Liquid-phase Hydrogenation Research Articles

Architecture of bimodal porous CuO/Al2O3-controlled continuous and low-temperature production of biomass-derived γ-butyrolactone

Biomedical activities of gamma butyrolactone (GBL) play an important role in the development of novel physiological and therapeutic agents. Maleic anhydride catalytic liquid phase hydrogenation allows for selective synthesis of GBL. However, this process is hampered by high cost noble metals and high reaction pressure conditions. Here, we demonstrate cyclic dehydrogenation of biomass-derived 1,4-butanediol (1,4-BDO) under atmospheric pressure and low-temperature conditions using highly dispersed and chemically stabilized Cu species on bimodal porous Al2O3. The bimodal porous Al2O3 exhibited both Lewis and Brønsted acidic properties along with high specific surface area and large pore volume. Among prepared catalysts, 15 wt% Cu/Al2O3 catalyst has shown an optimal crystallite size, bimodal porous nature, and high diffusion properties. Hence, high catalytic activity and remarkable GBL yields with very high 1,4-BDO conversion for 50 h of continuous time-on-stream. The unique bimodal textural properties help to enhance the dehydrogenation activity with a high turnover frequency (TOF) of about 5.0118 x 10-3 s-1via efficient chemical interaction between metallic Cu and 1,4-BDO molecules.

2-Methylfuran hydrogenation to 2-methyltetrahydrofuran utilizing Ni/SiO2 catalysts in vapor-phase: Excellent stability via enhanced metal-support interaction

Biomass-derived 2-methyltetrahydrofuran (2-MTHF) is a significant green solvent and a promising biomass fuel, and it is usually produced from 2-methylfuran (2-MF) hydrogenation in liquid phase. It is highly desirable and challenging to develop vapor-phase hydrogenation with such a catalyst that combines high efficiency, excellent stability, easy scale up and low cost. In the present work, we prepared three Ni/SiO2 catalysts using impregnation, urea-assisted impregnation, and deposition–precipitation methods (labeled as NS-IM, NS-UIM, and NS-DP), respectively, for the synthesis of 2-MTHF from 2-MF hydrogenation in vapor-phase. The NS-DP catalyst demonstrated the highest activity and the best stability among all catalysts. Under moderate reaction conditions, a 2-MF conversion of 99.9% with a 2-MTHF selectivity of 99% were achieved on the NS-DP catalyst over 140 h, and it showed a potential significant application prospect. N2 physisorption, ICP, XRD, H2-TPR, TG, HRTEM, and in situ XPS characterization revealed that the catalyst prepared by the deposition–precipitation method possessed the smallest Ni grain size and the strongest metal-support interaction, leading to the highest performance. It was demonstrated that reaction pressure affected the conversion of 2-MF while the reaction temperature affected the selectivity of 2-MTHF. In addition, the structures of the spent catalysts were characterized, and mechanism of deactivation have been discussed in this work.

Effect of Support Functionalization on Catalytic Direct Hydrogenation and Catalytic Transfer Hydrogenation of Muconic Acid to Adipic Acid

The liquid-phase hydrogenation of muconic acid (MA) to produce bio-adipic acid (AdA) is a prominent environmentally friendly chemical process, that can be achieved through two distinct methodologies: catalytic direct hydrogenation using molecular hydrogen (H2), or catalytic transfer hydrogenation utilizing a hydrogen donor. In this study, both approaches were explored, with formic acid (FA) selected as the hydrogen source for the latter method. Palladium-based catalysts were chosen for these processes. Metal’s nanoparticles (NPs) were supported on high-temperature heat-treated carbon nanofibers (HHT-CNFs) due to their known ability to enhance the stability of this metal catalyst. To assess the impact of support functionalization on catalyst stability, the HHT-CNFs were further functionalized with phosphorus and oxygen to obtain HHT-P and HHT-O, respectively. In the hydrogenation reaction, catalysts supported on functionalized supports exhibited higher catalytic activity and stability compared to Pd/HHT, reaching an AdA yield of about 80% in less than 2 h in batch reactor. The hydrogen-transfer process also yielded promising results, particularly with the 1%Pd/HHT-P catalyst. This work highlights the efficacy of support functionalization in improving catalyst performance, particularly when formic acid is used as a safer and more cost-effective hydrogen donor in the hydrogen-transfer process.

Catalytic Performance of CuZnAl Hydrotalcite-Derived Materials in the Continuous-Flow Chemoselective Hydrogenation of 2-Methyl-2-pentanal toward Fine Chemicals and Pharmaceutical Intermediates.

Hydrotalcite-derived materials are eco-friendly, cheap, and efficient catalysts of different reactions. However, their application in liquid-phase hydrogenation could be more extensive. Hence, this work concerns the application of three hydrotalcite-derived materials with different CuZnAl molar ratios in the liquid-phase continuous-flow hydrogenation of 2-methyl-2-pentenal (MPEA) at a wide range of temperature (298-378 K) and pressure (1 × 106-6 × 106 Pa). The catalytic investigations were supported by catalysts characterization by ICP-OES, TPR, in situ XRD, XPS, NH3-TPD, CO2-TPD, and TEM measurements on different stages of their biography. It was shown that the catalytic activity of these samples is related to the Cu0/Cu+ ratio. Depending on the reaction conditions, selectivity control is possible. All catalysts were 100% selective to 2-methylpentanal (MPAA)-sedative drug precursor, with low conversion, at temperatures ≤ 338 K at every pressure. However, the selectivity of the second desired product, fragrance intermediate, 2-methyl-2-penten-1-ol (MPEO), increased significantly at higher temperatures and pressures. It reached the unique value of 54% with 60% substrate conversion at 378 K and 6 × 106 Pa for the catalyst with the highest Cu loading. It was revealed that the production of significant amounts of MPEO is related to the reaction conditions, the Cu+ predominance on the surface, the hydrogen spillover effect, and the acid-base properties of these systems.

