CHEMICAL ENGINEERING TRANSACTIONS

VOL. 81, 2020

A publication of

The Italian Association
of Chemical Engineering
Online at www.cetjournal.it

Guest Editors: Petar S. Varbanov, Qiuwang Wang, Min Zeng, Panos Seferlis, Ting Ma, Jiří J. Klemeš

ISBN 978-88-95608-79-2; ISSN 2283-9216

Magnetically Recoverable Catalysts for Cellulose and Inulin

Conversion

Esther Sulmana, Oleg Manaenkova,*, Olga Kislitsaa, Ekaterina Ratkevicha, Mikhail

Sulmana, Valentina Matveevab

aTver State Technical University, Russian Federation
bTver State University, Russian Federation

ovman@yandex.ru

A new Ru-containing catalyst based on Fe3O4-SiO2 particles that exhibit magnetic properties is proposed for the

hydrogenolysis of cellulose to glycols and the hydrolytic hydrogenation of inulin to mannitol. Here, we also report

utilisation of a magnetically recoverable catalyst in the inulin hydrolytic hydrogenation to mannitol. The effect of

process parameters on the selectivity toward the main products is studied. In the hydrogenolysis of cellulose,

the highest selectivities for EG (19.1 %) and PG (20.9 %) are achieved within 50 min under conditions of 255

°C, H2 60 bar. The conversion of cellulose is 100 %. In the hydrolytic hydrogenation of inulin, maximum mannitol

selectivity (44.3 %) is reached within 45 min under conditions of 150 °C, H2 60 bar. The conversion of inulin is

100 %.The catalyst used in this work is stable under hydrothermal conditions of the process. It can be easily

magnetically separated from the reaction mixture and reused without any loss of selectivity and activity, making

this catalyst promising for practical applications in biomass conversion.

1. Introduction

Polyols are an important platform chemicals; they are commonly used in different branches of modern industry.

Ethylene glycol (EG) and propylene glycol (PG) are used in manufacturing medicines, fuels, surfactants,

antifreezes, lubricants (Yue et al., 2012), and solvents (Harlin A., 2011). Propylene glycol is also used for the

synthesis of lactic acid, which is used in the production of biodegradable polylactones (Sugiyama et al., 2013).

EG and PG can be obtained via cellulose hydrogenolysis in subcritical water in the presence of heterogeneous

catalysts (Manaenkov et al., 2019). Mannitol, C6H14O6, is employed in pharmaceutical (Okoromah et al., 2011),

chemical (Prabhakar et al., 2014), and food industry as well as in biotechnology (Bereczki et al., 2007). It is

used to treat brain diseases as a food supplement (E421) and a sweetener in diabetic foods (Lawson et al.,

2007), in the production of resins, linseed oil, coatings, surfactants, explosives (Imhof et al., 2013), and

cosmetics (Ohrem et al., 2014). Nontoxic and inexpensive mannitol can be utilised as a phase change material

for latent heat storage (Alva et al., 2018). These applications determine the high demand for mannitol. There

are numerous methods for mannitol syntheses. It can be obtained by electrolytic reduction of glucose or by

hydrogenation of invert sugars, monosaccharides, or sucrose (Budavari, 1996). The shortcoming of the above

methods is that they use food sugars, and interfering with the food supply. This makes the development of novel,

effective methods for mannitol syntheses using non-food polysaccharides a high priority (Rinaldi, 2014). One of

such methods is the hydrolytic hydrogenation of inulin (Heinen et al., 2001). Inulin is a naturally occurring

polysaccharide, widely available as plant biomass (Pinheiro et al., 2011) and used in food biotechnology (Mayuri

et al., 2017).

The inulin hydrolytic hydrogenation can be carried out as a one-pot procedure in the presence of heterogeneous

catalysts containing various precious metals. The reaction is carried out in subcritical water, which is both a

hydrolysis catalyst and a reagent. Because polysaccharide (including inulin) hydrolysis in subcritical water is

fast, the hydrolytic hydrogenation efficiency is mainly determined by the activity of the hydrogenation catalyst.

Ru-containing catalysts are considered most active in hydrolytic hydrogenation and hydrogenolysis (Matveeva

et al., 2017).

