Functional use of CO₂ for environmentally benign production of hydrogen through catalytic pyrolysis of polymeric waste

A benign route for hydrogen (H₂) production is environmentally desirable. To achieve this, H₂ synthesis from polymeric waste was investigated. A new route was sought to maximize H₂ production with the least formation of coke during catalytic pyrolysis of fishing net waste (FNW) by using CO₂ (as reaction media) and a Ni/SiO₂ (as catalyst). The thermolytic characteristics of FNW were also evaluated under the CO₂ condition (and N₂ as reference environment) both with and without catalysts to assess the full scope of variabilities involved in catalytic pyrolysis of FNW. The use of Ni/SiO₂ catalyst in each of the N₂ and CO₂ conditions improved the reaction kinetics in terms of syngas formation with significant production of H₂ (1,543 and 770 mmol g⁻¹_cat h⁻¹) and CO (11 and 1157 mmol g⁻¹_cat h⁻¹), respectively. However, H₂ production rate dropped when the catalyst was deactivated due to (hydro)carbon deposition onto the catalyst surface under N₂ environment. Under CO₂ environment, CO₂ served as an oxidant during FNW thermolysis with additional CO formation and prolonged lifetime of catalyst (via suppressed deactivation). H₂ production mediated by CO₂ increased to ≥1,093 mmol g⁻¹_cat h⁻¹ during five repeated cycles of FNW pyrolysis, coupling with water–gas shift reaction (WGS: CO+H₂O⇌H₂+CO₂). This new approach to H₂ production is demonstrated as a practical measure for producing H₂ while extending catalyst life.