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Metal-organic framework templated Pd/CeO₂@N-doped carbon for low-temperature CO oxidation.

ABSTRACT: A new Pd/Ce based metal-organic framework is designed and synthesized as a self-sacrificial template for fabrication of an efficient catalyst for CO oxidation. The catalyst obtained by thermal annealing at 700 °C (Pd/CeO₂@NC-700) is composed of N-doped carbon with embedded Pd and CeO₂ nanoparticles, which are highly dispersed and closely connected in the N-doped carbon; the high Pd loading (33.7 wt%) and the coupling between Pd and the CeO₂ phase synergistically boost the CO oxidation performance. The Pd/CeO₂@NC-700 catalyst exhibits a 100% conversion temperature of 89 °C and excellent long-term stability. By combining structural characterization with density functional theory calculations, two possible CO oxidation pathways of TPB and TOP are revealed, in which the adsorbed O₂ directly dissociates to O* atoms and activates CO* molecules. The transfer of O* between Pd and Ce (TPB) or Pd and Pd (TOP) facilitates the formation of intermediates and finally results in the production of CO₂. This work provides a new insight into the development of novel efficient catalysts for CO oxidation based on metal-organic frameworks.

SUBMITTER: Fan W

PROVIDER: S-EPMC9419610 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Metal-organic framework templated Pd/CeO2@N-doped carbon for low-temperature CO oxidation.

Fan Weidong W Liu Dongyuan D Wang Xia X Liu Xiuping X Cao Dongwei D Fan Lili L Huang Zhaodi Z Guo Wenyue W Sun Daofeng D

Nanoscale advances 20191231 2

A new Pd/Ce based metal-organic framework is designed and synthesized as a self-sacrificial template for fabrication of an efficient catalyst for CO oxidation. The catalyst obtained by thermal annealing at 700 °C (Pd/CeO2@NC-700) is composed of N-doped carbon with embedded Pd and CeO2 nanoparticles, which are highly dispersed and closely connected in the N-doped carbon; the high Pd loading (33.7 wt%) and the coupling between Pd and the CeO2 phase synergistically ...[more]

PMID: 36133235

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Project description:CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO2 with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation. The oxides were prepared using microwave-assisted sol-gel synthesis to improve catalyst's performance for the reaction of interest. The effect of heteroatoms on the physicochemical properties (structure, morphology, porosity, and reducibility) of the binary oxides M-Ce-O was meticulously investigated and correlated to their CO oxidation activity. It was found that the catalytic activity (per gram basis or TOF, s-1) follows the order Cu-Ce-O > Ce-Co-O > Ni-Ce-O > Mn-Ce-O > Fe-Ce-O > Ce-Zn-O > CeO2. Participation of mobile lattice oxygen species in the CO/O2 reaction does occur, the extent of which is heteroatom-dependent. For that, state-of-the-art transient isotopic 18O-labeled experiments involving 16O/18O exchange followed by step-gas CO/Ar or CO/O2/Ar switches were used to quantify the contribution of lattice oxygen to the reaction. SSITKA-DRIFTS studies probed the formation of carbonates while validating the Mars-van Krevelen (MvK) mechanism. Scanning transmission electron microscopy-high-angle annular dark field imaging coupled with energy-dispersive spectroscopy proved that the elemental composition of dopants in the individual nanoparticle of ceria is less than their composition at a larger scale, allowing the assessment of the doping efficacy. Despite the similar structural features of the catalysts, a clear difference in the Olattice mobility was also found as well as its participation (as expressed with the α descriptor) in the reaction, following the order αCu > αCo> αMn > αZn. Kinetic studies showed that it is rather the pre-exponential (entropic) factor and not the lowering of activation energy that justifies the order of activity of the solids. DFT calculations showed that the adsorption of CO on the Cu-doped CeO2 surface is more favorable (-16.63 eV), followed by Co, Mn, Zn (-14.46, -4.90, and -4.24 eV, respectively), and pure CeO2 (-0.63 eV). Also, copper compensates almost three times more charge (0.37e-) compared to Co and Mn, ca. 0.13e- and 0.10e-, respectively, corroborating for its tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy), apart from the oxidation state of the elements, revealed a heteroatom-ceria surface interaction (Oa species) of different extents and of different populations of Oa species.

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Dataset Information

Metal-organic framework templated Pd/CeO₂@N-doped carbon for low-temperature CO oxidation.

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Metal-organic framework templated Pd/CeO<sub>2</sub>@N-doped carbon for low-temperature CO oxidation.

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