Reducing the Irreducible: Dispersed Metal Atoms Facilitate Reduction of Irreducible Oxides

Abstract

Oxide reducibility is a central concept quantifying the role of the support in catalysis. While reducible oxides are often considered catalytically active, irreducible oxides are seen as inert supports. Enhancing the reducibility of irreducible oxides has, however, emerged as an effective way to increase their catalytic activity while retaining their inherent thermal stability. In this work, we focus on the prospect of using single metal atoms to increase the reducibility of a prototypical irreducible oxide, zirconia. Based on extensive self-consistent DFT+U calculations, we demonstrate that single metal atoms significantly improve and tune the surface reducibility of zirconia. Detailed analysis of the observed single atom induced reducibility allows us to attribute the enhanced reducibility to strong interactions between the metal atom and the electrons trapped in the vacancy and d−p orbital interactions between the metal atom and oxygen. This analysis enables transferring the obtained theoretical understanding to other irreducible oxides as well. The detailed understanding of how oxide reducibility can be tuned offers precise control over the catalytic properties of metal oxides.

Oxidative dehydrogenation of cyclohexene on atomically precise subnanometer Cu4−nPdn (0 ≤ n ≤ 4) tetramer clusters: the effect of cluster composition and support on performance

“…These phenomena can mirror, for example, the apparent hysteresis visible in some of the data presented in this study. The partial reduction of zirconia 49,69 or an encapsulation of the clusters by it cannot be fully excluded either. 82–84…”

“…49,68 It is to be noted that even the prototypical irreducible zirconia may undergo superficial reduction as well when hydrogen spill-over takes place or metal atoms are present on its surface. 49,69…”

Exploring the materials space in the smallest particle size range: from heterogeneous catalysis to electrocatalysis and photocatalysis

“…146 Note however that it has recently been claimed that dopant atoms can increase the reducibility of irreducible supports. 147,148 Doping, alloying and support effects on stability and catalyst performance Modification of ultrasmall clusters by doping, overcoating, changing size and composition with atomic precision or through cluster support interactions provides high-fidelity tuning knobs to control not only their stability, but their activity and, importantly, their selectivity as well. 75,116,124,132,[149][150][151][152][153][154][155][156][157] Investigation of atomically dispersed Pt/TiO 2 catalysts by pre-/postreaction scanning transmission electron microscopy and operando X-ray absorption spectroscopy-mass spectrometry under gas-phase ethanol dehydrogenation conditions under ultraviolet-visible light irradiation shows that the general effect of the reaction on initially fully oxidized (Pt IV) single-atom catalysts (SACs) is Pt reduction and aggregation.…”

“…146 Note however that it has recently been claimed that dopant atoms can increase the reducibility of irreducible supports. 147,148…”

Understanding and controlling the formation of surface anion vacancies for catalytic applications

“…23 In addition, the vacancy formation energy (E vac ) is not always experimentally obtainable, 23 which has led to many theoretical studies on anion vacancies in recent years. [24][25][26][27][28][29][30][31][32] Although many contributions toward obtaining E vac values and employing them as descriptors of catalytic performance have been reported, especially for bulk systems, only a limited number of surfaces have been investigated, and no comprehensive studies have been conducted. 2,23,31 Indeed, this is a major reason for why data-science-based approaches, which have attracted much recent attention in the fields of molecular and materials science, remain in their infancies in the heterogeneous catalysis field.…”