Elsevier

Journal of Rare Earths

Volume 39, Issue 4, April 2021, Pages 434-439
Journal of Rare Earths

Lattice expansion and smaller CuOxCeO2−δ particles formation by magnesium interaction for low temperature CO oxidation

https://doi.org/10.1016/j.jre.2020.07.005Get rights and content

Abstract

A series of magnesia doped CuOxCeO2−δ catalysts were prepared by co-precipitation followed by impregnation method and investigated for CO oxidation. The manuscript is devoted to explaining the role of MgO for the formation of active species on the CuOxCeO2−δ surface. The improvement in catalytic activity is ascribed to the formation of various active species due to the interaction of magnesia with CuOxCeO2−δ. The catalysts were characterized by PXRD, N2 adsorption, H2-TPR, XPS, SEM, EDS and HRTEM techniques. The Mg doped catalyst shows lattice expansion of ceria due to the formation of smaller Ce3+ species with oxygen vacancies. The Mg–O bond also takes part in CO activation and oxidation, which results in the increase of CO oxidation. The Mg doped CuOxCeO2−δ catalyst shows improvement in low temperature activity compared with the CuOxCeO2−δ.

Graphical abstract

The doping of MgO increases the lattice expansion in CuOxCeO2−δ catalyst due to the formation of more Ce3+ species, which leads to the improvement in low temperature CO oxidation.

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Introduction

The copper supported on ceria has been widely studied for the CO oxidation, water–gas shift reaction, diesel soot removal, and wastewater treatment, etc.1, 2, 3 Cu also supplies the oxygen by forming a solid solution with Ce and or the separate nanorods.4 The improvement in CO oxidation activity of CuOxCeO2−δ was observed due to the oxygen vacancies, facile redox properties of Cu and Ce, oxygen storage capacity, and presence of Cu+ species.5,6 However, the low temperature oxidation activity could be improved by modifying oxygen vacancies, redox and adsorption properties of CuOxCeO2−δ catalyst. The addition of the third metal was improved due to the acidic–basic sites, mobility of lattice oxygen, oxygen vacancies, Cu, Ce interactions and surface properties of CuOxCeO2−δ.7, 8, 9 Fe, Cu and Ni doped CoOCeO2 showed an increase in the oxygen storage capacity, lattice to surface oxygen mobility and adsorbed oxygen. The improvement in these properties was responsible for the increase in propene and CO oxidation activity compared with the CoCe at lower temperature.10 Au–Ag supported MgO donates the electron to the active (Ag–Au) metal and consequently favours the oxidation of n-octanol by improving the metal support interaction.11 The doping of rare earth metal like La and Sm increased the reducibility of Cu.9 Mg doping increased the adsorption properties of Pt/CeO2 with active sites.12 However, the increase in oxygen vacancies was observed in MnCe solid solution due to the Mg doping.13

Mg doping in Ce increases the dispersion of Cu and surface area of the catalyst.8 However, the role of Mg doping in CuCe for different physico chemical properties like metal support interaction, oxygen vacancies and the formation of active species for low temperature CO oxidation is ambiguous.

The basic Mg acts as an electron donor and used for various applications such as Fischer-Tropsch reaction, steam reforming of methane, water-gas shift reaction, HC-SCR and many organic transformations.11,14, 15, 16 In our previous work, Mg doped MnCe was reported for the improvement in metal support interaction, oxygen vacancies, and responsible for the oxidation of simulated diesel engine exhaust at lower temperature.13 The present study devoted to the fundamental understanding of Mg for improvement in CuCe properties for CO oxidation. The various weight percents of Mg doped CuCe catalysts were prepared and investigated for low temperature CO oxidation. The catalytic activity was correlated to the physico chemical properties and studied here in detail.

Section snippets

Catalyst synthesis

The co-precipitation method was used to prepare the CuOxCeO2−δ (Cu/Ce = 0.15/0.85 mol/mol, O/Ce = 2−δ) catalyst. Furthermore, Mg was impregnated on CuOxCeO2−δ catalyst. In a typical procedure, 2.8 g of copper nitrate (99.5% pure, Loba Chemie) and 27.8 g of cerium nitrate (99.9% pure, Loba Chemie) were dissolved in 100 mL of distilled water. The aqueous solution of 10% w/v sodium hydroxide solution was added in above transparent solution with continuous stirring. Furthermore, the catalyst was

Phase identification and surface area study

The powder X-ray diffraction patterns of CuCe and Mg doped CuCe are shown in Fig. 1. The standard XRD peaks were observed at 2θ 28.36°, 33.28°, 47.37° and 58.94° (JCPDS, 43-1002), corresponding to the cubic fluorite structure of ceria. The inset graph shows the shift of ceria (111) from 2θ = 28.36° to 28.34°, 28.31°, 28.22° and 28.12° for 2 wt%, 4 wt%, 6 wt% and 8 wt% Mg doped CuCe catalyst, respectively. The shift of ceria XRD peaks is suggesting the distortion/expansions in ceria lattice. The

Conclusions

Various mass percentage of Mg doped CuCe catalysts were investigated for CO oxidation. The optimum loading of magnesium (6 wt%) over CuCe shows improvement in CO oxidation activity at lower temperature. The lattice expansion of ceria is observed, which is attributed to the synergistic interaction of CuCe with Mg. The formation of less amount of rod indicates that the Mg interaction with CuCe also decreases the particle size. The synergistic interaction between Mg with CuCe is responsible for

Acknowledgement

Science and Engineering Research Board, DST, Delhi, India is acknowledged for financial support as an early career research award (ECR/2016/000823). Prof. G.D. Yadav, ICT acknowledged for TPR study.

References (25)

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Foundation item: Project supported by the Science and Engineering Research Board, DST, Delhi, India (ECR/2016/000823).

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