Cobalt–molybdenum interaction in oxidic precursors of zeolite-supported HDS catalysts

Abstract

Two methods of synthesis of oxidic precursors of zeolite-supported HDS catalysts have been compared—the co-impregnation of cobalt nitrate and ammonium heptamolybdate, and the one-step impregnation of the Anderson cobaltomolybdate anion. ²⁷Al MAS NMR and Raman spectroscopic characterisations have shown that in the first case, the Anderson aluminomolybdate anion is formed, whereas the cobalt Anderson entity is preserved in the second case. Mo and Co K-edges EXAFS measurements have shown that in the first case no cobalt–molybdenum interaction is observed, unlike in the second case. It has finally been seen that a calcination–rehydration treatment gives the same final product for both preparations, with the presence of the aluminomolybdate anion, to the detriment of the cobalt–molybdenum interaction.