Identifying Oxygen Activation/Oxidation Sites for Efficient Soot Combustion over Silver Catalysts Interacted with Nanoflower-Like Hydrotalcite-Derived CoAlO Metal Oxides

Abstract

Catalytic oxidation is an effective way to eliminate soot pollution emitted from diesel engines. However, the origination and specific location of active oxygen species are still unclear over noble metal catalysts because of the complex gas (oxygen)–solid (catalyst)–solid (reactant) reaction systems. Herein, we report the high catalytic performance of the nanoflower-like hydrotalcite-derived CoAlO-supported Ag catalyst synthesized by a facile hydrothermal method for soot combustion. Our characterization results demonstrate that metallic Ag nanoparticles (NPs) are highly dispersed on the CoAlO support because of their interactions through electron donation from Co to Ag species. The isotopic 18O2 adsorption/desorption results reveal that gaseous oxygen is readily adsorbed and dissociated on these electron-enriched Ag NPs rather than oxygen vacancies of the CoAlO support. From the 18O2 isothermal soot oxidation results, we newly discover that surface oxygen species adsorbed on Ag sites directly participate in soot oxidation, while those on the CoAlO support only play a negligible role. The kinetic results show that the strengthened Ag–CoAlO interactions can promote not only the quantity but also the intrinsic activity of oxygen species on Ag sites for soot combustion. In addition, the nanoflower-like morphology of the catalyst can greatly improve the soot–catalyst contact efficiency to further enhance the catalytic performance. Our work brings an insight into the identification of oxygen activation/oxidation sites involved in soot oxidation over Ag catalysts supported on hydrotalcite-derived CoAlO metal oxides by systematic isotopic and kinetic investigations, which is beneficial to the rational design of other related catalytic systems.

Boosting the Long-Term Stability of Hydrotalcite-Derived Catalysts in Hydrogenolysis of Glycerol by Incorporation of Ca(II)

“…As shown in Figure a, the Co 6 -Al 3 _HT catalyst presented two hydrogen consumption peaks extending from 200 to 400 °C and 450 to 870 °C, respectively. The weak peak extending from 200 to 400 °C could be attributed to the more easily reducible cobalt oxide species (CoO x ) at the surface of the catalyst, while the broad peak arising from 450 to 870 °C with a maximum at 751 °C corresponded to the further reduction of Co­(II) formed in the first reduction step and/or present in the spinel. , On the other hand, TPR profiles of Co 6‑x -Ca x -Al 3 _HT samples also showed two similar hydrogen consumption peaks extending from 200 to 400 °C and 450 to 800 °C, respectively (Figure b–f). The first reduction step was related to the reduction of more easily reducible CoO x at the surface, and the second (with a maximum at 700 °C) was attributed to the reduction of Co­(II) species.…”

Developing a thermally stable Co/Ce-Sn catalyst via adding Sn for soot and CO oxidation

“…As is well known, the higher the Ce 3+ and Co 2+ concentration in these samples, the more oxygen defects are generated ( Zhao et al., 2019 ; Liu et al., 2009 ). Therefore, the surface oxygen defects associating with the Co 2+ and Ce 3+ of the 3%Co/CeO 2 catalyst gradually disappeared, with the increase of aging temperature ( Zhao et al., 2019 ; Cui et al., 2020 ; Wang et al., 2018 ; Ren et al., 2019 ). Figure S10 showed that the O 1s spectra of all catalysts can be deconvoluted into two kinds of O species, with the peak at higher binding energy being attributed to the surface oxygen species (O α ) and the peak at lower binding energy being ascribed to the lattice oxygen species (O β ) ( Xu et al., 2020 ; Ren et al., 2019 ; Sellers-Anton et al., 2020 ).…”

Preparation of K Modified Three-Dimensionally Ordered Macroporous MnCeOx/Ti0.7Si0.3O2 Catalysts and Their Catalytic Performance for Soot Combustion

“…Nowadays, post-treatment technology is considered to be one of the effective ways to eliminate soot particles. However, since the spontaneous combustion temperature of soot particles (550-650 • C) is higher than the exhaust temperature of the diesel engine (150-450 • C), the development of new catalysts with low cost and excellent catalytic performance is one of the main challenges in the application of post-treatment technology [5,6].…”