Acid leached Raney copper catalysts for the water–gas shift reaction

Abstract

Raney copper catalysts were prepared by leaching a ternary alloy of composition Cu(24.8) Zn(25.2) Al(48.3) in nitric and perchloric acid. The acid leaching process was examined as a function of acid strength and total leach time. Similarities in acid and caustic leaching were observed. For example, during the first hour of leaching in both media, aluminium was extracted at a faster rate than the zinc component of the alloy. For leaching times between 1 and 3 h, aluminium was precipitated from solution after extended exposure to caustic and acid solution. The major copper phase for the air dried, acid leached Raney catalyst was elemental copper, whereas for the caustic leached sample, CuO was the major phase present in the extracted product. Statistically designed experiments were used to determine the effect of the preparation variables alloy particle size, solvent strength and solvent/metal ratio on the BET surface area of the nitric and perchloric acid leached Raney copper catalyst. These variables were selected because they significantly influence the water–gas shift activity and stability of caustic extracted Raney copper catalysts. For both acids, 2 3 factorially designed experiments showed no main effects or two factor interactions. The BET and specific copper surface areas of the acid leached samples were at least 5 and 38 times lower, respectively, than the equivalent caustic leached catalysts. Under the experimental conditions evaluated, the water–gas shift activity and stability of the acid leached samples was lower than that observed for caustic extracted Raney copper catalysts. The results demonstrated that the leach process is less controllable when acid is used for the preparation of catalytic Raney copper for the water–gas shift reaction.