Cu‐Based Catalyst Resulting from a Cu, Zn, Al Hydrotalcite‐Like Compound: A Microstructural, Thermoanalytical, and In Situ XAS Study1. Issue 13 (24th February 2014)

• Record Type: Journal Article
• Authors: Kühl, Stefanie; Tarasov, Andrey; Zander, Stefan; Kasatkin, Igor; Behrens, Malte
• Is Part Of: Chemistry. Volume 20:Issue 13(2014)
• Page Start: 3782
• Page End: 3792
• Publication Date: 2014-02-24
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201302599
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>A Cu‐based methanol synthesis catalyst was obtained from a phase pure Cu, Zn, Al hydrotalcite‐like precursor, which was prepared by co‐precipitation. This sample was intrinsically more active than a conventionally prepared Cu/ZnO/Al<sub>2</sub>O<sub>3</sub> catalyst. Upon thermal decomposition in air, the [(Cu<sub>0.5</sub>Zn<sub>0.17</sub>Al<sub>0.33</sub>)(OH)<sub>2</sub>(CO<sub>3</sub>)<sub>0.17</sub>]<bold>⋅</bold><italic>m</italic>H<sub>2</sub>O precursor is transferred into a carbonate‐modified, amorphous mixed oxide. The calcined catalyst can be described as well‐dispersed "CuO" within ZnAl<sub>2</sub>O<sub>4</sub> still containing stabilizing carbonate with a strong interaction of Cu<sup>2+</sup> ions with the Zn–Al matrix. The reduction of this material was carefully analyzed by complementary temperature‐programmed reduction (TPR) and near‐edge X‐ray absorption fine structure (NEXAFS) measurements. The results fully describe the reduction mechanism with a kinetic model that can be used to predict the oxidation state of Cu at given reduction conditions. The reaction proceeds in two steps through a kinetically stabilized Cu<sup>I</sup> intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl<sub>2</sub>O<sub>4</sub> spinel‐like matrix. Due to the strong interaction of Cu and the oxide matrix, the small Cu particles (7 nm) of this catalyst are partially embedded leading to lower absolute activity in comparison with a catalyst comprised of less‐embedded particles. Interestingly, the exposed Cu surface area exhibits a superior intrinsic activity, which is related to a positive effect of the interface contact of Cu and its surroundings.</p> </abstract>