DOI: 10.3303/CET2081193

Paper Received: 31/03/2020; Revised: 22/06/2020; Accepted: 24/06/2020
Please cite this article as: Sulman E., Manaenkov O., Kislitsa O., Ratkevich E., Sulman M., Matveeva V., 2020, Magnetically Recoverable
Catalysts for Cellulose and Inulin Conversion, Chemical Engineering Transactions, 81, 1153-1158 DOI:10.3303/CET2081193

1153

Magnetically separable catalysts received considerable attention due to easy magnetic separation from reaction

mixtures, facilitating the catalyst repeated use and allowing one to save energy and materials, decreasing the

target product costs (Wang et al., 2014a). To date, Ru-containing magnetically separable catalysts have been

used in olefin metathesis, azide-alkyne cycloaddition, hydrogenation, oxidation, etc. (Wang et al., 2014b).

Among other reactions where such catalysts were employed, the biomass conversion is one of the most

promising for utilising renewable resources. Magnetically separable catalysts have shown good results in

cellulose conversion (Zhang et al., 2014).

In this work, a Ru-containing catalyst based on Fe3O4-SiO2 particles exhibiting magnetic properties is proposed

for the hydrogenolysis of cellulose to glycolsand the hydrolytic hydrogenation of inulin.

2. Experimental

2.1 Materials

Iron (III) nitrate, mesoporous silica gel (6 nm porosity, 200-425 mesh particle size) and ruthenium (III)

acetylacetonate (Ru(acac)3, 97 %) were purchased from Sigma-Aldrich and used without purification. Ethylene

glycol (99.0 %) and tetrahydrofuran (THF) were purchased from Macron Fine Chemicals and used as received.

Inulin (99 %) was purchased from TCI (Japan) and used without purification.

2.2 The catalyst synthesis

In a typical synthesis, to the solution of 2 g of Fe(NO3)3 dissolved in 10 mL of ethanol, 2.5 g of silica gel was

added. The mixture was allowed to stir overnight in air for ethanol evaporation. The sample was then dried in a

vacuum oven at room temperature for a minimum of 2 hours. The powder was then stirred with a spatula, adding

25 drops of ethylene glycol. This sample was then loaded into two porcelain boats and heated in a quartz tube

under argon to 250 °C with a heating rate of 2 °C/min. The heating at 250 °C was held for 5 h and then the

sample was cooled to room temperature.

Ru(acac)3 (0.495 g) was dissolved in 10 mL of THF and mixed with Fe3O4-SiO2 prepared in the previous step.

The suspension was stirred overnight in air to allow THF evaporation. The sample was then dried in vacuum at

room temperature until it was entirely dry. The powdered product was stirred with 25 drops of ethylene glycol.

The sample was then loaded into two porcelain boats and heated in a quartz tube in a tube furnace under argon

to 300 °C with a heating rate of 2 °C/min followed by 3 h heating at this temperature. After that the product was

allowed to cool to room temperature.

Reduction of this sample was carried out before catalytic experiments by hydrogen at 300 C for 2 h. After

cooling the catalyst was stored in a sealed container at room temperature.

2.3 Characterization

The transmission electron microscopy (TEM) images were acquired on a JEOL JEM1010 transmission electron

microscope. Images were analysed with image-processing package ImageJ to estimate nanoparticle diameters.

High resolution TEM (HRTEM) images and scanning TEM (STEM) energy dispersive X-ray spectra (EDS) were

acquired at an accelerating voltage of 300 kV on a JEOL 3200FS transmission electron microscope equipped

with an Oxford Instruments INCA EDS system. The same TEM grids were used for all analyses. X-ray

fluorescence (XRF) measurements to determine the Ru content were performed with a Zeiss Jena VRA-30

spectrometer. Atomic adsorption spectrometry (AAS) to determine Ru and Fe contents in the liquid phase after

a catalytic reaction was carried out MGA-915 (Lumex, Russia), equipped with hollow cathode lamps for Ru

(349.9 nm) and Fe (248.3 nm).

