Hydrogenation Of Cellulose Research Articles

Cellulose Depolymerization over Heterogeneous Catalysts.

Cellulosic biomass is the largest source of renewable organic carbon on our planet. Cellulose accounts for 40-50 wt % of this lignocellulose, and it is a feedstock for industrially important chemicals and fuels. The first step in cellulose conversion involves its depolymerization to glucose or to its hydrogenated product sorbitol. The hydrolysis of cellulose to glucose by homogeneous mineral acids was the subject of research for almost a century. However, homogeneous acids have significant drawbacks and are neither economical nor environmentally friendly. In 2006, our group reported for the first time the ability of heterogeneous catalysts to depolymerize cellulose through hydrolytic hydrogenation to produce sorbitol. Later, we reported the hydrolysis of cellulose to glucose using carbon catalyst containing weakly acidic functional groups. Understanding the reaction between cellulose and heterogeneous catalyst is a challenge as the reaction occurs between a solid substrate and a solid catalyst. In this Account, we describe our efforts for the conversion of cellulose to sorbitol and glucose using heterogeneous catalysts. Sorbitol is produced by sequential hydrolysis and hydrogenation of cellulose in one pot. We reported sorbitol synthesis from cellulose in the presence of supported metal catalysts and H2 gas. The reducing environment of the reaction prevents byproduct formation, and harsh reaction conditions can be used to achieve sorbitol yield of up to 90%. Glucose is produced by acid catalyzed hydrolysis of cellulose, a more challenging reaction owing to the tendency of glucose to rapidly decompose in hot water. Sulfonated carbons were first reported as active catalysts for cellulose hydrolysis, but they were hydrothermally unstable under the reaction conditions. We found that carbon catalysts bearing weakly acidic functional groups such as hydroxyl and carboxylic acids are also active. Weakly acidic functional groups are hydrothermally stable, and a soluble sugar yield of 90% was achieved in a 20 min reaction. We clarified that the polycyclic aromatic surface of the carbon adsorbs cellulose molecules on its surface by CH-π and hydrophobic interactions driven by a positive change in entropy of the system. The adsorbed molecules are rapidly hydrolyzed by active sites containing vicinal functional groups that recognize the hydroxyl groups on cellulose to achieve a high frequency factor. This phenomenon is analogous to the hydrolysis of cellulose by enzymes that use CH-π and hydrophobic interactions along with weakly acidic carboxylic acid and carboxylate pair to catalyze the reaction. However, in comparison with enzymes, carbon catalyst is functional over a wide range of pH and temperatures. We also developed a continuous flow slurry process to demonstrate the feasibility for commercial application of carbon-catalyzed cellulose hydrolysis to glucose using inexpensive catalyst prepared by air oxidation. We believe that further efforts in this field should be directed toward eliminating roadblocks for the commercialization of cellulose conversion reactions.

Carbon supported Ru-Ni bimetallic catalysts for the enhanced one-pot conversion of cellulose to sorbitol

Ru and Ni mono- and bimetallic catalysts were prepared by impregnation of two different supports (activated carbon and carbon nanotubes) and were characterized by TPR, TEM and N2 adsorption at −196°C. The prepared Ru mono- and bimetallic catalysts were highly efficient for the hydrolytic hydrogenation of cellulose to sorbitol. Regardless of the support used, when nickel was incorporated into the supported ruthenium catalyst a promoting effect was observed, with an increase in both conversion and selectivity to sorbitol, which was explained by the interaction between both metals. Yields of sorbitol around 50–60% were achieved after 5h of reaction when using Ru-Ni/AC and Ru-Ni/CNT as catalysts. Moreover, a yield of sorbitol over 70% could be reached in just 1h of reaction if the Ru-Ni catalysts were ball-milled together with cellulose.

High hexitols selectivity in cellulose hydrolytic hydrogenation over platinum (Pt) vs. ruthenium (Ru) catalysts supported on micro/mesoporous carbon

