CHEMSUSCHEM
COMMUNICATIONS
DOI: 10.1002/cssc.201400039
Hydrogenation of Biofuels with Formic Acid over
a Palladium-Based Ternary Catalyst with Two Types of
Active Sites
[a]
[b]
[a]
[b, c]
[a]
Liang Wang, Bingsen Zhang, Xiangju Meng, Dang Sheng Su,
and Feng-Shou Xiao*
A composite catalyst including palladium nanoparticles on tita-
The dehydrogenation of formic acid (FA; HCOOH!CO +H )
2
2
nia (TiO ) and on nitrogen-modified porous carbon (Pd/
is a process with potential for large-scale production of hydro-
gen because FA is cheap and can be easily obtained by hydrol-
2
TiO @NꢀC) is synthesized from palladium salts, tetrabutyl tita-
2
[7–10]
nate, and chitosan. N sorption isotherms show that the cata-
ysis of sugars and cellulose.
Using FA as a source of biohy-
2
2
ꢀ1
lyst has a high BET surface area (229 m g ) and large porosity.
XPS and TEM characterization of the catalyst shows that palla-
dium species with different chemical states are well dispersed
drogen for the reduction of vanillin is strongly desirable be-
cause FA offers obvious transportation advantages compared
to hydrogen. This alternative process could be performed in an
atmosphere of inert gas and avoids the use of high-pressure
hydrogen, which is favorable for sustainable catalytic hydroge-
nation of biofuels. Despite successful examples of carbohy-
across the TiO and nitrogen-modified porous carbon, respec-
2
tively. The Pd/TiO @NꢀC catalyst is very active and shows ex-
2
cellent stability towards hydrogenation of vanillin to 2-me-
thoxy-4-methylphenol using formic acid as hydrogen source.
This activity can be attributed to a synergistic effect between
[7,8]
drate hydrogenation by FA in recent years,
the hydrogena-
tion of biofuels by FA remains a challenge. This difficulty lies in
a shortage of active sites known to simultaneously catalyze
both FA dehydrogenation and biofuel hydrogenation. Al-
though FA dehydrogenation and biofuel hydrogenation over
palladium-based catalysts have been reported separately, at-
tempts at a tandem reaction do not appear to have been suc-
cessful yet as both reactions require palladium species with dif-
the Pd/TiO (a catalyst for dehydrogenation of formic acid) and
2
Pd/NꢀC (a catalyst for hydrogenation of vanillin) sites.
The production of fuels and fine chemicals from biomass has
received much attention recently, owing to the shortage of
[
1–4]
0
2+ [7,8]
fossil resources.
Biofuel hydrogenation in particular is inten-
ferent chemical states: Pd and Pd
.
sively studied, because it significantly increases the energy
Therefore, it is imperative to design a composite catalyst
[
5,6]
0
2+
0
density of the biofuel.
For example, sustainable fuels ob-
that includes both Pd and Pd
species. The Pd species
2
+
tained by the hydrogenation of oils formed by pyrolysis of
lignin and cellulose offer good prospects for industrial applica-
tions. As a model molecule, vanillin (4-hydroxy-3-methoxyben-
zaldehyde; a common component of pyrolysis oil) can be ef-
fectively hydrogenated into 2-methoxy-4-methylphenol (MMP),
should be active for FA dehydrogenation while the Pd spe-
cies should be active for biofuel hydrogenation. If both reac-
tions would run in tandem, the hydrogenation of biofuels with
FA could be realized. In this work, we design and successfully
0
synthesize a bifunctional palladium catalyst with both Pd and
[
6]
2+
which is a potential future biofuel. However, the hydrogena-
tion of vanillin normally requires high hydrogen pressures, and
there is always formation of byproduct (4-hydroxymethyl-2-
methoxyphenol; HMP) as a result of incomplete hydrogena-
tion.
Pd species. The synthesis involves impregnation of a compo-
site support (comprising titania and nitrogen-modified porous
carbon) with a palladium salt, followed by reduction with
NaBH , leading to Pd/TiO @NꢀC. The Pd/TiO @NꢀC catalyst is
4
2
2
highly efficient towards hydrogenation of vanillin into MMP by
FA, and offers excellent stability.
Chitosan, a polysaccharide biomass with high nitrogen con-
tent (C/N ratio of 6), was used as precursor for synthesis of the
nitrogen-modified porous carbon. The composite titania and
[
a] Dr. L. Wang, Dr. X. Meng, Prof. F.-S. Xiao
Key Laboratory of Applied Chemistry of Zhejiang Province
Zhejiang University
Hangzhou 310028 (PR China)
E-mail: fsxiao@zju.edu.cn
nitrogen-modified porous carbon support (TiO @NꢀC) was pre-
2
pared by hydrothermal treatment of chitosan and tetrabutyl ti-
[
b] Dr. B. Zhang, Prof. D. S. Su
tanate in acetic acid aqueous solution at 2008C for 8 h
Shenyang National Laboratory of Materials Science
Institute of Metal Research, Chinese Academy of Science
Shenyang 110016 (PR China)
(
(
TiO @chitosan), followed by calcination at 5508C for 2 h in N
2 2
for comparison, an sample of only NꢀC was synthesized by
this route by not adding tetrabutyl titanate to the starting gel).
[
c] Prof. D. S. Su
Department of Inorganic Chemistry
Fritz Haber Institute of the Max Planck Society
Berlin 14195 (Germany)
Palladium nanoparticles were loaded onto the TiO @NꢀC sup-
2
port by using an impregnation method. The palladium and ti-
tania loadings in the Pd/TiO @NꢀC catalyst were 2.1 and
2
Part of a Special Issue for the 6th Asia-Pacific Catalysis Congress (APCAT-
4
2.0 wt%, respectively (Scheme 1).
6
). A link to the full Table of Contents will appear here. Supporting Infor-
0.1002/cssc.201400039.
13
Figure 1a shows C NMR spectra of TiO @chitosan and
2
1
TiO @NꢀC samples. The spectrum of the TiO @chitosan sample
2
2
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 0000, 00, 1 – 5
&
1
&
ÞÞ
These are not the final page numbers!