Copper Catalysts Supported on Barium Deficient Perovskites for CO Oxidation Reaction

Abstract

Mixed oxides with perovskite-type structure (ABO3) present interesting physico-chemical properties to be used as catalyst for atmospheric pollution control. In this work, a series of CuX/Ba0.7MnO3 catalysts (being x: 0, 4, 8 and 12 wt%) has been synthesized, characterized and tested for CO oxidation reaction. All the catalysts were active for CO oxidation in the two reactant mixtures tested: low CO mixture (0.1% CO and 1% O2 in He) and near stoichiometric mixture (1% CO and 1% O2 in He). Copper-free perovskite is the most active catalyst in the less demanding conditions (0.1% CO and 1% O2), as it presents the highest amount of oxygen vacancies working as active sites. However, at higher CO concentrations (1% CO in near stoichiometric mixture), copper-containing catalysts were more active than the perovskite support because, due to the saturation of the oxygen vacancies of perovskites, CuO seems to participate as active site for CO and O2 activation. Cu4/Ba0.7MnO3 and Cu12/Ba0.7MnO3 are more active than Cu8/Ba0.7MnO3 catalyst, since they present a larger amount of active sites on surface. These two copper-containing catalysts present a high stability and recyclability during the reaction at 300 °C in an ideal near stoichiometric mixture (1% CO and 1% O2).

Ni-BaMnO3 Perovskite Catalysts for NOx-Assisted Soot Oxidation: Analyzing the Effect of the Nickel Addition Method

“…From the soot-TPR profiles shown in Figure 10, the temperature to achieve 50% soot conversion (T 50% ) was obtained and included in Table 7, where the selectivity to CO 2 (calculated by Equation ( 4)) is also featured. As expected, based on the soot-TPR profiles, both catalysts show a lower T 50% value and a higher selectivity to CO 2 than the uncatalyzed reaction (blank) and than BMN2E (see data in Table 4), with BMN2H presenting the lowest T 50% and the highest CO 2 selectivity, as expected since it has more surface active sites that favor the total soot oxidation [21][22][23]41]. This is because BMN2H presents a lower NiO average crystal size than M5 (see XRD results, Table 5), so there is a higher number of active sites for soot oxidation.…”

“…From these conversion profiles, the temperature to achieve 50% soot conversion (T50%) was determined and is included in Table 4, where the selectivity to CO2 (calculated by Equation ( 4)) is also featured. As expected, a higher selectivity to CO2 and a lower T50% value is found for all samples than for uncatalyzed reactions (blank in figure) [21][22][23]41]. BMN2E and BMN4E present a lower T50% value and a higher selectivity to CO2 than BME as nickel samples present additional active sites for soot oxidation.…”

“…The BaMn 1−x Ni x O 3 (x = 0, 0.2 and 0.4) samples were obtained by the sol-gel method [19][20][21][22][23]25,36,41,45,46] using citric acid and EDTA as complexing agents. Briefly, 40 mL of a solution of EDTA (Sigma-Aldrich, 98.5% purity) at 60 • C (in a 1:2 Mn: EDTA molar ratio) was prepared, followed by the addition of barium nitrate (Ba(NO 3 ) 2 , Sigma-Aldrich, 99.0% purity), manganese(II) nitrate tetrahydrate (Mn(NO 3 ) 2 •4 H 2 O, Sigma-Aldrich, 99.0% purity), and nickel(II) nitrate hexahydrate (Ni(NO 3 ) 2 •6 H 2 O, Panreac, 98.0% purity) as metal precursors, and finally, citric acid (C 6 H 8 O 7 , Sigma-Aldrich, 99.0% purity) was incorporated in the same molar ratio than of EDTA (1:2, Mn: citric acid).…”

Ba0.9A0.1MnO3 (A = Ce, La, Mg) Perovskite-Type Mixed Oxides: Effect of Partial Substitution of Ba on the Catalytic Performance for the Oxidation of CO in Simulated Automobile Exhaust Conditions

“…The incorporation of metals with different oxidation states by the partial substitution of A and/or B cations leads to structural defects, such as anionic or cationic vacancies, or modifications in the oxidation state of the B metal (usually a transition metal) [12,18,24,27], that could significantly enhance the catalytic activity [28]. According to previous results [14,22,29], manganese-based perovskites are promising catalysts for CO oxidation reactions, as this metal presents atomic orbitals with the appropriate symmetry and energy levels for CO and O 2 activation. Thus, for Mn(III), the electronic configuration presents three electrons in the t 2g orbitals and one in the e g orbitals, which allows effective interaction with CO molecules.…”

“…As using noble metal-based catalysts for CO oxidation is limited by its prohibitive cost [11,12], the challenge is the design of efficient (i.e., with high activity and with long-term stability) noble-metal free catalysts (or with very low content) that adhere to the present and future legislation for automotive emissions [13]. Thus, developing a new generation of catalysts for CO oxidation in automobile exhaust conditions is imperative [14]. So, to achieve this purpose, the first step is to reduce the amount of noble metals in the catalytic formulations by using supported catalysts, in which the role of support (in the case of catalytically active supports) is not only the stabilization of the metallic particles by minimizing or avoiding their sintering [15], but also providing additional active sites for the reaction.…”