253
materials are preferred for the process involving adsorption and surface reactions
owing to its high BET surface area of about 2600 m
2
/g [49]. Fructose dehydration
to 5-hydroxymethylfurfural (5-HMF) was carried out using GO in the presence of
isopropanol mediated dimethyl sulfoxide (DMSO), and 87% yield of HMF was
obtained. The high performance of the catalyst was attributed to the synergistic
effect between hydrogen bonding and fructose [50].
In the process of producing fuel precursors, the hydroxyalkylation/alkylation
condensation of 2-methyl furan with hydroxyl group-containing compounds is
catalyzed by improved GO (IGO) to yield C 12 to C 21 fuel precursors in liquid form.
The IGO was highly selective to C 15 fuel precursor (yield 95% at 60 °C) and found
to be a promising acid catalyst for C-C coupling reactions when compared with
commonly used framework zeolites [51]. GO-based materials have the potential to
become alternative conventional catalysts and need focused efforts for their
development. Though there are numerous advantages of graphene-based catalysts,
the synthesis of graphene and its derivatives remains a challenge [48]. Also, attention
is to be paid for possible health issues for humans.
Carbon Nanotubes (CNTs) as Catalysts
Carbon nanotubes are used as catalyst support and show excellent performance for
stabilizing metal nanoparticles (NPs), metal oxides, and acid/base functionalities. It
also prevents particle aggregation on the support surface, thereby suppressing the
formation of metal complex on the catalyst surface. For example, sorbitol was
converted to ethylene glycol and 1,2-propanediol over Ru/CNTs catalyst. The
reaction results can be further improved by the addition of WOx to Ru/CNTs due to
synergy between WO x and Ru. The catalyst was recycled several times and found to
be stable against leaching and poisoning. The yield of ethylene glycol and
1,2-propanediol was reported as 25.6% and 34.6%, respectively, when the reaction
is conducted using Ru0.25WO x /CNTs at 205 °C and 5.0 MPa. This can be the
alternate route for the production of ethylene glycol and 1,2-propanediol, which, at
present, produced commercially from petroleum-derived ethylene and propylene
[52]. In another study, 2,5-diformylfuran (DFF) was produced by aerobic oxidation
for biomass-based 5-hydroxymethylfurfural (5-HMF) over vanadium dioxide
immobilized on polyaniline-functionalized CNTs (VO 2 -PANI/CNT). The maximum
yield of DFF was 96% when 100% 5-HMF was converted with O 2 as the oxidant.
The selective adsorption of HMF on the catalyst surface inhibited the undesired
oxidation of DFF, resulting in higher yield [53].
CNT-based solid acid catalyst (CNT-P-SO 3 H) showed excellent results for
transesterification as well as esterification reactions to produce biodiesel. The
catalyst suffered a loss of partial activity after six cycles, which cannot be regenerated [54]. A multiwalled carbon nanotube (Net 3 -MWCNT) catalyst with a
grafted amino group is also reported for the transesterification reaction. The 77%
conversion of glyceryl tributyrate was observed after 8 h. The conversion was on
the higher side compared to commonly used hydrotalcite catalyst (51%
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…
materials are preferred for the process involving adsorption and surface reactions
owing to its high BET surface area of about 2600 m
2
/g [49]. Fructose dehydration
to 5-hydroxymethylfurfural (5-HMF) was carried out using GO in the presence of
isopropanol mediated dimethyl sulfoxide (DMSO), and 87% yield of HMF was
obtained. The high performance of the catalyst was attributed to the synergistic
effect between hydrogen bonding and fructose [50].
In the process of producing fuel precursors, the hydroxyalkylation/alkylation
condensation of 2-methyl furan with hydroxyl group-containing compounds is
catalyzed by improved GO (IGO) to yield C 12 to C 21 fuel precursors in liquid form.
The IGO was highly selective to C 15 fuel precursor (yield 95% at 60 °C) and found
to be a promising acid catalyst for C-C coupling reactions when compared with
commonly used framework zeolites [51]. GO-based materials have the potential to
become alternative conventional catalysts and need focused efforts for their
development. Though there are numerous advantages of graphene-based catalysts,
the synthesis of graphene and its derivatives remains a challenge [48]. Also, attention
is to be paid for possible health issues for humans.
Carbon Nanotubes (CNTs) as Catalysts
Carbon nanotubes are used as catalyst support and show excellent performance for
stabilizing metal nanoparticles (NPs), metal oxides, and acid/base functionalities. It
also prevents particle aggregation on the support surface, thereby suppressing the
formation of metal complex on the catalyst surface. For example, sorbitol was
converted to ethylene glycol and 1,2-propanediol over Ru/CNTs catalyst. The
reaction results can be further improved by the addition of WOx to Ru/CNTs due to
synergy between WO x and Ru. The catalyst was recycled several times and found to
be stable against leaching and poisoning. The yield of ethylene glycol and
1,2-propanediol was reported as 25.6% and 34.6%, respectively, when the reaction
is conducted using Ru0.25WO x /CNTs at 205 °C and 5.0 MPa. This can be the
alternate route for the production of ethylene glycol and 1,2-propanediol, which, at
present, produced commercially from petroleum-derived ethylene and propylene
[52]. In another study, 2,5-diformylfuran (DFF) was produced by aerobic oxidation
for biomass-based 5-hydroxymethylfurfural (5-HMF) over vanadium dioxide
immobilized on polyaniline-functionalized CNTs (VO 2 -PANI/CNT). The maximum
yield of DFF was 96% when 100% 5-HMF was converted with O 2 as the oxidant.
The selective adsorption of HMF on the catalyst surface inhibited the undesired
oxidation of DFF, resulting in higher yield [53].
CNT-based solid acid catalyst (CNT-P-SO 3 H) showed excellent results for
transesterification as well as esterification reactions to produce biodiesel. The
catalyst suffered a loss of partial activity after six cycles, which cannot be regenerated [54]. A multiwalled carbon nanotube (Net 3 -MWCNT) catalyst with a
grafted amino group is also reported for the transesterification reaction. The 77%
conversion of glyceryl tributyrate was observed after 8 h. The conversion was on
the higher side compared to commonly used hydrotalcite catalyst (51%
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…