Y.L. Lam

Synthesis and characterization of niobium oxide layers on silica and the interaction with nickel

Abstract A surface phase oxide containing niobiuma oxide, deposited on non-porous silica was prepared by two different methods. The photoelectron spectroscopy (XPS) and infrared results show that the method using five-stage attaching reactions between Nb(OC2O5)5 and silanol led to a very close one-atomic-layer niobium oxide structure on SiO2. This sample presented two oxygen species comparable to model systems and it was possible to distinguish them in the XPS spectral even when using a silica powder. Cyclohexane dehydrogenation was used to characterize the reduced metallic surface. The nickel compounds interact preferentially with niobia rather than with silica. These nickel species favored lower dehydrogenation activity, suggesting the choice of niobia as a nickel trap.

Cyclohexane as a Probe to Nickel Vanadium Interaction in FCC Catalysts

Abstract Nickel and vanadium were responsible for a great number of deactivation problems in the FCC. To understand their mutual influences, the metals were introduced by incipient wetness impregnation of organometallic compounds onto a highly dealuminated zeolite that had a constant lattice similar to the equilibrium FCC catalyst. Catalyst tests, TPR, DRS and X-ray diffraction were used to characterize the samples. After calcination, the acid sites of the zeolite were poisoned by vanadium without damage to the Crystallinity. Water vapor and high temperature treatment on vanadium/zeolite samples leads to a severe damage of the zeolite framework. The presence of nickel slightly attenuated this problem. The amount of benzene formed was affected by the Ni/V ratio.

Passivation of nickel activity in the nickel-Nb2O5-SiO2 system at low metal contents

Abstract Niobia/silica systems were used as a nickel trap. A great decrease in the catalytic activity of the cyclohexane reaction (hydrogenolisis and dehydrogenation) was observed, with a remarkable effect on the selectivity. The nickel/silica systems presented a great deal of hydrogenolisis product formation, while the major product on the nickel/niobia/silica surfaces was benzene. Nickel was reimpregnated three times to obtain the limit of passivation. A preferential interaction was observed between the nickel compounds and niobia.