The “one-pot” hydrolyltic hydrogenation of cellulose towards C2-C6 sugar alcohols has been recognized as one of the most promising biomass valorization routes for the production of high added-value chemicals. In this work, we studied the performance of Ru and Pt catalysts supported on micro/mesoporous activated carbon, in the hydrolytic hydrogenation of microcrystalline and ball-milled cellulose, in neat water, at 180°C and at relatively low hydrogen pressure of 2MPa. The impact of metal loading (1–5wt.%), metal reduction method (H2 at 350°C or NaBH4) and acidification (sulfonation) of the AC support on cellulose conversion and selectivity to the various products were systematically addressed. It was shown that Pt is significantly more selective towards hexitols (sorbitol and mannitol) compared to Ru, in glucose-rich reaction media, such as those offered by the easily hydrolyzed ball-milled cellulose. For example, the 5wt%Pt/AC-SO3H catalyst afforded hexitols yield of 69.5wt.% (at 96.1% conversion) compared to 10.9wt.% (at 95.2% wt.% conversion) obtained by the corresponding Ru catalyst, the latter being also selective towards glycerol and propane-1,2-diol (propylene glycol). A relatively moderate metal loading, such as in 3wt.%Ru/AC-SO3H, was more favorable for hexitols production (44.5wt.% yield, at 94.8wt.% conversion) with Ru catalysts. These results were also verified by glucose hydrogenation experiments that were conducted at the same experimental conditions. Both Pt and Ru exhibited relatively high glucose hydrogenation activity towards hexitols, versus retro-aldol reactions that lead directly to smaller C2–C4 compounds, while the difference in the final product yields between the two metals was attributed to the higher hexitols hydrogenolysis (CC cleavage) reactivity of Ru. HRTEM data showed the formation of metallic crystalline Pt and Ru nanoparticles (≤4nm, depending on loading) as well as of amorphous oxygen-rich M(O)xδ+ phases, which were also confirmed by the XPS data. The presence of these phases which may be a source of acidity, as well as the bacisity of the parent AC used in this study, were mainly responsible for inducing isomerization, retro-aldol and dehydration reactions leading eventually to increased glycerol and propylene glycol selectivity, as was observed for both low-metal catalysts, i.e. 1wt.% Pt or Ru/AC.

Catalytic conversion of cellulose into polyols using carbon-nanotube-supported monometallic Pd and bimetallic Pd–Fe catalysts

A series of carbon nanotube (CNT)-supported monometallic Pd and bimetallic Pd–Fe catalysts were synthesized and employed for catalytic hydrogenolysis of cellulose into polyols, including hexitol, ethylene glycol (EG), 1,2-propanediol (1,2-PG), and glycerol (Gly). The physicochemical properties of the catalysts were characterized by nitrogen physical adsorption measurements, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy. The total yield of hexitol, EG, 1,2-PG, and Gly in hydrolytic hydrogenation of cellulose was 37, 55, and 53% for Pd/CNTs, Pd–Fe/CNTs (Pd:Fe = 1:1), and Pd–Fe/CNTs (Pd:Fe = 1:2), respectively. Addition of Fe to Pd significantly modified the physicochemical properties of the nanoparticles and their catalytic performance, especially regarding hexitol selectivity. The promoting effect of Fe, especially for hexitol selectivity, compared with the monometallic catalyst is due to the fact that incorporation of Fe may stabilize Pd0 nanoparticles and lead to downshift of the d-band center of Pd metal nanoparticles by charge transfer from Fe to Pd. Recycling experimental results showed that leaching of Fe resulted in a significant decrease in the hexitol yield obtained using the Pd–Fe/CNTs after the first recycle, further demonstrating that Fe element plays a promoting role for hexitol formation.

Cellulose conversion to polyols in subcritical water

Subcritical water is shown to be an efficient medium for the cellulose conversion process to produce polyols. A novel type of Ru-containing hyper-crosslinked polystyrene (HPS)-immobilized catalyst is suggested. Application of the catalyst containing 1% Ru can achieve a total yield of sorbitol and mannitol of about 50%; that is comparable with the results obtained in the presence of more complex and, therefore, more expensive catalytic systems. The influence of both the process conditions and the catalyst properties on the target product yield is studied. The hydrolytic hydrogenation of cellulose in subcritical water using Ru-containing HPS-immobilized catalysts can become a base for novel technologies of cellulose biomass conversion and production of raw materials for chemical synthesis and industrial production of second generation biofuels.

Hydrolytic hydrogenation of cellulose in subcritical water with the use of the Ru-containing polymeric catalysts

The study presents the results of cellulose hydrolytic hydrogenation process in subcritical water in the presence of Ru-containing catalysts based on hypercrosslinked polystyrene (HPS) MN-270 and its functionalized analogues: NH2-HPS (MN-100) and SO3H-HPS (MN-500). It was shown that the replacement of the traditional support (carbon) by HPS increases the yield of the main cellulose conversion products – polyols – important intermediates for the chemical industry. The catalysts were characterized using transmission electron microscopy (TEM), high resolution TEM, and porosity measurements. Catalytic studies demonstrated that the catalyst containing 1.0% Ru and based on MN-270 is the most active. The total yield of sorbitol and mannitol was 50% on the average at 85% cellulose conversion.

