Study on furfural conversion into aromatics over Zn/HZSM-5 and Fe/HZSM-5 catalysts

Cite this paper: Vietnam J. Chem., 2020, 58(5), 602-609 Article 
DOI: 10.1002/vjch.202000025 
602 Wiley Online Library © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH 
Study on furfural conversion into aromatics over Zn/HZSM-5 and 
Fe/HZSM-5 catalysts 
Huynh Van Nam
1,2
, Truong Thanh Tam
2
, Van Dinh Son Tho
1* 
1
School of Chemical Engineering, Hanoi University of Science and Technology, 
1 Dai Co Viet, Hai Ba Trung district, Hanoi 10000, Viet Nam 
2
Faculty of Natural Sciences, Quy Nhon University, 
170 An Duong Vuong, Quy Nhon City, Binh Dinh province 55000, Viet Nam 
Received February 26, 2020; Accepted July 28, 2020 
Abstract 
ZSM-5 zeolite material (Si/Al ratio = 25) was synthesized with silica source of TEOS and TPAOH template. The 
zeolite is modified into proton form (HZSM-5) with 343 m
2
/g of BET surface area, 324 m
2
/g of micropore area, 0.1491 
cm
3
/g of micropore volume and 5.77 nm of BJH adsorption average pore width. Zinc oxide and iron oxide are dispersed 
onto HZSM-5 catalyst surface with different contents by wet impregnation method. The results of HZSM-5, Zn/HZSM-
5, Fe/HZSM-5 catalyst materials still retain the micropore structure of ZSM-5 zeolite. These materials are used as 
catalysts for furfural pyrolysis in the inert atmosphere (N2) with the temperatures ranged from 400 to 700 °C. The 
conversion of furfural to aromatic hydrocarbons on catalysts is evaluated by furfural conversion, conversion into 
aromatics and aromatic hydrocarbons selectivity. Result shows that 3 %Zn/HZSM-5 and 2 %Fe/HZSM-5 catalyst favor 
for furfural pyrolysis at 600 
o
C. The furfural conversion, the conversion into BTXN and the BTXN selectivity are 
respectively 48.36 %, 21.18 %, 16.18 % with 3 %Zn/HZSM-5 catalyst and 64.41 %, 16.47 %, 26.81 % with 
2%Fe/HZSM-5 catalyst. These results are the basic research for the upgrade of pyrolysis oil into fuels. 
Keywords. Furanic, aromatic, ZSM-5 zeolite, pyrolysis, biomass. 
1. INTRODUCTION 
Fossil fuel resources are dwindling along with 
environmental concerns that have spurred various 
studies to produce alternative fuels from renewable 
carbon neutral sources (agricultural and forestry by-
products such as wood, sawdust, bagasse, rice husks, 
straw, etc.). The process of converting biomass on 
catalysts into biofuels is expected to replace part of 
fossil fuels (oil, coal) and solve existing problems,
[1]
which has attracted a lot of interested in research of 
scientists in the world. Furanic compounds (furan, 
furfural, 5-methyl furan, etc.) are one of the main 
components of pyrolysis oil, they are formed from 
the decomposition process of hemicellulose and 
cellulose in biomass.
[2,3]
 Among them, furfural is of 
highest interest due to its high specificity for furanic 
compounds as well as its high reactivity and 
versatility.
[4-6]
 In addition to the need to remove the 
element oxygen to improve the quality of bio-oil, the 
excess functions present in furanic compounds (such 
as high toxicity, high oxygen content, low calorific 
value, incomplete combustion and deposit 
formation, etc.) are also detrimental when it is used 
directly as a fuel. Therefore, study on furanic 
compounds conversion is needed to upgrade 
pyrolysis oil. The different types of catalysts for 
furfural conversion to biofuels, fuel additives and 
chemicals are seriously studied.
[5]
Furanic compounds are converted into aromatic 
hydrocarbons and other hydrocarbons by process of 
pyrolysis on ZSM-5 zeolite. The reaction medium 
can be inert gas (N2, He), hydrogen, methane, 
propylene, etc., the reaction temperature usually 
ranges from 400 to 700 
o
C.
