Catalytic conversion of cellulose for efficient ethylene glycol production and insights into the reaction pathways

Article abstract of DOI:10.1039/c6ra10183f

As promising and environmentally friendly catalysts, tungsten-containing heteropoly acids combined with supported noble metals were used for one-pot hydrothermal conversion of cellulose into polyols in the presence of pressurized hydrogen. The microcrystalline cellulose was completely converted over a mixed catalyst consisting of a low concentration of phosphotungstic acid (PTA) (0.03 wt%) and Ru/activated carbon (Ru/AC) via an one-pot hydrothermal reaction, with an ethylene glycol (EG) yield of up to 53.1% under optimal conditions. The catalytic activity of the mixed catalyst gradually decreased with increasing reaction runs, which could be mainly ascribed to the aggregation of Ru/AC particles, and to the coverage of the active sites of Ru due to the deposition of organic materials. Cellobiose was used as a model feedstock for a comparative study on the reaction pathways of the conversion of cellulose, and the results revealed that catalytic conversion of cellobiose consisted of at least three important parallel reactions under the present hydrothermal conditions, which were also most likely involved during the catalytic conversion of cellulose for EG production. Effective control of these reactions would be helpful to further maximize the EG yield during the catalytic conversion of cellulose.

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DOI: 10.1039/C6RA10183F
Catalytic conversion of cellulose for efficient ethylene glycol
production and insights into the reaction pathways
Kai Zhang,a Shubin Wu,a* He Yang,a Huimin Yin,b Gang Lia*
aState Key Laboratory of Pulp and Paper Engineering, South China University of Technology,
Guangzhou 510641, China
bLinyi Institute of Product Quality Supervision & Inspection, Linyi 276000, China
*Corresponding author: shubinwu@scut.edu.cn (S. Wu); fegli@scut.edu.cn (G. Li).
Tel./fax: +86 2022236808.
Abstract
As promising and environmentally friendly catalysts, tungstenꢀcontaining
heteropoly acids with the conbination of supported noble metals were used for
oneꢀpot hydrothermal conversion of cellulose into polyols in the presence of
pressurized hydrogen. The microcrystalline cellulose was completely converted over a
mixed catalyst consisting of a low concentration of phosphotungstic acid (PTA) (0.03
wt%) and Ru/activated carbon (Ru/AC) via an oneꢀpot hydrothermal reaction, with an
ethylene glycol (EG) yield up to 53.1% under optimal conditions. The catalytic
activity of the mixed catalyst gradually decreased with increasing reaction runs, which
could be mainly ascribed to the aggregation of Ru/AC particles, and to the coverage
of active sites of Ru due to the deposition of organic materials. Cellobiose was used as
a model feedstock for a comparative study on the reaction pathways of the conversion
of cellulose, and the results revealed that catalytic conversion of cellobiose consisted
of at least three important parallel reactions under the presnet hydrothemal conditions,
which also were most likely involed during the catalytic converison of cellulose for
EG production. Effective control of those reactions would be helpful to further
maximize the EG yield during the catalytic conversion of celllulose.
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Keywords: cellulose, mixed catalyst, ethylene glycol, reaction pathway, deactivation
mechanism
1. Introduction
Cellulose is a polysaccharide simply consisting of a large amount of βꢀ1,4 linked
glucose structural units, which is the most abundant renewable carbon source on the
earth, thus has been considered as a fascinating alternative to fossil resources for the
sustainable production of various chemicals.1ꢀ4 Currently, efficient catalytic
conversion of cellulose to ethylene glycol (EG) has attracted significant attention,
because EG is a very important bulk chemical that is mainly produced using
petroleum so far.5 To enable this new route for industrial application, the development
of highꢀperformance catalysts for efficient conversion of cellulose to EG is of
significant importance.
