Catalytic Transfer Hydrogenation Process Research Articles

Catalytic aqueous hydrodeoxygenation of palmitic acid with in-situ hydrogen donor

Algal bio-oil obtained from hydrothermal liquefaction of algae contains a large amount of water and long-chain fatty acids. High acidity and corrosiveness seriously restrict the application of algal bio-oil. The aqueous-phase catalytic upgrading was a promising approach to solve this problem, and the hydrogen donor was one of the most important parameters to the conversion of the algal bio-oil and the quality of the products. Catalytic transfer hydrogenation (CTH) reaction was an efficient, economical and green method for hydrogenation reaction, which can directly transfer hydrogen from the hydrogen donor to the reaction substrate. In this work, the CTH reaction of algal bio-oil model compound palmitic acid was investigated to deal with the problem of high oxygen content in the algal bio-oil. Several common hydrogen donors, included methanol, ethanol, formic acid, and isopropanol, as well as different reaction conditions were experimented to study the CTH process of palmitic acid. The results showed that, with the reaction conditions of 350 °C and 10 h, formic acid achieved the best oxygen removal, carbon retention and energy efficiency, the C16 selectivity reached the highest at 33.3 % as the formic acid addition ratio was 1:2, and the C15 selectivity reached the highest at 48.3 % as the formic acid addition ratio was 1:3. In general, the best ratio of formic acid added was 1:3, which showed the highest yield of C15 and above alkanes of 79.6 %. This result indicates that the catalytic transfer hydrogenation reaction of formic acid has practical value in improving the combustion performance of algal bio-oil.

Confining Co-Based Nanocatalysts by Ultrathin Nanotubes for Efficient Transfer Hydrogenation of Biomass Derivatives.

Catalytic transfer hydrogenation (CTH) based on non-noble-metal catalysts has emerged as an environmentally friendly way for the utilization of biomass resources. However, the development of efficient and stable non-noble-metal catalysts is crucially challenging due to their inherent inactivity. Herein, a metal-organic framework (MOF)-transformed CoAl nanotube catalyst (CoAl NT160-H) with unique confinement effect was developed via a "MOF transformation and reduction" strategy, which exhibited excellent catalytic activity for the CTH reaction of levulinic acid (LA) to γ-valerolactone (GVL) with isopropanol (2-PrOH) as the H donor. Comprehensive characterizations and experimental investigations uncovered that the confined effect of the ultrathin amorphous Al2O3 nanotubes could modulate the electronic structure and enhance the Lewis acidity of Co nanoparticles (NPs), thus contributing to the adsorption and activation of LA and 2-PrOH. The synergy between the electropositive Co NPs and Lewis acid-base sites of the CoAl NT160-H catalyst facilitated the transfer of α-H in 2-PrOH to the C atom of carbonyl in LA during the CTH process via a Meerwein-Ponndorf-Verley mechanism. Moreover, the confined Co NPs embedded on am-Al2O3 nanotubes endowed the CoAl NT160-H catalyst with superior stability and the catalytic activity was nearly unchanged for at least ten cycles, far surpassing that of the Co/am-Al2O3 catalyst prepared by the traditional impregnation method.

Surface-sealing encapsulation of phosphotungstic acid in microporous UiO-66 as a bifunctional catalyst for transfer hydrogenation of levulinic acid to γ-valerolactone.

The efficient production of γ-valerolactone (GVL) from renewable lignocellulose that is synthesized in plants by photosynthesis to replace the declining fossil resources conforms to the principles of circular economy. Compared to direct hydrogenation by H2 molecules, catalytic transfer hydrogenation (CTH) of levulinic acid (LA) and/or its esters to GVL with organic alcohols as a hydrogen source is a much milder route. The synergistic catalysis between Lewis and Brønsted acids is indispensable in the CTH process. Considering that unsaturated coordinated Zr species could act as Lewis acid sites and phosphotungstic acid (PTA) could dissociate protons as Brønsted acid sites, UiO-66 (Zr) was thus "acidified" by encapsulating PTA in its channels to tune the ratio of Brønsted to Lewis acid sites as a bifunctional catalyst so as to better understand the catalytic structure-performance relationship in the CTH process. To address the dilemma of encapsulated PTA that is prone to leach, a rapid surface sealing strategy was adopted to establish a polyimide (PI) coating over the surface of UiO-66 introducing a space confinement effect via an anhydride-amine coupling reaction. The as-synthesized PTA/UiO-66@PI catalyst exhibited 100% of LA conversion, a 93.2% of GVL yield and high recyclability for at least five consecutive cycles. Moreover, a reaction pathway followed by esterification, hydrogenation and dealcoholization as well as a catalytic hydrogenation mechanism based on intermolecular hydride β-H transfer were proposed. Current work not only provides a high-performance and high-stability catalytic system to selectively produce GVL from LA or its esters, but also sheds light on the catalytic mechanism of the CTH process at the molecular level.

