Influence of Bimetallic Catalysts on Hydrogen Yield and H2:CO Syngas Ratio From the Pyrolysis-Catalytic Steam Reforming of Polypropylene

Abstract

Pyrolysis-catalytic steam reforming of polypropylene has been investigated using bimetallic-alumina catalysts to determine the influence on hydrogen yield, H₂:CO syngas ratio, and catalyst coke formation. The presence of different metals coupled with nickel significantly influences the reforming process, for example, producing high hydrogen yield (>100 mmol g⁻¹_plastic), defined H₂:CO ratio (between 1.96 and 3.41), or heavy catalyst coking. For example, the Ni-Cu/Al₂O₃ catalyst produced a H₂ yield of 99.13 mmol g⁻¹_plastic, H₂:CO ratio of 3.41, but with high catalyst coke deposition of 15.76 wt%. Whereas, the Ni-Mg/Al₂O₃ catalyst gave a H₂ yield of 92.19 mmol g⁻¹_plastic, H₂:CO ratio of 2.56, and moderate coke deposition of 6.60 wt%. The Ni-Mn/Al₂O₃ and Ni-Mo/Al₂O₃ catalysts gave hydrogen yields of 87.55 and 82.26 mmol g⁻¹_plastic, respectively. Bimetallic catalysts containing no Ni, such as Fe-Co/Al₂O₃, and Co-Cu/Al₂O₃, showed reduced H₂ yield and H₂:CO syngas ratio. The results highlight the critical role of active metal choice and loading in maximising hydrogen production and minimising catalyst coking. Nickel remains the most effective reforming metal, while carefully designed bimetallic catalysts, particularly those containing Co, Mo, or Mg, offer targeted gains in hydrogen selectivity, targeted H₂:CO ratio, or catalyst coke resistance.