Among the reported catalysts, so far, the catalyst consisting of a transition metal
and tungsten species has been identified as the most active for conversion of cellulose
to EG, and the multifunction of this catalyst has been clarified during the catalytic
process.6–9 Under hydrothermal conditions, cellulose is first hydrolyzed to
waterꢀsoluble oligosaccharides and glucose at elevated temperatures. The catalysis of
tungsten species enable CꢀC bond cleavage in the waterꢀsoluble oligosaccharides and
glucose, yielding the important intermediate product of glycolaldehyde (GA), while
the transition metal subsequently catalyzes the hydrogenation of GA, eventually
resulting in the formation of EG7–11. Since GA is the key intermediate product for the
synthesis of EG during this reaction, selective conversion of cellulose to GA at the
early stage over a highly active tungsten species is, thus, of vital importance.
Experimental observations have confirmed that the final EG yield is significantly
affected by the tungsten species.7–11 Therefore, the use of a highly active tungsten
species in the catalyst is very important to achieve a high EG yield.
Phosphotungstic acid (PTA) is a commercial available waterꢀsoluble heteropoly
acid, which has been known as a lowꢀcost and environmentally friendly catalyst in
various reactions.12,13 Considering the acidic properties of the aqueous solution of
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phosphotungstic acid, the presence of considerable H+ would effectively facilitate the
hydrolysis of cellulose under hydrothermal conditions,14 which ensures that cellulose
is completely hydrolyzed to waterꢀsoluble oligosaccharides and glucose. Furthermore,
as a waterꢀsoluble tungsten species, phosphotungstic acid can act as a homogeneous
catalyst, which would further enhance the CꢀC bond cleavage reaction to form GA in
comparison with most of the heterogeneous catalysts, finally resulting in a high yield
of EG.
In the present study, a mixed catalyst combining PTA and activated carbon
supported Ru (PTAꢀRu/AC) was developed for the catalytic conversion of cellulose
into EG. This mixed catalyst was highly active and a high EG yield was successfully
achieved even though the concentration of PTA was extremely low in the reaction
solution. The durability and deactivation mechanism of the PTAꢀRu/AC mixed
catalyst were discussed. Finally, in order to gain insights into the reaction pathways of
catalytic conversion of cellulose for EG production, cellobiose was selected as a
model feedstock for a comparative study of this catalytic process.
2. Experimental
2.1 Materials
Ru/AC, Pt/AC, Pd/AC (5 wt% loading), microcrystalline cellulose (average
particle size: ~50 ꢁm) and cellobiose were purchased from Aladdin Industry Inc. PTA
and silicotungstic acid (STA) were obtained from Tianjin Kemiou Chemical Reagent
Co. Ltd.
2.2 Catalytic tests
Hydrothermal conversion of cellulose (or cellobiose) to EG was carried out in a
100 ml highꢀpressure stainlessꢀsteel autoclave (Series 5100 HP Compact Reactors,
Parr Instrument Company). Briefly, Ru/AC (or Pt/AC, Pd/AC) (0ꢀ0.1 g), PTA (or STA)
(0ꢀ900 ppm), water (50 g) and microcrystalline cellulose (or cellobiose) (0.5 g) were
transferred into the reactor. Then, the reactor was first purged with H2 to remove the
air in the system at atmospheric pressure, and the reactor was subsequently
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pressurized with hydrogen at a pressure of 6 MPa at room temperature. After sealing
the reactor, the mixture was heated up to temperatures of 230–250 °C and maintained
for 30–90 min, under at a constant stirring rate of 1000 rpm. After the reaction, the
reactor was rapidly cooled down to room temperature with ice water. The liquid
products were collected after permeating through a membrane filter with an average
pore size of 0.45 ꢁm, and the components in the liquid phase were analyzed using an
ultra performance liquid chromatography instrument (Agilent 1290, Agilent
Technologies) coupled with a quadrupole timeꢀofꢀflight mass spectrometer (Agilent
6540, Agilent Technologies). Solid residue obtained after filtration was washed with
deionized water, followed by drying at 105 °C in a vacuum oven overnight. The yield
of EG was approximately calculated based on the weight of EG and original cellulose
sealed into reactor. Cellulose conversion was calculated by the weight difference of
cellulose before and after the reaction with an uncertainty of ±3%.