Catalytic transfer hydrogenation of ethyl levulinate into γ-valerolactone over air-stable skeletal cobalt catalyst

A fast and easy handled batch air diffusion method (BA) was developed to obtain a non-pyrophoric, air-stable skeletal Co catalyst (A-SCo) for catalytic transfer hydrogenation (CTH) of ethyl levulinate (EL) into γ-valerolactone (GVL). A batch air diffusion method (BA) consumed the active adsorbed H2 on the surface of skeletal Co (SCo) but maintained structure catalyst and avoided excessive oxidation of metallic Co, Ni and Al. The 96% yield of GVL was obtained over the A-SCo and HZSM-5 at 140 °C. Further study of CTH process shows that metallic state of A-SCo provides important active sites for dehydrogenation of i-PrOH, which is critical step for hydrogenation of EL. This study provides a simple, efficient method to prepare an air-stable skeletal metal catalyst for CTH and hydrogenation process.

Environmentally-friendly and sustainable synthesis of bimetallic NiCo-based carbon nanosheets for catalytic cleavage of lignin dimers

This paper reports on a study of 2D metal-based (Ni-, NiCo-) carbon nanosheet (CNs) material that were synthesized via a template method and the synthetic materials showed an ultra-thin lamellar structure. The structures were characterized using different analytical methods including XRD, SEM, EDX, TEM, XPS, NH3-TPD. The synthesized NiCo-based CNs are ultrathin sheet shape with good crystallinity and uniform particle distributions. In the synthetic route of NiCo-based CNs, sodium lignosulfonate was employed as carbon and sulfur source and boric acid was used as 2D template to form a perfect lamellar structure. It manifested an environmentally-friendly and sustainable concept for preparation of the 2D NiCo-CNs. Although simple CNs was a poor catalyst, after Ni and NiCo doping, it became highly active in cleavage of β-O-4 ether bond in lignin through a catalytic transfer hydrogenation process and led to very high product yields.

Design and preparation of metal‐based carbon nanosheets for C–O bond cleavage in the absence of external H2

AbstractA facile yet sustainable approach for the production of Ni3S2‐doped ultrathin carbon nanosheets in one‐pot with very thin thickness of 30 nm was reported. Reaction of nickel nitrate hexahydrate, sodium lignosulfonate with boric acid could produce ultrathin carbon nanosheets. In comparison with the conventional method for the synthesis of Ni3S2‐doped ultrathin carbon nanosheets, this reaction did not require second vulcanization step. Sodium lignosulfonate was used as carbon and sulfur source. Boric acid was used as 2D template and it could also be readily recycled for repeated use by simply evaporative crystallization. Ni3S2‐doped ultrathin carbon nanosheets was expected to be an excellent catalyst for C–O bond cleavage under 260°C through catalytic transfer hydrogenation process. In addition, the optimal catalyst could also be recovered in the end.

Mechanistic study of the catalytic transfer hydrogenation of biodiesel catalyzed by Raney-Ni under microwave heating

The use of microwave heating (MH) constitutes a promising way to upgrade biodiesel via catalytic transfer hydrogenation (CTH) catalyzed by Raney-Ni. However, mechanistic reports on this reaction are rare and the mechanisms involved in CTH process remains unclear. Herein, we presented a thorough mechanistic study of CTH of Jatropha oil biodiesel catalyzed by Raney-Ni under MH, using isopropyl alcohol as hydrogen donor and water as solvent. The intensification effect under microwave radiation has been studied from three aspects of catalyst, water, and hydrogen donor. It was found that microwave made an adverse effect on the activity of Raney-Ni. The solvent of water could provide hydrogen to some extent for the CTH of biodiesel, and the influence of Raney-Ni from microwave radiation had a positive role for the water to provide hydrogen during CTH reaction. Under microwave irradiation, the activity of isopropyl alcohol would be enhanced, and the transfer of hydrogen atoms from hydrogen donors to hydrogen acceptors became easy. Based on the characterization of catalyst by SEM, XRD, FTIR and TGA, it was found that the reason for the catalyst deactivation was mainly the carbonaceous deposits of fatty acid methanol esters (FAMEs) on the surface of the catalyst. A schematic representation of mechanism of microwave-assisted CTH has been presented. Furthermore, combining theory of heterogeneous catalytic process with mechanism of six-membered cyclic transition state, the reaction course for the CTH of Jatropha oil biodiesel under microwave heating has been explained successfully. Lastly, the performance improvement of the upgraded Jatropha oil biodiesel was briefly analyzed in view of composition change of biodiesel. Overall, our results provide a systematic understanding of CTH of biodiesel catalyzed by Raney-Ni under microwave heating, and our findings help to develop a green technology for the upgrading of biodiesel in industry.

