The influence of impregnating pH on the postnatal and steam reforming characteristics of a Co-Ni/Al2O3 catalyst

Bimetallic alumina supported Co-Ni catalysts were prepared by impregnation under low (2) and high (8) pH values. Higher dispersion and superior metal surface area at low-pH catalyst is ascribed to the charged-induced migration of metal cations towards the grain centre. On the other hand, in the high-pH catalyst, metal deposition occurred primarily around the pore mouth, and so blockage due to carbon lay-down would be more severe as the metal sites for hydrocarbon adsorption would be more readily accessible. However, as carbon build-up continues conversion appears to drop more quickly because of rapid loss of metal sites, whereas the more uniformly dispersed metal sites in pH 2 catalyst seems to maintain a steadier conversion level due to relatively low carbon coverage. Post-mortem TOC analysis also confirmed that while pH 2 catalyst has a carbon content of 44%, pH 8 catalyst used under exactly the same S:C ratio possessed 56%.