Surface Characterization of Chromia for Chlorine/Fluorine Exchange Reactions

Abstract

The dismutation of CCl(2)F(2) was used to probe the effect of halogenation of chromia by Cl/F exchange reactions to find out the difference between the halogenated inactive and active catalysts. The heterogeneous reactions were performed in a continuous flow Ni reactor and also under simulated reaction conditions in a reactor where after the reaction X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) analyses are possible without air exposure of the catalyst, i.e., under so-called "in situ" conditions. The Cr(III) 2p XP spectra, which revealed multiplet splitting features and satellite emission, were used for chemical analysis by using a simple evaluation procedure which neglects this inherent complexity. Chemical analysis was also applied by using chemical state plots for Cr 3s in order to cross-check Cr 2p related results. Both ex and in situ XPS show that as soon as Cr(2)O(3) is exposed to CCl(2)F(2) at 390 degrees C fluorination as well as chlorination takes place at the catalyst surface. When the XPS surface composition reaches approximately 4 at. % fluorination and 6 at. % chlorination, maximum catalytic activity was obtained. Application of longer reaction times did not change significantly the obtained surface composition of the activated chromia. The fluorination and chlorination of chromia was further investigated by various HF and HCl treatments. The activated chromia samples and the Cr(2)O(3), Cr(OH)(3), CrF(2)OH, CrF(3) x H(2)O, alpha-CrF(3), beta-CrF(3), and CrCl(3) reference samples with well-known chemical structures were also characterized by X-ray absorption near edge structure (XANES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), pyridine-FTIR, wet chemical (F and Cl) analysis, X-ray powder diffraction (XRD), and surface area (BET) analysis. The results suggest that the formation of chromium oxide chloride fluoride species, e.g., chromium oxide halides, at the surface is sufficient to provide catalytic activity. The presence of any CrF(3) and/or CrCl(3) phases on the activated chromia samples was not found.

Fabrication and Characterization of Anodic Films onto the Type-304 Stainless Steel in Glycerol Electrolyte

“…Also, the peak centered at 713.1 eV is not clear. From the publication of Unveren et al, it could possibly be ascribed to Fe(III) hydroxide–fluoride mix compound. The BE of Cr2p 3/2 , which peaked at 576.7 eV, is close to BE of Cr 2 O 3 (575.9–576.8 eV).…”

Fluorination of dichlorodifluoromethane to synthesize tetrafluoromethane over Cr2O3–AlF3 catalyst

“…Moreover, Ü nveren et al [29] reported that the interaction of CCl 2 F 2 and surface Cr oxide could generate chromium oxide chloride species, which are also active in the reaction. Thus, the gradual interaction between CCl 2 F 2 and partial Cr 2 O 3 may result in the transfer of Cl element to the catalyst surface, and formed a few amorphous and more active chromium oxide chloride species, which could cause the initial induction period during the reaction.…”

Morphological effects of ordered Cr2O3 nanorods and Cr2O3 nanoparticles on fluorination of 2-chloro-1,1,1-trifluoroethane

“…Various fluorocarbons could be synthesized by chlorine/fluorination exchange reactions, in which Cr-based catalysts have been widely applied. These Cr-based catalysts include chromium oxides [1][2][3][4][5] and chromium-based catalysts [6][7][8][9] supported on Al 2 O 3 , AlF 3 , MgO, or MgF 2 and the deactivation of CrO x F y -AlF 3 -based catalysts in commercial processes of Cl/F exchange reaction has been investigated by Albonetti et al [10]. The performance of the Cr-based catalysts is determined by various factors such as surface area and morphologies of the Cr species.…”