254
conversion) under identical conditions [55]. Thus, CNTs provide a good option as
catalysts and support for the biomass conversion process.
2.3.2 Metal-Organic Frameworks (MOFs) as Catalysts
Zeolites are known for their well-defined porous structures. Similarly, the metalorganic frameworks (MOFs) exhibit zeolite-like structure and a potential alternative
to zeolites as well as metal oxide catalysts. MOFs perform better in selected
reactions such as fructose dehydration in dimethyl sulfoxide (DMSO). MOFs are
highly crystalline and possess required acid, base, and redox functionalities. It can
also allow the immobilization of functional groups like –SO 3 H and -NH 2 as well as
metal nanoparticles such as Ru, Pd, Cu, etc. MOFs exhibit mesoporous structures
and are highly tunable materials in terms of pore size and anchoring of active phases.
Approximately 20,000 MOFs are reported in the literature, but all may not be
suitable for biomass conversion. The MOFs with a certain degree of thermal,
chemical, and water stability only are suitable for biomass conversion. For example,
zinc-carboxylate MOFs have shown poor water tolerance and are not suitable,
whereas MIL-type compounds (MIL101-Cr, MIL-53Al-NH 2 , UiO-66) exhibit
higher water stability [56]. MOFs have also been used as active catalyst phase,
catalyst support as well as a precursor material for the catalyst. MOFs and their
composites are discussed in the following section.
MOF-Supported Metal Nanoparticles (NPs)
MOFs have shown greater properties to prevent agglomeration of NPs, hence
improving their catalytic activities. Ning et al. [57] prepared Pt/MOF-5 by confining
Pt nanoparticles into the pores of MOF-5 and used for conversion of furfural derived
from biomass. Furan-2-acrolein was selectively produced from furfural (selectivity
90.7%) using Pt/MOF-5 as a catalyst. The catalyst showed good activity for the
conversion of furfural (84.1%) in the presence of ethanol as a solvent. The catalyst
was active after five reaction cycles due to the synergistic effect between NPs and
MOF. The other MOF-supported catalysts used for furfural conversion are Pt/
UIO-66-NH 2 and Pt/UIO-66. Hydrogenation of furfural to furfuryl alcohol was
carried out with Ru NPs supported on several MOFs supports such as Zr6-NDC,
UiO-66, MIL-140A, and UiO-67. High selectivity of furfuryl alcohol was obtained
under mild reaction conditions. Ru/UiO-66 was found to be the most stable catalyst
resulting in the highest activity and reusability for five reaction cycles without
appreciable loss of activity.
γ-Valerolactone (GVL) is an important platform chemical and produced from
ethyl levulinate derived from biomass via hydrogenation and transesterification
reactions. Ethyl levulinate can also be obtained by esterification of levulinic acid
with ethanol [58]. The MOF catalyst (UiO-66) with various functionalities (-SO 3 H,
R. Bhoi et al.
conversion) under identical conditions [55]. Thus, CNTs provide a good option as
catalysts and support for the biomass conversion process.
2.3.2 Metal-Organic Frameworks (MOFs) as Catalysts
Zeolites are known for their well-defined porous structures. Similarly, the metalorganic frameworks (MOFs) exhibit zeolite-like structure and a potential alternative
to zeolites as well as metal oxide catalysts. MOFs perform better in selected
reactions such as fructose dehydration in dimethyl sulfoxide (DMSO). MOFs are
highly crystalline and possess required acid, base, and redox functionalities. It can
also allow the immobilization of functional groups like –SO 3 H and -NH 2 as well as
metal nanoparticles such as Ru, Pd, Cu, etc. MOFs exhibit mesoporous structures
and are highly tunable materials in terms of pore size and anchoring of active phases.
Approximately 20,000 MOFs are reported in the literature, but all may not be
suitable for biomass conversion. The MOFs with a certain degree of thermal,
chemical, and water stability only are suitable for biomass conversion. For example,
zinc-carboxylate MOFs have shown poor water tolerance and are not suitable,
whereas MIL-type compounds (MIL101-Cr, MIL-53Al-NH 2 , UiO-66) exhibit
higher water stability [56]. MOFs have also been used as active catalyst phase,
catalyst support as well as a precursor material for the catalyst. MOFs and their
composites are discussed in the following section.
MOF-Supported Metal Nanoparticles (NPs)
MOFs have shown greater properties to prevent agglomeration of NPs, hence
improving their catalytic activities. Ning et al. [57] prepared Pt/MOF-5 by confining
Pt nanoparticles into the pores of MOF-5 and used for conversion of furfural derived
from biomass. Furan-2-acrolein was selectively produced from furfural (selectivity
90.7%) using Pt/MOF-5 as a catalyst. The catalyst showed good activity for the
conversion of furfural (84.1%) in the presence of ethanol as a solvent. The catalyst
was active after five reaction cycles due to the synergistic effect between NPs and
MOF. The other MOF-supported catalysts used for furfural conversion are Pt/
UIO-66-NH 2 and Pt/UIO-66. Hydrogenation of furfural to furfuryl alcohol was
carried out with Ru NPs supported on several MOFs supports such as Zr6-NDC,
UiO-66, MIL-140A, and UiO-67. High selectivity of furfuryl alcohol was obtained
under mild reaction conditions. Ru/UiO-66 was found to be the most stable catalyst
resulting in the highest activity and reusability for five reaction cycles without
appreciable loss of activity.
γ-Valerolactone (GVL) is an important platform chemical and produced from
ethyl levulinate derived from biomass via hydrogenation and transesterification
reactions. Ethyl levulinate can also be obtained by esterification of levulinic acid
with ethanol [58]. The MOF catalyst (UiO-66) with various functionalities (-SO 3 H,
R. Bhoi et al.