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

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%.