Minerals as Model Compounds for Cu/ZnO Catalyst Precursors: Structural and Thermal Properties and IR Spectra of Mineral and Synthetic (Zincian) Malachite, Rosasite and Aurichalcite and a Catalyst Precursor Mixture

Abstract

The Cu/ZnO system is a model for Cu/ZnO/Al2O3 catalysts, which are employed industrially for the synthesis of methanol. These catalysts are usually prepared from mixed basic carbonate precursors. A complex phase mixture, with constituents structurally related to the minerals rosasite andaurichalcite, is present at the industrially applied composition (Cu/Zn ≈ 70:30). Using minerals and phase‐pure synthetic samples as references, a comprehensive characterisation of such a phase mixture, including the determination of the individual compositions of the different phases, has been attempted by complementary analytical laboratory techniques (XRD, TGA, IR). The results are critically discussed in light of the complexity of the system. A thermally very stable carbonate species ― well‐known for mixed synthetic systems ― is also detected for the mineral reference samples. Significant amounts of amorphous phases are found to be present in the synthetic zincian malachite sample but not in synthetic aurichalcite or the catalyst precursor. A simplified explanation for the shift of the characteristic 20$\bar {1}$ reflection of the malachite structure as a function of Zn incorporation based on the varying average Jahn–Teller distortion of the MO6 octahedra is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Understanding the complexity of a catalyst synthesis: Co-precipitation of mixed Cu,Zn,Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments

“…In the region of 1800 to 1000 cm -1 ( Figure 8a) the asymmetric C-O stretching mode of the carbonate anions could be observed. Both samples show four bands around 1512, 1394, 1102 and 1053 cm -1 [28]. In the range of 1200-600 cm -1…”

“…The crystallinity of the formate-derived precursor was extraordinary low. The position of the 20-1 reflection of the zincian malachite phase, which is indicative of the degree of Zn incorporation into this phase [28], is near 31.2 °2 in pure malachite. For the Zn-containing precursors, a strong shift of the 20-1 reflection angles beyond 32 °2 was observed due to the incorporation of Zn in the malachite lattice.…”

Thermokinetic investigation of binary Cu/Zn hydroxycarbonates as precursors for Cu/ZnO catalysts

“…The crystalline components of the binary Cu/Zn hydroxycarbonates are related to the phases of zincian malachite [M 2 (CO 3 )(OH) 2 ] and aurichalcite M 5 (CO 3 ) 2 (OH) 6 , where M is Cu x Zn (1-x) [12,15]. The appearance of each phase depends on the Сu/Zn ratio, with a preference for zincian malachite at Zn contents lower than 30%, two-phase regime at 30 -50% and aurichalcite above 50% [20].…”

“…At the same time, the number of publications focusing on the description of the decomposition process and the influence of calcination conditions on the catalytic activity is quite limited [8,9,10,11]. Some studies [12,13] deal with the characterization of binary precursors for Cu/ZnO catalysts, which serve as a suitable model for technical ternary Cu/ZnO/Al 2 O 3 systems.…”

Methanol Steam Reforming

“…These changes occur rather step-like than gradually and are accompanied by a transient minimum in pH. The phase composition of the ageing product is mostly determined by the Cu:Zn ratio [60,72], but also by the mode of precipitation [72], and the speed of addition of the precipitating agent [73]. Typical phases obtained when going from Cu-rich to Zn-rich compositions are mal- This insight results in a simple geometrical model for the preparation of industrial Cu/ZnO catalysts comprising subsequent mesoand nano-structuring of the material (Fig.…”