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Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2 materials

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Abstract

The cerium(III) hydroxide chloride Ce(OH)2Cl crystallises directly as a polycrystalline powder from a solution of CeCl3·7H2O in poly(ethylene) glycol (Mn = 400) heated at 240 °C and is found to be isostructural with La(OH)2Cl, as determined from high-resolution synchrotron powder X-ray diffraction (P21/m, a = 6.2868(2) Å, b = 3.94950(3) Å, c = 6.8740(3) Å, β = 113.5120(5)°). Replacement of a proportion of the cerium chloride in synthesis by a second lanthanide chloride yields a set of materials Ce1−xLnx(OH)2Cl for Ln = La, Pr, Gd, Tb. For La the maximum value of x is 0.2, with an isotropic expansion of the unit cell, but for the other lanthanides a wider composition range is possible, and the lattice parameters show an isotropic contraction with increasing x. Thermal decomposition of the hydroxide chlorides at 700 °C yields mixed-oxides Ce1−xLnxO2−δ that all have cubic fluorite structures with either expanded (Ln = La, Gd) or contracted (Ln = Pr, Tb) unit cells compared to CeO2. Scanning electron microscopy shows a shape memory effect in crystal morphology upon decomposition, with clusters of anisotropic sub-micron crystallites being seen in the precursor and oxide products. The Pr- and Tb-substituted oxides contain the substituent in a mixture of +3 and +4 oxidation states, as seen by X-ray absorption near edge structure spectroscopy at the lanthanide LIII edges. The mixed oxide materials are examined using temperature programmed reduction in 10%H2 in N2, which reveals redox properties suitable for heterogeneous catalysis, with the Pr-substituted materials showing the greatest reducibility at lower temperature.

Graphical abstract: Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2 materials

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Article information


Submitted
05 Oct 2020
Accepted
12 Oct 2020
First published
13 Oct 2020

This article is Open Access

Dalton Trans., 2020, Advance Article
Article type
Paper

Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2 materials

A. J. A. Dunn, J. W. Annis, J. M. Fisher, D. Thompsett and R. I. Walton, Dalton Trans., 2020, Advance Article , DOI: 10.1039/D0DT03435E

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