Cu‐Based Catalyst Resulting from a Cu,Zn,Al Hydrotalcite‐Like Compound: A Microstructural, Thermoanalytical, and In Situ XAS Study

Abstract

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/Al2O3 catalyst. Upon thermal decomposition in air, the [(Cu0.5Zn0.17Al0.33)(OH)2(CO3)0.17]⋅mH2O precursor is transferred into a carbonate-modified, amorphous mixed oxide. The calcined catalyst can be described as well-dispersed "CuO" within ZnAl2 O4 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 ZnAl2 O4 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.

Cu/Zn/Al/Zr catalysts via phase-pure hydrotalcite-like compounds for methanol synthesis from carbon dioxide

“…Hydrotalcite-like compounds (HTlcs) with the general formula of [M 1Àx 2+ M x 3+ (OH) 2 ] x+ (A nÀ ) x/n ÁmH 2 O, where M 2+ and M 3+ are the divalent cation and trivalent cation respectively, are a typical component of the complex phase mixture in conventionally prepared precursor materials [14,15]. In addition, HTlcs with a wide variety of mono-to tetravalent metal cations have been among the most investigated catalyst precursors for the remarkable properties of the final catalysts [16][17][18][19]. In our previous work, we presented a series of promoted Cu/Zn/Al catalysts with promising catalytic performance in the CO 2 hydrogenation to methanol obtained from hydrotalcite-like (HTl) precursors [11,12,20].…”

Impact of the synthesis route of supported copper catalysts on the performance in the methanol synthesis reaction

“…The interface area between the metal particles and the support is dependent on the preparation route [33]. It might be larger in case of precipitation due to incomplete segregation [34][35][36]. During reaction the interface area might change due to a change in particle size, particle shape or support structure [28,37].…”

Coprecipitation: An excellent tool for the synthesis of supported metal catalysts – From the understanding of the well known recipes to new materials

“…At this composition the Zn:Al ratio was close to 1:2 and the oxide matrix tended to form ZnAl 2 O 4 [13]. The resulting catalyst showed a different microstructure than the zincian malachite-derived industrial Cu/ZnO/(Al 2 O 3 ) catalyst [11].…”

“…Herein, it is shown how the lessons learned from the industrial recipe can be applied to synthesize new materials through co-precipitation of different precursor compound in various catalyst systems. This work reviews our recent results obtained on Cu/ZnO-based catalysts [10][11][12][13] as well as supported Pd [14], intermetallic Pd 2 Ga [15][16][17] and Ni [18] catalysts with a focus on co-precipitated layered double hydroxide (LDH) precursors.…”