ACID LEACHED RANEY COPPER-CATALYSTS FOR THE WATER-GAS SHIFT REACTION

Raney copper catalysts were prepared by leaching a ternary alloy of co mposition Cu(24.8) Zn(25.2) A1(48.3) in nitric and perchloric acid. Th e acid leaching process was examined as a function of acid strength an d total leach time. Similarities in acid and caustic leaching were obs erved. For example, during the first hour of leaching in both media, a luminium was extracted at a faster rate than the zinc component of the alloy. For leaching times between 1 and 3 h, aluminium was precipitat ed 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 desig ned experiments were used to determine the effect of the preparation v ariables alloy particle size, solvent strength and solvent/metal ratio on the BET surface area of the nitric and perchloric acid leached Ran ey copper catalyst. These variables were selected because they signifi cantly influence the water-gas shift activity and stability of caustic extracted Raney copper catalysts. For both acids, 2(3) factorially de signed 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 sampl es was lower than that observed for caustic extracted Raney copper cat alysts. The results demonstrated that the leach process is less contro llable when acid is used for the preparation of catalytic Raney copper for the water-gas shift reaction. (C) 1998 Elsevier Science B,V. All rights reserved.