Kyushu University Global COE Program
Journal of Novel Carbon Resource Sciences, Vol. 6, pp. 1-8, Sep. 2012

Micro Review

Applications of Catalysis in the Selective Conversion of
Lignocellulosic Biomass by Pyrolysis
Shinji Kudo*1, Koyo Norinaga*2, Jun-ichiro Hayashi*1,*2*1Research and Education Center of Carbon Resources, Kyushu University*2
Institute for Materials Chemistry and Engineering, Kyushu University(Received July 6, 2012; accepted July 23, 2012)

Pyrolysis is one of the thermochemical methods to decompose lignocellulosic biomass that has a great potential
for sustainable production of chemicals and fuels. This microreview focuses on catalytic reactions employed in thepyrolysis processes for the selective conversion of the biomass. The catalytic reactions are categorized into twogroups according to the objective of the use of catalysis, and recent advances in each group are briefly reviewed. Our
recent works on the pyrolysis of biomass with catalysis are summarized as well, and their originality, advantages
over the other methods and challenges for the future were discussed.

1. Introduction

Lignocellulosic biomass is the most abundant,
inexpensive and sustainable source of carbon, which
includes various naturally derived materials such as
woody and herbaceous species, bagasse, agriculturaland industrial residues, sawdust, waste paper, etc. The
conversion into renewable fuels and commodity/valueadded chemicals have attracted a strong political andtechnical attention over the past few decades due todeclining petroleum resources, combined with increased
demand for fossil fuels by emerging economies. With
the contributions of countless researches devoted to thisfield, many technologies have been developed to convert
biomass resources into gas, char (solid residue), and liquid
product. Thermochemical conversion methods, apartform biochemical methods that convert the biomass into
alcohols or oxygenated products by biological activity,
generally involve the gasification, pyrolysis, liquefaction
and sub/super-critical fluid extraction1). The gasification
produces a gas product called syngas or producer gas that
contains CO/H2/CO2/CH4 in various proportions, while
the other methods are generally used for the purpose of
producing liquid products.
Pyrolysis has several advantages over other methods to
produce the liquid product: a simple reactor configuration
resulting in low capital cost, a short reaction time,
concentrated liquid products (less energy-intensive for
product separation), and an adaptability to a wide rangeof feedstocks2). It is difficult or almost impossible toselectively convert the biomass into monomer units by thepyrolysis only due to the complex and recalcitrant natureof biomass, while the liquid product from the pyrolysis,
which is a multi-component mixture of organics, hasreceived increasing attention as a fuel alternative topetroleum derived fuels, so-called bio-oil. Fast pyrolysis,an effective conversion with high heating rate over 102ºC/s, achieves the yield of bio-oil as much as 70—80%3)
and is regarded as the most reasonable and promisingtechnology. It is, however, still required to upgrade

the bio-oil with respect to the heating value, moisture
content, stability, corrosiveness, and incomparability
with standard petroleum fuels4,5). On the other hand, if thefeedstock is not biomass but cellulose, the production ofmonomer units is feasible because it is composed of unitsof glucose. The conversion of cellulose is worth given
priority also in the context of processing lignocellulosic
biomass because nearly half of the organic carbon in
the biosphere is present in the form of cellulose. The
recent report from US department of energy identified
twelve chemicals that can be produced from biomass
and converted to a number of high-value chemicals ormaterials6). The proposed scheme planned to produce
those chemicals from sugars as an intermediate platform.
Hydrolysis with liquid or solid acid catalysts would bea candidate for the selective conversion of cellulose tosugars among the thermochemical methods7). Pyrolysis
of cellulose, however, produces a multi-component
mixture of dehydrated sugars, furans, etc., with only a
trace amount of sugars.
While the pyrolysis thus seems like not suitable forthe production of fuels and chemicals, an employmentof catalyst causes the liquid product to undergo a drasticchange in the composition. Although the use of catalytic
reactions in the pyrolysis processes is not yet wellstudied as compared to plenty of researches in catalytichydrolysis, solvolysis, liquefaction, hydrogenolysis, andhydrogenation, it does offer tremendous potential for
future development of a route to produce chemicals or tomodify fuel properties8). Studies on catalysis in biomass
pyrolysis can be categorized into two groups dependingon the purpose: 1) in-situ reforming of volatiles evolved
from the pyrolysis, 2) changing the mechanism of thermal
decomposition, i.e., pyrolysis. These are generally calledwith the same name, catalytic pyrolysis, but the roles ofcatalyst in the biomass conversion processes are clearly
different by the group.
In the present work, the catalytic reactions are
distinguished as in-situ catalytic reforming of volatiles

