Page 116 - Advances in bioenergy (2016)

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et al. assembled, from zeolite beta seeds, two aluminosilicate MSU-S materials with
different mesopore structure and compared them with conventional Al-MCM-41 in the
upgrading of biomass pyrolysis vapors in a fixed bed reactor. The MSU-S materials
significantly reduced the bio-oil's organic phase and led to higher coke yields as compared
with noncatalytic pyrolysis and to the Al-MCM-41 material. The MSU-S materials were also
very selective toward PAHs and heavy fractions, but produced negligible amounts of acids,

alcohols, carbonyls, and very few phenols. The MSU-S materials possessed stronger acid sites
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than the Al-MCM-41, resulting in enhanced yields of aromatics, PAHs, and coke. Pattiya
et al. studied Al-MCM-41 and Al-MSU-F materials in a Py-GC–MS system and found them to
demonstrate a potential for bio-oil improvement in terms of initial viscosity and heating value,
as they tend to reduce the oxygenated lignin-derived compounds and produce hydrocarbons,
although the effect was less pronounced, when compared with that of a ZSM-5 zeolite. On the
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downside, they observed an increase of the acetic yield. Jackson et al. also compared an
HZSM-5 zeolite to a mesoporous Al-MCM-41 for the upgrading of lignin pyrolysis vapors and
observed that the Al-MCM-41 catalyst behaved similarly to the HZSM-5, although it was not
as effective at deoxygenating the liquid phase and gave more naphthalenics than simple
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aromatics. Lu et al. also used a Py-GC–MS system to study siliceous SBA-15 and Al-SBA-
15 materials and found them to be mild catalysts as compared with acidic zeolites. They
favored the formation of acetic acid, light phenols, furan, furfural, and other light furan
compounds and decreased the yields of heavy phenols, heavy furans, and many light carbonyls.
The Al-SBA-15 materials were more active than the siliceous SBA-15 and the catalytic effects
were enhanced when decreasing the Si–Al ratio of the catalyst. 34,43

Lately, mesoporous zeolites have been synthesized and studied for the catalytic pyrolysis of
biomass. Lee et al. synthesized ordered mesoporous aluminosilicates (MMZ) using
commercially available beta and ZSM-5 zeolites and applied them to the pyrolysis of woody
biomass. The material had well-developed mesoporosity and exhibited excellent hydrothermal
stability. Considering both their selectivity to phenolics and organic fraction yield and also the

reduction of undesirable compounds such as oxygenates, the synthesized catalysts were found
to be promising catalysts for the upgrading of bio-oil. Moreover, the high catalytic activities of
the synthesized catalysts were maintained through the regeneration-upgrading cycles, whereas
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the activity of Al-MCM-41 significantly decreased. Park et al. synthesized a mesoporous
mordenite framework inverted (MFI) zeolite and compared its catalytic activity with those of
conventional HZSM-5 and mesoporous material from HZSM-5 (MMZ HZSM–5 ). The

mesoporous MFI zeolite exhibited the best activity in terms of deoxygenation and
aromatization. In particular, they observed high selectivity toward valuable BTX
hydrocarbons, but organic fraction yield was decreased. Incorporation of gallium into the
mesoporous MFI zeolite resulted in less cracking of the pyrolytic vapors, as well as an
increase in the organic fraction of bio-oil and resistance to coke deposition. The amount of
gallium incorporated into the mesoporous MFI zeolite played an important role in the
selectivity of aromatics. The addition of the appropriate amount of gallium optimized the
bifunctional mechanism and the consequent enhancement of the selectivity for BTX aromatics,
whereas the excess gallium brought a negative effect on formation of aromatics because of