[7-9]
 ZSM-5 zeolite 
catalyst is a reasonable choice because its pore size 
and structure that is suitable for a higher selectivity 
of aromatics. The metals such as Zn, Ga, Ag, Pt, Pd, 
Ir, etc. are chosen to be doped into zeolite because 
these metals are reported to be beneficial for the 
formation of aromatic compounds such as 
deoxygenation and hydrogenation reactions.
[7-14]
 In 
this paper, furfural, a specific compound of the furan 
family, will be conducted pyrolysis on HZSM-5 
catalyst and HZSM-5 catalyst is modified by oxides 
of zinc (Zn) and iron (Fe). Results are valuated 
according to conversion into aromatics and aromatic 
hydrocarbons selectivity such as benzene, toluene, 
Vietnam Journal of Chemistry Van Dinh Son Tho et al. 
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 603 
xylene and naphthalene (BTXN). 
According to Cheng et al. (2011),
[7]
 conversion 
of furan on HZSM-5 catalyst occurs by the 
mechanism as shown in figure 1. The furan 
molecules are adsorbed onto the capillary of HZSM-
5 to form intermediate compounds such as 2,2-
methylenebisfuran, benzofuran at temperatures of 
400-600 
o
C. The products are composed of CO, 
CO2, olefin (C2H4, C3H6) and aromatic compounds 
(benzene, toluene, xylene and naphtalene). The 
selectivity of aromatic hydrocarbons and olefins 
decreases with increasing WHSV, whereas the 
selectivity of unsaturated hydrocarbon compounds 
(ethylene, cyclopentadien) increases. The 
appropriate temperature for the formation of 
aromatic hydrocarbons is ranges from 450-600 
o
C. 
The selectivity of CO, CO2 and olefin increases 
when the reaction temperature is over 600 
o
C. In 
addition, the process also causes Diels-Alder 
reaction (benzofuran and water are formed by 
condensation of two furans), decarbonylation (CO 
and allene are formed from furans), oligomerization 
(olefins, aromatics and hydrogen are formed from 
allen), alkylation (forms furan and olefins) and 
condensation create coke on the catalyst surface, 
reducing catalytic activity after about 30 minutes of 
reaction. 
Figure 1: Mechanism of furan conversion into 
aromatics on HZSM-5 catalyst
[7] 
F ... ies of catalyst samples 
ID Catalyst samples SBET (m
2
/g) Smicro (m
2
/g) Sext (m
2
/g) Vp (cm
3
/g) dp (nm) 
1 HZ 343 324 19 0.1494 5.77 
2 3ZnHZ 302 280 22 0.1294 5.86 
3 2FeHZ 313 271 41 0.1247 4.94 
SBET: BET surface area; Smicro: Micropore area; Sext: External surface area; Vp: Micropore volume; 
dp: BJH Adsorption average pore width. 
3.2. Effect of metal content on HZSM-5 
To compare the effect of zinc and iron oxides 
content on the HZSM-5 catalyst activity, the study 
conducts many changes of zinc and iron oxides 
content on the surface of HZSM-5 catalyst. The 
results are evaluated by the furfural conversion and 
aromatics selectivity (BTXN). During the 
experimental process, the study selects three 
representative catalyst samples for comparison. 
Figure 6 shows the selectivity of aromatic 
hydrocarbons during furfural pyrolysis on different 
catalysts at 600 
o
C. When furfural pyrolysis is non-
catalytic it doesn't produce aromatic hydrocarbons. 
The BTXN selectivity of HZSM-5 catalyst is quite 
low about 2.32 %. The main product is benzene 
accounting for 54.95 % of total BTXN products, the 
remaining is toluene, naphthalene and without 
xylene. When catalyst is added by zinc or iron 
oxides, the BTXN selectivity is significantly 
increased. Specifically, HZSM-5 catalyst contains 1 
wt.% Zn, the BTXN selectivity is up to 15.52 %, 
16.18 % for the catalyst containing 3 wt.% Zn and 
36.34 % for the catalyst containing 5 wt.% Zn. 
Aromatic hydrocarbon products are BTX and only a 
small amount of naphthalene. 
