Co-doped LaAlO3 perovskite oxide for NOx-assisted soot oxidation

Abstract

In the framework of nowadays challenges in the automotive catalysis, directed to the mitigation of pollution caused by the emissions of internal combustion engines, a series of LaAl1-xCoxO3 perovskites were investigated with the purpose of enhancing the oxidation of soot in the presence of NOx. Perovskite oxides LaAl1-xCoxO3 (x=0; 0.25; 0.5; 0.75 and 1) were synthesized by a solgel route and characterized by different methods: X-Ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), N2-sorption, O2/NOx-temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The perovskite oxides were tested as catalysts for NO oxidation in isothermal mode and for NOx-assisted soot oxidation in temperature programmed reaction. Structural results reveal that Co is well incorporated in the perovskite structure expanding the unit cell, and doping Co may result in the distortion of the BO6 octahedra of the general ABO3 perovskite structure. An increase in Co substitution with x up to 0.75 remarkably promotes the oxidation activity, whereas total replacement of Al by Co degrades the catalytic performance. Among the prepared solids, LaAl0.25Co0.75O3 is the most active for NO oxidation, with a conversion of 78% at 320 °C, and it also exhibits the highest activity for NOxassisted soot oxidation, with a T10% of 377 °C while maintaining high NO2 production (71%). The outstanding performance of LaAl0.25Co0.75O3 is associated with the high mobility of lattice oxygen species and the role of surface adsorbed oxygen seems not to be prominent. The strong correlation of catalytic activity with NOx-TPD profiles suggests that NOx adsorption on catalyst surface is an essential step in soot oxidation. It is also shown that higher calcination temperature promotes the crystallinity of perovskite phase and leads to the improvement in the catalytic activity. The present work indicates that the prepared perovskite catalysts are competitive with noble-metal rivals for NOx-assisted soot oxidation and outperform them in NO2 production for further NOx abatement.

Promotion of A-Site Ag-Doped Perovskites for the Catalytic Oxidation of Soot: Synergistic Catalytic Effect of Dual Active Sites

“…Figures C and S5A and Table display the O 1s XPS signal. According to a previous work, three peaks located at 529.0, 531.3, and 533.4 eV could be obtained by deconvolution of the O 1s spectrum, which can be ascribed to the surface lattice oxygen (denoted as O latt ), the chemisorbed oxygen on the perovskite surface (denoted as O ads ), and the surface physical adsorption oxygen species (denoted as O surf ), respectively.…”

“…The crystal structures of all prepared perovskites were studied by XRD, as shown in Figure A. All the tested catalysts exhibited an ideal perovskite crystal structure (PDF#84-0848) with a space group of R 3̅ c . The strong and sharp diffraction peaks demonstrate the high crystal quality with a good perovskite structure …”

“…O 2 -TPD in Figure B was used to measure the oxygen adsorption and desorption capacity on the catalyst surface. The desorption peaks of oxygen at different temperatures were assigned as the physically adsorbed oxygen (O surf ) around 100 °C, the surface chemically adsorbed oxygen (O 2– and O – ) between 100 and 350 °C, the surface lattice oxygen (O latt 2– ) in the range of 350–500 °C, and the bulk O latt 2– higher than 500 °C . The intensities of the desorption peaks associated with surface O latt 2– were decreased significantly with the addition of Ag, which indicated that the number of oxygen vacancies on the catalyst surface was increased .…”

Transition Metal B-Site Substitutions in LaAlO3 Perovskites Reorient Bio-Ethanol Conversion Reactions

“…La-based perovskites have been proposed as effective catalysts for oxidative steam reforming or mild oxidation reactions [50][51][52]. Doped La-perovskites can answer environmental concerns for VOC and NOx abatement [53][54][55][56][57][58], as well as for soot oxidation in diesel exhausts [59,60]. Partial reduction of transition metal components of perovskites has provided interesting, supported catalysts for biomass hydrogenation [61,62].…”

Nickel and cobalt transfigured natural clay: a green catalyst for low-temperature catalytic soot oxidation

“…Also, the poisoning of Pt occurs very readily; hence, economically viable catalysts have been promoted to replace Pt. Consequently, as an alternative to Pt catalyst for soot oxidation, various materials have been reported, such as ceria, hafnia, zirconia, transition metal catalysts based on Co, Cu, Fe, and Mn -doping on ceria, and composition of ceria with Pr, La, etc., [5][6][7][8][9][10][11][12][13][14] which are summarized in Table S1 (ESI †). Apart from these, transition metals, rare earth oxides, and mixed oxides such as CeO 2 , SiO 2 , and Al 2 O 3 have been explored to boost soot oxidation activity.…”