In situ IR studies

Schematic representation of the experimental setup for an in situ IR study of the electrode-electrolyte interface is given in Fig. 1.5. From the radiation leaving the IR source only, the p-polarized light is used for the reflection-absorption experiment in...

Most results of in situ IR studies on Pt in acidic methanol solutions so far have been obtained using a relatively fast (8.5-13.6) Hz) modulation of electrode potential. As already pointed out by Bockris [27], collection of spectral data alternatively at two potentials is not appropriate for processes which are not reversible to follow the change of potential. In this study the SPAIRS version of SNIFTIRS was performed by stepping the potential from a reference potential in the anodic direction, allowing sufficient time at each potential to reach stationary conditions. 

Fig. 21 Cyclic voltammogram and corresponding in situ STM images of 3 mM 4,4 -bipyridine (44-BP) on Au(lll) in 0.05 M KCIO4, scan rate 10 mV s-1. The sizes of the STM images are 10 x 10 nm2. The following 44-BP adlayer structures have been observed in the potential regions I, II, and III (a) high coverage densely packed phase, (b) striped structure, and (c) rhombohedral phase. The corresponding molecular orientations as derived from in situ IR studies on Au(l 11) are shown in panels (d-f) [303], The pairs of peaks Pl/Pl, P2/P2, and P3/P3 indicate first-order phase transitions between the respective adlayers [304]...

The reaction conditions chosen for the in situ IR studies are often much milder (25-100 °C, 100 bar) than the process conditions (140 °C, 250 bar), which may not affect the equilibria, as the higher pressure compensates for the higher temperature. The relative rate, however, of isomerisation of 1-alkenes may increase dramatically between room temperature and 140 °C. 

Zheng, S., Jentys, A., and Lercher, J.A. (2006) Xylene isomerization with surface-modified HZSM-5 zeolite catalysts an in situ IR study. ]. Catal, 241 (2), 304-311. 

A summary of aniline N-methylation mechanistic features on Cui xZnxFe204 ferrospinel catalysts is given in Figure 27. It was possible, due to in-situ IR studies, to observe a dissociative adsorption and possible orientation of reactants on the catalyst surface, their conversion to product at low temperatures, and desorption-limited kinetics, all under conditions that are close to the reaction conditions. Although Cu is the active center for the aniline A-methylation reaction, and IR studies reveal that Zn acts as the main methyl species source. 

We have observed similar IR bands (1520, 1352 and 1295 cm ) on the Pt wire/ FSM-16 sample in an in situ IR study of the PROX reaction. From these results, we propose that the selective CO oxidation in the PROX on Pt wire/FSM-16 proceeds through the reaction of a carboxyl intermediate (COOH) on Pt nanowires (and particles) supported on FSM-16 with active OH groups (Figure 15.26). CO reacts with an active silica surface OH of FSM-16 to convert the HCOO intermediate on Pt wires and particles into CO2, thereby leading to selective CO oxidation. The subsequent H2/O2 chemisorption generates active surface OH groups near the Pt wires and particles on FSM-16. Smaller HCOO intermediates due to the smaller OH interaction on Pt particle/HMM-1 and Pt necklace wire/HMM-1 may reflect in their lower TOFs and lower CO selectivity in the PROX reaction (Figure 15.25a and b). 

Rh6(CO)i6 impregnated on basic oxides such as MgO, ZnO, CaO, La203, Nd203, or Y2O3 (Table XII). In situ IR studies of oxide-bound cluster carbonyls indicate that the CO ligand reacts with hydroxyl groups at 200-260° to form the corresponding formates, which were characterized by IR bands at 1580, 1370, and 1440 cm (114) ... 

In situ IR studies of sorbed toluene and methanol under non reactive conditions showed that both reactants assume different adsorption structures on HZSM5 and Rb-X. While methanol is stabilized as hydrogen bonded methoxonium ion in the pores of HZSM5, it is coordinatively bound via its oxygen to the cations in zeolite Rb-X. In addition to this coordinative bond, strong lateral interactions of the hydroxyl group of methanol with the basic oxygens of the lattice of zeolite Rb-X were detected. 

Yu Z, Chuang SSC (2007) In situ IR study of adsorbed species and photo-generated electrons during photo-catalytic oxidation of ethanol on TiO. J Catal 246 118... 

The approach by Dautzenberg et al. emphasizes in our opinion a valid and hitherto hardly exploited inroad to the FT kinetics. In retrospect, with the knowledge now available from surface spectroscopy, an experimental verification of the complicating factors mentioned appears desirable. This would be valuable in particular because the main conclusion, viz. a high coverage of steady-state catalysts with growing chains, has not been confirmed by the in. situ IR studies, discussed in the next section. 

To April 1987, the in-situ IR studies on the electro-oxidation of small organic molecules show that the strongly adsorbed fragments which act as poisons in these reactions are all CO species. There has been no spectroscopic evidence for the presence of COH, even for conditions of less than saturation coverage by (CO)ads. In addition, the adsorbed CO is very stable, requiring fairly high potentials for its oxidation to C02 [55]. The reader is referred to the reviews by Bewick and Pons [55] and Foley et al. [56, 69] and the references cited therein for a more detailed treatment. 

Pt(lll) [116]. Bi causes a decrease of CO oxidation [117] on Pt(lOO), which agrees with its stabilization of this adsorbate deduced from in situ IR studies [118, 119], while As has an opposite effect [119]. Both adatoms modify the CO-stripping process with a small catalytic effect observed at very positive potentials (0.7 V). The catalysis has been ascribed to the adatom-mediated oxygen transfer with a possible electronic effect for As [119]. Similar behavior is observed with Sb, which decreases the adsorption of CO on Pt(lOO) and Pt(lll) surfaces by removing the twofold bridging geometry, as deduced from the relative vco band intensities [76]. At the saturation Sb coverage, only linear CO is observed. 

Friedel-Crafts acylation was studied and kinetic and spectroscopic evidence was reported for acylium ions as the key reactive intermediate. The acetyl cation was detectable (absorption band at 2308 cm ) in low concentration by in situ IR studies, during the acetylation of toluene. The 4-tert-butylbenzoyl cation was also observed as a weak band at 2283 cm during the course of an acylation of mesitylene. 

Figure 25.3. Heatable IR ceU for in situ IR studies in dense and SCCO2.

Jollie D.M., Harrison P.G. An in situ IR study of the thermal decomposition of trifiuoroacetic acid. 

Xu, J., Mojet, B.L., vanOmmen, J.G., andLefferts, L. Propane selective oxidation on alkaline earth exchanged zeolite Y Room temperature in situ IR study. Phys. Chem. Chem. Phys. 2003, 5, 4407-4413. 

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