Graphene-Encapsulated Transition Metal@N/C Catalysts for Catalytic Copyrolysis of Biomass and Waste Plastics: Production of Linear α-Olefins and Aromatics

Herein, we report N-graphitic modified transition metal nanoparticles supported on graphene as an efficient catalytic material for the production of valuable aromatics and linear α-olefins via copyrolysis of wheat straw (WS) biomass and postconsumer high-density polyethylene (HDPE) waste plastic. The catalytic materials comprise transition metals (Mn, Ni, and Zn) supported on N-doped reduced graphene oxide (N-RGrO), prepared by pyrolyzing an in situ generated metal: phenanthroline complex with exfoliated graphene oxide. The catalytic performance of these materials was evaluated in pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS) analysis. The catalysts had different N configurations that acted as metal anchoring sites and enhanced the basicity of the support. The effects of catalysts on the copyrolysis products of WS and HDPE with various feed ratios (100:0, 75:25, 50:50, 25:75, 0:100) were investigated. The results showed that the catalysts decreased the amount of oxygenates and increased the yield of monocyclic aromatics (MAHs) and linear α-olefins. The Zn@N-RGrO catalyst exhibited the highest activity, producing 25, 22, and 21% of MAHs for WS/HDPE ratios of 50:50, 25:75, and 75:25, respectively. During the copyrolysis process, the Zn and Ni@N-RGrO catalysts also generated relatively more long-chain α-olefin contents, 21% (25:75) and 21% (75:25). The present work demonstrated the potential of metal-based-N-doped RGrO catalysts as substitutes for zeolites in the green synthesis of valuable chemicals from waste biomass and plastics.