2.3 Characterization methods
The concentration of Ru ions in the liquid phase after reaction was determinated
using a flame atomic absorption spectrometry (AAS) (novAA 350, Analytik Jena).
Xꢀray photoelectron spectra (XPS) was recorded using an Xꢀray photoelectron
spectrometer (ESCALAB 250XI, Thermo Scientific) with nonmonochromatized Al
Kα radiation as the excitation source. Thermogravimetric analysis was carried out
using an analyzer (STA449 F3, NETZSCH) operated at temperatures that ranging
from 25 to 700 °C under a nitrogen atmosphere. The morphologies of fresh and
recycled solid catalysts were determined using a scanning electron microscope (SEM)
(Merlin, Zeiss) and transmission electron microscope (TEM) (JEMꢀ2100F, JEOL).
3. Results and discussion
3.1 Screening of mixed catalysts for cellulose conversion
A variety of mixed catalysts consisting of different tungsten species and supported
noble metals were screened for the cellulose conversion process, and their catalytic
performances are summarized in Table 1. Although all the mixed catalysts showed
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quite high cellulose conversions (95~100%), however, the final product distribution
differed significantly under the same reaction conditions. Among these mixed
catalysts, the PTAꢀRu/AC mixed catalyst was the most selective for the production of
EG and sorbitol, and the yields of EG and sorbitol were up to 53.1 and 12.4%,
respectively. However, for the production of 1,2ꢀpropylene glycol (1,2ꢀPG), the
PTAꢀPd/AC and PTAꢀPt/AC mixed catalysts were much more active than the
PTAꢀRu/AC mixed catalyst. On the other hand, comparing the catalytic performance
of PTAꢀRu/AC and STAꢀRu/AC mixed catalysts with the same noble metal
component, PTAꢀRu/AC showed a much higher EG yield (53.1%) than that of
STAꢀRu/AC (16.3%). This result indicated that tungsten species also exerted a very
important effect on the catalytic performance, since tungsten species was the active
phase for the CꢀC cleavage reaction during the catalytic process7–11. Therefore, based
on the EG productivity, the PTAꢀRu/AC was selected as the most active mixed
catalyst for catalytic conversion of cellulose for EG production. It should be noted
that attempts using a higher cellulose amount of 1.5wt% to increase the EG
productivity generally resulted in a much lower EG yield < 30% even the reaction
time was increased from 50 to 150 min, which could be mainly ascribed to the serious
cocking effect under a high cellulose concentration during the reaction.15 Therefore, a
relatively low cellulose concentration was necessary in order to convert into EG very
selectively.
3.2 Catalytic performance of the PTAꢀRu/AC mixed catalyst for cellulose conversion
Fig. 1 shows the catalytic performance of the PTAꢀRu/AC catalyst for cellulose
conversion under difference conditions. The effects of the amount of PTA and Ru/AC
in the mixed catalyst on the catalytic activity for cellulose conversion were studied,
and the distribution of the main polyol products is illustrated in Fig. 1a and b. When
the PTA amount in the reactor was fixed at 500 ppm, the conversion of cellulose
increased with increasing the Ru/AC amount in the mixed catalyst, and the cellulose
was completed converted when the Ru/AC amount in the mixed catalyst was larger
than 0.025 g. However, both EG and 1,2ꢀPG yields followed almost the same trend
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that showed a maximum value as the amount of Ru/AC further increased. This was
mainly because a high Ru/AC amount in the mixed catalyst favored the hydrogenation
of glucose into sorbitol.16 However, much excess Ru/AC amount in the mixed catalyst
caused a decrease in the sorbitol yield, due to the enhanced isomerization of glucose
to fructose.17 Fig. 1b shows the effect of PTA amount on the catalytic performance of
cellulose conversion, with a fixed Ru/AC amount of 0.025 g in the mixed catalyst. As
the PTA amount increased, the conversion of cellulose increased to 100%, because the
hydrolysis of cellulose was enhanced under acidic conditions.18 The EG yield initially
increased rapidly at low PTA concentrations, and it was much higher than the yields
of 1,2ꢀPG and sorbitol, which could be attributed to selective CꢀC bond cleavage via a
retroꢀaldol reaction by the catalysis of PTA.19 It should be noted that the enhancement
of the EG yield was very notable although the PTA concentration was extremely low,
this was mainly because the PTA acted as a homogeneous catalyst. The EG yield
gradually decreased with a further increase of PTA concentration, which could be
ascribed to that a high acidity facilitated the conversion of glucose to byꢀproducts.20
Obviously, the tuning of composition of the PTAꢀRu/AC is of significance to control
the product distribution of the catalytic conversion of cellulose, and the use of a low
PTA concentration allow both high catalytic activity and selectivity for the production
of EG from cellulose.
