(645f) Highly Selective Catalytic Conversion of Furfural to ?-Butyrolactone

Highly selective catalytic conversion of furfural to ¦Ã-butyrolactone

Tiefeng Wang* and Xiaodan Li, Yafei Li

Beijing Key Laboratory of
Green Reaction Engineering and Technology

Department of Chemical
Engineering, Tsinghua University, Beijing 100084, China

*Corresponding author:
wangtf@tsinghua.edu.cn

The depletion of fossil fuel
reserves and growing demand for energy are drawing efforts to find alternative
sources of energy and organic carbon. Biomass-derived molecules can serve as
renewable substitutes for petroleum-based building blocks to produce fuels and
chemicals.¹ Furfural, a renewable platform compound produced by
hydrolysis and dehydration of xylan contained in lignocellulose, has already
been used to produce fine chemicals such as furfuryl alcohol, tetrahydrofurfuryl alcohol, furan, and furfural resin in industry.^2-4 During the past
decades, novel technologies and processes have been developed for furfural
production. This will necessarily promote the further utilization of furfural
to produce more value-added chemicals.

One of the most promising products
is ¦Ã-butyrolactone (GBL), which has wide applications in the fields of solvents, medicine, spice and fine organic synthesis.⁵
Currently, GBL is mainly produced by dehydrocyclization of 1,4-butanediol (BDO) and hydrogenation of maleic anhydride, but they usually have problems of harsh operating conditions,
complicated process, and environmental pollution.⁶ Therefore, it is
attractive to sustainably produce GBL from a renewable biomass-derived molecule
with high atom economy. This work reports a two-step process to produce GBL
from furfural with 2(5H)-furanone
as the intermediate. In the first step, furfural was
oxidized to 2(5H)-furanone with a promising yield over 60%. In the
second step, the purified 2(5H)-furanone was further hydrogenated to GBL
using SiO₂ supported metal catalysts.

The catalytic oxidation of furfural
to 2(5H)-furanone was studied using
hydrogen peroxide as the oxidant and formic acid as the catalyst. A 60-62%
yield of 2(5H)-furanone, with a total
yield of diacids (i.e., maleic acid
and succinic acid) in the range of 15-20% as by-products, was obtained in a
bi-phasic system using 1,2-dichloroethane or ethyl acetate as the solvent. The
good solubility in the organic phase and the strong oxidizing nature of
performic acid, which was the real active oxidant generated from formic acid
and hydrogen peroxide, contributed to the promising yield of 2(5H)-furanone.⁷

Having obtained 2(5H)-furanone
by furfural oxidation, we next turn to the hydrogenation of 2(5H)-furanone
to GBL. With only one more additional C=C bond than GBL, 2(5H)-furanone is an ideal intermediate for
converting furfural to GBL. The selective hydrogenation of the C=C bond in 2(5H)-furanone was first studied in a liquid
phase over a series of SiO₂ supported monometallic catalysts (M =
Pt, Pd, Rh, Ru, Ni, Co and Cu) prepared by incipient wetness impregnation. The catalyst
activity followed the trend of Pd0.5/SiO₂~ Rh0.5/SiO₂> Ru0.5/SiO₂ >
Pt0.5/SiO₂, and Ni4.5/SiO₂ > Co4.5/SiO₂
> Cu4.5/SiO₂. Furthermore, the initial TOF for 2(5H)-furanone hydrogenation over these
monometallic catalysts showed a volcano-type dependence on their metal d-band center values, with Pd having the
highest activity.⁸ This correlation further guided our design of non-noble
metal-based bimetallic catalysts to reduce cost.

Ni was shown to be active and
selective for the hydrogenation of the C=C bond in 2(5H)-furanone. The activity and selectivity of a metal catalyst can
be significantly altered by incorporating a second metal due to electronic and
geometric effects.⁹ Thus, a series of Ni-based bimetallic catalysts,
Ni-M/SiO₂ (M= Fe, Co, Cu and Zn), were prepared and evaluated for
the selective hydrogenation of 2(5H)-furanone
to GBL. Among the prepared bimetallic catalysts, Ni-Fe/SiO₂ showed
the best performance. The effect of addition of Fe on the catalyst performance
was further studied with different Ni/Fe ratios. It was found that the
introduction of a suitable amount of Fe significantly enhanced the activity
while maintaining the selectivity of the Ni/SiO₂ catalyst.
Characterization measurements by XRD, BET, TEM and chemisorption were used to
investigate the promotional effect of Fe, showing that the formation of NiFe
alloy, optimized reducibility and metal particle size distribution contributed
to the enhanced catalytic performance of the Ni-Fe/SiO₂ bimetallic
catalyst.

In summary, a two-step process was
developed for producing GBL from furfural, providing a new strategy for
converting biomass-derived platform compound to high value-added fine
chemicals. In the oxidation step, the highest yield of the intermediate, 2(5H)-furanone, was obtained in a bi-phasic
system with formic acid as the catalyst, ethyl acetate as the solvent, and
hydrogen peroxide as the oxidant. In the subsequent hydrogenation step, a
series of Group VIII monometallic catalysts were first investigated and their
catalytic performances were correlated with intrinsic properties of the metals,
based on which an efficient non-noble bimetallic catalyst, Ni-Fe/SiO₂,
was further designed.

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