Fluorinated hydrotreatment catalysts. Acidity and carbon deposition on fluorine–nickel–molybdenum/γ-alumina catalysts

Abstract

Using a model coking procedure and measuring the carbon content on fluorinated Ni–Mo/γ-Al₂O₃ catalysts we found that fluorination decreased markedly the extent of coke formation on the surface of the nickel-promoted MoO₃/γ-Al₂O₃ catalysts. The influence of fluorination on the acidity of the oxidic precursors of the title catalysts was also studied. Both temperature-programmed desorption of ammonia and an FTIR study of the chemisorbed pyridine were used to obtain information on the Lewis and total acidity. It was found that both decreased upon fluorination but different trends with F^– content were followed. An excellent relationship found between the total amount of desorbed ammonia and the amount of carbon formed on the catalyst surface demonstrated that the extent of the coke formation is controlled by the total acidity of the oxidic precursors.

Finally, sulfur analysis confirmed previous findings, namely that the fluorination inhibits the reduction and/or the sulfidation of Mo^VI species as well as the sulfidation of the supported-nickel species.