2.4 Experimental procedure

Our tests were conducted in a 50 cm3 high-pressure steel reactor (Parr Instruments, United States) equipped

with a PARR 4843 controller and a propeller stirrer. In a typical test, the polysaccharide, the catalyst, and 30 mL

of distilled water were placed into the reactor. The reactor was triply purged with hydrogen at a pressure of 60

bar; heating and stirring (≈ 100 rpm) were then switched on to prevent the formation of local zones of overheating

and the saturation of the catalyst surface with hydrogen. Upon reaching the operational temperature, the speed

of the stirrer was increased to 600 rpm. This time was considered to be the starting point of the test. After each

test, the catalyst was separated from the reaction mass using a neodymium magnet.

The liquid phase of the catalyst was analysed on an UltiMate 3,000 liquid chromatograph (Dionex, United States)

equipped with a refractometric detector. Polysaccharide conversion was calculated using the formula X = [(mp0

– mp)/mp0] × 100 %, where mp is the weight of the polysaccharide residue after the reaction and mp0 is the initial

weight of the polysaccharide. Selectivity was calculated with the formula S = [mpr/(mp0 – mp)] × 100 %, where

mpr is the weight of the respective product.

1154

3. Results and discussion

3.1 Catalyst characterization

Figure 1 displays the TEM image of 5 % Ru-Fe3O4-SiO2 and its EDS spectrum. The EDS spectrum shows Ru,

Fe, Si, and O from the catalyst, Cu from the TEM grid and Cr from the grid holder. TEM and HRTEM images

confirm the presence of nanoparticles. While the iron oxide NP diameter is difficult to determine from TEM

because of the low electron contrast difference between iron oxide and silica, the Ru-containing nanoparticles

were measured and showed a diameter of 2.0 nm. The XRD pattern of this sample displays a broad signal at

approximately 22 degrees two theta which is due to amorphous silica and the set of reflections that is typical of

that of magnetite (Guivar et al., 2014). Analogous XRD pattern is observed for Fe3O4-SiO2 (Figure 1c). The

magnetite crystallite size calculated using Scherrer’s formula for the (311) reflection is 12.3 nm. Considering

that the magnetite NPs are located in the 6 nm silica pores (Figure 1a), it is surprising that the crystallite size is

larger by a factor of 2. We assume that two or more magnetite NPs are connected due to oriented attachment,

forming larger single crystals.

Figure 1: TEM image (a), EDS spectrum (b), and XRD pattern (d) of 5 % Ru- Fe3O4-SiO2. XRD pattern of Fe3O4-

SiO2 is shown in (c) for comparison. Inset in (a) shows the HRTEM image

It is worth noting that the (400) reflection of magnetite is overlapped with the (101) reflection of the Ru (0) phase.

The X-ray photoelectron spectroscopy (XPS) data presented in our preceding paper (Manaenkov et al., 2016)

demonstrated the presence of Ru (IV) and Ru (0) species at the 1/1 atomic ratio, indicating that the RuO2 phase

is amorphous. It is worth noting that the XPS is a surface method, allowing one to conclude that RuO2 is most

likely located on the nanoparticle surface. Liquid nitrogen adsorption measurements show that for Fe3O4-SiO2

and 5 % Ru- Fe3O4-SiO2, the BET surface areas are 304 m2/g and 280 m2/g, indicating that the incorporation of

Ru-containing NPs in the magnetic silica pores decreases the surface area by ~8 %.

3.2 Cellulose hydrogenolysis

A catalyst of 5 % Ru-Fe3O4-SiO2 was used in the hydrogenolysis of microcrystalline cellulose to glycols. A

previously developed catalyst based on hypercrosslinked polystyrene (HPS) – 3 % Ru/HPS MN270 – was used

for comparison (Matveeva et al., 2017). The main products of cellulose hydrogenolysis are EG (selectivity of

10–19 %, depending on the reaction conditions) and PG (15–23 %). Small amounts of glycerol (up to 5 %),

sorbitol (up to 4 %), mannitol (up to 2 %), and xylitol (up to 1 %) also form. Chromatography–mass spectrometry

analysis showed that the liquid phase contained trace amounts of 1,4-sorbitan, hexane-1,2,5,6-tetraol, hexane-

