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TRANSCRIPT
Accepted Manuscript
Production of glucose by hydrolysis of cellulose at 423 K in the presence of
activated hydrotalcite nanoparticles
Zhen Fang, Fan Zhang, Hong-Yan Zeng, Feng Guo
PII: S0960-8524(11)00879-0
DOI: 10.1016/j.biortech.2011.06.052
Reference: BITE 8596
To appear in: Bioresource Technology
Received Date: 13 February 2011
Revised Date: 6 June 2011
Accepted Date: 13 June 2011
Please cite this article as: Fang, Z., Zhang, F., Zeng, H-Y., Guo, F., Production of glucose by hydrolysis of cellulose
at 423 K in the presence of activated hydrotalcite nanoparticles, Bioresource Technology (2011), doi: 10.1016/
j.biortech.2011.06.052
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Production of glucose by hydrolysis of cellulose at 423 K in the presence of activated
hydrotalcite nanoparticles
Zhen Fang1,*,$, Fan Zhang1,2,$, Hong-Yan Zeng2, Feng Guo1
1Biomass Group, Laboratory of Tropical Plant Resource Science,
Xishuangbanna Tropical Botanical Garden,
Chinese Academy of Sciences
88 Xuefulu, Kunming, Yunnan province 650223, China
Tel: +86-871-5163360; Fax: +86-871-5160916;
E-mail: [email protected] (ZF)
Web: http://brg.groups.xtbg.ac.cn/
2Department of Chemical Engineering
Xiangtan University
Yanggutang, Xiangtan, Hunan province, 411105, China.
* Corresponding author
$ Both are first authors
Revised for Bioresource Technology
(June 2011)
1
Abstract
Hydrotalcite nanoparticles were synthesized by co-precipitation of aqueous Mg(NO3)2·6H2O and
Al(NO3)3·9H2O in the presence of urea and subsequent with microwave-hydrothermal treatment. The
nanoparticles were activated with saturated aqueous Ca(OH)2, and used to hydrolyze cellulose. A
maximum hydrolysis yield of 47.4% with high glucose selectivity (85.8%) was achieved at 423 K.
The nanocatalyst was stable and leached little as confirmed by ICP, XRD, and neutral effluent
aqueous solution after reactions. It can be concluded that hydrotalcite nanoparticles activated with
Ca(OH)2 were a highly active, selective and stable catalyst for hydrolysis.
Keywords: Hydrotalcite; Cellulose hydrolysis; Glucose; Solid nanocatalyst; Calcium hydroxide
2
1. Introduction
Hydrolysis of cellulose to glucose is a key technology for effective use of lignocellulose
because glucose can be efficiently converted into various chemicals, biofuels, foods and medicines
(Cortright et al., 2002; Sartbaeva et al., 2008; Kamm 2007; Fang and Fang 2008). Cellulose
hydrolysis can be achieved with enzymes (Yu and Chen, 2010), dilute acids (Sun and Cheng, 2005)
and sub- or super-critical water (Fang and Fang 2008; Fang 2010; Zhao et al., 2009; Peterson et al.,
2008); however, these processes have significant drawbacks such as high cost of enzymes, difficulty
in separation of catalysts, corrosion of reactors, waste effluents and severe reaction conditions.
Some of these problems can potentially be overcome with the application of solid acid/base
catalysts. Onda et al. (2008b) showed highly selective hydrolysis of cellulose into glucose under
hydrothermal conditions at 423 K in the presence of sulfonated activated carbon (AC-SO3H) and
demonstrated that this catalyst was superior to zeolite (Onda et al. 2008b), mixed-oxide TiO2-ZrO2
(Chareonlimkun et al., 2010) and ionic liquids (Li et al., 2009). However, it proved difficult to
recover the AC-SO3H catalyst after completion of the reaction. In contrast, an inorganic catalyst such
as hydrotalcite [Mg4Al2(OH)12CO3·4H2O] would be expected to be recoverable from the product
mixtures by filtration, centrifugation, calcination or oxidation.
Therefore, in this work, hydrotalcite nanoparticles were synthesized, activated with saturated
aqueous Ca(OH)2 and used as catalyst for cellulose hydrolysis. The catalyst was stable, highly active
and selective for cellulose hydrolysis to glucose.