Journal of Novel Carbon Resource Sciences, Vol.6, Sep. 2012

and catalyzed pyrolysis, respectively (Fig. 1), and recent
advances in each group are briefly reviewed. The focus
is on the works that exploited the complex chemistryof pyrolysis for the catalysis to selectively produce thetarget product. Along with the current research trends,
our recent contribution is presented with the originalityof the research concept.
Catalysis
Pyrolysis

Volatiles

Upgraded-bio-oil
SyngasIn-situ catalytic reforming of volatiles

Biomass
Pyrolysis

products then enter the catalyst where they are converted
into aromatics, CO, CO2 and water through a series ofvarious reactions. Coke formation is the major competing
reaction with aromatic production. A maximum carbon
yield of 32% aromatics was obtained at 600 ºC using a
ZSM-5 catalyst and a pyroprobe reactor. CFP of glucose
can simulate an essential reaction pathway of cellulose
and hemicellulose, while some reports demonstrated thepotential of lignin as a source of aromatic hydrocarbons
15,16). Ma et al.17) reported 40 wt% yield of aromatichydrocarbons from lignin using H-USY zeolite that has
high number of acid sites and relatively large pores (Fig.
2 (b)).

Value-added chemicals

Catalysis

Catalyzed pyrolysis

Fig. 1 Pyrolysis processes with catalytic reaction andtypical products.

OH
O

HO
HO

O

HO OH

glucoseO

x H2 OOOO
HO

2. In-situ catalytic reforming of volatiles

OH
OH
HO

O

O

O

O

O

OH

OH

O

anhydrosugars

2.1 Catalytic fast pyrolysis

OOH

dehydraiton

One of the emerging technologies for biomass
processing is fast pyrolysis that produces high yields of aliquid product, called bio-oil, which contains up to 70%of the energy of the biomass feed9), but aforementioned
problematic properties restrict its application. The
compounds found in bio-oil have been classified into
the following six broad categories: hydroxyaldehydes,hydroxyketones, sugars, dehydrated sugars, carboxylic
acids, and phenolic compounds with molecular weights
ranging up to 5000 or more depending on operating
variables of the pyrolysis process8). The as-preparedbio-oils require upgrading at least to remove oxygen
functional groups before they are compatible withexisting fuel infrastructure.
By pyrolyzing biomass in the presence of a catalyst,
it is possible to convert the volatiles evolved from thepyrolysis into aromatic hydrocarbons such as benzene,
toluene, and xylenes2). This approach to upgrade bio-oils
is generally called catalytic fast pyrolysis (CFP), although
the name is likely not describing phenomena occurring in
the process because the catalysis is not aimed at thermal
decomposition (pyrolysis) of biomass, but to change thecomposition of volatiles. The research on the catalytic
production of hydrocarbons from biomass had alreadystarted since the late 1970s10), but become diminishedwith scattered researches until renewed attention
by considerable works on CFP of Huber’s researchgroup2,11–14). They investigated the overall reaction
pathway in CFP using glucose as a model compound(Fig. 2 (a))11). This reaction involves chemistry occurringin three phases: within the solid biomass, in the gas
phase, and within the catalyst. Glucose first thermallydecomposes into anhydrosugars, which are converted
by dehydration reactions into furans. The dehydrated

