Design of trifunctional catalysts for promoting sequential condensation, deoxygenation, and aromatization of pyrolyzed mixed waste

Abstract

The upgrading of bio-oil often leads to significant carbon losses due to excessive decarboxylation and decarbonylation. However, this may be alleviated by deploying an innovative multi-functional catalyst that promotes C–C coupling while catalyzing deoxygenation/hydrodeoxygenation reactions. In this work, we develop trifunctional catalysts by consecutive post-synthesis treatments of commercial ZSM-5 catalyst (ZSM-comm). These treatments include impregnation of alkaline metal (magnesium) followed by temporary pore blocking with CTAB prior to the growth of SBA-15 using P123 as a template and transition/noble metal salts (nickel nitrate and platinum chloride). The prepared trifunctional catalysts exhibit three active sites, namely acidity, basicity, and reducibility as confirmed by NH₃-TPD, CO₂-TPD, and TPR measurements. The integration of the three active sites results in a remarkable increase in oil yield from 4.9% over ZSM-comm to 17.1 and 13.5% over Mg–Ni/meso-ZSM and Mg–Pt/meso-ZSM catalysts, respectively. These trifunctional catalysts also exhibit enhanced selectivity toward alkenes and alkanes in oil, which increases from 7.6% over ZSM-comm to 26.3 and 19.6% over Mg–Ni/meso-ZSM and Mg–Pt/meso-ZSM, respectively. The oxygenates (phenols, furans, acids, and ketones) also show an apparent shift in the carbon number toward the fuel range (C5–C13), suggesting the occurrence of C–C coupling. Additionally, the trifunctional catalysts help in increasing the selectivity toward monocyclic aromatic hydrocarbons (MAHs) from 75.2 to 93.7%.