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Green Chemistry
but the reaction time was very long (usually 24 h). Compared Catalyst preparation
with liquid acids, it is difficult to achieve the transformation of
The zirconium phosphate catalyst (ZPA) was obtained by the
previously reported method.33,34 Namely, it was prepared by
precipitation of ZrOCl2·8H2O (1.0 mol dm−3, 100 mL) with
NH4H2PO4 (1.0 mol dm−3, 200 mL) at the P/Zr mole ratio of
2. The solution was stirred for 1 h and then filtered. The white
precipitate was washed with deionized water until the pH of
the filtrate was 4, and then was dried at 373 K overnight.
Before reaction, ZPA was calcined at 673 K for 4 h in air.
The preparation procedure for the SiO2–ZrO2 catalyst was in
line with the previously reported literature.35 The Si(OH)4 pre-
cipitate was obtained by adding NH4NO3 saturated solution
into the Na2SiO3 solution with continuous agitation until the
pH of solution was 8. The Zr(OH)4 precipitate was prepared by
the same method but with ammonia (28%) as the precipitator.
Namely, addition of the NH3·H2O solution into the
ZrOCl2·8H2O solution with continuous agitation until the pH
of solution was 8. Subsequently, the Si(OH)4 and Zr(OH)4 was
mixed at a mole ratio of Si/Zr = 3 and stirred. The mixed pre-
cipitate was aged at 348 K overnight. The precipitate was fil-
tered and washed with deionized water for the complete
removal of chloride ions. The filter cake was dried at 393 K for
12 h and then calcined at 773 K for 5 h prior to reaction.
Tungstated zirconia (ZrW) was prepared by the method
described in the literature.36 Zr(OH)4 was prepared by adding
the NH3·H2O solution into the ZrOCl2·8H2O solution with con-
stantly stirring until the pH of solution was 9. The precipitate
was filtered and washed with deionized water to completely
remove any chloride ions, and then the precipitate was dried
at 383 K overnight. Subsequently, tungstic acid (H2WO4) was
exchanged with Zr(OH)4 in hydrogen peroxide solution (30%),
and the process was performed in an ice–water bath. The solid
was filtered and dried at 353 K overnight. Finally, the solid was
calcined in air at 973 K for 3 h prior to reaction.
concentrated cellulose with these solid catalysts.
As a solid catalyst, ZPA has been used in the dehydration of
glucose or fructose to 5-hydroxymethylfurfural or levulinic
acid,22–27 in the transformation of sorbitol or xylitol to gasoline
or isosorbide,28–30 and in the production of high-quality diesel
from furfural and 2-methylfuran.31 However, studies on cellu-
lose depolymerization by ZPA are rare.32,33 Hence, we designed
a hybrid catalyst that combined amorphous zirconium phos-
phate (ZPA) with commercial 5 wt% Ru/C for the direct conver-
sion of cellulose to C6 alditols. In this approach, cellulose was
depolymerized to saccharides over acidic ZPA, followed by
hydrogenation of saccharides to C6 alditols over 5 wt% Ru/C.
The weak adsorption of C6 alditols over ZPA prohibited their
further dehydration to by-products, which allowed high target
product yields to be obtained.
Experimental section
Materials
Microcrystalline cellulose (MCC, Avicel®PH101, Fluka) was pur-
chased from Sigma-Aldrich, and was dried overnight at 343 K
prior to use. Zirconium oxychloride octahydrate (ZrOCl2·8H2O)
was purchased from Sinopharm Chemical Reagent Co., Ltd
(Shanghai, P. R. China). Ammonium dihydrogen phosphate
(NH4H2PO4) was purchased from Tianjin Fu Chen Chemical
Reagents Factory (Tianjin, P. R. China). Sodium silicate
(Na2SiO3·9H2O), hydrochloric acid (37% HCl), sulfuric acid
(98% H2SO4), ammonium hydroxide (NH3·H2O), ammonium
nitrate (NH4NO3) and aluminium hydroxide (Pural Boehmite)
were purchased from Guangzhou Chemical Reagent Factory
(Guangzhou, P. R. China). Tungstic acid (H2WO4) was pur-
chased from Aladdin Industrial Inc. (Shanghai, P. R. China).
Unless otherwise indicated, all chemicals were used as
received.
Tungstated alumina (AlW) was obtained using the same
method as for ZrW.36 The tungstic acid (H2WO4) was
exchanged with aluminium hydroxide (Pural Boehmite) in
hydrogen peroxide solution (30%). The solid was filtered and
dried overnight at 353 K. Finally, the solid was calcined in air
at 973 K for 3 h prior to reaction.
Sulfated zirconia (ZrS) was prepared by the method
reported in the literature.36 Firstly, Zr(OH)4 was prepared using
the above mentioned procedure. Then, the Zr(OH)4 was added
to H2SO4 solution under agitation. The sulfated solid was fil-
tered and dried at 353 K overnight. Finally, the solid was cal-
cined at 823 K for 2 h before reaction.
5 wt% Ru/C, Amberlyst 15 and zirconium oxide (ZrO2)
were purchased from Aladdin Industrial Inc. (Shanghai,
P. R. China) and were used as received. HZSM-5, HMOR and
γ-Al2O3 were purchased from The Catalyst Plant of Nankai Uni-
versity (Tianjin, P. R. China), and were calcined in air at 773 K
for 4 h prior to use.
Ball-milled cellulose (BMC)
Ball-milled cellulose was prepared using
(QM-3SP04, Nanjing NanDa Instrument Plant) at room temp-
a
ball-miller
Catalyst characterization
erature. Microcrystalline cellulose was charged in a 100 mL The X-ray powder diffraction (XRD) diffractogram of the
ZrO2 container and the ball-milling was carried out at a speed sample was measured by a X-ray diffractometer (XPert Pro
of 500 rpm with ZrO2 balls for 24 h. To avoid thermal degra- MPD, Philip) with Cu Kα radiation (λ = 0.154 nm) operated at
dation of the microcrystalline cellulose, the temperature of the 40 kV and 100 mA. The 2θ angles were scanned from 5° to 80°.
cellulose was kept below 333 K during the ball-milling. Ball-
The BET specific surface area and average pore diameter
milled cellulose was obtained as a powder and was dried at were measured by the N2 isothermal adsorption–desorption
343 K overnight prior to use.
profiles at 77 K using a QUADRASORB SI-MP-10/PoreMaster 33
3306 | Green Chem., 2014, 16, 3305–3312
This journal is © The Royal Society of Chemistry 2014