305
Lewis acidic sites (confirmed by DRIFT) along with metallic Ni active sites on the
surface (confirmed by CO pulse chemisorption) in Ni(0)/Al 2 O 3 -TiO 2 supports the
higher activity of the material. The Lewis acidity of support (Al 2 O 3 -TiO 2 ), i.e. peaks
at 1630–1600/cm and 1450/cm, influences the dehydration of LA for the formation
of angelica lactone (path-b mechanism in Scheme 4) which underwent subsequent
hydrogenation to Gvl using active metallic Ni(0). The catalyst was also tested for
transfer hydrocyclization of LA with formic acid as hydrogen donor, resulting in
higher angelica lactone yield compared to desired Gvl which may be due to insufficient hydrogen (obtained from decomposition formic acid) or deactivation/leaching of active Ni metal under such acidic conditions. The catalyst is active up to 17 h
time-on-stream using molecular hydrogen, and a further increase in time and/or
increase in reaction cycles, a decrease in the conversion of LA is observed due to
carbon (coke formation) deposition on the catalyst.
Transfer hydrocyclization of ethyl levulinate to Gvl using hierarchical multilevelsupported bimetallic catalyst (derived from Al 2 O 3 @NiCuAl-LDH precursor) was
reported [70]. The bimetallic NiCu catalyst with 0.5 Cu/Ni molar ratio resulted in
high activity (89% yield of Gvl) in the presence of isopropanol as hydrogen source
(Table 1, entry 27). Alumina-supported bimetallic catalyst (NiCu) has highest density of acidic and basic sites. Lewis acidic sites of catalytic material can interact
with carbonyl group of ethyl levulinate through the electron pair on the oxygen
atom and are active for C=O hydrogenation. The basic sites of the catalyst are also
responsible for MPV reduction and facilitate ethyl levulinate activation.
As-fabricated bimetallic NiCu catalyst has good stability and activity for recycling
studies. The bimetallic catalyst shows no metal leaching and no particle agglomeration during the reaction.
LDH-Supported Metal Catalysts for Hydrocyclization of LA to Gvl
LDH materials as catalytic support were also reported for hydrocyclization of
LA. Venugopal group reported Ru(0)/Mg-La CLDH prepared by impregnation procedure using RuCl 3 with Mg-La CLDH in aqueous medium. The Ru(0)-supported
CLDH catalyst was the first basic supported catalyst for this reaction which showed
good catalytic activity (92% LA conversion with >99% Gvl selectivity) in toluene
medium at 80 °C, 5 bar H 2 for 4 h (Table 1, entry 28) [71]. Furthermore, Rajaram
group also reported Pt-supported Mg-Al CLDH for LA to Gvl conversion in aqueous medium at room temperature, 30 bar H 2 for 24 h with >99% yield of Gvl
(Table 1, entry 29) [72].
Our group reported in situ-generated Ru(0)/MgAl-LDH catalyst from Ru(O/
OH)/LDH and hydrous ruthenium oxide (HRO)/MgAl LDH during the reaction.
The in situ-regenerated catalysts showed remarkable catalytic activity with >99%
yield of Gvl under mild reaction conditions (80 °C, 10 bar H 2 for 30 min) in water
(Table 1, entries 30 and 31). The Ru(0)/Mg-Al LDH material is prepared by wet
impregnation (Mg-Al LDH with RuCl 3 solution) followed by in situ reduction during the reaction [73]. The main advantage of this invention is to avoid prior
Levulinic Acid- and Furan-Based Multifunctional Materials: Opportunities…
Lewis acidic sites (confirmed by DRIFT) along with metallic Ni active sites on the
surface (confirmed by CO pulse chemisorption) in Ni(0)/Al 2 O 3 -TiO 2 supports the
higher activity of the material. The Lewis acidity of support (Al 2 O 3 -TiO 2 ), i.e. peaks
at 1630–1600/cm and 1450/cm, influences the dehydration of LA for the formation
of angelica lactone (path-b mechanism in Scheme 4) which underwent subsequent
hydrogenation to Gvl using active metallic Ni(0). The catalyst was also tested for
transfer hydrocyclization of LA with formic acid as hydrogen donor, resulting in
higher angelica lactone yield compared to desired Gvl which may be due to insufficient hydrogen (obtained from decomposition formic acid) or deactivation/leaching of active Ni metal under such acidic conditions. The catalyst is active up to 17 h
time-on-stream using molecular hydrogen, and a further increase in time and/or
increase in reaction cycles, a decrease in the conversion of LA is observed due to
carbon (coke formation) deposition on the catalyst.
Transfer hydrocyclization of ethyl levulinate to Gvl using hierarchical multilevelsupported bimetallic catalyst (derived from Al 2 O 3 @NiCuAl-LDH precursor) was
reported [70]. The bimetallic NiCu catalyst with 0.5 Cu/Ni molar ratio resulted in
high activity (89% yield of Gvl) in the presence of isopropanol as hydrogen source
(Table 1, entry 27). Alumina-supported bimetallic catalyst (NiCu) has highest density of acidic and basic sites. Lewis acidic sites of catalytic material can interact
with carbonyl group of ethyl levulinate through the electron pair on the oxygen
atom and are active for C=O hydrogenation. The basic sites of the catalyst are also
responsible for MPV reduction and facilitate ethyl levulinate activation.
As-fabricated bimetallic NiCu catalyst has good stability and activity for recycling
studies. The bimetallic catalyst shows no metal leaching and no particle agglomeration during the reaction.
LDH-Supported Metal Catalysts for Hydrocyclization of LA to Gvl
LDH materials as catalytic support were also reported for hydrocyclization of
LA. Venugopal group reported Ru(0)/Mg-La CLDH prepared by impregnation procedure using RuCl 3 with Mg-La CLDH in aqueous medium. The Ru(0)-supported
CLDH catalyst was the first basic supported catalyst for this reaction which showed
good catalytic activity (92% LA conversion with >99% Gvl selectivity) in toluene
medium at 80 °C, 5 bar H 2 for 4 h (Table 1, entry 28) [71]. Furthermore, Rajaram
group also reported Pt-supported Mg-Al CLDH for LA to Gvl conversion in aqueous medium at room temperature, 30 bar H 2 for 24 h with >99% yield of Gvl
(Table 1, entry 29) [72].
Our group reported in situ-generated Ru(0)/MgAl-LDH catalyst from Ru(O/
OH)/LDH and hydrous ruthenium oxide (HRO)/MgAl LDH during the reaction.
The in situ-regenerated catalysts showed remarkable catalytic activity with >99%
yield of Gvl under mild reaction conditions (80 °C, 10 bar H 2 for 30 min) in water
(Table 1, entries 30 and 31). The Ru(0)/Mg-Al LDH material is prepared by wet
impregnation (Mg-Al LDH with RuCl 3 solution) followed by in situ reduction during the reaction [73]. The main advantage of this invention is to avoid prior
Levulinic Acid- and Furan-Based Multifunctional Materials: Opportunities…