Effect of the order of potassium introduction on the texture and activity of Mo/Al2O3 catalysts in water gas shift reaction

The effect of deposition and order of potassium introduction on the texture and activity of Mo/gamma-Al2O3 catalysts in water gas shift (WGS) reaction was investigated. The samples were synthesised by incipient wetness impreg nation of the carrier with aqueous solutions of the corresponding salts fol lowed by drying and calcination after each deposition step. The prepared ca talyst precursors were sulphided at 400 degrees C for 2 h with 6% H2S in H- 2 before testing in WGS reaction in a glass flow apparatus at 400 degrees C under atmospheric pressure. The results show that potassium deposition alone on the bare gamma-Al2O3 (s ample K/Al2O3) decreases the specific surface after calcination by blocking the constrictions between the pores in the primary porous texture. Ln the WGS reaction conditions part of the pores are deblocked and a redistributio n in the pore volumes occurs. The deposition of the Mo (sample Mo/Al2O3) also results in a decrease in bo th specific surface and total pore volume with respect to the bare support. However after catalytic activity test no substantial changes in its textur e were observed, The addition of K to the Mo (sample KMo/Al2O3) leads to nonuniformity in di stribution of molybdenum-oxygen entities due to partial migration of the Mo Ox species to the external surface. The specific surface is not changed dur ing the reaction test. The deposition of Mo on K/Al2O3 contributes to the uniform distribution of oxomolybdenum species in the porous texture of the support. This uniformity is preserved to a high extent in the catalytic reaction as well. The activ ity in the synthesised samples in the WGS reaction decreases in the order M oK/Al2O3 > Mo/Al2O3 > KMo/Al2O3. (C) 2000 Elsevier Science B.V. All rights reserved.