Unsupported NiMoAl hydrotreating catalysts prepared from NiAl-terephthalate hydrotalcites exchanged with heptamolybdate

Unsupported NiMoAl hydrotreating catalysts were prepared starting from NiAl-terephthalate layered double hydroxides (LDHs) with x values (Al/(Al + Ni) ratios) in the 0.3–0.8 range by ion exchange with ammonium heptamolybdate, followed by calcination at 723 K. Mixed oxides containing ca. 33–43 wt% molybdenum and Ni/Mo atomic ratios in the 0.5–1.4 range were obtained. There was loss in the long-range ordering of the LDHs in the c direction during the ion-exchange, but the local structure of the brucite layers was maintained. The calcined mixed-oxides had surface areas ranging from 26 to 122 m2 g−1. The catalysts were sulphided in situ and subsequently tested in the simultaneous dibenzothiophene (DBT) HDS and tetralin (THN) hydrogenation reactions in a high pressure batch reactor at 613 K and 70 bar. The catalysts had higher specific activity for both the HDS and the HDA reactions and much higher selectivity for the ring hydrogenation (HYD) route in the HDS of DBT than a conventional NiMo/Al2O3 catalyst. Their activities in both reactions were similar to those of an Al-free unsupported NiMo catalyst, but their preference for the HYD route was higher than that of the latter.