Situ FTIR

While it was long recognized that it would be valuable to apply IR spectroscopy in situ to the study of the electrode-electrolyte interface, realization of the technique was prevented by two main problems  

The extremely strong absorption of IR light by all common solvents and most 

The need to pick out the weak absorption of near-electrode or adsorbed species 

The first problem is relatively easy to solve by employing a thin layer of electrolyte, and it has been approached in three ways, according to the mode and angle of incidence of the IR light on the electrode. 

A thin-layer cell is fabricated based on two optically transparent windows. The thickness of the electrolyte layer is dictated by the thickness of the optically transparent working electrode, usually a gold minigrid, indium-doped tin-oxide-coated glass slide or a reticulated vitreous carbon slice. This approach is not surface-sensitive, and it is effectively restricted to nonaqueous solvents, because the minimum electrolyte thicknesses that can be achieved cause severe attenuation in the IR beam. 

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Carbon dioxide has been proposed as an additive to improve the performance of lithium batteries [60]. Aurbach et al. [61] studied the film formed on lithium in electrolytes saturated with C02, and using in situ FTIR found that Li2C03 is a major surface species. This means that the formation of a stable Li2C03 film on the lithium surface may improve cyclability [62], Osaka and co-workers [63] also studied the dependence of the lithium efficiency on the plating substrate in LiC104-PC. The addition of C02 resulted in an increase in the efficiency when the substrate was Ni or Ti, but no effect was observed with Ag or Cu substrates. 

The accumulation of carbonates is another reason for gold catalyst deactivation [9]. The in-situ FTIR experiments in Fig. 6 show that the carbonate build-up is slower in the 03/02-treated gold catalyst (Fig. 6a) compared to the air-treated sample (Fig. 6b). Also, the air-treated catalyst displays a strong band at 1435 cm" corresponding to the non-coordinated carbonate. Although our understanding of the process is incomplete, it is clear from the results that O3 pretreatment inhibits the deactivation of gold catalyst. 

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. 

As described above, the temperature needed for the formation of the adsorbed peroxide was ca. 573 K, which was almost the same as that for the initiation of the oxidation of CH to CHjOH in the presence of H, and 0,. This peroxide may directly be related to the selective oxidation of CH to CH OH. Therefore, the reactivity of this adsorbed peroxide with CH., was investigated by in situ FTIR spectroscopy as follows. 

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... 

The surface species formed on the working catalyst surface were also studies by in situ FTIR. Only one adsorbed CO band at ca 1989 cm was observed on the Ru/ri02 catalyst, presumably due to the bridged adsorbed CO, which tended to be stable after 6 min of reaction time. In contrast, two adsorbed CO bands at ca. 2064 and ca. 1963 cm were observed over the RU/AI2O3 catalyst, assigned as the... 

Lin W-F, Sun S-G, Tian Z-W. 1994. Investigations of coadsorption of carbon monoxide with S or Bi adatoms at a platinum electrode by in-situ FTIR spectrocopy and quantum chemistry analysis. J Electroanal Chem 364 1-7. 

Kabbabi A, Faure R, Durand R, Beden B, Hahn F, Leger JM, Lamy C. 1998. In situ FTIRS study of the electrocatalytic oxidation of carbon monoxide and methanol at platinum-ruthenium bulk alloy electrodes. J Electroanal Chem 444 41-53. 

Christensen PA, Hamnett A, Weeks S A. 1988. In-situ FTIR study of adsorption and oxidation of methanol on platinum and platinized glassy carbon electrodes in sulphuric acid solution. J Electroanal Chem 250 127-142. 

Ean Q, Pu C, Ley KL, Smotkin ES. 1996. In situ FTIR-diffuse reflectance spectroscopy of the anode surface in a direct methanol fuel cell. J Electrochem Soc 143 L21-L23. 

Partitioning of azo-dyes between PMMA and scCC>2 has been measured by means of in situ FTIR and UV/VIS spectroscopy. The use of CO2 to incorporate... 