Fig. 1c shows the effect of temperature on the catalytic performance of
conversion of cellulose with optimal amounts of PTA and Ru/AC in the mixed
catalyst. With the temperature increased from 230 to 250 °C, the yields of 1,2ꢀPG and
sorbitol showed slightly changes, while the EG yield increased from 40 to 51% due to
the increased conversion of cellulose at high temperatures. Fig. 1d shows the time
course of catalytic performance of the mixed catalyst for EG production. The EG
yield was as high as 37% although the reaction had been conducted for only 20 min,
which again confirmed a quite high reaction rate even a small amount of PTA in the
mixed catalyst. The EG yield initially increased with increasing the reaction time and
then reached a maximum EG yield of 53.5% at 50 min. This high EG yield is
comparable with that of reported catalysts19 although the amount of tungsten species
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was much lower in the present system.
3.3 The stability and reusability of the PTAꢀRu/AC mixed catalyst
The stability and reusability of the mixed catalyst is an important concern for
practical EG production. Since PTA is soluble in water and acts as homogenous
catalysis, the stability of the mixed catalyst would be mainly dominated by the Ru/AC
component for the final hydrogenation reaction. Therefore, the catalytic performance
of the catalyst was evaluated using recycled Ru/AC with fresh PTA for several
reaction runs. Fig. 2 shows the catalytic performance of the mixed catalyst for EG
production at different reaction runs. The EG yield decreased with increasing the
recycled times of Ru/AC, e.g., the EG yield decreased obviously from 53.5 to 33%
after 3 reaction runs, which indicated that deactivation had occurred for Ru/AC in the
mixed catalyst under present hydrothermal conditions.
To gain insights into the deactivation mechanism of Ru/AC in the mixed catalyst,
the recycled Ru/AC was studied using various techniques. The AAS measurements
showed that there was no Ru ion in the liquid phase after each catalytic runs (Table 2),
which indicated that no leaching occurred for the Ru metal during the entire catalytic
process. Fig. 3 shows the Ru 3p XPS spectra of the fresh and recycled catalysts with
different catalytic runs. The binding energies centered at 462.7 and 484.3 eV, which
could be ascribed to the metallic state of Ru,21 were almost the same. This result
revealed that the metallic Ru in the catalyst was maintained during the whole
hydrothermal treatment. Fig. 4 shows the SEM images of the fresh and recycled
Ru/AC with different catalytic runs. Compared with the fresh Ru/AC catalyst (Fig.