O

OH
HO

O

x H2O; y HCOH;
z COx

O

furan compounds

acid catalyzed
oligomerization
decarboxylation
decarbonylationx H2O; y COx
x H2O;
y COx

coke

x H2O; y COxhydrocarbon pool

olefinsx H2O; y COx

oxygenates

PC aromatics

MC aromatics(a) Reaction pathway of glucose CFP proposed by Carlson et al.11)
O
O

O

Dehydration
Decarboxylation
Cracking
H
Aromatization
O
Isomerization
Oligomerization
H-ZSM5 -H2O

H
OH

HO

O

HO

O

Lignin
HO

OH

-CO2

O
OH
O

O

O
HO

Aromatic hydrocarbons(b) Reaction pathway of lignin CFP proposed by Ma et al.17)

Fig. 2 Reaction pathways in CFP.
Zeolite ZSM-5 is a catalytic cracking catalyst
commonly used in petroleum industry for upgrading
low-octane components18). A wide range of catalyst
has been tested for CFP of biomass including zeolites,
mesoporous materials (such as Al-MCM-41), Co-Mo
catalyst, and Ni/Al catalyst8,12). The majority of studies
on zeolites concluded that ZSM-5 was the catalyst
that gave the highest yield of aromatics. Jae et al.12)
investigated the influence of zeolite having variety ofApplications of Catalysis in the Selective Conversion of Lignocellulosic Biomass by Pyrolysis

pore sizes and shapes (ZK-5, SAPO-34, Ferrierite, ZSM23, MCM-22, SSZ-20, ZSM-11, ZSM-5, IM-5, TNU-9,
SSZ-55, Beta zeolite, and Y zeolite) on the conversionof glucose to aromatics, and found medium pore zeolites
with moderate internal pore space and steric hindrance(ZSM-5 and ZSM-11) had the highest aromatic yield andthe least amount of coke.
Pyroprobe is a convenient semi-batch type reactor totest the catalytic activity for reforming of the volatiles
evolved from biomass. Fixed catalyst bed reactors arealso often used for in-situ reforming or gasification ofvolatiles10,19). Those reactors, however, cannot practicallyand economically be scaled up toward commercial
production. Recently, Carlson et al.13) demonstrated that
CFP can be done efficiently in a fluidized bed reactor
with an appropriate reactor configuration and optimized
operating conditions. Fluidized bed reactors have been
proven in a vast number of processes across industry
due to their excellent mass and heat transfer properties,
scalability and simplicity of operation. The highest yieldof aromatics from sawdust was 14% on carbon basis
using ZSM-5 catalyst at 600 ºC. After ten reactionregeneration (by combustion) cycles of the catalyst,
they found impurities (alkali and alkaline metal species)
deposited on the catalyst surface and broken pieces ofcatalyst, however, the acid sites on the zeolite were notaffected.
Significant advantages of CFP would include: 1) all
the desired chemistry occurs in a single reactor and 2)
main products, aromatics and olefins, are already fit into
existing infrastructure14). In fact, CFP can produce fiveof the six primary petrochemicals, including benzene,
toluene, xylene, ethylene and propylene13). If the objective
is to use the aromatics as a gasoline additive, toluene
and xylene would be the best aromatics to produce as
they are higher in octane number than benzene andnaphthalene20). However, benzene is more valuable than
toluene due to its use in the chemical industry. One of
the critical challenges with CFP is to increase the yieldof these chemicals by reducing the formation of coke.
The recovery of product chemicals on an energy basis
is still low as compared with other technologies suchas fermentation and gasification. Co-feeding of otherhydrocarbons, such as alcohols14,21) and olefins13), is oneof the options on this issue.

