Activity of molybdenum and tungsten oxycarbides in hydrodenitrogenation of carbazole leading to isomerization secondary reaction of bicyclohexyl. Results using bicyclohexyl as feedstock

Abstract

The catalytic activities of bulk tungsten and molybdenum oxycarbides, (W2C and Mo2C) have been specifically studied in the isomerization occurring during the hydrodenitrogenation (HDN) of carbazole. The two catalysts have been characterized by several physico-chemical techniques such as X-Ray Diffraction, H2-temperature programmed reduction analysis – H2-TPR, elementary chemical analysis and specific surface area measurement by BET method. Metallic sites and acid sites (Lewis and Brönsted ones) were respectively titrated using CO and iso-propylamine chemisorptions. The main detected isomers of bicyclohexyl (BCH) were ethylbicyclo[4.4.0]decane (EBC[4.4.0]Decane), and n-hexylcyclohexane (C6CH) coming from a ring opening reaction. W2C showed higher isomerization activity than Mo2C, in both pure BCH isomerization study and in the secondary reaction of BCH isomerization during the carbazole HDN process. The addition of 50 ppm of sulfur had a significant impact on the increase of the isomerization activity over both oxycarbides during the HDN of carbazole. The presence of a significant amount of isomerization products and their nature indicated that the present bulk oxycarbides are bifunctional catalysts with both metallic sites and acid sites (Brönsted and Lewis).