4a), there was no obvious difference in their particle size (~10 ꢁm) when the Ru/AC
catalyst was used once (Fig. 4b). This result was well consistent with their similar
catalytic performance. When the catalyst was used for 2 and 3 times (Fig. 4c and d),
the catalyst obviously aggregated to make particles as large as millimeters, which
corresponded to the much lower catalytic activities again, showing good correlation
between the catalytic performance and Ru/AC particle size. The above observation
indicated that the Ru/AC particles suffered from serious aggregation after several
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catalytic runs. This could be probably due to the hydrophobic surface of the activated
carbon support,22 which made the homogeneous dispersion of Ru/AC in water
difficult. The aggregation of Ru/AC particles might efficiently increase the diffusion
resistance of the reactant to the active sites of Ru nanoparticles, resulting in
degradation of catalytic performance of Ru/AC. Fig. 5 shows the TEM images of the
fresh and used Ru/AC after the catalytic conversion of cellulose. Ru nanoparticles
with an average size of several nanometers were homogeneously distributed on the
AC support for the fresh Ru/AC, while the Ru/AC used after 3 times was largely
covered by unknown materials. To further confirm that, both the fresh Ru/AC and
recycled Ru/AC with 3 catalytic runs were analyzed using TG (Fig. 6). It clearly
showed that the weight loss of recycled Ru/AC catalyst was much larger than the
fresh one at high temperatures, which confirmed the deposition of organic materials
on the recycled catalyst. As a result, the effective active sites of Ru nanoparticles
significantly decreased and the channels in the support for mass transport were partly
blocked, which also should be substantially contributed to the deactivation of catalytic
activities. Previously, Tai et al. reported19 catalytic conversion of cellulose into EG
using Ru/AC and H2WO4 mixed catalyst, the acid in that system was much higher and
the catalyst showed better stability, which could be most likely ascribed to the fact
that a higher acidity probably be helpful to suppress the deposition of polymer on the
catalyst.
Although the mixed catalyst consisting of an extremely low concentration of
phosphotungstic acid and AC supported Ru showed excellent catalytic activity for
efficient production of EG, the durability of the catalytic performance was efficient
hindered by the deactivation of Ru/AC during the catalytic reaction. The analyses of
the deactivation mechanism described above lead us to believe that the catalyst
support must be improved for Ru loading in the present system, because the
hydrophobic properties of AC make the Ru/AC easily aggregated in aqueous solution
at high temperatures, and the small pore size of AC make the diffusion difficult and
thus is easily blocked since the involvement of relatively large molecules in this
catalytic reaction (e.g., glucose). This conclusion inspires us to further improve the
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catalytic performance by designing new catalytic support materials with excellent
hydrophilic properties and looser structures.
3.4 Comparative study on catalytic conversion of cellulose and cellobiose for EG
production
According to the previous studies,6–11 catalytic conversion of cellulose into EG
involves multiꢀstep reactions including (
and soluble monosaccharide under acidic conditions, (
form glycolaldehyde via retroꢀaldol reaction over W species, and (
Ⅰ
) hydrolysis of cellulose to form glucose
) CꢀC cleavage of glucose to
) the
Ⅱ
Ⅲ
hydrogenation of glycolaldehyde to EG with the aid of metal catalysts, as the reaction
pathways illustrated in the Scheme 1. Since cellulose is a polysaccharide with
considerable large amount of βꢀ1,4 linked glucose structural units, further study of the
details of the reaction mechanism becomes inconvenient. To simplify the problem,
cellobiose, which is glucose dimer connected by the same βꢀ1,4ꢀglycosidic bond as in
glucose and represents the simplest model compound for cellulose, is usually used as
an ideal model compound to study the transformation behaviors of cellulose in
different systems.23–25 Therefore, in order to gain insights into the reaction pathways
for catalytic conversion of cellulose, catalytic conversion of cellobiose into EG was
examined as a model reaction for a comparative study in the present work.
Fig. 7 shows the mass spectra of the liquid products of catalytic conversion of
cellobiose using the PTAꢀRu/AC catalyst. As expected, glucose and sorbitol were
clearly identified in the products when cellobiose was used as the feedstock, and their
formation could be mainly ascribed to the hydrolysis of cellobiose and subsequent
hydrogenation
of
glucose.
However,
new
components,
such
as
3ꢀβꢀglucopyranosylꢀDꢀglucitol, glucosylꢀerythrose and glycosylꢀethylene glycol, also
were detected. The formation of 3ꢀβꢀglucopyranosylꢀDꢀglucitol could be attributed to
the hydrogenation of cellobiose over the Ru/AC catalyst, while the generation of
glucosylꢀerythrose and glycosylꢀethylene glycol could be thought as the evidence of
retroꢀaldol condensation of cellobiose. Based on the above results, we could conclude
that the catalytic conversion of cellobiose over Ru/ACꢀTPA consisted of at least three
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parallel reactions that occurred simultaneously during the catalytic process: hydrolysis,
hydrogenation and retroꢀaldol condensation of cellobiose, as shown in Scheme 2.