2.2 Utilization of coke formation potential ofvolatiles
The formation of coke on/in porous materials proceeds
through the entrance and adsorption of volatiles into
micropores and the succeeding coking as illustrated inFig. 2. In CFP, the coke formation is the major competing
reaction to the formation of aromatics, resulting in thesignificant loss of aromatics yield. Hosokai et al.22,23)
also demonstrated the coke formation over charcoal andmesoporous alumina.
We have recently proposed three methods fully

utilizing coke-forming potential of volatiles to produce
light oil24) and syngas free from heavy tar25,26). Fig. 3
illustrates conceptual process diagrams. They employeda raw biomass (process (a)), potassium-loaded biomasschar (process (b)), and low-grade iron ore (process (c))
as materials for capturing volatiles, especially heavy tar,and the succeeding reactions.
In the production of light oil, feedstock biomass was
firstly loaded in the sorber to capture heavy oil from thepyrolysis by condensation, adsorption, and/or absorption.
Because the temperature of the sorber was maintained at
110—180 ºC, the captured heavy oil was not converted
to coke, while light oil was allowed to escape from thesorber. The feedstock biomass loaded with heavy oil
was subjected to the pyrolysis to simulate recycling ofheavy oil and a continuous operation of this process.
The cycle of capturing and pyrolysis of heavy oil was
repeated 10 times. Recycled heavy oil was successfully
converted into light oil and char by self-pyrolysis andwith some contribution of a type of catalysis by biomass.
The proposed process, a recycling of heavy oil, wasthus effective for the selective production of light oil.
The produced bio-oil was highly volatile that 99.8% of
its portion was evaporated in heating to 250 ºC, in otherwords, nearly free from coke precursors. This property
is beneficial in the applications of the bio-oil, such as
catalytic steam reforming for syngas production, that are
intolerant of coke/carbon formation.
The processes (b) and (c) aimed at simultaneous steam
reforming of volatiles and steam gasification of charfrom the pyrolysis of biomass with materials loaded in
the reformer. Potassium (K)-loaded char was produced
from the pyrolysis of K-loaded biomass and loaded in
the reformer. Volatiles from the pyrolysis were reformed
over the char in a sequence of carbon deposition onto thepore surface and steam gasification of the deposit. Evenat the low temperature of 600—700 ºC, the catalysis of K
simultaneously realized the concentration of heavy tar in
the product gas as low as 20 mg/Nm3-dry and progressof the char gasification as fast as that of char formationfrom the pyrolysis, at the steam/carbon molar ratio of0.55—1.10, wherein the steam was supplied as a moisturein the feedstock biomass and from water produced by
the pyrolysis. Furthermore, it was suggested a major
portion of K retained by the spent K-loaded char could
be recycled to the process by the extraction with water at
the ambient temperature.
The process with the natural iron ore was also effective
to produce clean syngas. With the reformer loaded with
the iron ore, the yield of heavy tar from the pyrolysisreforming process was less than 0.01% by its oxidation
with the ore and coking into/onto the ore. The ore was
reduced from hematite to magnetite/wustite after thereaction, but it was possible to further reduce to iron/
wustite upon reheating up to 800 ºC in the absence ofvolatiles. It was suggested that the coke formed in/on theore played a role of an agent for its further reduction.

Journal of Novel Carbon Resource Sciences, Vol.6, Sep. 2012

Condensation & sorptionof heavy oil

Biomass

Light oil Light oil yield:
26 wt% dry-biomassGas(excluding water)

Heavy-oil sorber

Highly volatile

Char

Pyrolysis

Heavy-oil-loaded biomass

Process (a): production of bio-oil by pyrolysis with feedstock-mediated recycling of heavy oil

Deposition of coke from volatiles
Biomass

Reforming of tar
Gasification of coke and char

K-loadingK-loaded biomass
Moisture in biomass

Pyrolysis

Volatiles
K-loaded char

Reformer loaded with
K-loaded char
RecyclingChar
Recycling

Spent
K-loadedchar

Washing

Aq. solution of K

SyngasH2 conc.: > 50 vol%Heavy tar conc.:
20 mg/Nm3-dry

Process (b): syngas production by steam reforming of tar and steam gasification of coke/char with potassium (K)-loaded char