2. Material and methods
2.1 Materials
Microcrystalline cellulose (particle size of 100 µm, density of 0.3 g/mL) was bought from
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Biobasic Inc. (Shanghai) and treated by ball-milling (SHQM-0.4L, Chunlong Petroleum Instrument
Co., Ltd. Lianyungang, Jiangsu) using ZrO2 balls (mass of 1.8 kg and diameter of 2 mm) with a
spinning speed of 230 rpm for 24 h (Onda et al., 2009). Glucose (purity > 99%) was from Momei
(Heifei, Anhui). Mg(NO3)2·6H2O and Al(NO3)3·9H2O (99.8% purity) used in the hydrotalcite
synthesis were obtained from Guangdong Fine Chemical Co. Ltd. KOH, Ca(OH)2, NaOH, Mg(OH)2,
Al(OH)3, Ba(OH)2 and CaCO3 (99.8% purity) were from Tianjin Fine Chemical Co. Ltd. Urea
(99.9% purity) was from Shanghai Fine Chemical Co. Ltd.
2.2 Catalyst preparation and its characterization
A solution of 0.10 M Mg(NO3)2·6H2O and 0.05 M Al(NO3)3·9H2O in deionized water was
prepared in a three-neck flask. Solid urea was added into the flask with 4 mol urea per mol of [NO3-]
in the solution. The flask was submerged in an oil bath at 373 K with stirring about 500 rpm in an
ultrasonic reactor (AS10200BDT, Boda Ultrasonic Reactor Co., Ltd, Tianjin) for 2 h. The produced
slurry with the mother liquor was transferred to a Teflon reactor and subjected to hydrothermal
treatment in a microwave oven (MC85-1000, Huiyan Microwave System, Nanjing) for 2 h at 393 K
with a duty-ratio control at 100 w. The product was filtered, washed thoroughly with deionized water
and dried at 373 K for 10 h under vacuum (Deng et al., 2011). Ten g of the hydrotalcite (HT)
particles were soaked in 500 mL of saturated aqueous Ca(OH)2 (pH 12.8) at 423 K for 10 h with
stirring, and heated at 473 K for 1 h in an autoclave. The particles were washed with distilled water
until the washing-water was neutral. After filtrated and dried at 373 K, they were ground in a mortar.
The activated particles were designated as HT-OHCa. Similarly, under the same conditions, HT-OHBa,
HT-OHNa and HT-OHK nanoparticles were obtained by replacing the saturated Ca(OH)2 solution with
saturated Ba(OH)2, NaOH and KOH solutions (pH 12.8), respectively. After cellulose hydrolysis
4
under hydrothermal conditions, the HT-OHCa catalyst with residual cellulose was collected by
filtration and centrifugation, and dried at 373 K. The residual cellulose was removed by oxidation at
523 K, and the HT-OHCa was reused as catalyst four times. The respective catalysts were designated
as HT-OHCa, HT-OHCa2, HT-OHCa3 and HT-OHCa4.
The structures of HT, activated HT (HT-OHCa) and used HT-OHCa2-4 particles were analyzed by
X-ray diffraction (XRD, Rigaku Rotaflex RAD-C, Japan) using a CuKα radiation source. Particle
size was determined by atomic force microscope (AFM, WET-SPM-9500-J3, Shimadzu, Japan), and
elemental compositions by energy-dispersive X-ray spectrometry (EDX, EDAX Phoenix System,
NJ). Metal ion concentrations in the aqueous phase were analyzed by inductively coupled plasma
atomic emission spectrometry (ICP, IRIS Advantage-ER, USA). Temperature programmed
desorption (TPD) was used to assess surface basicity and acidity of catalyst using an automated
chemisorption analyzer (Chembet Pulsar, Quantanchrome Instruments, USA). Two-hundred mg of
catalyst was exposed to a stream of 10% CO2-He (or NH3-He) mixture at 673 K for 2 h. The sample
was cooled to room temperature and flushed with pure CO2 (or NH3) for 1 h until saturation. The
sample was heated to 673 K at a heating rate of 10 K/min under a He stream flowing at 80 mL/min.
The number of desorbed molecules was assumed to be equal to that of the adsorption sites present on
the catalyst surface, acidity or basicity was estimated as the total amount of CO2 (or NH3) released
through TPD per gram of catalyst. The desorbed probe gas was measured by titration and
potentiometry (Azzouz et al., 2006).
