Deactivation of Nickel Catalysts by Sulfur and Carbon for the Pyrolysis-Catalytic Gasification/Reforming of Waste Tires for Hydrogen Production

摘要

Hydrogen, production from the two-stage pyrolysis—gasification/reforming of waste tires has been investigated using Ni/Al3O3 and Ni/doloraite catalysts in the relation to four cycles of use. The Ni/dolomite catalyst produced a higher hydrogen yield and the highest theoretical hydrogen potential to produce hydrogen gas compared to the Ni/Al2O3 catalyst. In addition, the used Ni/dolomite catalyst had the lower carbon deposition, as determined by temperature-programmed oxidation, being 18.2 wt % for the Ni/Al2O3 catalyst and 2.8 wt % for the Ni/dolomite catalyst. Detailed analysis of the reacted catalysts using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDXS) was used to characterize the presence of nickel, sulfur, and carbon, on the used catalysts. The results showed that, for the Ni/Al2O3 catalyst, sulfur was mainly present on the surface of the nickel particles. However, for the used Ni/dolomite catalyst, no sulfur peaks were detected whether in the bulk metal or on the surface-of the nickel particle. In addition, carbon deposition was closely associated with the nickel particles of the used Ni/Al2O3, catalyst but not for the used Ni/dolomite catalyst. The results suggest that nickel of the Ni/Al2O3 catalyst becomes deactivated because of sulfur reaction and carbon deposition, preventing reaction of the various reactant species generated from the pyrolysis of the tires. However, using dolomite as a support, the catalytic deactivation process was less pronounced and there was negligible deactivation of nickel by sulfur.