Synthesis of pyridine bases on zeolite catalyst

Abstract

For gas phase synthesis of pyridine bases from acetaldehyde, formaldehyde, and ammonia (known as the Chichibabin reaction), we have developed an efficient catalyst based on the pentasil zeolite (ZSM-5) treated with a metal cation such as Pb, Tl, or Co. Compared with a conventional amorphous silica-alumina catalyst, this catalyst affords not only a much higher yield of total pyridine bases, but also a higher yield of more valuable pyridine. The comparison between synthesis reactions of pyridine, 2,6-lutidine and 2,4,6-collidine has clarified that the high pyridine selectivity comes from the shape-selectivity of the pentasil zeolite, and that the density of the active sites in an inner channel of zeolite is much higher than those on the outer surface. The activity of the zeolite catalyst decreased gradually with repeated reaction-regeneration cycles. We have solved this problem by developing a new regeneration method. This method consists of two elements: (1) an addition of a trace amount of a noble metal (Pt) to the zeolite as a co-catalyst for aeration; and (2) an addition of a small amount of alcohol in the aeration gas. As a result, the catalyst life has been extremely improved.