1155

1,2,3,4,5-pentanol, and some other products. Our study revealed that the optimum ratio between Ru (in the

catalyst’s composition) and cellulose is 0.1167 : 1 (mmol/g). This optimum is due to the following reasons. At

low Ru contents, the yield of С6–С3 polyols grows with a simultaneous drop in the yield of EG and PG. An

increase in the Ru content also reduces the yield of EG and PG; this finding can be attributed to the subsequent

hydrogenolysis of these products to ethanol, methanol, and methane. The temperature dependence of cellulose

conversion is shown in Figure 2a. At 240°C, the conversion reaches 100 % within 60 min. The effect of the

temperature on glycol selectivity is shown in Figure 2b. The highest selectivity toward EG and PG is observed

at 255 °C (12 and 22 %). In a temperature range of 205–235 °C, the selectivities toward EG and PG remain

low, while С6–С3 polyols are present in the catalysate in considerable amounts, testifying to the low degree of

these materials’ hydrogenolysis. At 235 °C in particular, sorbitol selectivity was 4.3 %, while the selectivities

toward mannitol, 1,4-sorbitan, xylitol, and erythritol lie in the range of 1.1–1.3 %. At temperatures above 255 °С,

EG selectivity diminishes, while PG selectivity remains virtually the same.

(a) (b)

Figure 2: (a) Cellulose conversion as functions of the process temperature (0.1167 mmol of Ru per

gram of cellulose; 0.3 g of cellulose; 0.07 g of catalyst; 30 mL of H2O; = 60 bar, 60 min) (b) EG and PG selectivity

as functions of the process temperature (0.1167 mmol of Ru per

gram of cellulose; 0.3 g of cellulose; 0.07 g of catalyst; 30 mL of H2O; = 60 bar, 60 min)

The dependence of cellulose conversion and the selectivity toward the main products on the process time was

studied. The highest glycol selectivity was observed at a reaction time of 30 min, but the amount of С6–С3

polyols was still considerable. By the 50th minute, these alcohols were barely present in the reaction mixture.

100 % cellulose conversion was observed even after 20 min of the test.

Table 1: Productivity (Ak) and glycol selectivity (S) for 5 % Ru-Fe3O4-SiO2 and the reference catalysta

Catalyst
Ak (product weight/catalyst weight per hour), h-1 S, %

EG PG EG PG

5 % Ru-Fe3O4-SiO2 0.62 1.18 12.0 22.9

5 % Ru-Fe3O4-SiO2b 0.99 1.08 19.1 21.0

3 % Ru/HPS MN270 0.22 0.38 7.2 12.3
a0.1167 mmol of Ru per gram of cellulose; 0.3 g of cellulose; 30 mL of H2O; 255 °C; 60 bar H2; 50 min
b0.195 mol of Ca(OH)2 per mol of cellulose

Table 1 lists the productivities (activity Ak) of the catalysts and the glycol selectivity under optimum reaction

conditions. The data in Table 1 show the productivity of the magnetically recoverable catalyst was approximately

three times higher than that of the 3 % Ru/HPS MN270 catalyst, which earlier showed good results in

thehydrolytic hydrogenation of cellulose to sorbitol (Matveeva et al., 2017). It was shown that adding a retroaldol

cleavage catalyst (Ca(OH)2) to the reaction mixture increased the yield of EG.

To study its stability, the 5 % Ru-Fe3O4-SiO2 catalyst was separated from the reaction medium using a

neodymium magnet and used in the next test with a fresh portion of cellulose, distilled water, and Ca(OH)2. The

1156

selectivity toward EG and PG and the productivity of the catalyst remained virtually the same, testifying to the

stability of the catalyst under the hydrothermal conditions of cellulose hydrogenolysis.