Similar results also were reported in a previous study.23 Table 3 compares the
distribution of main products in the liquid phase for the catalytic reaction using
cellulose and cellobiose as the feedstock. The yield of EG together with that of the
other components were comparable for both cellulose and cellobiose as the feedstock,
which indicated that cellulose and cellobiose might undergo similar reaction pathways,
since cellobiose represents the basic structural unit for cellulose and can be obtained
via the hydrolysis of cellulose. Therefore, when cellulose was used as the feedstock
for EG production, in addition to the retroꢀaldol condensation of glucose that is
hydrolyzed completely from cellulose during the catalytic process, effective tuning of
other reactions, such as retroꢀaldol condensation of cellobiose, also would be of
significant in order to maximize the EG yield.
Conclusions
A highly active mixed catalyst with Ru/AC and an extremely low concentration
of phosphotungstic acid was studied for catalytic conversion of cellulose to EG. The
catalyst showed excellent catalytic performance, with a cellulose conversion and EG
yield of 100 and 53.1%, respectively, under optimal conditions. The durability of the
catalyst was investigated and confirmed the deactivation of the catalyst during the
hydrothermal reaction. The decreased catalytic performance could be mainly
attributed to the degradation of Ru/AC, due to the aggregation of Ru/AC particles and
the loss of active site of Ru due to the deposition of organic materials. This finding
revealed that a catalyst support with hydrophilic property and a looser structure would
result in better catalytic performance. Cellobiose was used as model feedstock for a
comparative study in order to gain insights into the reaction pathways of catalytic
conversion of cellulose for EG production. The results showed that catalytic
conversion of cellobiose consisted of at least three parallel reactions including direct
retroꢀaldol condensation of cellobiose to produce EG, which also might involved in
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the catalytic conversion of cellulose. Effective tuning of the above reactions would be
helpful to further maximize the EG yield via catalytic conversion of cellulose.
Acknowledgments
This work was supported by the National High Technology Research and
Development Program of China (No. 2012AA101806), the Science and Technology
Department of Guangdong Province (No. 201607020025), the Fundamental Research
Funds for the Central Universities (No. 2014ZP0014，No. 2015ZZ136), and the State
Key Laboratory of Pulp and Paper Engineering (No. 2014T05, No. 2015QN02).
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Figures and tables:
Fig. 1 Catalytic performance of the PTAꢀRu/AC mixed catalyst for conversion of
cellulose under different reaction conditions.
Reaction conditions: (a) 0.5 g microcrystalline cellulose, 50 g deionized water, 500 ppm PTA, 6 MPa H2 (room
temperature), 250 °C and 60 min; (b) 0.5 g microcrystalline cellulose, 50 g deionized water, 0.025 g Ru/AC, 6
MPa H2 (room temperature), 250 °C and 60 min; (c) 0.5 g microcrystalline cellulose, 50 g deionized water, 0.025 g
Ru/AC, 300 ppm PTA, 6 MPa H2 (room temperature) and 60 min; (d) 0.5 g microcrystalline cellulose, 50 g
deionized water, 0.025 g Ru/AC, 300 ppm PTA, 6 MPa H2 (room temperature) and 250 °C.
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Fig. 2 Catalytic performance of the PTAꢀRu/AC mixed catalyst with recycled Ru/AC.
Reaction conditions: 0.5 g microcrystalline cellulose, 50 g deionized water, 0.025 g Ru/AC, 300 ppm
phosphotungstic acid, 250 °C and 50 min.
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Fig. 3 XPS spectra of Ru 3p of the fresh and recycled Ru/AC. (a) fresh; (b) used once;
(c) used twice; (d) used thrice .
