Improving the Performance of BaMnO3 Perovskite as Soot Oxidation Catalyst Using Carbon Black during Sol-Gel Synthesis

Abstract

A series of BaMnO3 solids (BM-CX) were prepared by a modified sol-gel method in which a carbon black (VULCAN XC-72R), and different calcination temperatures (600 °C–850 °C) were used. The fresh and used catalysts were characterized by ICP-OES, XRD, XPS, FESEM, TEM, O2-TPD and H2- TPR-. The characterization results indicate that the use of low calcination temperatures in the presence of carbon black allows decreasing the sintering effects and achieving some improvements regarding BM reference catalyst: (i) smaller average crystal and particles size, (ii) a slight increase in the BET surface area, (iii) a decrease in the macropores diameter range and, (iv) a lower temperature for the reduction of manganese. The hydrogen consumption confirms Mn(III) and Mn(IV) are presented in the samples, Mn(III) being the main oxidation state. The BM-CX catalysts series shows an improved catalytic performance regarding BM reference catalyst for oxidation processes (NO to NO2 and NO2-assisted soot oxidation), promoting higher stability and higher CO2 selectivity. BM-C700 shows the best catalytic performance, i.e., the highest thermal stability and a high initial soot oxidation rate, which decreases the accumulation of soot during the soot oxidation and, consequently, minimizes the catalyst deactivation.

Analyzing the role of copper in the soot oxidation performance of BaMnO3-perovskite-based catalyst obtained by modified sol-gel synthesis

“….1 in the Appendix A), indicate that, as observed in the absence of copper [25], most of the carbon black has been efficiently removed during the synthesis as the percentage of remaining carbon black ranges from 6% for BMC3-C600 to 1% for BMC3-C850 (see data in Table A.1 in the Appendix A).…”

“…[26]. As observed for BM-CX catalysts series [25], the use of carbon black allows the synthesis of perovskite-like mixed oxides (BaMnO 3 hexagonal PDF number: 026-0168, denoted by the ICDD) at lower temperatures than the conventional sol-gel method [26]. Additionally, it is observed that the formation of the BaMnO 3 polytype, the main crystal phase in BMC3 [26], is hindered in presence of carbon black.…”

“…Among other use, these solids are potential substitutes of PGM-based catalysts [21][22][23][24], highly used in the current automotive exhausts to remove the pollutants before being emitted to the atmosphere. 43 Previous results of the authors [25] reveal that the use of a modified sol-gel synthesis seems to improve the chemical and physical properties of the BaMnO 3 perovskite and, for hence, the catalytic activity for NO to NO 2 conversion and for diesel soot oxidation. The use of carbon black during sol-gel synthesis allows a decrease in the calcination temperature to obtain a perovskite-like structure from 850ºC to 600ºC and, consequently, the sintering effects decreased, and an enhanced catalytic performance is observed.…”

“…This fact is due to the enhancement of initial soot oxidation rate which allows a reduction in the carbon deposition and, hence, the catalyst deactivates more slowly than the copper-free perovskite (BaMnO 3 ) [26]. 55 Therefore, the aim of this paper is to analyse the effect of the modified sol-gel synthesis (using carbon black and different calcination temperatures [25]) combined with the partial substitution of manganese by copper [26] in the chemical and physical properties of the BaMnO 3 perovskite. Furthermore, the catalytic activity of synthetized catalysts for NO to NO 2 conversion and, for diesel soot oxidation is also analysed.…”

“…Finally, the dried solid is calcined at 150ºC (1ºC/min) for 1h, and at 850ºC (5ºC/min) for 6h. 74 The modified sol-gel synthesis follows the steps of the conventional sol-gel synthesis above described but adding carbon black (Vulcan XC-72R) with a 1:1 (carbon black: BaMn 0.7 Cu 0.3 O 3 ) mass ratio [25]. Then, the mixture is vigorously agitated for 1 h, and after drying the mixture at 90ºC for 48h, the solid is calcined at 150ºC (1ºC/min) for 1h, and at different temperatures ranging from 600ºC to 950ºC (5ºC/min) for 6h.…”