Selective synthesis of 3-picoline via the vapor-phase methylation of pyridine with methanol over Ni1-xCoxFe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0) type ferrites

A series of Ni–Co ferrites with the general formula Ni1-xCoxFe2O4 (x = 0, 0.2, 0.5, 0.8 and 1.0) was prepared by a low-temperature hydroxide coprecipitation route. The catalyst systems were characterized by adopting various physico-chemical techniques. Alkylation of pyridine with methanol was carried out in a down-flow vapor-phase reactor. The influence of surface acid–base properties, cation distribution in the spinel lattice and various reaction parameters are discussed. It was observed that the systems possessing x values ≥0.5 are selective for 3-picoline formation, whereas the ones with x values 0 and 0.2 give a mixture of 2- and 3-picolines. Pyridine conversion increased with the progressive substitution of Ni2+ ions by Co2+ ions. Cation distribution in the spinel lattice influences their acidic and basic properties, and these factors have been adequately considered as helpful to evaluate the activity of the systems.