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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Au and Pt Remain Unoxidized on a CeO 2 -Based Catalyst during the Water–Gas Shift Reaction

The active form of Au and Pt in CeO 2 based catalysts for the WGS reaction is an issue that although it has been widely studied remains unclear. On one hand, ionic species might be responsible of weakening the Ce-O bonds increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO 2 oxygen vacancies at the metal/CeO 2 interface might provide the active sites for an efficient reaction. In this work, by using in-situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Here, remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the pre-reduced Pt catalyst, an increase of the conversion coincided with a re-structuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt 0 , Au 0 nanoparticles exhibited a sequence of particle splitting and agglomeration whilst maintaining a zero oxidation state, even though not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic being such electrostatic interaction fundamental for a top performance in the WGS process.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeO by Materials Project

CeO is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ce is bonded to six equivalent O atoms to form a mixture of edge and corner-sharing CeO6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ce–O bond lengths are 2.49 Å. O is bonded to six equivalent Ce atoms to form a mixture of edge and corner-sharing OCe6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2O3 by Materials Project

Ce2O3 crystallizes in the trigonal P321 space group. The structure is two-dimensional and consists of one Ce2O3 sheet oriented in the (0, 0, 1) direction. Ce3+ is bonded in a distorted T-shaped geometry to three equivalent O2- atoms. All Ce–O bond lengths are 2.09 Å. O2- is bonded in a bent 120 degrees geometry to two equivalent Ce3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeO2 by Materials Project

CeO2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ce4+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Ce–O bond lengths are 2.37 Å. O2- is bonded to four equivalent Ce4+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce7O12 by Materials Project

Ce7O12 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Ce+3.43+ sites. In the first Ce+3.43+ site, Ce+3.43+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.30–2.63 Å. In the second Ce+3.43+ site, Ce+3.43+ is bonded in a distorted octahedral geometry to six equivalent O2- atoms. All Ce–O bond lengths are 2.30 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Ce+3.43+ atoms to form a mixture of corner and edge-sharing OCe4 tetrahedra. In the second O2- site, O2- is bonded to four Ce+3.43+ atoms to form a mixture of distorted corner and edge-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2O3 by Materials Project

Ce2O3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ce3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.31–2.67 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Ce3+ atoms to form OCe4 tetrahedra that share corners with six equivalent OCe6 octahedra, corners with six equivalent OCe4 tetrahedra, edges with three equivalent OCe6 octahedra, and edges with three equivalent OCe4 tetrahedra. The corner-sharing octahedra tilt angles range from 17–56°. In the second O2- site, O2- is bonded to six equivalent Ce3+ atoms to form OCe6 octahedra that share corners with twelve equivalent OCe4 tetrahedra, edges with six equivalent OCe6 octahedra, and edges with six equivalent OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce11O20 by Materials Project

Ce11O20 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are six inequivalent Ce+3.64+ sites. In the first Ce+3.64+ site, Ce+3.64+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ce–O bond distances ranging from 2.32–2.66 Å. In the second Ce+3.64+ site, Ce+3.64+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ce–O bond distances ranging from 2.34–2.56 Å. In the third Ce+3.64+ site, Ce+3.64+ is bonded to seven O2- atoms to form a mixture of distorted edge and corner-sharing CeO7 pentagonal bipyramids. There are a spread of Ce–O bond distances ranging from 2.30–2.44 Å. In the fourth Ce+3.64+ site, Ce+3.64+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.30–2.55 Å. In the fifth Ce+3.64+ site, Ce+3.64+ is bonded to seven O2- atoms to form a mixture of distorted edge and corner-sharing CeO7 pentagonal bipyramids. There are a spread of Ce–O bond distances ranging from 2.31–2.41 Å. In the sixth Ce+3.64+ site, Ce+3.64+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.29–2.46 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra. In the second O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra. In the third O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra. In the fourth O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the fifth O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the sixth O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the seventh O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the eighth O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra. In the ninth O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra. In the tenth O2- site, O2- is bonded to four Ce+3.64+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2O3 by Materials Project

Ce2O3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Ce3+ sites. In the first Ce3+ site, Ce3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.34–2.76 Å. In the second Ce3+ site, Ce3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.33–2.79 Å. In the third Ce3+ site, Ce3+ is bonded to six O2- atoms to form a mixture of distorted corner and edge-sharing CeO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Ce–O bond distances ranging from 2.29–2.59 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to four Ce3+ atoms to form distorted OCe4 trigonal pyramids that share a cornercorner with one OCe6 octahedra, corners with two equivalent OCe5 square pyramids, corners with nine OCe4 tetrahedra, corners with two equivalent OCe4 trigonal pyramids, edges with three equivalent OCe5 square pyramids, and edges with two equivalent OCe4 trigonal pyramids. The corner-sharing octahedral tilt angles are 34°. In the second O2- site, O2- is bonded to five Ce3+ atoms to form distorted OCe5 square pyramids that share corners with seven OCe4 tetrahedra, corners with two equivalent OCe4 trigonal pyramids, edges with two equivalent OCe6 octahedra, edges with two equivalent OCe5 square pyramids, edges with three OCe4 tetrahedra, and edges with three equivalent OCe4 trigonal pyramids. In the third O2- site, O2- is bonded to four Ce3+ atoms to form OCe4 tetrahedra that share corners with two equivalent OCe6 octahedra, corners with two equivalent OCe5 square pyramids, corners with four OCe4 tetrahedra, corners with six equivalent OCe4 trigonal pyramids, an edgeedge with one OCe6 octahedra, edges with two equivalent OCe5 square pyramids, and an edgeedge with one OCe4 tetrahedra. The corner-sharing octahedral tilt angles are 14°. In the fourth O2- site, O2- is bonded to four Ce3+ atoms to form OCe4 tetrahedra that share a cornercorner with one OCe6 octahedra, corners with five equivalent OCe5 square pyramids, corners with four OCe4 tetrahedra, corners with three equivalent OCe4 trigonal pyramids, edges with two equivalent OCe6 octahedra, an edgeedge with one OCe5 square pyramid, and edges with two equivalent OCe4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. In the fifth O2- site, O2- is bonded to six Ce3+ atoms to form OCe6 octahedra that share corners with six OCe4 tetrahedra, corners with two equivalent OCe4 trigonal pyramids, edges with two equivalent OCe6 octahedra, edges with four equivalent OCe5 square pyramids, and edges with six OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce5O9 by Materials Project

Ce5O9 crystallizes in the tetragonal I-4 space group. The structure is three-dimensional. there are two inequivalent Ce+3.60+ sites. In the first Ce+3.60+ site, Ce+3.60+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ce–O bond distances ranging from 2.29–2.43 Å. In the second Ce+3.60+ site, Ce+3.60+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.31 Å) and four longer (2.59 Å) Ce–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Ce+3.60+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the second O2- site, O2- is bonded to four Ce+3.60+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the third O2- site, O2- is bonded to four Ce+3.60+ atoms to form a mixture of distorted edge and corner-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeO2 by Materials Project

CeO2 is Hydrophilite-like structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ce4+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing CeO6 octahedra. The corner-sharing octahedral tilt angles are 53°. All Ce–O bond lengths are 2.27 Å. O2- is bonded in a trigonal planar geometry to three equivalent Ce4+ atoms.

36 MATERIALS SCIENCE↗