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

Abstract

c Cu/ZnO catalysts were prepared by coprecipitation using tetraethylammonium bicarbonate (TEA(+)HCO(3)(-)), 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 H-2 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(+)HCO(3)(-) was used as a precipitation agent, which is effective in preparing an active methanol synthesis catalyst.