BaTi1−xCuxO3 perovskites: The effect of copper content in the properties and in the NOx storage capacity

Abstract

Please cite this article as: V. Albaladejo-Fuentes, F.E. López-Suárez, M.S. Sánchez-Adsuar, M.J. Illán-Gómez, −x Cu x O 3 perovskites: the effect of copper content in the properties and in the NOx storage capacity., Applied Catalysis A, General (2014), http://dx.doi.org/10.1016/j.apcata. 2014.09.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. XRD and Raman spectroscopy results indicate that all the copper containing catalysts present a distortion of the original tetragonal structure due to the incorporation of copper into the lattice.The XPS and H 2 -TPR results reveal that the copper catalysts, except for BaTiCu0.5 catalyst, present two copper species (with different electronic interaction with the perovskite) and active surface oxygen species. Additionally, it seems that the fraction of copper with a strong electronic interaction with the perovskite or incorporated into the perovskite structure increases with the copper content.The active sites created on the BaTi 1-x Cu x O 3 perovskite surface bring to the catalysts activity for the NO to NO 2 oxidation and for the NOx adsorption. The NOx storage capacity increases with the copper content and reaches a limit for the BaTiCu2 catalyst (300 µmol/g, at 420ºC) which is within the range of the values reported for the noble metal-based catalysts.

Tailoring the properties of BaTi0.8Cu0.2O3 catalyst selecting the synthesis method

“…As it was previously reported, the high fraction of segregated phases formed during the sol-gel synthesis of the copper catalysts [37] proves that copper was incorporated into the perovskite structure. For Cu-BAKOH, Cu-BASOH, Cu-BNKOH, Cu-BNSOH, and Cu-BBOH catalysts, only the diffraction peaks corresponding to CuO are observed.…”

“…Using the sol-gel method (Cu-BTOsg), an increase of the crystal size is observed due to the incorporation of copper into the perovskite structure, whilst when the hydrothermal route is employed (Cu-BBOH), the crystal size decreases suggesting a lower crystallinity. As it was previously reported [37], by comparing the FWHM of the (2 0 0) and (1 1 1) XRD peaks, it is possible to determine if a perovskite presents a cubic or a tetragonal structure based on the (2 0 0)/(1 1 1) FWHM ratio. (This value is higher than 1 for a tetragonal perovskite structure due to the (0 0 2) peak of the tetragonal structure can appear overlapped with the (2 0 0) peak [48,49].)…”

“…Thus, the two contributions of the Cu-BTOsg catalyst can be ascribed to: i) copper with stronger interaction with support or incorporated into the structure (CuL at high eV) and ii) copper with weaker interaction with the support or supported copper (CuS at low eV) [37]. The Cu XPS spectra of the Cu-BBOH catalyst is the expected for supported copper oxide [30].…”

“…BaTiO3 and BaTi0.8Cu0.2O3 were prepared using a sol-gel method based on the Pechini-type reaction route modified to be used in an aqueous media [37]. In brief, the titanium isopropoxide (Ti) was hydrolysed and the resulting specie was solved in an aqueous solution of citric acid (CA) (Ti:CA = 1:2) and hydrogen peroxide (Ti:H2O2 = 2:1), forming the citrate-peroxo-titanate (IV) complex.…”

“…In a previous preliminary study [37], titanium was partially substituted by copper [38,39] in the BaTiO3 perovskite structure, showing the resulting BaTi1-xCuxO3 perovskites a high activity for NOx storage, which was attributed to the presence of oxygen vacancies created on the catalyst surface as a consequence of the copper incorporation into the structure. It was also concluded that for BaTi0.8Cu0.2O3 catalyst the NOx storage capacity increases with the copper content until a certain limit is reached.…”