Direct conversion of cellulose to sorbitol over ruthenium catalysts: Influence of the support

Ruthenium-based catalysts were prepared by incipient wetness impregnation of different supports and characterized by TPR, TEM, ICP and N2 adsorption at −196°C. The catalytic performances of the catalysts were evaluated in the hydrolytic hydrogenation of cellulose. The prepared catalysts were highly efficient, allowing conversions of cellulose higher than 75% after 5h of reaction. The highest selectivity to sorbitol (over 60%) was reached when using carbon nanotubes (CNT) as support. Moreover, if this catalyst was ball-milled together with cellulose, that selectivity to sorbitol could be achieved in only 1h of reaction and with complete conversion of cellulose.

Influence of ZrO2 on catalytic performance of Ru catalyst in hydrolytic hydrogenation of cellulose towards γ-valerolactone

This work is focused on the study of the influence of the surface properties of different zirconia supports on the catalytic performance of ruthenium catalyst in hydrolytic hydrogenation of cellulose towards γ-valerolactone. The surface properties of the synthesized catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The reaction products were analyzed by high-performance liquid chromatography (HPLC). The obtained results evidenced that the presence of small ruthenium crystallites supported on the tetragonal zirconia phase was beneficial to achieve the highest γ-valerolactone yield in the studied reaction.

The importance of pretreatment and feedstock purity in the reductive splitting of (ligno)cellulose by metal supported USY zeolite

The influence of physicochemical cellulose parameters and cellulose purity on the heterogeneous hydrolytic hydrogenation of (ligno)cellulose to hexitols.

Efficient Hydrolytic Hydrogenation of Cellulose on Mesoporous HZSM-5 Supported Ru Catalysts

Hydrolytic hydrogenation of cellulose requires both functionalities of a metal and acid site. HZSM-5 has strong acid sites inside the micropores. However, those sites are not easily accessible to large molecules derived from cellulose. In this work, NaOH treatment of ZSM-5 was applied to introduce mesopores to the crystallite of ZSM-5. Characterizations showed that mesopores of 4–20 nm were successfully created on the surface of ZSM-5, and mesopore volume and total acid density (particularly Lewis acid density) increased as the severity of treatment increased. Loading of Ru on the mesoporous HZSM-5 resulted in a highly active and selective catalyst for conversion of cellulose to hexitols. The optimized hexitols yield of 39.4 % is 6 times higher than that of Ru supported on the parent HZSM-5. Model reaction studies (hydrolysis of cellobiose and hydrogenation of glucose) indicated that the enhanced acid density (particularly Lewis acid in mesopores) promotes the hydrolysis of oligosaccharides from primary depolymerization of cellulose. Furthermore, the uniform dispersion of smaller Ru nanoparticles due to the increased surface area caused by the mesopore enhanced the activity of the hydrogenation reaction. Consequently, a high yield of hexitols with reduced yield of small polyols was achieved on the optimized mesoporous Ru/HZSM-5.

ZSM-5-supported multiply-twinned nickel particles: Formation, surface properties, and high catalytic performance in hydrolytic hydrogenation of cellulose

Nickel multiply-twinned particles (Ni MTPs) imbedded onto ZSM-5 were prepared, and their formation and chemical and electronic properties were characterized by HRTEM, XPS, CO-FTIR, and H2-TPD. HRTEM showed the formation of Ni MTPs with triangular, square, hexagonal, and spherical shapes. The multiply-twinned particles were composed of f.c.c. nanocrystals dominated by (111) crystal face. Ni MTPs indicate an enhanced CO adsorption capability as compared with ordinary Ni particles. Ni MTPs were electron deficient and inherently strained, which is responsible for high catalytic activity in the hydrolytic hydrogenation of cellulose.

Comparative study of different catalysts for the direct conversion of cellulose to sorbitol

AbstractThe catalytic conversion of lignocellulosic biomass to obtain high added value compounds and fuels is a rapidly developing field. Given the abundance of this renewable raw material and its reduced impact on the food chain, it is an attractive source for obtaining chemicals or fuels in the context of a sustainable economy. In this work, bi-functional catalysts were developed that were capable of performing in a single step the hydrolysis and hydrogenation of cellulose to produce compounds that may be used in the production of fine chemicals or easily converted into fuels (e.g., sorbitol). Different activated carbon (AC) supported metal catalysts were examined for the one-pot hydrolytic hydrogenation of cellulose. Among the prepared catalysts, 0.4% Ru/AC was shown to be the most active and selective for the conversion of cellulose into sorbitol. When microcrystalline cellulose was used, a conversion of 32% was reached after 5 h of reaction, with a selectivity to sorbitol of 30%. Moreover, ball-milled cellulose allowed attaining conversions over 50%, with selectivities to sorbitol of 45%. The results obtained showed that Ru/AC is effective for the hydrolytic hydrogenation of cellulose to sugar alcohols and that the conversion can be greatly improved by using the substrate after pre-treatment by ball-milling.

