ACTIVITY OF P-NI-W AL2O3 CATALYSTS WITH VARYING PHOSPHORUS-CONTENT INTHE HYDROGENATION OF NAPHTHALENE/

A series of co-impregnated (pH 1) P-Ni-W/Al2O3 catalysts of low tungst en content (1.6 W atoms/nm(2)) and varying phosphorus concentration (0 -5.9 wt.-% P2O5) have been studied in the reaction of hydrogenation of naphthalene in a batch Parr reactor at 573 K and P = 44 atm. In addit ion to a previous characterization by XRD, DRS and XPS, the catalysts have been characterized here by DRS, FTIR spectroscopy in their oxide state and by FTIR spectroscopy of NO chemisorbed on the sulphided cata lysts. A promoting effect of phosphorus is observed in all phosphorus containing samples. The catalytic activity vs. phosphorus content curv e has a complex behavior passing through a maximum and a minimum. Phas e transitions are observed in the samples with the change of the phosp horus content. The form of the catalytic activity curve is discussed i n the light of these phase transitions and the structure and propertie s of the different phases. The highest catalytic activity is observed for the sample with 0.6% P2O5. This sample is also characterized by th e highest amount of chemisorbed NO and by a local maximum in the relat ive number of terminal W=O bonds. When strong overlapping of the bands is observed, the NO adsorption technique should be applied with care. Also, NO might adsorb on sites which are not active in the correspond ing hydrotreatment reaction and the trend predicted by the total amoun t of chemisorbed NO should not necessarily coincide with the form of t he catalytic activity curve. The catalytic activity curves indicate th at during the reaction changes in the number of active sites or the fo rmation of new active sites are possible.