297
problem of separation and catalyst disposal are bottlenecks in homogeneous catalytic systems. Often expensive chemicals and multistep reaction protocols are
required for catalyst preparation, thus limiting their applicability in large scales.
Non-noble metal-supported heterogeneous catalysts including Fe, Ni, Cu, Cr, Co
and Mo were reported towards this hydrocyclization. Raney Ni
®
and Cu-/Ni- metal
supported and combination of these two are exclusively reported using three hydrogen sources (H 2 gas, isopropanol and formic acid) in either static or continuous
vapour phase. The Zr-based catalysts were mainly reported for Meerwein-PonndorfVerley (MPV) of levulinic acid followed by cyclization to Gvl using alcohol as
hydrogen source. Heterogeneous catalytic systems based on supported noble metals
such as Ru, Pd, Pt and Au are active towards LA to Gvl conversion. Among these,
Ru catalysts are most active under comparatively milder reaction conditions.
Layered double hydroxide (LDH) materials were found to be attractive in many
catalytic applications because of its multifunctionality and tunable nature.
Pristine LDH, calcined LDH (CLDH), LDH-derived ex situ and in situ catalysts and
metal supported on LDH materials were extensively reported for levulinic acid conversion to Gvl. The following section reviewed the prior art of this conversion using
LDH materials including the contribution from our group.
Hydrocyclization of LA to Gvl Using Layered Double Hydroxide-Based Materials
LDH-Derived Catalysts for Hydrocyclization of LA to Gvl
The LDH-derived catalysts for LA to Gvl conversion, were first reported by Yan
et al. who introduced Cu-Cr, Cu-Al and Cu-Fe CLDH catalyst precursors (derived
from LDH by calcination). All the mentioned CLDH catalyst precursors showed
good catalytic activity for Gvl (yield 90.7% for Cu-Cr, 87.3% for Cu-Al and 87.3%
for Cu-Fe) (Table 1, entries 1–4). The Cu
2+
oxide of CLDH generates Cu(0) under
reaction conditions (200 °C, 70 bar H 2 for 10 h in water) confirmed by PXRD,
which is the active catalyst for hydrogenation. The authors observed a decrease in
the catalytic activity (in the case of Cu-Cr) upon reuse because of carbon deposits
on the surface of the catalyst during the reaction. To avoid this problem, they reactivated the catalyst by calcination (550 °C for 3 h) and was rewarded with similar
catalytic activity up to monitored three reaction cycles [58–60].
Li research group demonstrated a series of Al-LDH-based catalyst precursors
using different metals such as Fe, Cu, Ni and Co. From these M-Al LDH (M = metal)
precursors, the active catalyst species was prepared by reduction under H 2 (50 mL/
min) at 700 °C for 2.5 h, and obtained catalysts are denoted as M(0)/Al 2 O 3 . Among
the catalysts screened by the Li group, Co/Al 2 O 3 (derived from Co-Al LDH) showed
excellent activity towards LA to Gvl conversion with 100% conversion and >99%
selectivity at 180 °C, 50 bar H 2 for 3 h in 1,4-dioxane medium (Table 1, entries 5–9).
The LDH precursor-derived Co/Al 2 O 3 is more active than Co/γ-Al 2 O 3 (prepared by
Co impregnation on γ-Al 2 O 3 followed by reduction) and Co/Al 2 O 3 -CR (derived
from Co-Al LDH through calcination followed by pre-reduction), suggesting that
Levulinic Acid- and Furan-Based Multifunctional Materials: Opportunities…
problem of separation and catalyst disposal are bottlenecks in homogeneous catalytic systems. Often expensive chemicals and multistep reaction protocols are
required for catalyst preparation, thus limiting their applicability in large scales.
Non-noble metal-supported heterogeneous catalysts including Fe, Ni, Cu, Cr, Co
and Mo were reported towards this hydrocyclization. Raney Ni
®
and Cu-/Ni- metal
supported and combination of these two are exclusively reported using three hydrogen sources (H 2 gas, isopropanol and formic acid) in either static or continuous
vapour phase. The Zr-based catalysts were mainly reported for Meerwein-PonndorfVerley (MPV) of levulinic acid followed by cyclization to Gvl using alcohol as
hydrogen source. Heterogeneous catalytic systems based on supported noble metals
such as Ru, Pd, Pt and Au are active towards LA to Gvl conversion. Among these,
Ru catalysts are most active under comparatively milder reaction conditions.
Layered double hydroxide (LDH) materials were found to be attractive in many
catalytic applications because of its multifunctionality and tunable nature.
Pristine LDH, calcined LDH (CLDH), LDH-derived ex situ and in situ catalysts and
metal supported on LDH materials were extensively reported for levulinic acid conversion to Gvl. The following section reviewed the prior art of this conversion using
LDH materials including the contribution from our group.
Hydrocyclization of LA to Gvl Using Layered Double Hydroxide-Based Materials
LDH-Derived Catalysts for Hydrocyclization of LA to Gvl
The LDH-derived catalysts for LA to Gvl conversion, were first reported by Yan
et al. who introduced Cu-Cr, Cu-Al and Cu-Fe CLDH catalyst precursors (derived
from LDH by calcination). All the mentioned CLDH catalyst precursors showed
good catalytic activity for Gvl (yield 90.7% for Cu-Cr, 87.3% for Cu-Al and 87.3%
for Cu-Fe) (Table 1, entries 1–4). The Cu
2+
oxide of CLDH generates Cu(0) under
reaction conditions (200 °C, 70 bar H 2 for 10 h in water) confirmed by PXRD,
which is the active catalyst for hydrogenation. The authors observed a decrease in
the catalytic activity (in the case of Cu-Cr) upon reuse because of carbon deposits
on the surface of the catalyst during the reaction. To avoid this problem, they reactivated the catalyst by calcination (550 °C for 3 h) and was rewarded with similar
catalytic activity up to monitored three reaction cycles [58–60].
Li research group demonstrated a series of Al-LDH-based catalyst precursors
using different metals such as Fe, Cu, Ni and Co. From these M-Al LDH (M = metal)
precursors, the active catalyst species was prepared by reduction under H 2 (50 mL/
min) at 700 °C for 2.5 h, and obtained catalysts are denoted as M(0)/Al 2 O 3 . Among
the catalysts screened by the Li group, Co/Al 2 O 3 (derived from Co-Al LDH) showed
excellent activity towards LA to Gvl conversion with 100% conversion and >99%
selectivity at 180 °C, 50 bar H 2 for 3 h in 1,4-dioxane medium (Table 1, entries 5–9).
The LDH precursor-derived Co/Al 2 O 3 is more active than Co/γ-Al 2 O 3 (prepared by
Co impregnation on γ-Al 2 O 3 followed by reduction) and Co/Al 2 O 3 -CR (derived
from Co-Al LDH through calcination followed by pre-reduction), suggesting that
Levulinic Acid- and Furan-Based Multifunctional Materials: Opportunities…