Coke/iron composite
SyngasReformer loaded with coke/wustite
Reforming of tar
Gasification of coke

Biomass

Pyrolysis

Volatiles

Char

Coke/wustite(FeO) (Fe)Yield: H2 57.1 mol%a
Light tar 0.0188 wt%b
Heavy tar 0.0010 wt%bReheating

Deposition of coke from volatiles(Fe3O4)

Reforming of tar
Gasification of cokewustite(FeO)

Reformer loaded with iron ore(Hematite, Fe2O3)

Yield: H2 19.4 mol%a
Light tar 0.63 wt%b
Heavy tar 0.0023 wt%b

Syngasa mol per100-mol biomass Cb wt% dry-biomasscIron orec
Process (c): coproduction of syngas and iron from biomass and low-grade iron ore

for dehydration and formation ofmesoporous hematite structure before use

Fig. 3 Conceptual diagrams of biomass conversion processes proposed by our research group: process (a)24),
process (b)25), and process (c)26).

The reduced ore was more active as a catalyst for thereforming/gasification reactions, producing syngas withtar (including both light tar and heavy tar) concentration
below 10 mg/Nm3-dry. Although not demonstrated in
the work, the long time use of the ore would lead to its
deactivation. The spent coke/iron composite, however, isa useful feedstock in steel production, in particular, thatto be fed to electric arc furnaces.
Clean syngas produced from the processes (b) and (c)can be directly used as a fuel for internal combustion
engines, which limits the residual concentration of tar
to a level below 50—100 mg/Nm3-dry, and even in theapplication to Fischer-Tropsch synthesis26,27). There

have been many reports on the catalytic gasification ofvolatiles from pyrolysis, however, most of them sufferedfrom the loss of catalyst activity by coking and poisoning
due to metallic species, chlorine, sulfur, and ash 28). The
concept employed here, i.e., acceleration of coking andthe succeeding gasification of the coke with the catalystlike materials (K-loaded char and iron ore), allowed us toovercome this problem.
These studies were conducted with a fixed bed ofreformer or heavy oil sorber to simulate the proposed
processes. In their practical application, the process
would include a type of moving bed reactor, which
continuously receives and drops the solid materials.

Applications of Catalysis in the Selective Conversion of Lignocellulosic Biomass by Pyrolysis

Challenges with this technology exist in maintenance ofthe product quality by adjusting the balance between thefeeding and dropping rates. To cope with this issue, forexample, one of our current researches focuses on kinetic
analysis to simulate the reactions, which occur in themoving bed reactor, such as pyrolysis and gasification.
The application to other feedstocks such as a low-grade
coal is also in progress.

3. Catalyzed pyrolysis of biomass

To increase a content of the target compound in the
product liquid, several methods have been proposed tocatalytically-change the mechanism of pyrolysis, but the
number is very limited. The presence of alkaline cations
in biomass is known to affect the mechanism of thermal
decomposition during the pyrolysis. These cations
cause fragmentation of the monomers that comprise thenatural polymer chains, rather than the predominant
depolymerization that occurs in their absence8). Liquidacids such as sulfuric acid, hydrochloric acid, phosphoricacid, and Lewis acids, if impregnated, also work as acatalyst for pyrolysis.
Typical products from the catalyzed pyrolysis ofbiomass are summarized in reports by Mohan et al.8)
and Zhou et al.7). The products include levoglucosan,
levoglucosenone and furans as a main product, all ofwhich are cellulose derivatives (Fig. 4). The catalysis
thus seems to be effective for the selective conversion ofcellulose, but not for hemicellulose and lignin.

