In-situ characterization of water-gas shift catalysts using time-resolved X-ray diffraction

Abstract:

Time-resolved X-ray diffraction (XRD) has emerged as a powerful technique for studying the behavior of heterogeneous catalysts (metal oxides, sulfides, carbides, phosphides, zeolites, etc.) in-situ during reaction conditions. The technique can identify the active phase of a heterogeneous catalyst and how its structure changes after interacting with the reactants and products (80 K < T < 1200 K; P < 50 atm). In this article, we review a series of recent works that use in-situ time-resolved XRD for studying the water-gas shift reaction (WGS, CO + H<inf>2</inf>O → H<inf>2</inf> + CO<inf>2</inf>) over several mixed-metal oxides: CuMoO<inf>4</inf>, NiMoO<inf>4</inf>, Ce<inf>1-x</inf>Cu<inf>x</inf>O<inf>2-δ</inf> and CuFe<inf>2</inf>O<inf>4</inf>. Under reaction conditions the oxides undergo partial reduction. Neutral Cu⁰ (i.e. no Cu¹⁺ or Cu²⁺ cations) and Ni⁰ are the active species in the catalysts, but interactions with the oxide support are necessary in order to obtain high catalytic activity. These studies illustrate the important role played by O vacancies in the mechanism for the WGS. In the case of Ce<inf>1-x</inf>Cu<inf>x</inf>O<inf>2-δ</inf>, Rietveld refinement shows expansions/contractions in the oxide lattice which track steps within the WGS process: CO(gas) + O(oxi) → CO<inf>2</inf>(gas) + O(vac); H<inf>2</inf>O(gas) + O(vac) → O(oxi) + H<inf>2</inf>(gas). © 2008 Elsevier B.V.

Año de publicación:

2009

Keywords:

• X-Ray diffraction
• Hydrogen production
• water-gas shift reaction
• In-situ characterization

Fuente:

scopus

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