3.3 Inulin hydrolytic hydrogenation

The magnetically recoverable 5 % Ru-Fe3O4-SiO2 catalyst was also tested in the hydrolytic hydrogenation of

inulin to mannitol. The maximum mannitol selectivity reached in the work was 44.3 %, slightly higher than the

result obtained with the 1 % Ru/C catalyst (40 %). Depending on the test conditions, the liquid phase of the

catalysate can contain, in addition to mannitol, sorbitol (selectivity of up to 15 %), glycerol (up to 6.5 %), EG (up

to 4 %), PG (up to 5 %), and other polyhydric alcohols in trace amounts. In our studies, we selected the optimum

values of the main process parameters: temperature, reaction time, hydrogen partial pressure, and Ru:inulin

ratio. Figure 3a shows the effect of the test temperature on the selectivity toward mannitol and the secondary

reaction products in the range of 140–180 °C.

(a) (b)

Figure 3: (a) Dependence of selectivity toward mannitol, sorbitol, glycerol, and PG on the process temperature

(0.1167 mmol of Ru per gram of inulin; 0.3 g of inulin; 0.07 g of catalyst; 30 mL of H2O; H2 60 bar; 45 min) (b)

Dependence of selectivity toward mannitol and secondary products on process time (0.1167 mmol of Ru per

gram of inulin; 0.3 g of inulin; 0.07 g of catalyst; 30 mL of H2O; 150 C; H2 60 bar)

Figure 3b shows our results from studying the dependence of the selectivity toward mannitol and other products

on the process time. The highest mannitol selectivity was observed at a reaction time of 45 min. We determined

the optimum values of H2 partial pressure (60 bar) and the Ru:inulin ratio (0.1167 mmol of Ru in the catalyst’s

composition per gram of inulin). To study the catalyst’s stability, it was separated from the reaction mass using

a neodymium magnet and used in the next test. The results show that the selectivity of mannitol and the

productivity of the catalyst remained virtually the same, testifying to the catalyst’s stability in the hydrolytic

hydrogenation of inulin.

4. Conclusions

It was shown that magnetically recoverable Rucontaining catalysts can be used in the one-pot conversion of

such natural polysaccharides as cellulose and inulin to the high added-value products EG and PG (cellulose)

and mannitol (inulin). The effect of the reaction parameters on the selectivity toward the main products was

studied. In the hydrogenolysis of cellulose, the highest selectivities for EG (19.1 %) and PG (20.9 %) are

achieved within 50 min under conditions of 255 °C, H2 60 bar, 0.1167 mmol of Ru in the catalyst composition

per gram of cellulose, and 0.195 mol of Ca(OH)2 per mole of cellulose. The conversion of cellulose is 100 %. In

the hydrolytic hydrogenation of inulin, maximum mannitol selectivity (44.3 %) is reached within 45 min under

conditions of 150 °C, H2 60 bar, and 0.1167 mmol of Ru in the catalyst composition per gram of inulin. The

conversion of inulin is 100 %. The experiments were performed in triplicate. The value of the standard error of

the experiment does not exceed 4.1 %. Our results, the stability of the 5 % Ru-Fe3O4-SiO2 catalyst under

hydrothermal conditions, and the easy way in which the catalyst can be separated from the reaction mixture

using an external magnetic field make this catalyst promising for industrial application in the biomass conversion

to high added-value chemicals and feedstock for biofuel production.

1157

Acknowledgements

Studies of polysaccharides conversion was financially supported by the Russian Science Foundation, project

no. 19-19-00490. Catalyst development and characterisation was supported by the Russian Foundation for

Basic Research, project nos. 18-08-00404, 20-08-00079, 19-08-00414.

References

Alva G., Lin Y., Fang G., 2018, An overview of thermal energy storage systems, Energy, 144, 341–378.

Bereczki D., Liu M., Fernandes do Prado G., Fekete I., 2007, Mannitol for acute stroke, Cochrane Database of

Systematic Review, 3, CD001153.

Budavari S. (ed.)., 1996, The merck index - an encyclopedia of chemicals, drugs, and biologicals, whitehouse

station, Merck and Co., Inc., NJ, USA.

Guivar J.A.R., Martinez A.I., Anaya A.O., De Los Santos Valladares L., Felix L.L., Dominguez A.B., 2014,

Structural and magnetic properties of monophasic maghemite (γ-Fe2O3), nanocrystalline powder, AdvAnces

in Nanoparticles, 3, 114–121.

