33
option as hydrogen donors because they are not corrosive, and they may be obtained
from ethanol or butanol using biomass as a substrate [237, 238].
The biggest challenge of having a competent and reasonable HDO is the selection of the catalyst which should be efficient, economical and environmentally
friendly. The catalyst stability may be an issue to convert furfural into 2-MF due to
the high temperatures, which increases the energy cost and the coke production as
well [220]. The deactivation catalysts during the 2-MF production through furfural
hydrogenation is the main issue of the process because of the production of undesired co-products (furan, tetrahydrofuran and C-4 compounds) [239]. Additionally,
this method of conversion is quite exothermic (142 kJ/mol), causing difficulties in
terms of temperature control [240].
Chromium-based catalysts were described as efficient for 2-MF production,
while their toxicity makes them less attractive [224]. Molybdenum carbide has a
high selectivity to convert furfural into 2-MF, but it presents very acidic features,
stimulating the polymerization of furfural and creating an unstable environment for
the HDO process [241]. Although precious metals such as ruthenium and palladium
showed a good furfural conversion yield, they are extremely expensive, easily deactivated, hard to regenerate and not economically viable [215]. Mesoporous silica
catalysts contain large surface areas, and they can convert 82% of furfural; nevertheless, the process is extremely slow (more than 25 h), and it leads to the formation
and deposit of carbon in the catalyst substrate, which leads to catalyst deactivation
and consequent reduction of HDO reactions between the surface and the product [220].
Copper-based catalysts are mentioned as the most promising option to convert
furfural into 2-MF [226, 242]. Recently, the combination between Cu and Zn or Cu
and Mn as a catalyst showed strong stability and efficiency in 2-MF production by
HDO. The good interaction among these two groups of metals brings the production
of mixed oxide phases and, consequently, a breakage of the C-O bond [228, 239].
Moreover, the combination between manganese/zinc Cu-based catalysts and Al 2 O 3
and SiO 2 supports increases the selectivity and activity of the HDO process [239].
Both catalytic supports are cheap, practical to be used in industry, and they promote
the interaction and dispersion of copper, improving the catalytic performance [226].
8.1 Xylose-Rich Biomass
One of the most accessible and inexpensive green resources for the biofuel production and bioenergy area is lignocellulosic agricultural wastes [243]. Present
approaches to exploit biomass such as pure cellulose extraction or combustion to
produce electricity are damaging the environment and not profitable for the industry
[244]. Therefore, thermochemical processes become more prevalent for converting
biomass into valued products and thus establishing a different pathway for the
application of lignocellulosic residues regarding profitability and sustainability [81].
Thermochemical Conversion of Biomass and Upgrading of Bio-Products to Produce…
option as hydrogen donors because they are not corrosive, and they may be obtained
from ethanol or butanol using biomass as a substrate [237, 238].
The biggest challenge of having a competent and reasonable HDO is the selection of the catalyst which should be efficient, economical and environmentally
friendly. The catalyst stability may be an issue to convert furfural into 2-MF due to
the high temperatures, which increases the energy cost and the coke production as
well [220]. The deactivation catalysts during the 2-MF production through furfural
hydrogenation is the main issue of the process because of the production of undesired co-products (furan, tetrahydrofuran and C-4 compounds) [239]. Additionally,
this method of conversion is quite exothermic (142 kJ/mol), causing difficulties in
terms of temperature control [240].
Chromium-based catalysts were described as efficient for 2-MF production,
while their toxicity makes them less attractive [224]. Molybdenum carbide has a
high selectivity to convert furfural into 2-MF, but it presents very acidic features,
stimulating the polymerization of furfural and creating an unstable environment for
the HDO process [241]. Although precious metals such as ruthenium and palladium
showed a good furfural conversion yield, they are extremely expensive, easily deactivated, hard to regenerate and not economically viable [215]. Mesoporous silica
catalysts contain large surface areas, and they can convert 82% of furfural; nevertheless, the process is extremely slow (more than 25 h), and it leads to the formation
and deposit of carbon in the catalyst substrate, which leads to catalyst deactivation
and consequent reduction of HDO reactions between the surface and the product [220].
Copper-based catalysts are mentioned as the most promising option to convert
furfural into 2-MF [226, 242]. Recently, the combination between Cu and Zn or Cu
and Mn as a catalyst showed strong stability and efficiency in 2-MF production by
HDO. The good interaction among these two groups of metals brings the production
of mixed oxide phases and, consequently, a breakage of the C-O bond [228, 239].
Moreover, the combination between manganese/zinc Cu-based catalysts and Al 2 O 3
and SiO 2 supports increases the selectivity and activity of the HDO process [239].
Both catalytic supports are cheap, practical to be used in industry, and they promote
the interaction and dispersion of copper, improving the catalytic performance [226].
8.1 Xylose-Rich Biomass
One of the most accessible and inexpensive green resources for the biofuel production and bioenergy area is lignocellulosic agricultural wastes [243]. Present
approaches to exploit biomass such as pure cellulose extraction or combustion to
produce electricity are damaging the environment and not profitable for the industry
[244]. Therefore, thermochemical processes become more prevalent for converting
biomass into valued products and thus establishing a different pathway for the
application of lignocellulosic residues regarding profitability and sustainability [81].
Thermochemical Conversion of Biomass and Upgrading of Bio-Products to Produce…