Combating Deactivation in Methane Non-Oxidative Dehydrocyclization via Hydrogen Feed Pulsing

Abstract

The non-oxidative dehydrocyclization of methane was carried out over Ru–Mo/HZSM-5 catalyst in a fixed-bed catalytic reactor between 873 and 973 K. The catalyst, prepared by incipient wetness co-impregnation, was highly selective towards benzene production. The formation and deposition of low-H/C carbonaceous species was found to be more important at high temperatures and high methane space velocities. Intermittent hydrogenation of the catalyst by periodically switching from CH4 stream to pure hydrogen in the feedstream contributed significantly to the regeneration of active sites through hydrogenation of the carbonaceous species. Coke removal from the catalyst during H2 exposure was confirmed through temperature programmed oxidation and mass spectrometry analyses of spent catalyst. Alternating sequences of dehydrocyclization and hydrogenation under moderate and high feed flow rates resulted in improving catalyst stability due to efficient reduction of coke formation. These results might suggest an option for maintaining relatively high catalyst activity towards benzene production for prolonged reaction times.