2.3 Cellulose hydrolysis with catalyst
Cellulose (0.450 g), catalyst (0.5 g) and water (150 mL) were loaded into an autoclave lined
with ZrO2 (500 mL; FCFD05-30, Jianbang Chemical Mechanical Co., Ltd. Yantai, Shandong). The
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vessel was sealed, purged with nitrogen several times to remove oxygen, and heated to 423 K for 24
h with stirring (400 rpm). The solid phase was separated by filtration and a high-speed centrifugal
machine at 50,000 rpm for 30 min, and the aqueous phase was filtered through a filter (0.22 µm pore
size) for further analyses.
2.4 Analyses of products
Quantification and identification of glucose in the aqueous phase were conducted by
high-performance liquid chromatography (HPLC-20A, Shimadzu, Japan) using a 101c column and
refractive detector. Water-soluble organic compounds (WSOCs) were determined with a total organic
carbon analyzer (TOC-5000A, Shimadzu, Japan). Glucose, WSOCs (hydrolysis) and by-products
yields as well as glucose selectivity were calculated as follows:
Glucose yield (%) = (carbon mass of glucose)/(carbon mass of cellulose) × 100%.
WSOCs yield (%) = (carbon mass of water-soluble organic compounds)/(carbon mass of
cellulose) × 100%.
By-products yield (%) = WSOCs yield (%) - glucose yield (%).
Glucose selectivity = (carbon mass of glucose)/(carbon mass of water-soluble organic
compounds) × 100%.
3. Results and discussion
3.1 Characterization of catalyst
XRD patterns (Fig. 1) showed that HT, HT-OHCa and used HT-OHCa2-4 samples had similar
structure. The XRD pattern of fresh HT (Fig. 1a) indicated that it had layered and well-crystallized
structures with characteristic and symmetric reflections. Compared with the fresh HT, activated HT
(HT-OHCa) had an additional weak diffraction peak at 2θ of 29.42º that was from Ca2CO3 (Fig. 1b).
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Calcium carbonate formed through replacement of carbonate ions in the hydrotalcite layers by
hydroxyl ions when HT particles were soaked in saturated calcium hydroxide solution. This
hypothesis is confirmed by EDX spectra (supplemental Fig. S1), since the relative carbon content
(peak area ratio of C/O) decreased to 0.3 (Fig. S1-c) from 0.6 (Fig. S1-a&b) after activation and
first-time use for hydrolysis. Thus, HT-OHCa had more hydroxyls near the edges of HT platelets than
those of fresh HT (Deng et al., 2011; Roelofs et al., 2001; Onda et al., 2008a) that could catalyze the
hydrolysis reaction. Except for the disappearance of the calcium carbonate peak at 2θ of 29.42º due
to the dissolution and decomposition of calcium carbonate into calcium ion and carbon dioxide under
the hydrothermal conditions, there was little change in the XRD spectrum for HT-OHCa2 particles
(Fig. 1c vs. 1b). EDX spectra (Fig. S1-c vs. b) confirmed that calcium peak of the catalyst
disappeared after first-time use. ICP analyses (Table 1) also showed that calcium carbonate was
leached from HT-OHCa sample because calcium ion concentration increased significantly in the
hydrolysate solution after first-time use but dropped dramatically after recycled two times. XRD
spectra and ICP results showed that the activated HT-OHCa catalyst were quite stable because its
XRD spectrum changed little (Fig. 1), and little Mg and Al (e.g., 0.01~0.25 mg/L) was leached into
the aqueous solutions even recycled for four times (Table 1). AFM observation showed that the size
of HT-OHCa particles is about 2.0~2.4 µm width and 0.8~2.4 nm thickness (Fig. S2). According to
Scherrer equation (Birks and Friedman, 1946), there was little change in particle size after activation
and four hydrolysis reactions because of similar XRD peaks width at half-maximum (Fig. 1).
3.2 Catalyst basicity and acidity measurement
CO2-TPD and NH3-TPD profiles of HT and activated HT samples are presented in Fig. 2. All
samples showed two major peaks at 350-400 K and 550-650 K for CO2 desorption (Fig. 2A),
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indicating that two types of basic sites with different intensity were present. Compared with
HT-OHNa, HT-OHK and HT samples, HT-OHBa and HT-OHCa catalysts (curves a-e) exhibited stronger
desorption peaks. The two strong peaks changed little for HT-OHCa catalyst even after it was
recycled for four times (curves a, c-e). In Fig. 2B, all samples showed that NH3 desorption had one
major peak at around 375 K that was stronger for HT-OHBa and HT-OHCa catalysts. Similarly, the
peak remained strong for HT-OHCa catalyst after it was reused for four times.