Continuous flow conversion of alkyl levulinates into γ-valerolactone in the presence of Ru/C as catalyst

The present work explored a catalytic transfer hydrogenation process with several supported noble metal on carbon as catalysts for the production of γ-valerolactone (GVL) from methyl levulinates (ML) in iso-propanol (2-PrOH) and the performance of the commercial 5%Ru/C in continuous flow were investigated, GVL yields up to 83% at 150 °C (40 bar) using a high load (0.4 M ML) feed at 0.8 mL/min flow rate. The catalyst productivity (Pr) equal to 0.99 mol g−1 h−1. Methyl 4-hydroxypentanoate (MHP) were produced as major side product in lower amounts in continuous flow mode. Long-term (9 h) catalyst stability experiment showed good stability under optimum condition. The yield of GVL obtained from ethyl levulinate, butanol levuliante and levulinate acid were ca.21%, 54% and 26% less than ML in 2-PrOH and Pr were 0.43, 0.73 and 0.48 less respectively. There is no obvious hydrogenation process when changed 2-PrOH to ethanol and 1-butanol.

Simultaneous activation of copper mixed metal oxide catalysts in alcohols for gamma-valerolactone production from methyl levulinate

Catalytic transfer hydrogenation (CTH) of biomass-derivatives to value-added chemicals using metal-based catalysts is a promising process in biorefinery since it does not require high pressure of expensive and flammable hydrogen gas (H2). However, an activation of these catalysts using H2 treatment prior to the CTH process limits this advantage. Here, copper mixed metal oxides are introduced as simultaneously activated catalysts (SACs) in the presence of alcohol for a production of gamma-valerolactone (GVL) from methyl levulinate (ML) without requirement of additional H2 gas during both catalyst pretreatment and hydrogenation steps. Different alcohols were selected to function as hydrogen sources for both catalyst activation and ML hydrogenation. All copper mixed metal oxides, especially CuNiO showed significant potential as catalysts for ML conversion to GVL at 200 °C within 3 h. While 2-propanol and 2-butanol exhibited effective roles as hydrogen sources for simultaneous reductions of the catalysts to generate metal active sites and provided hydrogen species for hydrogenation of ML to GVL. Hydrogen temperature programmed reduction (H2-TPR), alcohol-assisted simultaneous reaction (ASR), in situ X-ray diffraction (in situ XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the complementary cooperation between secondary alcohols and catalysts is the important key for the high GVL production in this work.

Ultrarapid and Deep Debromination of Tetrabromodiphenyl Ether over Noble-Metal-Free Cu/TiO2 Nanocomposites under Mild Conditions.

Fast and deep debromination of polybrominated diphenyl ethers (PBDEs) under mild conditions is a challenge in the field of pollution control. A strategy was developed to achieve it by exploiting Cu/TiO2 composites as a noble-metal-free catalyst. Toward the debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE47) as a typical PBDE, the use of Cu/TiO2 as a catalyst and hydrazine hydrate (N2H4·H2O) as a reducing agent yielded a degradation removal of 100% and a debromination efficiency of 87.7% in 3 s. A complete debromination of BDE47 at 1500 mg L-1 was possible by successively adding N2H4·H2O. A debromination pathway involving active H atom species was proposed for the catalytic transfer hydrogenation (CTH) of PBDEs according to the identified degradation intermediates. A mechanism was further clarified by density functional theory calculations: electrons are delivered from N2H4·H2O to the metallic Cu atom via a coordination of N in N2H4·H2O with Cu atoms. The electron-trapped Cu atom interacts with adsorbed BDE47 to form a transition complex, and then the debromination of this complex occurs on the surface of Cu nanoparticles due to the hydrogen donation of N2H4·H2O through the CTH process. The new method provides a highly efficient method to remove brominated pollutants.

