Valorization of municipal solid wastes via pyrolysis and hydropyrolysis: Unveiling the role of natural zeolites as catalysts and supports for Ni and Cu

Pyrolysis and hydropyrolysis have emerged as an efficient and sustainable solution for valorizing municipal solid wastes (MSW) into value-added products. However, the effectivity of these thermochemical processes is hindered by low yields, high water content and low calorific value of pyro-oils, thus requiring for catalytic materials. Here, we report on the effectiveness of using natural zeolites and Ni and Cu-doped zeolites to produce fuels via pyrolysis and hydropyrolysis of MSW. A systematic analysis of the temperature effect, Cu-doped and Ni-doped catalysts, MSW-to-catalyst ratio, and reaction atmosphere (He or H2) on the product distribution from pyrolysis and hydropyrolysis was carried out. The chemical composition of pyro-oil precursors was investigated using a micropyrolyzer coupled to a gas chromatograph and mass spectrometer (Py-GC-MS). The most significant parameters for reducing oxygenated compounds in pyro-oil were the reaction atmosphere, temperature, and catalyst type, with the sample-to-catalyst ratio showing no statistically significant effect. Hydropyrolysis at 14 bar and 550 ºC reduced the oxygenated compounds content in pyro-oils by approximately 36 % compared to non-catalytic pyrolysis. Under these reaction conditions, Ni-doped natural zeolite (HZNHZ-Ni15R) led to a sharp increase in hydrocarbon selectivity, reaching a maximum of 88.2 %, while O-containing species were reduced to 5.1 %. The HZNHZ-Ni15R exhibited a high selectivity towards benzene, toluene, ethylbenzene, and xylene via a complex pyrolysis and hydropyrolysis reaction mechanism. In addition, the study proposed and exhaustively discussed the reaction mechanism governing the catalytic pyrolysis and catalytic hydropyrolysis of MSW. © 2024 The Authors