Influence of acid-base sites on ZnO–ZnCr2O4 catalyst during dehydrocyclization of aqueous glycerol and ethylenediamine for the synthesis of 2-methylpyrazine: Kinetic and mechanism studies

• A surface reaction mechanism proposed for 2-methylpyrazine on Zn–Cr–O catalyst.
• Adsorption of Lewis bases defined the product distribution in dehydrocyclization.
• Dehydrocyclization activity is dependent on acid-base strength of Zn–Cr–O catalyst.

The physicochemical characteristics of ZnO–ZnCr2O4 (Zn–Cr–O) mixed oxides were determined by adsorption and spectroscopic methods. The catalytic activities of Zn–Cr–O was investigated for dehydrocyclization of ethylenediamine and aqueous glycerol to synthesize 2-methylpyrazine (2MP). Reductive pre-treatment was required for better 2MP yields and rate of 2MP was dependent upon strong basicity of Zn–Cr–O. Product distribution revealed that cyclocondensation of glycerol and ethylenediamine followed by homo-coupling of 2-pyrazinylmethanol occurred on moderate acid and strong base sites. On the contrary weak to moderate acidic and base sites were inefficient for homo-coupling of 2-pyrazinylmethanol. Role of acid-base properties was examined by pyridine and 2,6-dimethylpyridine poisoning studies.

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