NC HZ 1ZnHZ 3ZnHZ 5ZnHZ 1FeHZ 2FeHZ 3FeHZ
0
10
20
30
40
50
60
S
e
le
c
ti
v
it
y
 (
%
)
 Benzene
 Toluene
 Xylene
 Naphthalene
 BTXN
Figure 6: BTXN selectivity of furfural pyrolysis on 
HZ, ZnHZ and FeHZ catalysts 
The results are similar to furfural pyrolysis with 
Fe-containing catalysts. When Fe content is 
increased from 1 to 3 wt.%, the BTXN selectivity 
also is increased, respectively by 16.47 %, 26.81 % 
and 32.10 %. In addition, if the BTXN selectivity is 
almost the same as with the Zn-containing catalyst, 
the selectivity of benzene is the highest with the Fe-
containing catalyst. Especially, the selectivity of 
naphthalene increases significantly compared to Zn-
containing catalysts. This result is completely 
consistent with the studies of Li et al. (2016)
[17]
 or 
the studies of Mullen et al. (2015).
[24]
 The 
Fe/HZSM-5 catalyst is highly activity for formation 
of benzene and naphthalene. 
Figure 7 shows the furfural conversion and 
conversion into BTXN of catalysis pyrolysis at 600 
o
C. The furfural conversion is the weight of furfural 
transformed into products. Meanwhile, conversion 
into BTXN is the weight of carbon in furfural 
transformed into carbon in aromatic hydrocarbons 
(BTXN). Results show that furfural catalysis 
pyrolysis has a lower furfural conversion than non-
catalytic pyrolysis. If the furfural conversion of 
non-catalytic pyrolysis (NC sample) is 71.3 %, the 
furfural conversion of HZSM-5 catalytic pyrolysis is 
only 14.14 %. The addition of zinc and iron oxides 
to HZSM-5 catalyst makes the increassing 
conversion of pyrolysis. The furfural conversion 
increases in proportion to the amount of metal on 
NC HZ 1ZnHZ 3ZnHZ 5ZnHZ NC HZ 1FeHZ 2FeHZ 3FeHZ
0
10
20
30
40
50
60
70
80
90
C
o
n
v
e
rs
io
n
 (
%
)
 Furfural conversion
 Conversion into BTXN
Figure 7: Furfural conversion and conversion into 
BTXN on HZ, ZnHZ and FeHZ catalysts at 600 
o
C 
Vietnam Journal of Chemistry Van Dinh Son Tho et al. 
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 607 
catalyst. Fe-containing catalysts have higher furfural 
conversion than Zn-containing catalysts. The 
furfural conversion is 21.35 %, 48.36 % and 55.09 
% with 1, 3 and 5 wt.% Zn-containing catalyst, 
respectively. While the furfural conversion is 53.41 
%, 64.41 % and 67.16 % with 1, 2 and 3 wt.% Fe-
containing catalyst, respectively. 
On the other hand, adding metal oxide to surface 
of HZSM-5 catalyst significantly increases aromatic 
hydrocarbon conversion of furfural. The conversion 
into BTXN of furfural is only 3.22 % with HZSM-5 
catalyst. But if adding 1 wt.% Zn to catalyst, the 
conversion into BTXN of furfural is 21.02 %. This 
value is 21.18 % with 3 wt.% Zn-containing catalyst 
and 34.39 % with 5 wt.% Zn-containing catalyst. 
The same phenomenal also observed with Fe-
containing catalysts but it is lower than Zn-
containing catalysts. The conversion into BTXN of 
furfural on Fe-containing catalysts are respectively 
13.22 %, 16.47 % and 16.27 % for catalysts 
containing 1, 2 and 3 wt.% Fe. So, when the Fe 
content on the catalyst increases, the furfural 
conversion increases but the conversion into BTXN 
is approximately the same. Therefore, it can be 
concluded that the aromatic hydrocarbon generation 
activity of the Zn-containing catalyst is higher than 
that of the Fe-containing catalyst. 
The activity aromatization of HZSM-5 catalyst 
increases when the metal oxides of Zn and Fe are 
added to the surface of the catalyst. Especially, the 
increasing of Zn content also lead to the increase of 
catalytic activity for aromatization. However, during 
the study we also found that, when the metal content 
on the catalyst is increased, the efficiency of liquid 
products decreases and gas efficiency increases. 