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Fig. 4 SEM images of the fresh and recycled Ru/AC in the mixed catalyst. (a) fresh;
(b) used once; (c) used twice; (d) used thrice.
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Fig. 5 TEM images of the fresh (a) and used Ru/AC (b) in the mixed catalyst for the
conversion of cellulose into EG.
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Fig. 6 TG curves of the fresh and used Ru/AC for the conversion of cellulose into EG
under a N2 atmosphere.
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Fig. 7 Mass spectra of the products for catalytic conversion of cellobiose over the
PTAꢀRu/AC catalyst.
Reaction conditions: 0.5 g cellobiose, 50 g water, 300 ppm PTA, 0.025 g Ru/AC, 6 MPa H2 (room teperature),
230 °C and 20 min. A: 3ꢀβꢀglucopyranosylꢀDꢀglucitol (C12H24O11), B: glycosylꢀerythritol (C10H20O9), C:
glycosylꢀethylene glycol (C8H16O7), D: sorbitol (C6H14O6), E: glucose (C6H12O6), F: anhydroglucose (C6H10O5).
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Scheme 1 Reaction pathways of oneꢀpot conversion of cellulose for EG production.
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Scheme 2 Reaction pathways for cellobiose conversion catalyzed by PTAꢀRu/AC for
EG production.
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Table 1 Catalytic performance of different mixed catalysts for cellulose conversion
Entry Catalyst
Conversion (%) Yield (%)
Ery
EG 1,2ꢀPG Sor 1,2ꢀBOD 1,3ꢀPG Man
1
2
PTAꢀRu/AC
100
95.0
100
95.5
N
2.7
T
53.1
27.1
23.2
16.3
27.4
28.2
5.5
15.1
12.8
6.8
12.4
3.0
3.3
8.5
5.7
2.6
6.2
1.9
6.0
4.0
7.0
3.6
2.2
T
T
PTAꢀPd/AC
PTAꢀPt/AC
STAꢀRu/AC
PTAꢀRu/AC
PTAꢀRu/AC
0.4
0.2
1.8
1.1
0.5
3
T
T
4
2.8
1.7
1.6
2.5
T
5a
6b
4.9
N
3.1
T
Reaction conditions: 0.5 g cellulose, 50 g water, 300 ppm PTA (or STA), 0.025g M/AC (M is the metal), 6 MPa H2
a)
(room temperature),1000 rpm stirring rate, 250 ºC and 50 min. 1.5 g cellulose; b) 1.5 g cellulose, 150 min
reaction time. EG, 1,2ꢀPG, 1,2ꢀBDO, 1,3ꢀPG, Ery, Man and Sor are abbreviations for ethylene glycol,
1,2ꢀpropylene glycol, 1,2ꢀbutanediol, 1,3ꢀpropylene glycol, erythritol, mannitol and sorbitol, respectively. T and N
represent trace amount and not calculated, respectively.
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Table 2 Ru concentrations in the liquid phase after each reaction detected by AAS.
Recycled time
Ru concentration (ppm)
Leached Ru (wt%)
0
1
2
3
0
0
0
0
0
0
0
0
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Table 3 Comparison of the catalytic performance of cellulose and cellobiose under
the same reaction conditions.
Feedstock Yield (%)
Sorbitol
3.32
Erythritol Glycerol
1,2ꢀPG
6.02
EG
1,3ꢀPG
trace
GA
cellulose
1.17
2.06
2.08
2.10
31.6
24.0
trace
trace
cellobiose 3.40
11.4
trace
Reaction conditions: 0.5 g cellulose (or cellobiose), 50 g water, 300 ppm PTA, 0.025 g Ru/AC, 6 MPa H2 (room
temperature), 1000 rpm stirring rate, 230 °C and 20 min. ,2ꢀPG, EG, 1,3ꢀPG and GA are the abbreviations of
1
1,2ꢀpropylene glycol, ethylene glycol, 1,3ꢀpropylene glycol, glycolaldehyde, respectively.
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468x176mm (72 x 72 DPI)