Adsorption FTIR spectroscopy

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. 

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. 

The most essential question is why the CO-free sites are secured for H2 adsorption and oxidation. Watanabe and Motoo proposed a so-called bifunctional mechanism originally found at Pt electrodes with various oxygen-adsorbing adatoms (e.g., Ru, Sn, and As), which facilitate the oxidation of adsorbed COad at Pt sites [Watanabe and Motoo, 1975a Watanabe et al., 1985]. This mechanism has been adopted for the explanation of CO-tolerant HOR on Pt-Ru, Pt-Sn, and Pt-Mo alloys [Gasteiger et al., 1994, 1995], and recently confirmed by in sim FTIR spectroscopy [Yajima et al., 2004]. To investigate the role of such surface sites, we examined the details of the alloy surface states by various methods. 

For environmental reasons, reaction (Eqn. 21) (NO -> N2) should be promoted, N20 having a dramatic greenhouse gas effect. The different steps of reaction (Eqn. 23) have been investigated in detail, mainly by FTIR spectroscopy [61-63], One of the possible intermediate is isocyanate. NCO species could be formed on the metal and migrate on the support, which may explain the large differences observed when Rh is supported on different oxides (alumina, silica, zirconia, ceria-alumina, etc.). However, the main step should be the dissociative adsorption of NO ... 

The acidic character of 5A zeolite as a function of the calcium content has been explored by different techniques propylene adsorption experiments, ammonia thermodesorption followed by microgravimetry and FTIR spectroscopy. Propylene is chemisorbed and slowly transformed in carbonaceous compounds (coke) which remain trapped inside the zeolite pores. The coke quantities increase with the Ca2+ content. Olefin transformation results from an oligomerization catalytic process involving acidic adsorption sites. Ammonia thermodesorption studies as well as FTIR experiments have revealed the presence of acidic sites able to protonate NH3 molecules. This site number is also correlated to the Ca2+ ion content. As it has been observed for FAU zeolite exchanged with di- or trivalent metal cations, these sites are probably CaOH+ species whose vas(OH) mode have a spectral signature around 3567 cm"1. 

Acidity of both zeolites was investigated by adsorption of ammonia, pyridine, d3-acetonitrile and pivalonitrile ((CH3)3CCN) used as probe molecules followed by FTIR spectroscopy. All samples were activated in a form of self-supporting wafers at 450 °C or 550 °C under vacuum for 1 h prior to the adsorption of probe molecules. 

The NH4-Beta-300 (Zeolyst International, number denote Si02/Al203 molar ratio) was transformed to corresponding proton form using a step calcination procedure at 500 °C. H-Beta-300 was partially modified with Fe by repeated ion-exchange method (Fe(III)nitrate). The surface areas as well as acidities (Bronsted and Lewis acid sites) of Fe-Beta (iron content - 0.1 wt %) were determined by nitrogen adsorption and pyridine desorption at 250, 350 and 450 °C using FTIR spectroscopy [6]. 

Leon, C. R Kador, L. Peng, B. Thelakkat, M. 2006. Characterization of the adsorption of ru-bpy dyes on mesoporous Ti02 films with UV-Vis, Raman, and FTIR spectroscopies. J. Phys. Chem. B 110 8723-8730. 

The conclusions apply to the information before subtracting the spectra at the no adsorption condition. The upshot of all these considerations is that one has to be careful when using FTIR spectroscopy to see that the information is indeed surface information. One of the most encouraging ways of doing this is to look at the frequency of a peak as a function of electrode potential. If the information is truly coming from adsorbed substances, there will usually be a slight variation of the peak with potential. However, this is only confirmatory, and not a necessary characteristic of the information. 

Titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy are two techniques which have seldom been applied to study reactions at the solid-liquid interface. In this paper, we describe these two techniques and their application to the investigation of salicylate ion adsorption in aqueous goethite (a-FeOOH) suspensions from pH 4 to 7. Evidence suggests that salicylate adsorbs on goethite by forming a chelate structure in which each salicylate ion replaces two hydroxyls attached to a single iron atom at the surface. 

The interaction of adsorbed reactants (phenol and methanol adsorbed separately and coadsorbed) and possible reaction products of phenol methylation with the Cul-xCoxFe204 system has been studied at temperatures between lOOoC and 350oC and probed by in situ FTIR spectroscopy. The spectra of adsorbed methanol, phenol and methylated products on catalyst surface, at lOOoC, did not possess much changes compared to the spectra of pure components that indicated the molecular adsorption of species on catalyst surface. The remarkable changes in the spectra occur, above 100°C due to the chemisorption of substrates, were observed and correlated with the observed reaction trend. 

A detailed investigation of aniline N-methylation on Cui xZnxFc204 was carried out through in situ FTIR spectroscopy. The reactants (aniline and methanol) and possible products (NMA, DMA and o-toluidine) were adsorbed on the catalysts and analyzed [106,107]. Adsorption of methanol indicated a dissociative chemisorption as methoxy species on catalyst surface at 100°C. As the temperature increased, oxidation of methoxy species to formaldehyde to dioxymethylene to formate species was observed, and above 300°C complete oxidation takes place to CO, CO2 and H2. Indeed methanol alone on Cui xZnxFc204 and Cui.xCoxFc204 behaves in a similar way [79,107]. 

The adsorption and reduction of N03 ions at Au and Pt electrodes was studied by in situ fourier transform infrared (FTIR) spectroscopy [55]. Possible adsorption geometries were suggested for adsorbed nitrate ions and for nitrite ions formed by reduction. 

Applying in situ infrared spectroscopy and STM, Cai et al. [253] have studied adsorption of pyridine on Au(lll) electrodes from aqueous NaCl04 solutions. It has been found that pyridine molecule is flatly adsorbed on the surface at negative potentials. Its molecular plane rises up as the applied potential and surface concentration increase. Moreover, orientation of pyridine molecule changed with the applied STM potential. Ikezawa et al. [243] have used in situ FTIR spectroscopy to investigate adsorption of pyridine on Au(lll), Au(lOO),... 

In situ subtractively normalized interfacial FTIR spectroscopy has been employed [254] to study adsorption of pyridine on the Au(llO) electrode surface. The compound adsorbed via the nitrogen atom and the tilting angle decreased progressively with the increasing electrode potential, as it appeared from the IR data. 

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