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Interfacial Impregnation Chemistry in the Synthesis of Chromium Catalysts Supported on Titania
Author(s) -
Petsi Theano,
Panagiotou George D.,
Bourikas Kyriakos,
Kordulis Christos,
Voyiatzis George A.,
Lycourghiotis Alexis
Publication year - 2011
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201000446
Subject(s) - microelectrophoresis , chemistry , adsorption , inorganic chemistry , raman spectroscopy , catalysis , potentiometric titration , chromium , ion , analytical chemistry (journal) , organic chemistry , physics , chromatography , electrophoresis , optics
The interfacial impregnation chemistry involved in the synthesis of Cr VI catalysts supported on titania is presented. The mode of interfacial deposition of the Cr VI oxo‐species at the titania/electrolyte solution interface, the interfacial species, and the local structure of the deposited species were investigated. Several methodologies based on potentiometric titrations, microelectrophoresis, and adsorption experiments were used. Modeling of the interfacial deposition based on experimental results provided an integrated picture concerning the deposition features. The interfacial species were confirmed by using laser Raman spectroscopy. The deposited CrO 4 2− , HCrO 4 − , and Cr 2 O 7 2− ions are retained above the positively charged bridging hydroxyl groups (Ti 2 OH) of the titania surface as electrostatic forces cause the formation of ion‐pairs. Each CrO 4 2− or HCrO 4 − ion is located above a bridging hydroxyl, and each Cr 2 O 7 2− ion above two bridging hydroxyl groups. Only the CrO 4 2− and HCrO 4 − ions are deposited, with a preference for the CrO 4 2− ions, at low Cr VI surface concentrations (up to 0.3 μmol Cr VI m −2 ). Cr 2 O 7 2− ions were deposited in addition to CrO 4 2− and HCrO 4 − ions at higher Cr VI concentrations. The direct probing of the interfacial species by using laser Raman spectroscopy confirmed the interfacial species determined by modeling the deposition data. The deposition model developed describes all of the experimental data (from adsorption, titration, and microelectrophoresis experiments) very well. Moreover, it accurately predicts the displacements of pzc and iep caused by the presence of these species in the solution.