The basicity or acidity was estimated as the total amount of CO2 or NH3 released through TPD
per gram of catalyst sample. The results (Table 1) showed that HT-OHCa (1.76 and 1.17 m mol/g) and
HT-OHBa (1.57 and 1.12 m mol/g) have much higher basicity and acidity than HT-OHNa (0.75 and
0.52 m mol/g), HT-OHK (0.87 and 0.64mmol/g) and HT (0.42 and 0.21 m mol/g ). The basicity and
acidity of HT-OHCa decreased slightly with recycling: HT-OHCa2 (1.54 and 1.09 m mol/g), HT-OHCa3
(1.48 and 1.06 m mol/g) and HT-OHCa4 (1.47 and 1.05 m mol/g).
3.3 Cellulose pretreatment and hydrolysis
Original microcrystalline cellulose was treated by the ball-milling method because cellulose
with robust crystalline structure was less decomposable (Zhao et al., 2006). XRD patterns of
cellulose before and after the ball-milling for 24 h showed three diffraction peaks at around 2θ of 16°,
22° and 34° for untreated cellulose (Fig. S3-a), but, only one weak peak at around 22° after the
milling at 230 rpm (Fig. S3-b). This result indicated that cellulose crystallinity was markedly
decreased. When cellulose was hydrolyzed at 423 K for 24 h in distilled water without catalyst, less
than 3% of the crystalline cellulose was hydrolyzed to WSOCs (glucose level < 0.01 %), but the
WSOCs yield was 11.3 % with 0.4 % glucose yield when pretreated cellulose was used. The
corresponding values for pretreated cellulose heated in the presence of fresh HT catalyst were 27.2%
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WSOCs yield and 40.6% glucose selectivity. After activation with Ca(OH)2, HT-OHCa activity
increased by 70.9% with a 46.7% WSOCs yield and glucose selectivity of 85.3%. The WSOCs yield
was higher than that reported previously with sulfonated activated carbon (46.7% vs. 42.8%) (Onda
et al., 2008b; 2009); however, the glucose yield was slightly lower (39.8% vs. 40.5%). When the
catalyst was reused for four times, similar yields and glucose selectivity were obtained each time
(Table 2): 43.9, 43.8 and 43.5% WSOCs yield for the second, third and fourth recycles with more
than 80% glucose selectivity. The activated HT-OHBa catalyst with Ba(OH)2 also gave similar results
with 45.2% WSOCs yield and glucose selectivity of 84.6%. High activity and stability of the
activated HT-OHCa and HT-OHBa catalysts were also confirmed by the TPD, XRD and ICP analyses.
After reaction, the effluents were neutral (pH around 7.11~7.35). When the HT-OHCa catalyst
concentration grew from 0.45 to 2 g, WSOCs yield increased only marginally for the pretreated
cellulose (from 46.7 to 47.4%), but more substantially for the original crystalline cellulose (by 25.0%
as well as 32.2% growth in glucose selectivity) (Table 2). At the same time, pH of the effluents was
still neutral (pH of 7.31~7.42) that further confirmed the HT-OHCa catalyst was unleachable.
Since trace CaCO3 formed during activating the fresh HT (Fig. 1b; Fig. S1-b), CaCO3 was then
tested for its activity. It was found that it was even less active than fresh HT with only 25.6%
WSOCs yield as compared with 27.2% for the fresh HT and 46.7% for the activated HT. So, high
activity of the activated HT samples was from the HT-OHCa nano-crystals rather than CaCO3.
Mg(OH)2, Al(OH)3 and Ca(OH)2 catalysts had similar activities as fresh HT. These results suggest
that the activity of activated HT was from hydroxyl ions in hydrotalcite layer structure rather than
from any present in aqueous phase. When fresh HT particles were activated with NaOH and KOH,
144.5% and 149.1% increases in WSOCs yields were observed, but these increases were lower than
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that (170.9%) after Ca(OH)2 treatment presumably because of the formation of CaCO3 that
precipitated from the solution and allowed more [OH-] to replace [CO3-2] in the hydrotalcite.
Activated HT by Ba(OH)2 was as effective as Ca(OH)2-activated HT (Table 2), and this result is
further evidence for [OH-] replacement by [CO32-].
Hydrolysis of pretreated cellulose in the presence of activated HT catalyst produced maximum
WSOCs and glucose yields at 24 h (Fig. 3a), and HPLC analysis indicated that between 6 and 30 h,
the glucose concentration rising was mainly due to the hydrolysis of oligomers (Fig. 3b).