Catalytic transfer hydrogenation of levulinate ester into γ-valerolactone over ternary Cu/ZnO/Al2O3 catalyst

An effective catalytic transfer hydrogenation (CTH) process of bio-based levulinate esters into γ-valerolactone (GVL) was explored over ternary Cu/ZnO/Al2O3 catalyst which was prepared by co-precipitation method and could be sustainably used. As a result, quantitative conversion of ethyl levulinate (EL) and 99.0% yield of GVL were obtained in the CTH process using i-PrOH as hydrogen donor. The Cu/ZnO/Al2O3 catalyst with high-surface-area could be reused at least four times without the loss of catalytic activity. Furthermore, the structure and properties of Cu/ZnO/Al2O3 catalyst was characterized through XRD, BET, SEM, TEM and H2-TPR. Also, the influence of different support oxides and calcination temperatures was investigated.

Selective Reduction of Azines to Benzyl Hydrazones with Sodium Borohydride Catalyzed by Mesoporous Silica‐Supported Silver Nanoparticles: A Catalytic Route towards Pyrazole Synthesis

AbstractThe catalytic activity of supported silver nanoparticles on mesoporous silica was studied, for the selective reduction of azines into benzyl hydrazones using sodium borohydride as mild reducing agent. Different sizes of silver nanoparticles supported on mesoporous silica (Ag/HMS) were successfully prepared by two methods, i.e., wet impregnation followed by reduction with hydrogen at 350 °C and in situ deposition/reduction with a mixture of amines (ethanolamine and ethylenediamine). The Ag/HMS (amines) catalyst was found to promote the selective 1,2‐reduction of aryl‐substituted azines, compared to the corresponding 1,4‐reduction that occurs in general reduction processes. This catalytic transfer hydrogenation process found to be clean, fast and quantitative (>99% yields and selectivity) towards benzyl hydrazone synthesis under mild conditions. Of great importance is that under the present catalytic conditions reducible functional groups remain intact. Formal kinetics, support the in situ formation of silver hydride species being responsible for the reduction process. The presence of protic polar methanol enhanced the catalytic activity of Ag/HMS. Based on the recycling studies the catalytic system Ag/HMS‐NaBH4 was found to catalyze the selective reduction of azines nine times without significant loss of its activity. Finally, a one‐pot reaction between the in situ produced benzyl hydrazones and a series of nitrostyrenes readily provided the regioselective synthesis of 1,3,5‐subtituted pyrazoles, highlighting a useful synthetic application of the catalytic protocol.magnified image

Catalytic Transfer Hydrogenation of Biobased HMF to 2,5-Bis-(Hydroxymethyl)Furan over Ru/Co3O4

2,5-Bis-(hydroxymethyl)furan (BHMF) is an important biomass-based platform chemical that can be derived from the hydrogenation of biomass-based 5-hydroxymethylfurfural (HMF). In this paper, the formation of BHMF from HMF via the catalytic transfer hydrogenation (CTH) process, using isopropanol as the hydrogen source and Ru/Co3O4 as the catalyst, was studied. The results revealed that the Ru/Co3O4 catalyst displayed a high catalytic efficiency, and that a BHMF yield of up to 82% was obtained at 190 °C in 6 h. Moreover, it was found that the recovered Ru/Co3O4 exhibited a similar catalytic activity to the pristine Ru/Co3O4 catalyst. These results supported the conclusion that the present CTH process is an attractive green route for the synthesis of BHMF from biomass-based HMF.

Catalytic Conversion of Levulinic Acid and Its Esters to γ-Valerolactone over Silica-Supported Zirconia Catalysts

Abstract Levulinic acid and its esters, important intermediate chemicals produced from biomass resources, were converted to γ-valerolactone via a catalytic transfer hydrogenation process over silica-supported zirconia catalysts. Silica support with a higher surface area provided highly dispersed active zirconium oxide species, which exhibited superior catalytic activity to the conventional ZrO2 catalyst.

RANEY® Ni catalyzed transfer hydrogenation of levulinate esters to γ-valerolactone at room temperature

A catalytic transfer hydrogenation process was developed for the production of γ-valerolactone (GVL) from ethyl levulinate (EL) and a H-donor at room temperature. Ethyl levulinate was almost quantitatively converted to γ-valerolactone. Further, a two step process for producing GVL from biomass derived platform molecules was also reported.

