N.V. Gromov, et al.
AppliedCatalysisA,General595(2020)117489
model.
A JEM-2010 instrument (JEOL, Japan) with the accelerating voltage
200 kV and resolution 1.4 Å was used for transmission electron micro-
scopic (TEM) studies. For the studies, catalytic particles were mounted
on perforated carbon substrates fixed on cupper nets.
2. Experimental
X-ray diffraction patterns were acquired using
а X-ray dif-
2.1. Materials
fractometer (ThermoARL) with Cu-Kα (λ =1.5418 Å) radiation. The
POLYCRYSTAL program package was used to determine the unit lattice
constants by the least squares method [38].
Chemical analyses were done by an inductively coupled plasma-
atomic emission spectrometry (ICP-AES) using a PERKIN-ELMER in-
strument OPTIMA 4300.
5-Hydroxymethylfurfural (> 98 %, Acros), D-fructose (> 99 %,
Sigma-Aldrich), D-mannose (> 99 %, Sigma-Aldrich), D-glucose (99 %,
Fisher Chemical), D-cellobiose (> 99 %, Alfa Aesar), mannitol (> 98 %,
Alfa Aesar), sorbitol (98 %, Alfa Aesar) were used as HPLC standards.
Catalysts
were
prepared
using
H3PW12O40·19H2O,
Brønsted and Lewis surface acidity was analyzed by IR-spectroscopy
using pyridine as the probe molecule (SI) [39]. IR spectra were ac-
quired on a Shimadzu FTIR-8300S spectrometer in the range between
H4SiW12O40·7.5H2O, Cs2CO3 (99.5 %, Acros Organic), Ru(NO)(NO3)3
(31.5 % Ru content, Alfa Aesar) and carbon material Sibunit-4 (Center
of New Chemical Technologies of the FRC Boreskov Institute of
Catalysis SB RAS, Omsk, Russia). Microcrystalline cellulose (> 99 %,
fraction < 0.10 mm, Vekton Co., Russia) was used as a substrate. Argon
(99.998 %) as an inert gas and hydrogen (99.99 %) was used for hy-
drogenation. Water purified with a Milli-Q unit (Millipore, France) was
used for preparation of all catalysts and solutions.
400 and 6000 cm−1 with a resolution of 4 cm−1
.
DR UV-VIS studies of the Ru/Cs-HPA samples were performed with
a Shimadzu UV-2501PC spectrophotometer with a DR attachment ISR-
240A.
2.5. Catalyst tests
2.2. Mechanical activation of cellulose
Hydrolysis-hydrogenation of cellulose was conducted in a high-
pressure autoclave (Autoclave Engineers, USA) at 453 K and 5 MPa of
hydrogen under vigorous stirring 1500 rpm. Contents of cellulose and
catalyst were both 10 g L−1. Weighed cellulose and catalyst samples
were placed to the reactor, after that 45 mL of water were added. The
reactor was closed and cleaned with argon, and fed with hydrogen
(5 MPa), then heating was started. As soon as the required temperature
was reached (that took ca. 20 min), a zero sample was collected using a
sampler. Samples to be analyzed were drawn from the autoclave during
the reaction in 0, 1, 2, 3, 5 and 7 h. Sample volume was 1 mL.
Microcrystalline cellulose was activated in a discrete action plane-
tary mill Pulverizette 5 (Fristch, Germany) with a 0.25 dm3 bowl, seven
balls (20 mm diameter), cellulose sample weight 15 g, working power
1.5 kW, centrifugal acceleration (g =9.81 m s−2) 22 g. Activation time
was 40 min.
The size of activated cellulose particles was determined using an
optical microscope Biomed-5 (LLC Biomed-M, Russia) equipped with a
digital camera (Fig. S1, SI).
XRD analysis of the microcrystalline and mechanically activated
cellulose was conducted using a Bruker D8 diffractometer (Germany)
with Cu radiation (λ = 1.5418 Ǻ) in 0.05° steps at 2θ range from 10 to
40° (Fig. S1-S2, SI). The degree of cellulose crystallinity was calculated
as the ratio of summed area of peaks of crystalline cellulose to the
summed area of all peaks [34].
Reaction products were analyzed by HPLC (Shimadzu Prominence
LC-20) equipped with refractive index and diode array detectors and
Rezex RPM-Monosaccharide Pb2+ column thermostated at 343 K.
Deionized water prepared in a Milli-Q apparatus (Millipore, France)
was used as the eluent at the rate of 0.6 mL min−1
.
The total organic carbon (TOC) content was determined in the so-
lution after the reaction using a Multi N/C 2100S TOC Analyzer
(Analytik Jena, Germany). A 500 μL aliquot of the reaction mixture was
2.3. Synthesis of catalysts
added into an analyzer injector. The amount of organic carbon (g·L−1
was calculated based on the calibrations.
)
Cs2.1H0.9PW12O40 and Cs3HSiW12O40 were synthesized from HPAs
(H3PW12O40 and H4SiW12O40) and Cs2CO3 according to the procedure
described in literature [35]. Chemical composition of cesium salts is
shown in Table S2 (SI). The main physicochemical characteristics of Cs-
HPA are shown in Figs. S3-S6 (SI).
Bifunctional catalysts of Ru/Cs2.1H0.9PW12O40 and Ru/
Cs3HSiW12O40 were prepared by the incipient wetness impregnation of
the supports by aqueous Ru(NO)(NO3)3 solution. The load of Ru was
0.6, 1 and 3 wt.%. The amount of water corresponding to the wettable
pore network of the support and containing the appropriate amount of
metal was dispersed on the support [36]. The HPA salts impregnated by
ruthenium precursor were reduced in flowing hydrogen at 573 K
(heating rate 1 °C min−1 from room temperature to 573 K) for 2 h. A
similar procedure was used for supporting Ru on Sibunit-4 [37]. The
main physicochemical characteristics of Ru/Cs-HPA are shown in Figs.
S3-S6 (SI).
Each cellulose depolymerization experiment was repeated three
times. Each analysis of the reaction mixtures was carried out three
times. The standard deviation of the results was less 2%.
The yields of the reaction products were calculated according to the
n⋅Cproduct⋅V
Y=
⋅100%
6⋅(m
)
Cell
M
glucan
where Y is the yield, Cproduct (mol L−1) is the product concentration, V
is the reaction volume (0.045 L), n is the coefficient equal to the content
of carbon atoms in a product molecule, mcell is mass of cellulose charged
into the autoclave (0.45 g), Mglucan is the molar mass of glucan unit
(162 g mol−1).
The selectivity of products was calculated as follows:
2.4. Instrumental measurements
ω⋅Cproduct
S=
× 100%
CTOC
Texture of the prepared samples was characterized by low-tem-
perature nitrogen adsorption at 69 K using an ASAP-2400 apparatus
(Micrometritics, USA). All the samples were vacuumized at
403−423 K. Specific surface areas were calculated using the BET model
and STSA equation, as well as the comparative method with the Cabor
BP 280 carbon as the reference. Pore size distribution was estimated
based on QSDFT and NLDFT calculations.
where S is the selectivity, ω is the coefficient equal to the content of
carbon atoms in a product molecule, Cproduct is the product con-
centration, CTOC is the total concentration of organic carbon detected
with TOC analyzer.
3