LaMnO3+ı which is an environment-friendly and inexpensive material has been previously used as catalyst
in Post-Plasma Catalysis (PPC) in the total oxidation of trichloroethylene (TCE) which is a solvent
widely used in dry cleaning and degreasing processes. It has been shown that the process efficiency
increases in moist air (RH = 18%).The issue we want to address herein is the effect of water on the location
of chlorine at the surface of the catalyst as chlorine is able to alter the catalyst structure, activity
and stability. Therefore, a combined Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) and
X-ray Photoelectron Spectroscopy (XPS) study has been carried out on the fresh LaMnO3+ı catalyst (LM)
and used catalysts after performing PPC with TCE diluted in dry synthetic air (LM0) or with industrial
air containing water (LM18; 18 stands for the Relative Humidity) and CO2 (about 560 ppmv) at a temperature
of 150 ◦C. XPS and ToF-SIMS results both show the presence of chlorine on the tested catalysts
whose amount increases by exposure of the catalyst to the reactive mixture in dry synthetic air. XPS
results reveal that chlorine is present as both chloride ion and covalent chlorine on LM0 while organic
chlorinated residues are absent on LM18 catalyst. ToF-SIMS study indicates that lanthanum excess as
oxide(hydroxide) partially covering the perovskite mainly transforms into LaOCl and to a minor extent
into LaCl3. Extent of Mn chlorination seems to be favored over LM0 having a higher MnClx
±/MnOCl± ionic
ratio compared to LM18. Furthermore ToF-SIMS clearly identifies C1 chlorinated organic ions, mainly
CH2Cl+ and CHCl2
−, on LM0 which may contribute to the XPS Cl organic component. From the combined
ToF-SIMS and XPS results it is found that water delays the surface degradation extent of the perovskite
into related (oxy)(hydroxy)chlorinated inorganic phases by less molecular chlorine and related chlorine
species on the catalyst surface. A reaction scheme of Cl removal over LaMnO3+ı emphasing the role of
water is given taking into account the detection of ToF-SIMS ions representative of the successive Mn
intermediate states. As a consequence water allows tuning the degradation pathways of the main intermediate
of the reaction, dichloroacetyl chloride (DCAC), which decomposes to give phosgene, HCCl3 and
CCl4 by a successive Cl incorporation over (oxy)(hydroxy)chorinated perovskite or/and Mn species while
COx species are likely formed over the perovskite.
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