A Study on Low Temperature and Pressure Hydrogenation of Cyclopropenoid-Group Containing Non-Edible Oil for Biodiesel Feedstock

One of the potential non-edible biodiesel feedstocks in Indonesia is kapok seed oil (Ceiba pentandra). However, the biodiesel made directly from kapok seed oil will not comply with the requirement of Indonesian Biodiesel Standard, because the oil contains cyclopropenoid group, i.e. a reactive group that easily polymerizes, making the biodiesel viscous and thus could plug the fuel injection nozzle on the diesel engine. The aim of this study is to determine the suitable conditions for low T and P catalytic transfer hydrogenation process to eliminate the cyclopropenoid group in kapok seed oil. Potassium formate (10M) was used as a hydrogen donor solution and the catalyst was a 5%- palladium on carbon (5%-Pd/C) utilized at a level of 0,5%-mass to oil. The concentrations of cyclopropenoid group at the beginning and the end of the hydrogenation were determined titrimetrically using Durbetaki reagent. The best condition for catalytic transfer hydrogenation of kapok seed oil found in this study was at 65°C for 9hours, which resulted in about 61% decrease of the cyclopropenoid group. Iodine number measurements indicated that the hydrogenation process merely occured on the cyclopropenoid group, because the group was more reactive than the monoenoic/dienoic bonds on the aliphatic fatty acid chains of the oil.

Nickel-Catalyzed Alkylation and Transfer Hydrogenation of α,β-Unsaturated Enones with Methanol

Complexes of the type [{(dippe)Ni}n(η2-Cα,Cβ-1,4-dien-3-one)] (dippe = 1,2-bis(diisopropylphosphino)ethane); n= 1, 2; enone = aromatic 1,4-pentadien-3-ones) were synthesized. The “[(dippe)Ni]” moiety derived from [(dippe)Ni(μ-H)]2 η2-coordinated to the C,C double bonds of the corresponding α,β-unsaturated enone and was fully characterized using a variety of spectroscopic techniques, for instance, single-crystal X-ray diffraction, nuclear magnetic resonance (NMR), and mass spectrometry. The complexes were assessed in a catalytic transfer hydrogenation process using methanol (CH3OH) as a hydrogen donor. This alcohol turned out to be a very efficient reducing and alkylating agent of 1,4-pentadien-3-ones, under neat conditions. The current methodology allowed the selective reduction of C═C bonds in α,β-unsaturated enones to yield enones and saturated ketones by a homogeneous catalytic pathway, whereas by a heterogeneous pathway, the process leads to the formation of mono- and dimethylated ketones. In the latter case, the occurrence of nickel nanoparticles in the reaction media was found to participate in the catalytic alkylation of such dienones.

Studies in catalytic transfer hydrogenation of soybean oil using ammonium formate as donor over 5% Pd/C catalyst

Abstract The catalytic transfer hydrogenation (CTH) is a novel, alternative process for the selective hydrogenation of soybean oil due to the lower rate of formation of stearic acid and trans-isomer, which have an adverse health effects. Ruthenium and palladium supported catalysts were screened along with hydrogen donors during CTH process. The CTH of soybean oil was studied using aqueous ammonium formate solution over supported palladium catalyst. The method offered good selectivity in complete reduction of linolenic acid with a slight increase in stearic acid. The kinetics of CTH of soybean oil using ammonium formate as a hydrogen donor over 5% Pd/C catalyst was studied. The speed of agitation was sufficiently high enough to eliminate diffusional resistance. The CTH of soybean oil was described by pseudo-first order kinetic model. Runge–Kutta algorithm (RKS4) was used to determine the kinetic rate constants. The catalyst could be reused thrice without any adverse effect.

A Chemoselective Hydrogenation of the Olefinic Bond of α,β‐Unsaturated Carbonyl Compounds in Aqueous Medium under Microwave Irradiation

AbstractA microwave‐assisted mild and ecofriendly catalytic transfer hydrogenation process was developed to reduce various α,β‐unsaturated carbonyl compounds into the corresponding saturated carbonyl compounds in the presence of silica‐supported palladium chloride as catalyst and a combination of MeOH/HCOOH/H2O (1 : 2 : 3) as hydrogen source within 22–55 minutes in moderate to excellent yields with 100% chemoselectivity.

One-Step Reduction of Chalcones to Saturated Alcohols by Ammonium Formate/Palladium on Carbon: A Versatile Method

Several chalcones are reduced directly to the corresponding saturated alcohols, in a catalytic transfer hydrogenation process, by use of the ammonium formate/palladium on carbon system in very good yields.