Conceptual Frame Rationalizing the Self-Stabilization of H-USY Zeolites in Hot Liquid Water

The wide range of liquid-phase reactions required for the catalytic conversion of biomass compounds into new bioplatform molecules defines a new set of challenges for the development of active, selective, and stable catalysts. The potential of bifunctional Ru/H-USY catalysts for conversions in hot liquid water (HLW) is assessed in terms of physicochemical stability and long-term catalytic performance of acid sites and noble metal functionality, as probed by hydrolytic hydrogenation of cellulose. It is shown that zeolite desilication is the main zeolite degradation mechanism in HLW. USY zeolite stability depends on two main parameters, viz., framework and extra-framework aluminum content. The former protects the zeolite lattice by counteracting hydrolysis of framework bonds, and the latter, when located at the external crystal surface, prevents solubilization of the zeolite framework which is the result of its low water-solubility. Hence, the hot liquid water stability of commercial H-USY zeolites, in cont...

One-pot catalytic conversion of cellulose into polyols with Pt/CNTs catalysts

A series of Pt nanoparticles supported on carbon nanotubes (CNTs) were synthesized using the incipient-wetness impregnation method. These catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscope (TEM) techniques. The characterization results indicate that the Pt nanoparticles were highly dispersed on the surface of the CNTs, and the mean size was less than 5nm. These catalysts were utilized to convert cellulose to hexitol, ethylene glycerol (EG), and 1,2-propylene glycol (1,2-PG) under low H2 pressure. The total yields were as high as 71.4% for EG and 1,2-PG using 1Pt/CNTs as the catalyst in the hydrolytic hydrogenation of cellulose under mild reaction conditions.

Promoting Hydrolytic Hydrogenation of Cellulose to Sugar Alcohols by Mixed Ball Milling of Cellulose and Solid Acid Catalyst

Enhancing the contact or interaction between cellulose and solid catalyst is a significant aspect in its efficient catalytic conversion. Herein, mixed ball milling of cellulose and solid catalyst was presented to achieve this goal, and the promotion effect was measured by hydrolytic hydrogenation of cellulose to sugar alcohols (the platform compounds for biogasoline) with solid acid and commercial 5 wt % Ru/C in water. The effects of ball-milling modes, time, and reaction parameters were studied. The properties of cellulose and solid acid catalyst before and after treatment were also analyzed. The yield of sugar alcohols reached 90.3% at 463 K with amorphous zirconium phosphate and Ru/C (mixed ball-milling time of 2 h). This high yield of sugar alcohols achieved in the mixed ball-milling time of 2 h was 12 times faster than that by the single ball milling of 24 h under the same reaction conditions. It is ascribed to the enhanced contact between cellulose and catalyst, resulting in promoting cellulose depolymerization. The high concentration of sugar alcohols up to 67 mg/mL was obtained by augmenting the mass ratio of cellulose/catalyst.

One-Pot Transformation of Cellulose to Sugar Alcohols over Acidic Metal Phosphates Combined with Ru/C

ZrP with large surface, mesoporous volume, and size was prepared. Its catalytic performance was evaluated in hydrolytic hydrogenation of cellulose to sorbitol/mannitol combined with commercial Ru/C. A significantly enhanced sorbitol/mannitol yield was obtained as compared with that of the water-soluble acidic phosphates and buffer solution of potassium acid phthalate combined with the same Ru/C. The enhanced yield was attributed to the Lewis and Bronsted acid on ZrP surface improving the surface’s absorption and activation for cellulose and accelerating the rate-determined hydrolysis step. The maximal sorbitol/mannitol yield of 63% and 81% could be obtained by using microcrystalline and ball milling cellulose as the feedstock, respectively. The ZrP combined with Ru/C was adaptable to the high concentrated cellulose and obtained 5.8 wt % of sorbitol/mannitol concentration. The remarkably enhanced cellulose hydrolysis by ZrP sharply decreased the use of Ru/C, which is significant for the essential application.