OH
O
HO

O

OH

HO
O

O

OH

CelluloseOH

58.1% in volatiles,
phosphoric acid,fast pyrolysis 38)

42.4%, sulfuric acid,pyrolysis in sulfolane
under mild vacuum 39)
O
78.3% in volatiles,
phosphoric acid,fast
pyrolysis 36)
O
Levoglucosenone 8.1%, sulfatedzirconia, catalytic fastOpyrolysis 31)
O

n

O

OH

17.2%, ferrous sulfate, HOOHvacuum pyrolysis 29)
LevoglucosanOHOO

8.8%, sulfuric acid,pyrolysis in sulfolane
under steam/N2 flow 39)

5-HydroxymethylfurfuralO

O

Furfural
26.9%, sulfuric acid,pyrolysis in sulfolane
under steam/N2 flow 39)

Fig. 4 Typical products from catalyzed pyrolysis ofcellulose.
Richards and Zheng29) investigated the influence ofincorporation of several different individual metal ions
into cottonwood on the products from vacuum pyrolysis.
They observed K, Li and Ca induced the formation ofhigh char and low tar yields, while all of the other ions(Mg, Mn, Fe, Co, Ni, Cu, and Zn), especially transition
metals, increased the yield of levoglucosan. Julien etal.30) examined vacuum pyrolysis of acid-impregnated(H2SO4, HCl, HNO3) cellulose. X-ray scattering showed
SO42– and Cl– were incorporated into the cellulose
structure by the impregnation. Those inorganic ions
induced the formation of high yields of char and waterand low yields of tar, and favored the formation ofhydroxyacetaldehyde, acetic acid, and formic acid atthe expense of levoglucosan. In contrast, no significant
change in product yields was observed for cellulose
pretreated with HNO3.
Levoglucosenone(1,6-anhydro-3,4-dideoxy-β-D glycero-hex-3-enopyranose-3-ulose) is one of the
products from the pyrolysis of cellulose, having a
multifunctional C6 monomer structure. Due to its uniquestructure, levoglucosenone has been expected to serve asa feedstock for the synthesis of natural products (suchas tetrodotoxin, multistriatin, rare sugars, Ras activation
inhibitors) and chiral auxiliaries for application in otherreactions31). Other uses of levoglucosenone can be foundelsewhere32,33). However, the synthetic exploitationof levoglucosenone has been limited and has not led
to large-scale commercialized processes because
levoglucosenone is not available directly from natureand its preparation from monosaccharide precursors
requires several uneconomic steps34). In a series ofstudies, Dobele et al.35–38) reported that fast pyrolysis ofcellulose pretreated with phosphoric acid or iron (III)sulfate selectively produced levoglucosenone. Maximum
levoglucosenone content in the volatile product of 78%
was reached by impregnation of phosphoric acid at
160 ºC36). The result was attributed to the catalysis of
the cellulose depolymerization and dehydration in thepresence of acid from the pretreatment. Clearly, directly
employing catalysts in the pyrolysis of cellulose can
improve the selectivity to levoglucosenone. However,
the yield of levoglucosenone, so far observed, withphosphoric acid impregnation method is less than 10%
probably due to the accelerating effect of the acid forchar formation31,34). In contrast, the catalyzed pyrolysis insulfolane proposed by Kawamoto et al.39) produced lessor no char of the cellulose. The yield of levoglucosenone
reached up to 42.2% under mild vacuum condition.
They experimentally clarified the degradation pathwayof cellulose to levoglucosenone via levoglucosan, whilesuggested the partial existence of direct pathway tolevoglucosenone. The drawbacks of this method are
the low concentration of cellulose and difficulty inseparating the products from the solvent. Recently,
some new techniques utilizing a solid acid31) catalyst
and microwave40) have also been proposed to facilitatelevoglucosenone production.
Our approach to efficient production of levoglucosenone
is the use of ionic liquid (IL)41). ILs possess a varietyof special properties, including low vapor pressure,high thermal stability and especially solvent power forcellulose. Since the pioneering research by Rogers etal.42), ILs have been used as “green” solvents for liquidphase catalytic conversion of cellulose into valuable

