made IR cell which was equipped with two NaCl windows. The NaCI window s were cooled with water flow, thus the catalyst could be heated to 1000 K in the cell. A thermocouple was set close to the sample wafer to detect the temperature of the catalyst. The cell was connected to a closed-gas-circulation system which was linked to a vacuum line. The gases used for adsorption and reaction experiments were O, (99.95%), 0, (isotope purity, 97.5%), H2 (99.999%), CH4 (99.99%) and CD4 (isotope purity, 99.9%). For the reaction, the gases were circulated by a circulation pump and the products w ere removed by using an appropriate cold trap (e.g. dry-ice ethanol trap). The IR measurements were carried out with a JASCO FT/IR-7000 sprectrometer. Most of the spectra were recorded w ith 4 cm resolution and 50 scans. 

In situ FTIR spectroscopy was used to study the adsorbed species generated on the catalyst surface in the presence of Hj and Oj. Before the experiment, the catalyst wafer was pretreated by O, (5.3 kPa) at 723 K for 1 h followed by evacuation at the same temperature in vacuum ca. 6x10 Pa) for 2 h. After the pretreatment, the temperature was decreased to a desired one in vacuum and IR spectrum was recorded at that temperature. The spectra of the catalyst wafer recorded at different temperatures were used as the background ones for the adsorption studies described below. 

Room temperature CO oxidation has been investigated on a series of Au/metal oxide catalysts at conditions typical of spacecraft atmospheres CO = 50 ppm, COj = 7,000 ppm, H2O = 40% (RH) at 25 C, balance = air, and gas hourly space velocities of 7,000- 60,000 hr . The addition of Au increases the room temperature CO oxidation activity of the metal oxides dramatically. All the Au/metal oxides deactivate during the CO oxidation reaction, especially in the presence of CO in the feed. The stability of the Au/metal oxide catalysts decreases in the following order TiOj > FejO, > NiO > CO3O4. The stability appears to decrease with an increase in the basicity of the metal oxides. In situ FTIR of CO adsorption on Au/Ti02 at 25 C indicates the formation of adsorbed CO, carboxylate, and carbonate species on the catalyst surface. 

In situ FTIR studies of CO adsorption on a 1% Au/Ti02 have identified various surface species on the catalysts. Figure 5 shows the in situ FTIR spectra of CO... 

MoSx-CoSx/NaY catalysts, which were prepared by introducing Mo(CO) into CoSx/NaY (l.lCo/SC), showed the identical HDS activities with those of CoSx-MoSx/NaY at the same compositions, as illustrated in Fig.4. Figure-4 suggests that the dispersions of Mo and Co sulfides are not mutually affected by the presence of the other sulfide species or that the formation of catalytically active species, e.g. Co-Mo mixed sulfide species, is independent of the accommodation order. As shown telow, FTIR of NO adsorption, EXAFS, and XPS results supported the latter pwssibility. 

The major contributions of the Co sites in CoSx-MoSx/NaY to the HYD and HDS reactions were corroborated by a FTIR study of NO adsorption. Figure 7 shows the IR spectra of NO adsorbed on CoSx/NaY (2.1Co/SC) and CoSx-MoSx/NaY (2.1Co 2.1Mo/SC). Nitric oxide... 

Figure 7. FTIR spectra of NO adsorption on Figure 8. Fourier transforms of k -weighted CoSx/NaY (2. ICo/SC) and CoSx-MoSx/NaY EXAFS modulations of the Mo K-edge for (2.1MO-I- 2.IC0/SC). MoSx/NaY and CoSx-MoSx/NaY.

The samples were characterized by chemical analysis induced coupled plasma and atomic absorption techniques apparatus), nitrogen adsorption isotherms (at 77 K), XRD patterns ( Siemens diffractometer and (3uKa radiation), SEM observations (Hitachi S800 apparatus of the University C. Bernard, Lyon I) and TGA-DTA (Setaram 92-12 apparatus). The IR spectra were recorded with a Bruker IPS 48 FTIR spectrometer. 

Characterization of the Cu-ZSM-5 catalyst by in-situ diffuse reflectance FTIR spectroscopy after treatments in CO, air and NjO is presented in figure 10, the CO adsorption in figure 11. 

K did not produce tiny new paramagnetic species, despite FTIR observations confirming appearance of IR features attributable to adsorbed NjO (2234 and 1256 cm in Fig. 4a) upon contact with N2O at 300 K. Stepwise decreases in magnitude of those IR features were, however, observed in each of a sequence of FTIR spectra taken after separate NjO adsorptions at increasing adsorption temperatures (TJ up to 573 K (Fig. 4b-d). From these FTIR observations it could be inferred that increased T, for contact between N,0 and vacuum-outgassed CeOj resulted in increased fractional decomposition of the N O introduced. FTIR spectra did not show bands due to peroxide species after N,0 adsorption. 

In this paper we report (i) the catalytic activity for SCR of VOx/Zr02 samples prepared by various methods (adsorption from aqueous metavanadate solutions at different pH values, dry impregnation, and adsorption from VO(acetylacetonate)2 in toluene), (ii) sample characterization (nuclearity, dispersion and oxidation state) by means of XPS, ESR and FTIR and (iii) the nature and reactivity of the surface species observed in the presence of the reactant mixture. Catalytic results are here reported in full. Characterization data relevant to the discussion of the catalytic activity will be given, whereas details on the catalysts preparation and... 

These two-step features, which will be further proved by the FTIR spectra of adsorbed CO, can be summarized as follows. The adsorption of CO, being accompanied by the increase of the coordination munber due to the formation of mono- and dicarbonyl species, causes a shift of the d - d transitions toward the values more typical of the octahedral coordination. Furthermore, in the presence of CO (electron donor molecule) more energy is required to transfer electrons from O to Cr as a consequence, the O Cr(II) CT transition shifts at higher frequencies (from 28000-30000 to 33 700cm ). At increasing CO pressure the CO Cr(II) CT transition also becomes visible (band at 33400 cm ). Analogous features have been reported in the past for NO adsorption on the reduced Cr/Si02 system [48,82]. 

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