Quantitative analysis of the reactivity of formate species seen by DRIFTS over a Au/Ce(La)O2 water–gas shift catalyst: First unambiguous evidence of the minority role of formates as reaction intermediates

Abstract

(2007). Quantitative analysis of the reactivity of formate species seen by DRIFTS over a Au/Ce(La)O2 water-gas shift catalyst: First unambiguous evidence of the minority role of formates as reaction intermediates. Journal of Catalysis, 247(2)(2), 277-287. DOI: 10.1016DOI: 10. /j.jcat.2007 Published in: Journal of Catalysis Queen's University Belfast -Research Portal: Link to publication record in Queen's University Belfast Research Portal General rights Copyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. AbstractThe reactivity of the species formed at the surface of a Au/Ce(La)O 2 catalyst during the water-gas shift (WGS) reaction were investigated by operando diffuse reflectance Fourier transform spectroscopy (DRIFTS) at the chemical steady state during isotopic transient kinetic analyses (SSITKA). The exchanges of the reaction product CO 2 and of formate and carbonate surface species were followed during an isotopic exchange of the reactant CO using a DRIFTS cell as a single reactor. The DRIFTS cell was a modified commercial cell that yielded identical reaction rates to that measured over a quartz plug-flow reactor. The DRIFTS signal was used to quantify the relative concentrations of the surface species and CO 2 . The analysis of the formate exchange curves between 428 and 493 K showed that at least two levels of reactivity were present. "Slow formates" displayed an exchange rate constant 10-to 20-fold slower than that of the reaction product CO 2 . "Fast formates" were exchanged on a time scale similar to that of CO 2 . Multiple nonreactive readsorption of CO 2 took place, accounting for the kinetics of the exchange of CO 2 (g) and making it impossible to determine the number of active sites through the SSITKA technique. The concentration (in mol g −1 ) of formates on the catalyst was determined through a calibration curve and allowed calculation of the specific rate of formate decomposition. The rate of CO 2 formation was more than an order of magnitude higher than the rate of decomposition of formates (slow + fast species), indicating that all of the formates detected by DRIFTS could not be the main reaction intermediates in the production of CO 2 . This work stresses the importance of full quantitative analyses (measuring both rate constants and adsorbate concentrations) when investigating the role of adsorbates as potential reaction intermediates, and illustrates how even reactive species seen by DRIFTS may be unimportant in the overall reaction scheme.

Influence of the catalyst loading on the activity and the CO selectivity of supported Ru catalysts in the selective methanation of CO in CO2 containing feed gases

“…During the reaction experiments, 400 scans were co-added for one spectrum. The intensities were evaluated in KubelkaMunk units, which are linearly related to the adsorbate concentration [31] (for exceptions see [32]). Background subtraction and normalization of the spectra were performed by subtracting spectra recorded in a flow of N 2 directly after catalyst conditioning.…”

The Effect of Precipitants on Ce-La Solid Solution Prepared from Mixed Rare Earth Chloride by a Co-Precipitation Method

“…Figure 2 presents the XRD patterns of the CL samples. Except CL-Urea, for all of the CL samples, a single diffraction peak placed at 2θ = 10° indicates the presence of RE 8 (OH) 20 Cl 4 ·nH 2 O (Re=Ce, La) [33,34]. For CL-Na, CL-Na-R and CL-NaH-R samples, the diffraction peak placed at 2θ = 32° is attribute to the residual NaCl, which was not be washed clean [35].…”

“…These newly generated defects are expected to induce more number of surface active oxygen species and improve the rate of diffusion of bulk oxygen to the surface and exchange of oxygen with the environment thereby progress in the catalytic performance [18]. The oxygen vacancies also helped ceria to create a strong metal-support interaction, and promote the dispersion of noble metals [19,20]. Comparing to pure ceria, the advantage of CL were found in many catalytic applications, for example soot oxidation [6,21], CO oxidation [22][23][24], methane oxidation [25,26], steam reforming of methane [27] and water-gas shift reaction [28][29][30].…”

Preparation, Characterization and Optimization of High Surface Area Ce-La-Cu Ternary Oxide Nanoparticles

“…Ce-Mn-Al for soot oxidation [2], Ce-Cu-Zr for CO removal from hydrogen-rich gas [3] and catalyst deep oxidation of benzene [4], Ce-Zr-Nd for gasoline engine exhaust reduction [5], Ce-Cu-V for carbon black oxidation [6], Ce-Co-Zr for methane dry reforming [7], Ce-Au-La for water gas shift reactions [8], Ce-NiLa for partial oxidation of methane [9], Ce-Ca-Mn for CO2 oxidative coupling of methane [10], Ce-Zr-Al as an oxidation agent [11], and Ce-Ni-Zr for hydrogen storage [12] have been proposed. Given the importance of ternary oxide combinations, cerium-lanthanum-copper ternary oxide was studied in this research.…”