Journal of Novel Carbon Resource Sciences, Vol.6, Sep. 2012

chemicals, e.g., 5-hydroxymethylfurfural (5-HMF) and
furfural43–45). We used the IL as a reusable catalyst for
pyrolysis of cellulose (Fig. 5). Catalyzed pyrolysis withliquid acids (such as phosphoric acid) proceeds witha partial consumption of the acids46,47). It is therefore
difficult to recover the acids from the char after thepyrolysis.
IL: ionic liquid

High-value chemical

Pyrolysis(Levoglucosenone)

Catalysis of IL
Cellulose/IL
mixtureChar/IL
Cellulose

Extraction of IL
Reuse of IL

Char

Fig. 5 Process flow of the proposed cellulose pyrolysis
using IL as a reusable catalyst.
SeveralILs(1-butyl-2,3-dimethylimidazolium[BMMIM] type) having different anion were mixed withcellulose in equal amount, and the mixture was tested
for pyrolysis using a thermogravimetric analyzer (TGA).
Mass change curves in Fig. 6 provide useful information
concerning an applicability of IL to the proposed
process. The mixtures with [BMMIM]BF4, CF3SO3, and(CF3SO2)2N lost their weight in two steps. The first massloss (on the lower temperature side) was caused by thepyrolysis of cellulose, and the second one was primarily
caused by decomposition of IL. Among them, the massdecrease by the pyrolysis of cellulose started at thelowest temperature when [BMMIM]CF3SO3 was used.
The isolation of temperature range for cellulose pyrolysis
and IL decomposition strongly supports the possibility ofIL reutilization.

100

Mass change [%]Cellulose

80
60

0
100

X = (CF3SO2)2N

X = ClCellulose+N

20

X = BF4

X = CF3SO3

40

X = PF6N+

X: anion
BMMIM: cation

200

More importantly, the pyrolysis of cellulose at lower
temperature than pure cellulose indicates the catalysis
of IL toward the pyrolysis. Table 1 compares the yieldof levoglucosenone and char from the pyrolysis ofcellulose mixed with [BMMIM]CF3SO3 to that of purecellulose and phosphoric acid impregnated cellulose.
The highest yield of levoglucosenone, 27.6 mol%, wasobtained by the proposed method, while the char yield
was lower than that from phosphoric acid impregnatedcellulose. This result demonstrated that the catalysisof [BMMIM]CF3SO3 selectively directed toward thedehydration and the splitting of the glycosidic bond ofcellulose, not toward the formation of char. Furthermore,
IL could be fully recovered from the residue of pyrolysis
by extraction with ethanol, and the reused IL gave an
identical product distribution as shown in Table 1.

300

400

500

600

Fig. 6 Mass change curves of cellulose and cellulose
mixed with [BMMIM] type ILs at 1:1 on a mass
basis during pyrolysis: N2 200 mL/min, heating
rate = 5 ºC/min.

Table 1 Yield of levoglucosenone and char frompyrolysis41).
Yield [wt% on a cellulose mass basis]
SampleCellulose
Cellulose/PAb
Cellulose/ILc
Cellulose/ILd

TPa
350
300
300
300

Levoglucosenone (in mol%)
2.4 (3.1)
8.9 (11.5)
21.4 (27.6)
20.7 (26.6)

Char
24.6
50.7
32.7
31.4

. b Cellulose impregnated with 3 wt % ofphosphoric acid. c IL = [BMMIM]CF3SO3. d Using [BMMIM]CF3SO3
recovered from pyrolysis.
a