Harlin A., 2011, Biogenic precursors for polyphenol, polyester and polyurethane resins. In Handbook of

Bioplastics and Biocomposites Engineering Applications, Pilla, S., Ed. Scrivener Publishing: Salem, MA,

USA.

Heinen A.W., Peters J.A., van Bekkum H., 2001, The combined hydrolysis and hydrogenation of inulin catalyzed

by bifunctional Ru/C, Carbohydrate Research, 330, 381–390.

Imhof P.J., 2013, Van der Waal in: Сatalytic process development for renewable materials, Wiley-Vch

Weinheim, Germany.

Lawson P., 2007, Mannitol, Blackwell Publishing Ltd, 219–225.

Manaenkov O.V., Kislitsa O.V., Matveeva V.G., Sulman E.M., Sulman M.G., Bronstein L.M., 2019, Cellulose

conversion into hexitols and glycols in water: recent advances in catalyst development, FrontIers in

Chemistry,7, 834–841.

Manaenkov O., Mann J., Kislitza O., Losovyj Y., Stein B., Morgan D., Pink M., Lependina O., Shifrina Z.,

Matveeva V., Sulman E., Bronstein L., 2016, Ru-containing magnetically recoverable catalysts: a

sustainable pathway from cellulose to ethylene and propylene glycols, ACS Applied Material Interfaces, 8,

21285-21293.

Matveeva V.G., Sulman E.M., Manaenkov O.V., Filatova A.E., Kislitza O.V., Sidorov A.I., Doluda V.Y., Sulman

M.G., Rebrov E.V., 2017, Hydrolytic hydrogenation of cellulose in subcritical water with the use of the Ru-

containing polymeric catalysts, Catalysis Today, 280, 45–50.

Mayuri Omae J., Goto P.A., Rodrigues L.M., Santos S.S., Moser Paraiso C., Madrona G., Bergamasco R.D.C.,

2017, Beetroot extract encapsulated in inulin: storage stability and incorporation in sorbet, Chemical

Engineering Transactions, 57, 1843–1848.

Ohrem H.L., Schornick E., Kalivoda A., Ognibene R., 2014, Why is mannitol becoming more and more popular

as a pharmaceutical excipient in solid dosage forms? Pharmaceutical Development Technologies, 19(3),

257–262.

Okoromah C.A., Afolabi B.B., Wall E.C., 2011, Mannitol and other osmotic diuretics as adjuncts for treating

cerebral malaria, Cochrane Database of Systematic Reviews, 4, CD004615.

Pinheiro Oliviera R.D.S., Perego P., Nogueira De Oliviera M., Converti A., 2011, Growth and survival of mixed

probiotics in nonfat fermented milk: the effect of inulin, Chemical Engineering Transactions, 24, 457–462.

Prabhakar H., Singh G.P., Anand V., Kalaivani M., 2014, Mannitol versus hypertonic saline for brain relaxation

in patients undergoing craniotomy, Cochrane Database of Systematic Reviews, 7:CD010026.

Rinaldi R., 2014, Catalytic hydrogenation for biomass valorization, RSC Publishing, Cambridge, GB.

Sugiyama S., Tanaka H., Bando T., Nakagawa K., Sotowa K.-I., Katou Y., Mori T., Yasukawa T., Ninomiya W.,

2013, Liquid-Phase oxidation of propylene glycol using heavy-metal-free Pd/C under pressurized oxygen,

Catalysis Today, 203, 116–121.

Wang D., Astruc D., 2014a, Fast-growing field of magnetically recyclable nanocatalysts, Chemical Reviews,

114(14), 6949–6985.

Wang D., Astruc D., 2014b, Magnetically recoverable ruthenium catalysts in organic synthesis. Molecules, 19,

4635–4653.

Yue H., Zhao Y., Ma X., Gong J., 2012, Ethylene glycol: properties, synthesis, and applications, Chemical

Society Reviews, 41(11), 4218–4244.

Zhang J., Wu S., Liu Y., 2014, Direct conversion of cellulose into sorbitol over a magnetic catalyst in an extremely

low concentration acid system, Energy & Fuels, 28, 4240–4246.

1158