4. Conclusions
Hydrotalcite nanoparticles were synthesized and activated with Ca(OH)2 solution, and selective
cellulose hydrolysis into glucose was achieved at 423 K. Hydrolysis yield of milled cellulose to
water-soluble products was above 46% with over 85% glucose selectivity, and the aqueous solution
after reaction was still neutral. The catalyst was stable, could be easily separated from the reaction
mixture, and reused at least four times.
Acknowledgments
The authors wish to acknowledge the financial support from Chinese Academy of Sciences
[BairenJihua and Knowledge innovation key project (KSCX2-YW-G-075)], Yunnan Provincial
Government (Baiming Haiwai Gaocengci Rencai Yinjin), and China National Natural Science
Foundation (No: 21076220).
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Table captions
Table 1. Characterization of HT and the activated HT catalysts as well as their leachabilities
Table 2. Hydrolysis of cellulose in water with different catalysts at 423 Ka.
Figure captions
Fig. 1. XRD patterns of HT samples: (a) fresh HT, and (b)-(e) activated HT with Ca(OH)2 for recycled times 1-4: (b) HT-OHCa, (c)
HT-OHCa2, (d) HT-OHCa3, (e) HT-OHCa4.
Fig.2. CO2-TPD profile (A) and NH3-TPD profile (B) for samples (a) HT-OHCa, (b) HT-OHBa, (c) HT-OHCa2, (d) HT-OHCa3, (e) HT-OHCa4, (f) HT-OHK, (g) HT-OHNa and (h) HT.
Fig. 3. Changes in aqueous product yields vs. reaction time during cellulose hydrolysis (reaction condition: pretreated cellulose 0.45 g, HT-OHCa catalyst 0.50 g, distilled water 150 mL, reaction temperature 423 K and stirring rate 400 rpm):
(a) Product yields, and (b) HPLC graphs for the products.
Supplemental figure captions
Fig. S1. EDX spectra for (a) fresh HT, (b) activated HT-OHCa, and (c) the second reused HT-OHCa2. Fig. S2. AFM image of the HT-OHCa sample deposited on a mica:
(a) Scanning area of 1µm × 1µm deposited on a mica, and (b) Section analysis along the marked dark line.
Fig. S3. XRD patterns of cellulose: (a) Original microcrystalline cellulose, and (b) Pretreated cellulose.
14
Table 1. Characterization of HT and the activated HT catalysts as well as their leachabilities
Metal ion concentrationb Catalyst Mg/Ala
Ca mg/L Mg mg/L Al mg/LBasicityc (m mol/g)
Acidityd (m mol/g)
HT 2.0 - 0.05 0.01 0.42 0.21 HT-OHCa 2.0 3.38 0.25 0.01 1.76 1.17 HT-OHCa2 2.0 0.16 0.04 - 1.54 1.09 HT-OHCa3 2.0 0.07 0.02 - 1.48 1.06 HT-OH Ca4 2.0 0.04 0.01 - 1.47 1.05 HT-OH Ba 2.0 - 0.05 - 1.57 1.12 HT-OH K 2.0 - 0.07 0.02 0.87 0.64 HT-OH Na 2.0 - 0.05 0.01 0.75 0.52
a Mole ratio of Mg/Al in solid catalysts. b Metal ion concentration of aqueous phases. c CO2 released through TPD per gram of catalyst sample. d NH3 released through TPD per gram of catalyst sample.
15
Table 2. Hydrolysis of cellulose in water with different catalysts at 423 Ka.