In order to follow progress of elimination, reactions were also performed on thin films in a special sealed glass cell which permitted in situ monitoring of the electronic or infrared spectra at room temperature (23°C). Typically, the infrared or electronic spectrum of the pristine precursor polymer film was obtained and then bromide vapor was introduced into the reaction vessel. In situ FTIR spectra in the 250-4000 cm-- - region were recorded every 90 sec with a Digilab Model FTS-14 spectrometer and optical absorption spectra in the 185-3200 nm (0.39-6.70 eV) range were recorded every 15 min with a Perkin-Elmer Model Lambda 9 UV-vis-NIR spectrophotometer. The reactions were continued until no visible changes were detected in the spectra. 

Topspe, N.Y. (2006) In situ FTIR A versatile tool for the study of industrial catalysts, Catal. Today, 113, 58. 

Shimizu, K.I., Kawabata, H., Maeshima, H. et al. (2000) Intermediates in the selective reduction of NO by propene over Cu-Al203 catalysts Transient in-Situ FTIR study, J. Phys. Chem. B, 104, 2885. 

Captain, D.K. and Amiridis, M.D. (1999) In Situ FTIR studies of the selective catalytic reduction of NO by C3H6 over Pt/Al203, J. Catal., 184, 377. 

Sazama, P., Capek, L., Drobna, H. et al. (2005) Enhancement of decane-SCR-N()x over Ag/alumina by hydrogen. Reaction kinetics and in situ FTIR and UV-vis study, J. Catal. 232, 302. 

Chafik, T., Kondarides, D.I. and Verykios, X.E. (2000) Catalytic reduction of NO by CO over rhodium catalysts 1. Adsorption and displacement characteristics investigated by in situ FTIR and transient-MS techniques, / Catal. 190, 446. 

Dujardin, C., Mamede, A.-S., Payen, E. et al. (2004) Influence of the oxidation state of rhodium in three-way catalysts on their catalytic performances An in situ FTIR and MS study, Top. Catal. 30-31, 347. 

Catalyst Activation Gas phase activation of supported DENs was examined using in-situ FTIR spectroscopy and FTIR spectroscopy of adsorbed CO. For in-situ dendrimer decomposition studies, the spectra were collected under a gas flow composed of 20% 02/He or 20% H2/He. The supported DEN sample was pressed into a self-supporting wafer, loaded into a controlled atmosphere IR cell, and collected as the sample background. The temperature was raised stepwise and spectra were collected at each temperature until little or no change was observed. After oxidation, the sample was reduced in 20% H2/He flow with various time/temperature combinations. The sample was then flushed with He for lhr at the reduction temperature. After cooling under He flow, a background spectrum was collected at room temperature. A 5% CO/He mixture was flowed over the sample for 15 minutes, followed by pure He. IR spectra of CO adsorbed on the catalyst surface were collected after the gas phase CO had been purged from the cell. 

The three most commonly applied external reflectance techniques can be considered in terms of the means employed to overcome the sensitivity problem. Both electrically modulated infrared spectroscopy (EMIRS) and in situ FTIR use potential modulation while polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) takes advantage of the surface selection rule to enhance surface sensitivity. 

In the EMIRS (and in situ FTIR) technique, the potential of the working electrode is changed from a base value, Vb, at which the reflectivity of the electrode is R(v)b, to a value Kw, where the reflectivity is R(v)w. Spectra are usually plotted in the form (AR/R) vs, v, where ... 

Hence, another approach is required that will enable the study of a wider range of electrochemical processes. Two other techniques are potentially capable of fulfilling this role PM-IRRAS and in situ FTIR. 

In-situ Fourier transform infrared spectroscopy. The final technique in this section concerns the FTIR approach which is based quite simply on the far greater throughput and speed of an FTIR spectrometer compared to a dispersive instrument. In situ FTIR has several acronyms depending on the exact method used. In general, as in the EMIRS technique, the FTIR-... 

Figure 2.49 Block diagram of the equipment required to perform in situ FTIR.

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