249
get 2-methoxy phenylacetate [22]. Also, the MCM-41 catalyst was found to be
useful for converting ethanol to ethylene at temperatures above 350 °C [23]. For the
conversion of cellulose to hydrogen, a higher hydrogen yield was obtained with Ni/
KIT6 and Ni/SBA15 [24]. The better performance of the silica-supported catalyst is
attributed to higher BET surface area and reduced diffusional resistance due to large
pore diameter. The bimetallic catalyst can also be supported on silica (CoCu/
SBA-15) and used for hydrogenation reactions such as furfural to furan. In a similar
reaction, about 99% conversion of furfural can be achieved with 80% selectivity to
furfuryl alcohol. The high conversion is due to the synergistic effect of metal-metal
and metal-support interactions [25].
Metal, metal oxides, and their combinations are the commonly used catalysts for
oxidation and hydrogenation reactions. In general, the metals present on the left
side of the transition metal series in the periodic table exhibit good activity for
oxidation reactions in their bulk form. At the same time, many materials (like Au for
oxidation) that do not exhibit any activity in their bulk form become active catalysts
at the nanoscale (1–100 nm) due to improved surface and electronics properties
[26]. Hence, careful selection of metal catalysts for the oxidation process requires
information of their position in the periodic table as well as their properties at the
nanoscale. Mixed metal oxides exhibit attractive catalytic activity due to their
enriched acid-base, redox, and surface area properties. However, their oxidizing
ability for biomass oxidation can reduce due to excess basicity. As biomass
conversion is conducted at harsh hydrothermal conditions, the hydrothermal
stability of the catalyst is of paramount importance. Importantly, metal oxides such
as TiO 2 , ZrO 2 , CeO 2 , and ZrO 2 exhibit higher hydrothermal stability [27]. Despite
all these advantages, the control over the aggregation of metal nanoparticles during
synthesis and reaction remains a great challenge. This can be tackled by depositing
the nanoparticles on high surface area metal oxide support. Metal-support interaction
enhances the properties of nanoparticles [28]. For example, PtSn/γ-Al 2 O 3 was able
to convert mono- and polysaccharides with higher yield compared to PtSn/C [29].
A well-dispersed Ni nanoparticle on SiO 2 was used in the levulinic acid hydrogenation
to γ-valerolactone and performed well due to the presence of optimum porosity and
highly dispersed nanoparticles [30].
2.2.2 Micro- and Mesoporous Catalysts for Catalytic Processing
of Edible/Non-edible Biomass
The edible biomass comprises lipids and starch, whereas non-edible biomass
includes lignocellulosic materials. Among the edible biomass feedstocks, sugarcane
or corn is converted to bioethanol via the fermentation route, whereas edible oils
(sunflower, soybean, safflower, and palm), as well as non-edible oils (jatropha,
karanja), are converted to biodiesel via catalytic transesterification with alcohols
(methanol or ethanol). Both homogeneous (methanolic NaOH and KOH) and
heterogeneous catalysts (ZnO/HZMS-5, PbO/HZSM-5) are used for
transesterification reactions [31–33]. Homogeneous transesterification reactions are
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…
get 2-methoxy phenylacetate [22]. Also, the MCM-41 catalyst was found to be
useful for converting ethanol to ethylene at temperatures above 350 °C [23]. For the
conversion of cellulose to hydrogen, a higher hydrogen yield was obtained with Ni/
KIT6 and Ni/SBA15 [24]. The better performance of the silica-supported catalyst is
attributed to higher BET surface area and reduced diffusional resistance due to large
pore diameter. The bimetallic catalyst can also be supported on silica (CoCu/
SBA-15) and used for hydrogenation reactions such as furfural to furan. In a similar
reaction, about 99% conversion of furfural can be achieved with 80% selectivity to
furfuryl alcohol. The high conversion is due to the synergistic effect of metal-metal
and metal-support interactions [25].
Metal, metal oxides, and their combinations are the commonly used catalysts for
oxidation and hydrogenation reactions. In general, the metals present on the left
side of the transition metal series in the periodic table exhibit good activity for
oxidation reactions in their bulk form. At the same time, many materials (like Au for
oxidation) that do not exhibit any activity in their bulk form become active catalysts
at the nanoscale (1–100 nm) due to improved surface and electronics properties
[26]. Hence, careful selection of metal catalysts for the oxidation process requires
information of their position in the periodic table as well as their properties at the
nanoscale. Mixed metal oxides exhibit attractive catalytic activity due to their
enriched acid-base, redox, and surface area properties. However, their oxidizing
ability for biomass oxidation can reduce due to excess basicity. As biomass
conversion is conducted at harsh hydrothermal conditions, the hydrothermal
stability of the catalyst is of paramount importance. Importantly, metal oxides such
as TiO 2 , ZrO 2 , CeO 2 , and ZrO 2 exhibit higher hydrothermal stability [27]. Despite
all these advantages, the control over the aggregation of metal nanoparticles during
synthesis and reaction remains a great challenge. This can be tackled by depositing
the nanoparticles on high surface area metal oxide support. Metal-support interaction
enhances the properties of nanoparticles [28]. For example, PtSn/γ-Al 2 O 3 was able
to convert mono- and polysaccharides with higher yield compared to PtSn/C [29].
A well-dispersed Ni nanoparticle on SiO 2 was used in the levulinic acid hydrogenation
to γ-valerolactone and performed well due to the presence of optimum porosity and
highly dispersed nanoparticles [30].
2.2.2 Micro- and Mesoporous Catalysts for Catalytic Processing
of Edible/Non-edible Biomass
The edible biomass comprises lipids and starch, whereas non-edible biomass
includes lignocellulosic materials. Among the edible biomass feedstocks, sugarcane
or corn is converted to bioethanol via the fermentation route, whereas edible oils
(sunflower, soybean, safflower, and palm), as well as non-edible oils (jatropha,
karanja), are converted to biodiesel via catalytic transesterification with alcohols
(methanol or ethanol). Both homogeneous (methanolic NaOH and KOH) and
heterogeneous catalysts (ZnO/HZMS-5, PbO/HZSM-5) are used for
transesterification reactions [31–33]. Homogeneous transesterification reactions are
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…