Ru-containing catalysts on polymer supports for converting cellulose into polyols

Ru-containing catalysts on hyper-cross-linked polystyrene (MN 270) and its functionalized analogs (MN 100 and MN 500) are used in the hydrolytic hydrogenation of cellulose for the first time. The texture characteristics of the polymer supports and the catalysts are determined via low-temperature nitrogen adsorption. Experiments on converting cellulose into polyols are performed in a 50 cm3 steel reactor in subcritical water at 245°C, a partial pressure of hydrogen of 6 MPa, and a stirrer velocity of 600 rpm. The morphological parameters of the supports correlate with the activity of the catalysts. The 1.0% Ru/HPS MN 270 catalyst displays the highest activity. The total yield of sorbitol and mannitol is 50% on average at a cellulose conversion of 85%, which is comparable to the figures for more complex and expensive catalysts. The parameters of cellulose conversion can be further optimized and the proposed catalysts improved to develop a highly effective procedure for processing cellulose biomass into raw materials for chemical synthesis and the production of second-generation biofuels.

The Pt‐Enriched PtNi Alloy Surface and its Excellent Catalytic Performance in Hydrolytic Hydrogenation of Cellulose

Ni-based catalysts are currently a subject of intense research in the hydrolytic hydrogenation of cellulose. We previously reported that Ni/ZSM-5 catalyst gave high yield of hexitols. However, Ni-based catalysts suffered fast deactivation in hot-compressed water. In this follow-up study we designed highly active Ni-based bimetallic catalysts with excellent hydrothermal stability for the hydrolytic hydrogenation of microcrystalline cellulose. PtNi/ZSM-5 shows a 76.9 % yield of hexitols, which is the best obtained so far in the hydrolytic hydrogenation of microcrystalline cellulose over Ni-based catalysts. Furthermore, the yield of hexitols remained greater than 55 % after the catalyst was reused for 4 times. The results showed that PtNi nanoparticles were formed with a Pt-enriched alloy surface as confirmed by XRD, H2-TPR (temperature-programmed H2 reduction), XPS (X-ray photoelectron spectroscopy), and H2-TPD (temperature-programmed H2 desorption). The surface features of these nano-particles were characterized by CO-TPD (temperature-programmed CO desorption), CO-FTIR (CO adsorption FTIR spectroscopy), HRTEM (high resolution TEM), and O2-TPO (temperature programmed oxidation) and this special surface structure may be responsible for the high activity, selectivity, and stability in the hydrolytic hydrogenation of cellulose in hot-compressed water.

ToF‐SIMS study of the surface of catalysts used in biomass valorization

Hydrolytic hydrogenation of cellulose toward fuel additive – γ‐valerolactone (GVL) – has been studied, and the catalytic performance of Pt/TiO2 and Ru/TiO2 and reaction conditions were optimized. Additionally, new information about the changes of catalyst surface after the reactions of lignocelulose toward GVL was obtained. Two procedures were investigated: one‐pot hydrolysis‐hydrogenation and hydrolysis of cellulose followed by hydrogenation in two separate reactions. Spent catalysts were tested by time‐of‐flight SIMS (ToF‐SIMS). Reaction conditions strongly influence the GVL yield, which was much lower during one‐pot procedure where much higher carbon deposit and catalyst deactivation was observed by ToF‐SIMS and temperature‐programmed reduction. Ruthenium catalysts were more active than platinum ones in liquid phase reactions toward GVL, independently of the feedstock. Copyright © 2014 John Wiley & Sons, Ltd.

Control of selectivity, activity and durability of simple supported nickel catalysts for hydrolytic hydrogenation of cellulose

Efficient conversion of cellulose to sorbitol and mannitol by base metal catalysts is a challenge in green and sustainable chemistry, but typical supported base metal catalysts have not given good yields of hexitols or possessed durability. In this study, it has been demonstrated that a simple carbon-supported Ni catalyst affords up to 67% yield of hexitols in the conversion of cellulose, and that the catalyst is durable in the reuse experiments 7 times. In addition, the catalyst can be separated by a magnet thanks to a high content of Ni. Physicochemical analysis has indicated that the use of carbon supports has two benefits: no basicity and high water-tolerance. CeO2, ZrO2, γ-Al2O3 and TiO2 cause side-reactions due to basicity, and SiO2, γ-Al2O3 and CeO2 are less stable in hot water. Another important factor is high Ni loading as the increase of Ni content from 10 wt% to 70 wt% significantly improves the yield of hexitols and the durability of catalysts. Larger crystalline Ni particles are more resistant to sintering of Ni and surface coverage by Ni oxide species.