With the purpose to attain high proportion of liquid 
component, the favorable metal content added into 
the surface of the catalyst is 3 wt.% Zn or 2 wt.% Fe. 
This result is consistence to others reports.
[17,18,23,24]
3.3. The effect of temperature 
The influence of temperature on furfural pyrolysis is 
assessed through pyrolysis on 3ZnHZ catalyst from 
400 to 700 
o
C and the results are shown in Figure 8. 
Furfural conversion is only 8.31 % at 400 
o
C and 
there are not any aromatic hydrocarbons in liquid 
products. When the pyrolysis temperature increases 
to 500 
o
C, the furfural conversion increases to 13.2 
% with conversion into BTXN is 8.93 % and the 
BTXN selectivity is 6.75 %. The xylene content is 
obtained highest with the selectivity of about 35.29 
% in aromatic hydrocarbon composition. At 600 
o
C, 
the furfural conversion is 48.36 % with conversion 
into BTXN is 21.18 %. The BTXN selectivity 
increases to 16.18 % at this temperature. Benzene, 
toluene and xylene selectivity quite balances while 
naphthalene selectivity decreases (only 3 % 
compared to 7.75 % at 500 
o
C). This proves that the 
pyrolysis process begins to break intermediate 
compound molecules to produce more light products 
and gas in high temperatures. At 700 
o
C, the furfural 
conversion is 64.93 % with conversion into BTXN is 
21.98 % and the BTXN selectivity increases to 
36.85 %. The selectivity of benzene, toluene, xylene 
and naphthalene are similar at 600 
o
C. It is also 
observed that the liquid yield decreases significantly 
at temperatures higher than 700 
o
C, while the gas 
yield increases rapidly. Therefore, with the purpose 
for formation of aromatic hydrocarbons, the value of 
700 
o
C is most appropriate reaction temperature. 
400 500 600 700
0
10
20
30
40
50
60
70
C
o
n
v
e
rs
io
n
 (
%
)
T (
o
C)
 Furfural conversion
 Conversion into BTXN
400 500 600 700
0
10
20
30
40
50
S
e
le
c
ti
v
it
y
 (
%
)
T (
o
C)
 Benzene
 Toluene
 Xylene
 Naphthalene
 BTXN
Figure 8: The effect of temperature to furfural pyrolysis on catalyst 3ZnHZ 
Vietnam Journal of Chemistry Study on furfural conversion into aromatics 
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 608 
4. CONCLUSIONS 
ZSM-5 zeolite material has been successfully 
synthesized with Si/Al = 25 ratio. The ZSM-5 
zeolite was modified to form HZSM-5, Zn/HZSM-5 
and Fe/HZSM-5 with BET surface area is 
respectively 343 m
2
/g, 302 m
2
/g and 313 m
2
/g. They 
are used as catalyst for furfural pyrolysis. HZSM-5 
catalyst containing 3 wt.% Zn (3ZnHZ) and HZSM-
5 catalyst containing 2 wt.% Fe (2FeHZ) are the 
most suitable for furfural pyrolysis at 600 
o
C. The 
results of the furfural conversion, the conversion 
into BTXN and the BTXN selectivity are, 
respectively, 48.36 %, 21.18 %, 16.18 % on 3ZnHZ 
catalysts and 64.41 %, 16.47 %, 26.81 % on 2FeHZ 
catalysts. Furfural pyrolysis for the purpose of 
forming aromatic hydrocarbons, the 700 
o
C is most 
appropriate reaction temperature. 
Acknowledgement. The research team is grateful to 
the School of Chemical Engineering, Hanoi 
University of Science and Technology, and Faculty 
of Natural Sciences, Quy Nhon University for 
support. 
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Corresponding author: Van Dinh Son Tho 
School of Chemical Engineering 
Hanoi University of Science and Technology (HUST) 
1, Dai Co Viet street, Hai Ba Trung district, Hanoi 10000, Viet Nam 
E-mail: tho.vandinhson@hust.edu.vn.