259
transesterification due to the high acidity of the oil. Their activity improved after the
immobilization of ILs due to increased basic strength and basicity of supports. The
biodiesel yields catalyzed by IL/Mg-Al and IL/Mg-Al-La catalysts were 85.4% and
98.7%, respectively [74]. When waste cooking oil is transesterified with methanol
at 60 °C for 20 h with ILs supported on silica gel, 87.58% yield of biodiesel was
observed [75].
Polymeric IL-Based Catalysts
The ionic liquids are promising candidates for various applications and named after
the mobility of ions in ionic liquids. The ILs are neither liquids nor solids and do not
have advantages of liquids or solids. This limits their applicability due to leakage
issues and high viscosity. Polymeric ionic liquids (PILs) can address this problem
without losing the features of ILs. PILs are formed by the polymerization of ionic
liquids [76]. They can combine the functionalities of polymer and ILs and act as
bifunctional catalysts. They have high thermal stability, better corrosion resistance,
and flexibility of available structures. The dehydration process of 5-HMF from
glucose/fructose can be catalyzed by a series of PILs (mono- and bifunctional
polymeric ionic liquids). The PILs performed well compared to solid-supported
ionic liquids like ILs on silica and showed consistent activity for five reaction cycles
without significant loss of activity [77]. Among the other reusable PILs are poly(3butyl- 1-vinylimidazolium chloride) combined with CrCl 2 , P[BVIM]Cl-CrCl 2 ,
which was found suitable for dehydration of glucose and fructose to yield 68.8%
HMF at 120
o
C for 3 h. However, the recyclability test indicates poor performance
compared to its analogous catalyst, i.e., P[BVIM]Cl-Et 2 ALCl [78]. PILs are also
found suitable for oleic acid esterification to yield 92.6% biodiesel. The biodiesel
yield slightly decreased to 89.3% after six runs, indicating the consistent performance
of the catalyst. The catalyst, 1-vinyl-3-(3-sulfopropyl) imidazolium hydrogen
sulfate [VSIM][HSO 4 ], was synthesized from Brønsted acidic ionic liquid through
free radical polymerization from a novel approach, where Fe 3 O 4 particles acted as
hard template [79].
2.3.4 Magnetic Iron Oxide-Based Catalysts
Magnetic catalysts are different from other solid catalysts due to their easy separation
from the reaction mixture by the permanent magnet. They are mainly represented by
ferrous, cobalt, and nickel, especially ferrous. The commonly used magnetic catalyst/
support includes alloys (FePt, CoPt), metals (Fe, Co, Ni), and iron oxides (FeO, Fe 2 O 3 ,
Fe 2 O 4 ). Among them, Fe 2 O 4 is widely used for catalytic purposes [80]. Magnetic acid
catalysts are used for the conversion of cellulose to glucose, fructose to 5-hydroxymethylfurfural (5-HMF), and 5-HMF to 5-ethoxymethylfurfural (5-EMF) via hydrolysis, dehydration, and etherification processes, respectively. These catalysts also find
their use in transesterification reactions to synthesize biodiesel. The catalysts
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…
transesterification due to the high acidity of the oil. Their activity improved after the
immobilization of ILs due to increased basic strength and basicity of supports. The
biodiesel yields catalyzed by IL/Mg-Al and IL/Mg-Al-La catalysts were 85.4% and
98.7%, respectively [74]. When waste cooking oil is transesterified with methanol
at 60 °C for 20 h with ILs supported on silica gel, 87.58% yield of biodiesel was
observed [75].
Polymeric IL-Based Catalysts
The ionic liquids are promising candidates for various applications and named after
the mobility of ions in ionic liquids. The ILs are neither liquids nor solids and do not
have advantages of liquids or solids. This limits their applicability due to leakage
issues and high viscosity. Polymeric ionic liquids (PILs) can address this problem
without losing the features of ILs. PILs are formed by the polymerization of ionic
liquids [76]. They can combine the functionalities of polymer and ILs and act as
bifunctional catalysts. They have high thermal stability, better corrosion resistance,
and flexibility of available structures. The dehydration process of 5-HMF from
glucose/fructose can be catalyzed by a series of PILs (mono- and bifunctional
polymeric ionic liquids). The PILs performed well compared to solid-supported
ionic liquids like ILs on silica and showed consistent activity for five reaction cycles
without significant loss of activity [77]. Among the other reusable PILs are poly(3butyl- 1-vinylimidazolium chloride) combined with CrCl 2 , P[BVIM]Cl-CrCl 2 ,
which was found suitable for dehydration of glucose and fructose to yield 68.8%
HMF at 120
o
C for 3 h. However, the recyclability test indicates poor performance
compared to its analogous catalyst, i.e., P[BVIM]Cl-Et 2 ALCl [78]. PILs are also
found suitable for oleic acid esterification to yield 92.6% biodiesel. The biodiesel
yield slightly decreased to 89.3% after six runs, indicating the consistent performance
of the catalyst. The catalyst, 1-vinyl-3-(3-sulfopropyl) imidazolium hydrogen
sulfate [VSIM][HSO 4 ], was synthesized from Brønsted acidic ionic liquid through
free radical polymerization from a novel approach, where Fe 3 O 4 particles acted as
hard template [79].
2.3.4 Magnetic Iron Oxide-Based Catalysts
Magnetic catalysts are different from other solid catalysts due to their easy separation
from the reaction mixture by the permanent magnet. They are mainly represented by
ferrous, cobalt, and nickel, especially ferrous. The commonly used magnetic catalyst/
support includes alloys (FePt, CoPt), metals (Fe, Co, Ni), and iron oxides (FeO, Fe 2 O 3 ,
Fe 2 O 4 ). Among them, Fe 2 O 4 is widely used for catalytic purposes [80]. Magnetic acid
catalysts are used for the conversion of cellulose to glucose, fructose to 5-hydroxymethylfurfural (5-HMF), and 5-HMF to 5-ethoxymethylfurfural (5-EMF) via hydrolysis, dehydration, and etherification processes, respectively. These catalysts also find
their use in transesterification reactions to synthesize biodiesel. The catalysts
Sustainability of the Catalytic Process for Biomass Conversion: Recent Trends and…