Abstract
Hierarchical zeolites have been identified as special catalytic materials with improved catalytic properties. In this study, hierarchical bifunctional ZSM5 based catalysts were prepared by desilication for controlled mesoporosity development and have been modified by Co doping. Their performance in the catalytic pyrolysis of oak in a lab scale reactor was evaluated. Desilicated counterparts were proven more active in deoxygenation of bio oil, while carbon deposition on the catalysts reduced compared to non-desilicated counterparts. Increased Lewis acidity favors decarboxylation reactions, while higher olefins as well as PAH content indicate easier diffusion within and from the porous network and interactions in the mesopores. The conversion of bulky lignin molecules (alkoxy phenols) is enhanced by the mesopores, while acidity is of secondary importance. Coke deposition inside the pores is more profound in the desilicated catalysts due to larger pore size. Carbon deposition on the catalysts is reduced in the following order: HZSM5 > Co/HZSM5 > Ds-HZSM5 > Co/Ds-HZSM5. GC–MS characterization of the CH2Cl2 soluble coke indicated that for the desilicated counterparts the main coke precursors are the bulky lignin molecules which are partially deoxygenated.
Highlights
The development of a sustainable society prioritises the use of renewable energy sources
The average Co crystallite sizes for the Co/HZSM5 and Co/DsHZSM5 were evaluated at 2θ = 36.9° were equal to 60.2 and 36.1 nm respectively. This indicates better dispersion of additional Co species. H2-temperature programmed reduction (TPR) (Fig. 2) revealed the main reduction peaks at temperatures lower than 400 °C which are ascribed to the reduction of Co3O4 that proceeds via a multistep mechanism [29, 30]
Characterization of the catalytic materials showed that desilication resulted in increased mesopores formation and slightly reduced Brønsted acidity while the incorporation of Co resulted in increased Lewis acidity of the catalysts
Summary
The development of a sustainable society prioritises the use of renewable energy sources. Biomass is the main source of renewable carbon that can produce various valuable energy carriers providing one possible pathway for reshaping the present fossil based energy usage [1]
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