TY - JOUR

T1 - Cu-based catalyst resulting from a Cu,Zn,Al hydrotalcite-like compound

T2 - A microstructural, thermoanalytical, and in situ XAS study

AU - Kühl, Stefanie

AU - Tarasov, Andrey

AU - Zander, Stefan

AU - Kasatkin, Igor

AU - Behrens, Malte

PY - 2014/3/24

Y1 - 2014/3/24

N2 - 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 2 O 3 catalyst. Upon thermal decomposition in air, the [(Cu 0.5 Zn 0.17 Al 0.33 )(OH) 2 (CO 3 ) 0.17 ]×mH 2 O precursor is transferred into a carbonate-modified, amorphous mixed oxide. The calcined catalyst can be described as well-dispersed "CuO" within ZnAl 2 O 4 still containing stabilizing carbonate with a strong interaction of Cu 2+ 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 I intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl 2 O 4 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.

AB - 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 2 O 3 catalyst. Upon thermal decomposition in air, the [(Cu 0.5 Zn 0.17 Al 0.33 )(OH) 2 (CO 3 ) 0.17 ]×mH 2 O precursor is transferred into a carbonate-modified, amorphous mixed oxide. The calcined catalyst can be described as well-dispersed "CuO" within ZnAl 2 O 4 still containing stabilizing carbonate with a strong interaction of Cu 2+ 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 I intermediate. With reduction, a nanostructured catalyst evolves with metallic Cu particles dispersed in a ZnAl 2 O 4 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.

KW - copper

KW - heterogeneous catalysis

KW - kinetics

KW - methanol

KW - X-ray absorption spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=84896391912&partnerID=8YFLogxK

U2 - 10.1002/chem.201302599

DO - 10.1002/chem.201302599

M3 - Article

AN - SCOPUS:84896391912

VL - 20

SP - 3782

EP - 3792

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

SN - 0947-6539

IS - 13

ER -