Roles of Surface-Active Oxygen Species on 3DOM Cobalt-Based Spinel Catalysts M_xCo_3–xO₄ (M = Zn and Ni) for NO_x-Assisted Soot Oxidation

Abstract

Co 3 O 4 is a well-known catalyst in the oxidation reaction. In such a catalyst, the geometric and electronic structures of tetrahedrally coordinated Co 2+ and octahedrally coordinated Co 3+ can be regulated by directional metal ion substitution strategy, accompanied by the modification of catalytic activity. Herein, normal and inverse cobalt-based spinel catalysts M x Co 3−x O 4 (M = Zn and Ni) with a threedimensionally ordered macroporous (3DOM) structure were successfully fabricated through the carboxy-modified colloidal crystal templating (CMCCT) method. The relationship between the dopant and activity during NO x -assisted soot oxidation was systematically studied by means of XPS, H 2 -TPR, soot-TPR, isothermal anaerobic titrations, NO-TPO, soot-TPO, and so on. The well-defined 3DOM structure for M x Co 3−x O 4 catalysts can improve the contact efficiency of soot and catalysts. 3DOM NiCo 2 O 4 exhibits high catalytic activity for soot oxidation under a loose contact mode between soot and catalyst. For instance, its T 50 and TOF values are 379 °C and 1.36 × 10 −3 s −1 , respectively. The doping of Ni to Co 3 O 4 will induce the structural distortion, improve the density of oxygen vacancies, and enhance lattice oxygen mobility. It leads to more surface-active oxygen species. A vacancy-mediated pathway of NO oxidation on the spinel catalyst is proposed according to the experimental results of in situ DRIFT spectra, in situ Raman spectra, and the theoretical knowledge of coordination chemistry of metal−NO. The catalytic performance of soot oxidation is highly related to the capacity of a catalyst in oxidizing NO to NO 2 . Therefore, indirect NO 2 -assisted mechanism is proposed for soot oxidation under an NO/O 2 /N 2 atmosphere.

Catalytic performance of the Ce-doped LaCoO3 perovskite nanoparticles

“…With the introduction of 5% Ce, the H 2 -consumption peaks progressively shifted towards lower temperature. This could be due to the insertion of Ce ion, which significantly accelerate the reduction of lattice oxygen species, thus resulting to the weakening of Co-O bond 21,34,[55][56][57] . As shown in Fig.…”

Constructing 1D/2D BiOI/ZnWO4p‐n heterojunction photocatalyst with enhanced photocatalytic removal of NO

“…The peaks at 1341, 1377, 1398, 1495, 1507, 1587 and 1715 cm −1 are consistent with nitrites (NO 2 − ) . The strong peaks at 1237, 1277, 1520, 1652 and 1687 cm −1 can be ascribed to bridging nitrates (br‐NO 3 − ), monodentate nitrates (mo‐NO 3 − ) and bidentate nitrates (bi‐NO 3 − ) (Table ) . The intensity of these bands is gradually increased in the spectra, confirming that NO is oxidized to form other nitrogen species by the active groups under light illumination.…”

Electrocatalytic Methane Oxidation Greatly Promoted by Chlorine Intermediates

“…High-resolution TEM (HRTEM) images (Figure 2 d) displayed an interplanar distance of 0.47 nm, attributed to (111) facets in Co-Ni mixed spinels. [16] Energy dispersive spectroscopy element mappings (Figure 2 e) indicated Ni and Co were evenly distributed in these nanoparticles, confirming the formation of Co-Ni mixed spinels. [17] The chemical environments of the Co-Ni mixed spinels were first investigated by X-ray photoelectron spectroscopy (XPS).…”