Catalytic performance of platinum doped tungsten carbide in simultaneous hydrodenitrogenation and hydrodesulphurization
Résumé
The simultaneous hydrodesulphurization (HDS) and hydrodenitrogenation (HDN) reactions of refractory model compds. were performed for the first time over tungsten carbide doped with platinum before and after prepn. (0.3%). It was then compared to that of a pure non-modified W2C. The model compds. were 4,6-dimethyldibenzothiophene (4,6-DMDBT) and carbazole. The catalysts were characterized by x-ray diffraction. The surface properties were detd. by N2 BET sp. surface area and chemisorption of CO. Addn. of platinum before synthesis of carbide decreased the uptake of CO chemisorption, but did not change significantly the sp. surface area and the crystallog. structure of tungsten carbide--β-W2C. Addn. of platinum after prepn. of carbide did not decreased significantly the sp. surface area of W2C but extremely increased the uptake of chemisorption of CO. No influence of platinum on the HDS activity was obsd. for contact times between 0.08 and 0.31 s. At longer contact time (t c > 0.31 s) the highest activity was obsd. over W2C-Pt catalyst (platinum doped after prepn.) for the HDS of 4,6-DMDBT. The main products were 3,3-DMBPh (along DDS route) and MCHT (along HYD route). A strong influence of platinum, added after prepn. (W2C-Pt), was obsd. for the HDN of carbazole. Indeed, this catalyst was more active in the whole range of applied contact times than W2C and Pt-W2C. It was also more active in the consecutive reaction of isomerization of the main product of the HDN reaction, i.e. bicyclohexyl (BCH) transformed into methylcyclopenthylcyclohexane (MCPCH). Furthermore the activity in HDN over the W2C-Pt catalyst was highly dependent on the amt. of metallic sites introduced by platinum. [on SciFinder(R)]