Catalytic Activity and Reusability of Nickel-Based Catalysts with Different Biochar Supports during Copyrolysis of Biomass and Plastic

Abstract

Low-cost biochar is a promising catalyst support for catalytic pyrolysis to produce pyrolysis oil, pyrolysis gas, and carbon nanomaterials (CNMs). The effect of different Ni/biochar (four kinds of original biochar and three kinds of modified biochar) catalysts on the yield and properties of copyrolysis products from Chinese herb residue and reused polypropylene (PP) was studied. Results show that the modified biochar support had a high surface area and high catalytic activity. Particularly, Ni/ZC (ZnCl2-modified biochar) obtained higher yields of CNMs (2.92 wt %) and pyrolysis gas (55.44 wt %). Moreover, it exhibited high stability in repeated use experiments. Interestingly, the Ni/ZC catalyst showed the highest catalytic activity during second reuse (ZC-R2) due to moderate precoking. The high content of hydrocarbons and the C6–C20 component in the ZC-R2 group is attributed to the stronger secondary cracking capacity. The stronger secondary cracking capacity of the front-end catalyst may increase the content of CH4 in pyrolysis gas. Therefore, the Ni/ZC catalyst significantly increased the yield of a high-quality 3D graphitic carbon network structure in a second-stage reactor. This work contributes to the industrial application of catalytic pyrolysis technology by reducing the catalyst cost and increasing the product value.

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

“…The mesoporous structure of N-doped reduced graphene oxide support helped the bulky oxygenate intermediates and long-chain cracked products of waste plastic for the improved production of the hydrocarbon pool and its effective conversion to aromatics . The metal active sites also facilitated the cracking of macromolecules through β-scission and random-scission at high temperatures, resulting in more abundant hydrocarbon pools of olefins and alkanes, which further underwent oligomerization, cyclization, and aromatization. , The catalytic sites anchored the H 2 released during the cracking of HDPE and enabled the hydrogen transfer reactions, stabilizing the primary pyrolysis radicals of WS …”

“…The Zn metals or partially reduced metal oxides on the N-doped RGrO support improved the activation of the C−O/C�O bond and the selective aromatization of biomass-derived compounds due to their good dispersion. 19,22 The Zn-mediated copyrolysis increased the PAH formation from 2.33 to 3.48%. The PAH formation was a competitive reaction with MAHs; even though the metal ions improved the MAH formation selectively, the PAHs were also formed simultaneously, as the graphene oxide support provided the diffusion pathway and sufficient contact time for the condensation of monocyclic aromatics to polycyclic ones.…”

“…19,20 The catalytic sites anchored the H 2 released during the cracking of HDPE and enabled the hydrogen transfer reactions, stabilizing the primary pyrolysis radicals of WS. 22 During catalytic copyrolysis, the chemical interactions between cellulose and hemicellulose-derived furans with the olefins from HDPE cracking promoted the formation of the aromatic. The Diels−Alder reaction between furans and light olefins, followed by dehydration, formed BTX and other MAHs.…”

“…Moreover, the high synthesis cost and coking tendency of ZSM-5 zeolite hinder its long-term use. 22 Hence, finding alternative and affordable carbon matrix support-based catalysts for copyrolysis is essential for the process's economic feasibility.…”

“…Concurrently, “metalated zeolites” exhibit a high propensity for coke formation, attributed to the robust chemisorption of carbon on the metal sites, which impacts the product yield and restricts their practical use. Meticulous preparation and fine-tuning are essential to mitigate these challenges. − In general, the catalytic cracking efficiency for aromatics and olefins is limited by the steric hindrance effect of zeolites, which prevents large oxygenate molecules from accessing the inner acidic sites. Moreover, the high synthesis cost and coking tendency of ZSM-5 zeolite hinder its long-term use .…”