BaFe1−xNixO3 Catalysts for NOx-Assisted Diesel Soot Oxidation

Abstract

In this work, it is analyzed the effect of the partial substitution of Fe by Ni in a BaFeO3 perovskite to be used as the catalyst for NOx-assisted diesel soot oxidation. A series of BaFe1−xNixO3 (x = 0, 0.2, 0.4 and 0.8) catalysts have been synthesized by using the sol–gel method. The catalysts have been characterized by ICP-OES, XRD, XPS, O2-TPD, H2-TPR- and TEM. The catalytic activity for NO to NO2 oxidation and NOx-assisted diesel soot oxidation have been determined by Temperature Programmed Reaction experiments (NOx -TPR and Soot-NOx-TPR, respectively) and by isothermal reaction at 450 °C. Ni seems not to be inserted in the BaFeO3 perovskite and, instead of that, BaNiO3 perovskite and NiO are detected on the surface of the perovskite BaFeO3. XPS data reveal the coexistence of Fe(III) and Fe(IV) on the catalyst’s surface (being Fe(III) the main oxidation state) and the presence of oxygen vacancies. All catalysts are active for NO oxidation to NO2, showing BaFeO3 and BaFe0.6Ni0.4O3 the best catalytic performance. BaFe0.6Ni0.4O3 shows the highest proportion of nickel on surface and it combines the highest activity and stability for NOx-assisted diesel soot oxidation. Also, this catalyst presents the highest initial soot oxidation rate which minimizes the accumulation of unreacted soot during reaction.

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

“…Thus, it seems that nickel is not inserted into the BaMnO 3 perovskite structure and, instead of that, it forms two Ni-based perovskites. This fact, which was previously found for BaFe 1−x Ni x O 3 catalyst series [20][21][22][23], seems to be justified by the values of the tolerance factor (t), calculated using the ionic radius of the components of perovskites (Ba 2+ : 175 pm, Mn 3+ : 65 pm, Ni 2+ : 78 pm, and O 2− : 140 pm, corresponding to coordination numbers 12, 6, and 6 for cation A, cation B, and oxygen, respectively) [26] and shown in Table 2. So, as the t value is closer to 1 (theorical value) for BaNiO 3 than for BaMn 1−x Ni x O 3 perovskites, Ni is not inserted into the BaMnO 3 perovskite structure.…”

“…From a general point of view, the actual Ni content is very close to the nominal one, indicating that the method used for synthesis achieves the required amount of this metal. Moreover, the samples present a low BET surface area, as corresponds to mixed oxides with very low porosity development, such as perovskites [15,[19][20][21][22][23][24][25].…”

“…Recent results have revealed that these catalysts can be used for the control of pollutants generated by ICEs [17,18]. Accordingly, perovskites could be used for soot removal from diesel engines [19][20][21][22][23].…”

“…In a previous study [23], a series of BaFe 1−x Ni x O 3 (x = 0, 0.2, 0.4, and 0.8) catalysts were used to catalyze NO x -assisted diesel soot oxidation, allowing for determining the effect of the partial substitution of Fe by Ni. BaFeO 3 and BaFe 0.6 Ni 0.4 O 3 are the best catalysts, but the latter is more stable as it contains the highest proportion of Ni(II) on the surface, featuring the highest initial soot oxidation rate and the lowest amount of unreacted soot after the reaction.…”

Cerium Doping Effect in 3DOM Perovskite-Type La2−xCexCoNiO6 Catalysts for Boosting Soot Oxidation

“…To date, researchers have effectively developed an array of diverse, highly efficient catalysts for deep catalytic soot oxidation at lower temperatures, encompassing noble metals [12][13][14][15], transition metal oxides [16][17][18][19], perovskite-type oxides [20][21][22][23][24], spinel-type oxides [25][26][27], rare-earth-based materials [28][29][30], and various other materials. Noble metal catalysts, characterized by their abundant unoccupied d-orbitals, demonstrate exceptional catalytic performance and have been commercially preferred for a long time [31,32].…”