INFLUENCE OF THE SUPPORT IN THE SELECTIVITY OF NI CLAY CATALYSTS FOR VEGETABLE OIL HYDROGENATION

Two naturally occurring clays of Spanish origin, bentonite and palygorskite, have been used as support material for nickel hydrogenation catalysts in which the active phase has been deposited by means of the precipitation method. The structural and textural characteristics of the supports have been studied by XRD, N2 adsorption/desorption, and mercury porosimetry and the acid sites determined by thermogravimetry and infrared studies of adsorbed pyridine. The Ni phases present were characterized by XRD, TEM, XPS, FTIR of adsorbed CO, and the degree of reduction determined thermogravimetrically. XRD and TEM indicate Ni particle size to be equivalent for both supports although the detection by FTIR of a high proportion of bridging CO for the bentonite support suggests the presence of addition small particles for this support which may be located between lamellae. These smaller particles are consistent with the more difficult reduction of Ni in this support. Although activity for the hydrogenation of sunflower oil was similar for both catalysts, significant differences regarding the selectivity have been observed which may be attributed to the differences in morphology of the support materials. Mass transport limitations resulting from reaction of linoleic acid at Ni sites between lamellae of bentonite, leads to consecutive hydrogenation through to stearic acid, whereas the palygorskite supported catalyst remained highly selective to oleic acid even at high conversion levels.