Adsorption formic acid

Methanol, Formaldehyde, and Formic Acid Adsorption/Oxidation on a Carbon-Supported Pt Nanoparticle Fuel Cell Catalyst A Comparative Quantitative OEMS Study... 

Li, W.K., Gong, X.Q., Lu, G., and Selloni, A. (2008) Different reactivities of Ti02 polymorphs comparative DFT calculations of water and formic acid adsorption at anatase and brookite Ti02 surfaces. Journal of Physical Chemistry C, 112 (17), 6594-6596. 

In reviews on formic acid decomposition, Mars and coworkers194,198 wrote that the formation and decomposition of formate anions were monitored by infrared spectroscopy. These studies were carried out by Fahrenfort, Sachtler, and coworkers188,193 for the case of formates on metals produced by formic acid adsorption—Cu, Ni, Pd, Rh, Pt, and Zn and in the case of metal oxides, Hirota et al. investigated ZnO,187,189,190,197 while Scholten et al. studied MgO.199,200 The infrared... 

Madix and coworkers—facile formate formation/decomposition over Cu (110). In 1979-1981, Madix and coworkers219 220 226 studied formic acid adsorption and decomposition over Cu(l 10) and they showed facile formate production. TPD studies indicated that formate decomposed to yield C02 and H2 at temperatures as... 

Bowker et al.301 published spectroscopic and kinetic studies of formic acid adsorption on Cu(110). They observed that, at —73 °C, the sticking coefficient is high (0.9) but becomes low at 27 °C (0.1). The adsorption state switches from monodentate (—73 °C) to bidentate at 27 °C. 

Interest in studying formic acid adsorption on metals by XPS and UPS was stimulated largely by its use as a probe molecule for investigating the role of the electronic factor in heterogeneous catalysis as in the work of Schwab (70), Dowden and Reynolds (71), Eley and Leutic (72), and Fahren-fort et al. (73). The advantages of XPS and UPS are fourfold. 

Temperature programmed desorption studies of formic acid decomposition by metals was reviewed recently by Madix (7d) the significance of formate formation is paramount to the discussion. This is also apparent in the recent electron energy loss spectra of formic acid adsorption on Cu(lOO) reported by Sexton (77). 

The break-point temperature in dehydration (above which the rate was temperature insensitive) matched the maximum temperature for dehydrogenation, suggesting that a common intermediate exists for each reaction, and that the product selectivity is determined by interactions with other molecules and the surface. Above 650 K, the catalytic dehydration channel dominates, but the rate-determining step changes above 700 K. Below 700 K, the reaction rate is nearly independent of the partial pressure of formic acid (ca. 0.2 order). Above 700 K, the rate of the reaction is essentially independent of temperature, implying that reaction is limited by formic acid adsorption and dissociation thus, above 700 K, the rate becomes first-order with respect to the partial pressure of formic acid. Higher pressures of formic acid over the crystal surface should therefore increase the transition temperature - this behavior was observed by Iwasawa and coworkers, and the turnover frequency for catalytic dehydration approached the collision frequency of formic acid at high... 

Tanner RE, Sasahara A, Liang Y, Altman El, Onishi H (2002) Formic acid adsorption on anatase TiO (001)-(l X 4) thin films studied by NC-AFM and STM. 1 Phys Chem B 106 8211... 

Vittadini A., Selloni A., Rotzomger F. P. and Gratzel M. (2000), Formic acid adsorption on dry and hydrated Xi02 anatase (101) surfaces by DFX calculations , J. Phys. Chem. B. 104, 1300-1306. 

The first is from the early pioneering work of Madix and co-workers (Ying and Madix, 1980 Bowker and Madix, 1981b) and concerns formic acid adsorption on Cu(110). If labelling is combined with TPD studies, the mechanism of reaction can be elucidated completely. Figure 23 shows the desorption pattern observed after dosing formic acid on to the surface predosed with oxygen. The steps in the mechanism are as follows... 

Fig. 23. TPD experiment for deuterated formic acid adsorption on Cu(l10) (dashed lines) anti on Cu (110) with prcdoscd oxygen (solid lines). From Bowker and Madix (1981b).

In this way the energy of activation of the formic acid adsorption, is found to be 6.2 kcal/mole, whereas the activation energy for the decomposition of the intermediate, Edtcomp> is 15.8 kcal/mole. 

It is also possible that the formic acid adsorption was studied on a Ni-H layer instead of on free Ni sites. In their preparation technique, Eischens et al. (63, 66) cool down their sample to room temperature... 

Formic acid adsorption onto Pt requires either multiple sites for the dehydration pathway or (Mily one to activate C-H bond for the dehydrogenation pathway [46]. The onset of formic acid electrooxidation has been shown to be effected by both Pt particle size and reactant cmicentration (Fig. 3.5B, C). The dehydration pathway is favored on both the polycrystalline and 8.8 run Pt catalyst surfaces during the forward scan, as is apparent from the low currents and high overpotentials. The higher potentials are required to form the activated hydroxyl complexes required to oxidize the passivating CO moieties to CO2, similar to methanol. The formic acid... 

Wieckowski A, Sobkowski J, Zelenay P (1977) The potential dependence and kinetics of formic acid adsorption on rhodium electrodes. J Electroanal Chem Interfacial Electrochem... 

Abstract Direct formic acid fuel cells offer an alternative power source for portable power devices. They are currently limited by unsustainable anode catalyst activity, due to accumulation of reaction intermediate surface poisons. Advanced electrocatalysts are sought to exclusively promote the direct dehydrogenation pathway. Combination and structure of bimetallic catalysts have been found to enhance the direct pathway by either an electronic or steric mechanism that promotes formic acid adsorption to the catalyst surface in the CH-down orientation. Catalyst supports have been shown to favorably impact activity through either enhanced dispersion, electronic, or atomic structure effects. 

Breiter MW. The nature of formic acid adsorption at platinum electrodes in perchloric acid solution. Electrochim Acta 1965 10 503-8. 

Nunzi F, De Angelis F (2011) DFT investigations of formic acid adsorption on single-wall Ti02 nanotubes effect of the surface curvature. J Phys Chem C 115(5) 2179-2186... 

Diagne, C., Idiiss, H., Pepin, I., Hindermann, J.P., and Kiennemann, A. Temperature-programmed desorption studies on Pd/Ce02 after methanol and formic acid adsorption and carbon monoxide-hydrogen reaction. Appl. Catal 1989, 50, 43-53. 

The dependence of formic acid adsorption on cpi has been investigated in some detail [75]. Considerable adsorption of formic acid is retained in the hydrogen region of potentials, and this is probably due to the possibility of reaction between formic acid and adsorbed hydrogen with simultaneous formation of an adsorption product ... 

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