Although the selectivity of levoglucosenone was
71.3 wt% for condensable matter (excluding water) in
the study (reference 41)), recent study found that the
selectivity could be further increased with the slower
pyrolysis, e.g., heating rate of 1 ºC/min. In addition,condensation of volatiles from the pyrolyzer with asequence of three condensers successfully separated
the product compounds. In detail, the volatiles firstly
entered cold traps (–30 and -70 ºC), where the water andmajor part of furans were captured. Because dehydrated
sugars tend to form aerosol particle, nearly half of themincluding levoglucosenone escaped from the cold trap
and was finally captured by an aerosol filter trap. As
shown in Fig. 7, the concentration of levoglucosenone in
the filter trap exceeded 90 wt% (even including water)
with the yield of 17.1 wt% of cellulose. Optimizationof operating conditions, such as a flow rate of carrier
nitrogen and volume of cold traps, might further enhance
the purity of the product levoglucosenone.
The catalysis of ILs significantly depended on thetype of counterpart anion. The selective production oflevoglucosenone was observed only in the use of CF3SO3–
among the anions investigated, while the change ofcation from 1-butyl-2,3-dimethylimidazolium to 1-butyl3-methylimidazolium had little influence on the productdistribution. Further investigation of the effect of anion
may lead to the selective production of other cellulose
derivatives. A combined process with in-situ catalytic

Applications of Catalysis in the Selective Conversion of Lignocellulosic Biomass by Pyrolysis

0.4
6.0 2.1

2.0
0.9

0.9

Cold trap

1.1
0.5
0.5

Filter trap
Levoglucosenone
DGPa

Acknowledgements: Our works cited in this paper werecarried out with financial supports by an R&D projectcommissioned by The Ministry of Environment (MOE)of Japan, the Funding Program for the Next Generation
World-Leading
Researchers(NEXT
Program)established by The Japan Society for the Promotion of
Science (JSPS), Strategic Funds for the Promotion of
Science and Technology operated by Japan Science andTechnology Agency (JST), and JSPS Grant-in-Aid forYoung Scientists (B). Authors are also grateful to the
Global-Center of Excellence in Novel Carbon Resource
Sciences, Kyushu University.

FuransOther organics
Cold trapaWater

1,4:3,6-Dianhydro- -D-glucopyranose (DGP)

Fig. 7 Composition of liquid products in each condenser(wt%) from pyrolysis of cellulose/[BMMIM]
CF3SO3 mixture.

reforming of volatiles will also give a wider variety of
product chemicals. For example, because anhydrosugars
including levoglucosenone are one of the precursors
of furan compounds as shown in Fig. 2 (a), it might bepossible to develop a pyrolysis method to selectively
produce furans such as 5-HMF if levoglucosenone canbe catalytically converted. 5-HMF is expected as aplatform chemical that can be converted into a variety
of useful acids, aldehydes, alcohols, and amines, as wellas the promising fuel 2,5-dimethylfuran43). The use ofsaccharides or polysaccharides other than cellulose forcatalyzed pyrolysis would be an option.

4. Conclusions

Variety of the products, which can be selectively
produced from the pyrolysis of biomass, is still limited.
One of the reasons is that the pyrolysis decomposesbiomass into too many compounds to be refined. This
work presents two ways to cope with this problem bycatalytic reaction: 1) catalytic reforming of a coherent
group of compounds derived from volatiles, e.g.,hydrocarbon pool in Fig. 2 and coke in Fig. 3 process(b) and (c), and 2) controlling the pyrolysis mechanismwith catalysis. Our approach to the reforming of volatiles
resulted in high quality products by the utilization ofcoke formation potential of volatiles. The use of IL in thepyrolysis of cellulose gave new insight into not only the
production of levoglucosenone, but also the utilization of
ILs in the field of cellulose and/or biomass processing.
In technical and economic viewpoints, pyrolysis has
clear advantages over other conversion methods. As
described in this review, the application of catalysis has
a great potential to put the pyrolysis of biomass into use,although this research area is still in its infancy.

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