(429a) Operando Molecular Spectroscopy during Catalytic Biomass Pyrolysis

Operando
Molecular Spectroscopy during Catalytic Biomass Pyrolysis

Christopher J. Keturakis,^1* Olga B.
Lapina², Victor V. Terskikh³, and Israel E. Wachs¹

¹Operando
Molecular Spectroscopy and Catalysis Laboratory, Chemical Engineering
Department, Lehigh University, Bethlehem, PA 18015 USA

²Boreskov Institute of Catalysis, SB RAS, Prosp. Lavrentieva 5, 630090
Novosibirsk, Russia

³Department
of Chemistry, University of Ottawa, Ottawa, Ontario, Canada K1N6N5

*CJK209@lehigh.edu

Perpetually
increasing petroleum prices and finite petroleum resources have become large
societal concerns in recent decades, causing a search for new, renewable and
energy-efficient sources of liquid hydrocarbon fuel. With biomass being the
only sustainable source of carbon, advances in technology for biomass
conversion are critical for the development of renewable fuel sources.
Significant scientific understanding and improvement of catalysts for biomass
pyrolysis can only come from a fundamental research approach to all aspects of
biomass conversion.

We
have developed an operando
Raman/IR-MS spectroscopy system for catalytic biomass pyrolysis that
simultaneously monitors catalyst structure, biomass structure, surface reaction
intermediates, coking, char formation, and over 40 major gas phase pyrolysis
products (determined by GC-MS). Model supported 1-10% Al₂O₃/SiO₂
catalysts were synthesized and characterized (in situ Raman, in situ
IR, and high field (21.1T) ex situ
dehydrated ²⁷Al NMR spectroscopy). The chemical nature (Brönsted or
Lewis acid sites; BAS or LAS) of specific surface AlO_x
acid sites was determined from in situ
IR-CO adsorption and DFT calculations. These well-defined catalysts were
employed during the catalytic pyrolysis of cellulose, hemicellulose (xylan),
lignin, their monomers (glucose and xylose), and woody biomass to determine
correlations between specific value-added chemicals, required acid site nature,
and surface AlO_x active site coordination.
Results were also compared to popular HZSM-5 catalysts (Zeolyst)
with different Si/Al ratios (15 to 140).

Results
of operando spectroscopy experiments
during catalytic biomass pyrolysis revealed that there are several
intermediates on the catalyst surface depending on the biomass source,
including furans, conjugated alkenes, alkenes conjugated to aromatics, and
small cyclic rings with carbonyl groups. Demethylation
of small aromatics (such as toluene or xylene) was determined to be the pathway
for benzene production while methylation is the route to larger methylated
aromatics such as 1-methylnaphthalene. The catalytically assisted dehydration
of xylose into furfural was observed to be a key step in furfural production.
Aromatic polymerization into graphite-like coke was observed to be the major
catalyst deactivation mechanism. The production of furfural, benzene, toluene,
and xylene correlated with the presence of BAS associated with AlO₅
while large aromatics, such as naphthalene, correlated with AlO₆
LAS. Similar correlations were found for glucose and cellulose catalytic
pyrolysis. In general, cellulose and xylan (polymers) pyrolysis trends indicate
that greater acid site strength is needed than for glucose and xylose
(monomers) pyrolysis. For lignin pyrolysis, strong AlO₄ BAS selectively
cleaved the C₁-C_α propenyl ligand bond and enhanced demethoxylation.

This
talk will explore the developed correlations for value-added chemicals from
each major fraction of biomass (cellulose, hemicellulose, lignin and whole woody
biomass). This is the first application of operando spectroscopy to biomass
conversion and the method developed here paves the way for definitively
establishing catalytic structure-activity relationships for catalytic biomass
pyrolysis in future studies.