Performance research of metal-doped zeolite catalysts on the production of nitrogen-containing compounds via microwave pyrolysis

Abstract This study explores the microwave pyrolysis characteristics of raw tobacco stems and tobacco stems impregnated with urea using different metal-loaded zeolite catalysts. Due to the cracking effect of HZSM-5 and the dehydrogenation activity of Ni sites, the sum of CO and H 2 yields in both raw tobacco stem and tobacco stem impregnated with urea gas products exceeded 50 %. The 10Ni catalyst reduced the content of organic acids in the raw tobacco stem liquid product from 17.51 % to 10.88 %. The addition of catalysts increased the nitrogen-containing compounds (NCCS) content substantially. Catalytic pyrolysis promoted the decomposition of nicotine, resulting in a rapid decrease of the nicotine content in tobacco stem impregnated with urea liquid products. The content of amines increased rapidly with a maximum 30.79 %. The addition of Cr improved the selectivity of catalysts for indoles with a maximum yield 8.48 %. Cr sites promoted further dehydration, condensation and cyclization of some amines to produce indole. The content of pyridine in the liquid products of tobacco stems impregnated with urea is also high, reaching 27.91 %. This study first introduces the synergistic effect of Ni–Cr co-modification combined with an external nitrogen source (urea) to selectively regulate the formation of NCCs, providing a novel approach for the valorization of tobacco residues, such as tobacco stems.