303
complete LA conversion with 98% Gvl selectivity (Table 1, entries 15–17).
Reactivated (calcination at 450 °C for 1 h) MgO-Al 2 O 3 CLDH showed good results
during reusability studies as compared to the spent catalyst [65].
Fu and co-authors studied several Ni-supported catalysts for this conversion by
varying the supports such as MgO, Al 2 O 3 and Mg-Al CLDH. Among these supports, Ni(0) on Mg-Al CLDH (derived from Ni-Mg-Al LDH through calcination
followed by reduction) showed the highest yield (99.7%) of Gvl in 1,4-dioxane
medium at 160 °C, 30 bar H 2 for 1 h. High surface area and uniform dispersion of
Ni on Mg-Al CLDH was the reason for better catalytic activity as compared to other
examined catalysts (Table 1, entries 18–20). They also conducted reusability of
CLDH-derived active catalyst (Ni/Mg-Al CLDH) and showed good recyclability
even in the absence of reactivation [66].
The above-mentioned synthetic protocol for the generation of active catalyst
from LDH precursor consumes a significant amount of energy. To avoid these drawbacks, we recently reported Ni-Al LDH catalyst precursor (without calcination or
pre-reduction) for this conversion in water. Interestingly, Ni(0)/boehmite (Ni-Al
LDH-derived) was obtained during the reaction and confirmed by PXRD and
TEM. The PXRD of NiAl-LDH showed the presence of (003), (006), (012), (015),
(018), (110) and (113) planes that are characteristic of hydrotalcite (Fig. 2), which
completely converted to (020), (120), (140) and (051) planes of boehmite (JCPDS
Card No. 01-074-290), and (111) with (200) for Ni (0) (JCPDS Card No.:
00-004-0850). Platelet-like morphology of NiAl-LDH underwent a change to hexagonal rods of boehmite with embedded spherical Ni(0) particles having <20 nm
size as shown in Fig. 3. The generated active catalyst (Ni(0)/boehmite) showed
superior catalytic activity towards the reaction with 100% yield of Gvl (Table 1,
entry 21). The active catalyst was recyclable up to four cycles without any activation
and only a minor decrease in LA conversion in each cycle, maintaining the Gvl
selectivity [67].
Ma et al. disclosed in situ-reduced nano-Cu/AlOOH catalyst for alkyl levulinates
to Gvl using Cu 2 (OH) 2 CO 3 /AlOOH-LDH precursor using 2-propanol as hydrogen
source [68]. Under optimized condition (180 °C for 5 h), the in situ-reduced catalyst
showed 90.5% yield of Gvl (96% conversion of methyl levulinate) with Cu/Al
molar ratio 3/1 (Table 1, entry 22). The pre-reduced catalyst Cu/Al 2 O 3 has lower
activity towards the reaction and resulted in 78% yield of Gvl because of the agglutination of active catalytic Cu(0) metal particles on Al 2 O 3 (Table 1, entry 23). The in
situ Cu/AlOOH catalyst has strong acidic sites (obtained from TPD analysis) and
could reasonably enhance the reaction. Various alcohols as hydrogen sources including primary (methanol, ethanol, 1-propanol and 1-butanol), secondary (2-propanol
and 2-butanol) and tertiary (t-butanol) alcohols were studied for the reaction using
Cu 2 (OH) 2 CO 3 /AlOOH-LDH precursor. It was observed that primary and tertiary
alcohols are inefficient for hydrogen generation and cannot participate in the reaction, wherein secondary alcohols such as 2-propanol and 2-butanol showed remarkable activity to obtain Gvl. Using the in situ catalyst, authors identified significant
loss in Gvl yield while increasing the number of catalytic cycles, and they
Levulinic Acid- and Furan-Based Multifunctional Materials: Opportunities…
complete LA conversion with 98% Gvl selectivity (Table 1, entries 15–17).
Reactivated (calcination at 450 °C for 1 h) MgO-Al 2 O 3 CLDH showed good results
during reusability studies as compared to the spent catalyst [65].
Fu and co-authors studied several Ni-supported catalysts for this conversion by
varying the supports such as MgO, Al 2 O 3 and Mg-Al CLDH. Among these supports, Ni(0) on Mg-Al CLDH (derived from Ni-Mg-Al LDH through calcination
followed by reduction) showed the highest yield (99.7%) of Gvl in 1,4-dioxane
medium at 160 °C, 30 bar H 2 for 1 h. High surface area and uniform dispersion of
Ni on Mg-Al CLDH was the reason for better catalytic activity as compared to other
examined catalysts (Table 1, entries 18–20). They also conducted reusability of
CLDH-derived active catalyst (Ni/Mg-Al CLDH) and showed good recyclability
even in the absence of reactivation [66].
The above-mentioned synthetic protocol for the generation of active catalyst
from LDH precursor consumes a significant amount of energy. To avoid these drawbacks, we recently reported Ni-Al LDH catalyst precursor (without calcination or
pre-reduction) for this conversion in water. Interestingly, Ni(0)/boehmite (Ni-Al
LDH-derived) was obtained during the reaction and confirmed by PXRD and
TEM. The PXRD of NiAl-LDH showed the presence of (003), (006), (012), (015),
(018), (110) and (113) planes that are characteristic of hydrotalcite (Fig. 2), which
completely converted to (020), (120), (140) and (051) planes of boehmite (JCPDS
Card No. 01-074-290), and (111) with (200) for Ni (0) (JCPDS Card No.:
00-004-0850). Platelet-like morphology of NiAl-LDH underwent a change to hexagonal rods of boehmite with embedded spherical Ni(0) particles having <20 nm
size as shown in Fig. 3. The generated active catalyst (Ni(0)/boehmite) showed
superior catalytic activity towards the reaction with 100% yield of Gvl (Table 1,
entry 21). The active catalyst was recyclable up to four cycles without any activation
and only a minor decrease in LA conversion in each cycle, maintaining the Gvl
selectivity [67].
Ma et al. disclosed in situ-reduced nano-Cu/AlOOH catalyst for alkyl levulinates
to Gvl using Cu 2 (OH) 2 CO 3 /AlOOH-LDH precursor using 2-propanol as hydrogen
source [68]. Under optimized condition (180 °C for 5 h), the in situ-reduced catalyst
showed 90.5% yield of Gvl (96% conversion of methyl levulinate) with Cu/Al
molar ratio 3/1 (Table 1, entry 22). The pre-reduced catalyst Cu/Al 2 O 3 has lower
activity towards the reaction and resulted in 78% yield of Gvl because of the agglutination of active catalytic Cu(0) metal particles on Al 2 O 3 (Table 1, entry 23). The in
situ Cu/AlOOH catalyst has strong acidic sites (obtained from TPD analysis) and
could reasonably enhance the reaction. Various alcohols as hydrogen sources including primary (methanol, ethanol, 1-propanol and 1-butanol), secondary (2-propanol
and 2-butanol) and tertiary (t-butanol) alcohols were studied for the reaction using
Cu 2 (OH) 2 CO 3 /AlOOH-LDH precursor. It was observed that primary and tertiary
alcohols are inefficient for hydrogen generation and cannot participate in the reaction, wherein secondary alcohols such as 2-propanol and 2-butanol showed remarkable activity to obtain Gvl. Using the in situ catalyst, authors identified significant
loss in Gvl yield while increasing the number of catalytic cycles, and they
Levulinic Acid- and Furan-Based Multifunctional Materials: Opportunities…