Precursors of the copper-zinc oxide methanol synthesis catalysts

The coprecipitated hydroxycarbonate precursor of the methanol synthesis and shift reaction catalyst based on 30 at.% copper and 70 at.% zinc oxide, which was previously reported to be a mixture of hydrozincite Zn5(CO3)2(OH)6 and rosasite (Cu,Zn)2(CO3)(OH)2 (R. G. Herman, K. Klier, G. W. Simmons, B. P. Finn, J. B. Bulko, and T. P. Kobylinski, J. Catal. 56, 407, 1979) or a single-phase hydrozincite (G. Petrini, F. Montino, A. Bossi, and G. Gaybassi, in “Studies in Surface Science and Catalysis. Preparation of Catalysis III” (G. Poncelet, P. Grange, and P. A. Jacobs, Eds.), Vol. 16, p. 735. Elsevier, The Netherlands, 1983), is herein shown to be a single-phase aurichalcite (Cu0.3Zn0.7)5(CO3)2(OH)6. The orthorhombic B2212 aurichalcite is crystallograpically distinct from the monoclinic C2m hydrozincite, although these two compounds have the same ratio of metal ions to carbonate and hydroxyl anions. Both aurichalcite and hydrozincite are chemically and structurally distinct from the monoclinic P21a rosasite. The earlier erroneous assignments are attributed to the structural similarity of the three hydroxycarbonates in question. An energy-dispersive characteristic X-ray emission analysis of individual particles in the scanning transmission electron microscope reveals a uniform distribution of copper and zinc at the analytical concentration CuZn = 3070. Precursors with less than 30% copper consist of mixtures of aurichalcite and hydrozincite.