Use of tetraethylammonium bicarbonate as a precipitation agent on the preparation of coprecipitated Cu/ZnO catalysts

Abstract

Cu/ZnO catalysts were prepared by coprecipitation using tetraethylammonium bicarbonate (TEA+HCO3−), and their properties and methanol synthesis activities were compared to those of the catalysts prepared using Na+HCO3− usually employed for commercial Cu/ZnO/(Al2O3) catalysts. When washed fully, TEA+- and Na+-based precursors showed typical zincian malachite (zM) without any other structures, and both catalysts obtained after calcination and H2 reduction exhibited the similar specific copper surface area and, in turn, the similar methanol productivity. Since this result explains that TEA+ does not affect zM structure if Cu,Zn precipitate is fully washed, no washed and less washed TEA+- and Na+-based precursors were prepared. It was interesting that all TEA+-based catalysts exhibited the similar methanol productivity irrespective of the washing efficiency whereas Na+-based catalyst containing more residual Na+ showed the smaller copper surface area and lower methanol productivity (i.e., linear correlation between the two parameters). This resulted from the inhibiting effect of Na+ on the degree of Cu2+ substitution by Zn2+ and the formation of high-temperature carbonate, consequently leading to a lower catalytic activity. These negative effects of Na+ were absent or lessened when TEA+HCO3− was used as a precipitation agent, which is effective in preparing an active methanol synthesis catalyst.