SYNTHESIS OF PYRIDINE BASES ON ZEOLITE CATALYST

For gas phase synthesis of pyridine bases from acetaldehyde, formaldeh yde, and ammonia (known as the Chichibabin reaction), we have develope d an efficient catalyst based on the pentasil zeolite (ZSM-5) treated with a metal cation such as Pb, TI, or Co. Compared with a conventiona l 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 activi ty of the zeolite catalyst decreased gradually with repeated reaction- regeneration cycles. We have solved this problem by developing a new r egeneration method. This method consists of two elements: (1) an addit ion of a. trace amount of a noble metal (Pt) to the zeolite as a co-ca talyst 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. (C) 1998 Elsevier Science B.V. All rights reserved.