TPD-TPR-MS MECHANISTIC STUDY OF THE SYNTHESIS OF 2-METHYLPYRAZINE OVER PALLADIZED ZN-CR OXIDE

A mechanistic study of the cyclization of ethylenediamine (ED) and propyleneglycol (PG) to 2-methylpyrazine is reported, carried out by means of the TPD-TPR-MS technique. The reacting system proved to be complex, due to the presence of numerous intermediates and by-products, deriving either from one of the two reactants, or from both. The optimal reaction temperature, permitting the best selectivity to the desired product, was about 660 K. At least two different types of surface sites are present on the catalyst, and only the higher-energy ones activated the reactants. The reaction probably involves a rate-determining step of the Rideal-Eley type, between adsorbed PG and ED coming from the gaseous phase. This step leads to a fully hydrogenated intermediate, 2-methylpiperazine, which quickly dehydrogenates and aromatizes to 2-methylpyrazine. © 1991.