Original microcrystalline cellulose Pretreated cellulose Catalyst WSOCs
yield (%) Glucose
selectivity (%)Glucose yield (%)
pH WSOCs yield (%)
Glucose selectivity (%)
Glucose yield (%)
pH
without catalyst 2.8 0 0 7.23 11.3 3.5 0.4 7.12 HT 21.3 38.5 8.2 7.26 27.2 40.6 11.0 7.23
HT-OHCa 35.3 54.7 19.3 7.35 46.7 85.3 39.8 7.27 HT-OHCa
b 42.6 72.4 30.8 7.42 47.4 85. 8 40.7 7.31 HT-OHCa2 32.2 52.6 16.9 7.32 43.9 83.4 36.6 7.26 HT-OHCa3 32.5 51.5 16.7 7.23 43.8 82.3 36.0 7.15 HT-OHCa4 30.1 50.3 15.1 7.19 43.5 80.5 35.0 7.11 HT-OHBa 34.4 53.5 18.4 7.29 45.2 84.6 38.2 7.22 HT-OHK 30.2 48.9 15.8 7.56 40.6 72.9 29.6 7.45 HT-OHNa 29.6 46.7 13.8 7.51 39.4 69.0 27.2 7.42 Mg(OH)2 23.4 19.3 4.5 8.56 29.4 30.2 8.9 8.54 Al(OH)3 14.1 16.7 2.4 7.33 22.6 28.7 6.5 7.26 Ca(OH)2
c 21.4 36.5 7.8 11.74 26.7 39.8 10.6 11. 42 CaCO3 19.3 17.3 3.3 8.96 25.6 27.4 7.0 8.89
aReaction condition: cellulose 0.45 g, catalyst 0.5 g, distilled water 150 mL, stirring rate 400 rpm and reaction time 24 h. bCatalyst 2.0 g. cOriginal pH of Ca(OH)2 solution is 12.84.
0 10 20 30 40 50 60 70 802θ/degree
Inte
nsi
ty
Calcium carbonate
(a) HT
(b) HT-OHCa
(c) HT-OHCa2
(d) HT-OHCa3
(e) HT-OHCa4
Fig. 1. XRD patterns of HT samples: (a) fresh HT; (b)-(e) activated HT with Ca(OH)2 for recycled times 1-4: (b)
HT-OHCa, (c) HT-OHCa2, (d) HT-OHCa3, (e) HT-OHCa4.
Fig.2. CO2-TPD profile (A) and NH3-TPD profile (B) for samples
(a) HT-OHCa, (b) HT-OHBa, (c) HT-OHCa2, (d) HT-OHCa3, (e) HT-OHCa4, (f) HT-OHK, (g) HT-OHNa and (h) HT
300 350 400 450 500 550 600 650 700
Temperature (K)
CO
2 d
eso
rpti
on
(m
mo
l/g
)
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
A
300 350 400 450 500 550 600 650 700
Temperature (K)
NH
3 d
eso
rpti
on
(m
mo
l/g
)
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
B
Fig. 3. Changes in aqueous product yields vs. reaction time during cellulose hydrolysis (reaction condition: pretreated
cellulose 0.45 g, HT-OHCa1 catalyst 0.50 g, distilled water 150 mL, reaction temperature 423 K and stirring rate 400 rpm):
(a) Product yields, and (b) HPLC graphs for the products.
0
10
20
30
40
50
60
0 6 12 18 24 30 36 42
Reaction time (h)
Yie
ld %
Glucose By-products WSOCs(a)
3 4 5 6 7 8 9 10 11
Retention time (min)
Rela
tiv
e a
bu
nd
an
ce
6 h
12 h
18 h
24 h
30 h
Glucose(b)
By-productsOligomers
Fig. S1. EDX spectra for (a) fresh HT, (b) activated HT-OHCa and (c) the second reused HT-OHCa2
(a)
Area (%): C 19%, O 31%, Mg 33%, Al 17%
Area ratio of C/O = 0.6
(c)
Area (%): C 8%, O 29%, Mg 42%, Al 21%
Area ratio of C/O = 0.3
Area (%): C 19%, O 31%, Mg 32%, Al 16%, Ca 2%
Area ratio of C/O = 0.6
(b)
Fig. S2. AFM image of the HT-OHCa sample deposited on a mica:(a) Scanning area of 1µm 1µm, and (b) Section analysis along the marked dark line.
-9.5
9.5
0
0 2.00 4.00 6.00
nm Section Analysis
(b)
µm
(a)
5 10 15 20 25 30 35 40 45
2�/degree
Inte
nsity
(a)
(b)
Fig. S3. XRD patterns of cellulose:(a) Original microcrystalline cellulose, and (b) Pretreated cellulose.
Hydrolysis products yield of milled cellulose catalyzed by activated hydrotalcite nanoparticles at 423 K
0
10
20
30
40
50
60
0 6 12 18 24 30 36 42
Reaction time (h)
Yie
ld %
Glucose By-products WSOCs
16
Research highlights
Solid nanosized hydrotalcite nanoparticles were synthesized by co-precipitation; The nanoparticles were activated with Ca(OH)2, and used for cellulose hydrolysis; Over 46% hydrolysis yield with 85% glucose selectivity was achieved at 423 K; The nanocatalyst was stable and unleachable, and easily separated for four cycles.