Stable amorphous georgeite as a precursor to a high-activity catalyst

Hydroxycarbonate minerals such as zincian malachite and aurichalcite are well known precursors to catalysts for methanol-synthesis and low-temperature water–gas shift reactions; here, a supercritical antisolvent method is used to prepare highly stable georgeite—a hydroxycarbonate mineral that has hitherto been ignored because of its rarity, but which is found to be a superior catalyst precursor. Copper and zinc form an important group of hydroxycarbonate minerals widely used as precursors for industrially important catalysts. The catalyst precursors are usually obtained through a co-precipitation method that introduces the catalyst poison Na+ and involves transient formation of georgeite, a highly unstable and therefore rare and poorly known member of this mineral family. Simon Kondrat et al. now show that copper/zinc hydroxycarbonates with low Na+ content can be produced through supercritical anti-solvent precipitation, including stable georgeite that can be processed into highly active catalysts. This finding highlights the value of advanced synthesis methods in accessing unusual mineral phases, and that there remains room for exploring established industrial catalyst development. Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored1—georgeite. The first three of these minerals are widely used as catalyst precursors2,3,4 for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions5,6,7, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase2,3,8,9,10 is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite11; with few exceptions12 it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.