The liquid-phase hydrogenation of TMCB for preparation of CBDO by fluorine-modified Ruthenium-Stannum bimetallic catalysts

A series of Ruthenium-Stannum bimetallic catalysts were prepared using the isovolumetric impregnation method and investigated for the liquid-phase hydrogenation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione to its corresponding 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The effects of the reaction temperature and pressure, fluorine-modified alumina, reaction solvent, and catalyst particle size on the catalytic performance were discussed. The optimum reaction conditions were obtained with a temperature of 80 ℃, a hydrogen pressure of 4.0 MPa, and a reaction solvent of tetrahydrofuran. In addition, characterization techniques, such as BET, XRD, TEM, NH3-TPD, and Py-IR, showed that the active component nanoparticles were effectively introduced into the alumina carriers, and the alumina was modified by a low concentration of NH4F solution (0.05 mol/L), which ensured that the complete conversion of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was obtained while maintaining a selectivity of over 95 % for the 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

Liquid-phase hydrogenation of dimethyl maleate to 1,4-butanediol over a sorbitol-modified Cu@C/ZnO catalyst

Liquid-phase hydrogenation of dimethyl maleate to 1,4-butanediol over a sorbitol-modified Cu@C/ZnO catalyst

Phenol is its own selectivity promoter in low-temperature liquid-phase hydrogenation

Phenol hydrogenation is widely studied for selective production of the chemical intermediate cyclohexanone. A plethora of studies in the literature have reported catalysts aiming to achieve high selectivity compared to Pd/C. However, we demonstrate that selective and high-yielding reactions are inherent features of liquid-phase phenol hydrogenation using conventional Pd/C catalysts. We also show there is a very strong dependance of selectivity upon conversion, with high selectivity being maintained until near complete consumption of the phenol, after which subsequent reaction to the unwanted, fully hydrogenated cyclohexanol occurs rapidly. Furthermore, through competitive reactions with other aromatic molecules it is demonstrated that the phenol molecule effectively self-poisons the onwards reaction of weakly bound cyclohexanone, likely by virtue of its relative adsorption strength, and this is the source of the intrinsic selectivity. The implications of this to the reaction mechanism, and in turn to the rational design of catalysts, especially for obtaining chemicals from phenolic bio-oils, are discussed.

Highly Efficient and Selective Hydrogenation of Biomass-Derived Furfural Using Interface-Active Rice Husk-Based Porous Carbon-Supported NiCu Alloy Catalysts.

A series of bimetallic NixCuy catalysts with different metal molar ratios, supported on nitric acid modified rice husk-based porous carbon (RHPC), were prepared using a simple impregnation method for the liquid-phase hydrogenation of furfural (FFA) to tetrahydrofurfuryl alcohol (THFA). The Ni2Cu1/RHPC catalyst, with an average metal particle size of 9.3 nm, exhibits excellent catalytic performance for the selective hydrogenation of FFA to THFA. The 100% conversion of FFA and the 99% selectivity to THFA were obtained under mild reaction conditions (50 °C, 1 MPa, 1 h), using water as a green reaction solvent. The synergistic effect of NiCu alloy ensures the high catalytic activity. The acid sites and oxygen-containing functional groups on the surface of the modified RHPC can enhance the selectivity of THFA. The Ni2Cu1/RHPC catalyst offers good cyclability and regenerability. The current work proposes a simple method for preparing an NiCu bimetallic catalyst. The catalyst exhibits excellent performance in the catalytic hydrogenation of furfural to tetrahydrofurfuryl alcohol, which broadens the application of non-noble metal bimetallic nanocatalysts in the catalytic hydrogenation of furfural.

Kinetic Studies of Liquid Phase Hydrogenation of Acetylene for Ethylene Production Using a Selective Solvent over a Commercial Palladium/Alumina Catalyst

Kinetic Studies of Liquid Phase Hydrogenation of Acetylene for Ethylene Production Using a Selective Solvent over a Commercial Palladium/Alumina Catalyst

Experimental study and modeling of the liquid phase hydrogenation of acetylene

Selective hydrogenation of acetylene is an important process for both ethylene purification and ethylene production from acetylene in the industry. Herein, we proposed liquid phase acetylene hydrogenation for high feed concentrations of C2H2 (8 %) and CO (20 %), which is used to produce ethylene as a subsequent process of partial oxidation of natural gas. The experiments were carried out in a stirred tank reactor using N-methylpyrrolidone (NMP) as solvent and PdAg/SiO2 as catalyst. The liquid phase process obtained a much higher selectivity to ethylene (92 %) with only 8 % selectivity to green oil (GO) and C4, compared to 71 % ethylene selectivity in gas phase hydrogenation. Furthermore, in the liquid phase ethylene selectivity increased with increasing acetylene conversion, especially in the conversion range of 80–100 %. We developed a model incorporating reaction kinetics, mass transfer and reactor model to predict the acetylene conversion and ethylene selectivity in liquid phase hydrogenation. The calculation results indicated that hydrogenation in the liquid phase operated at a lower acetylene concentration and a higher H2/C2H2 ratio, especially under high acetylene conversions. This explains why the liquid phase hydrogenation of acetylene has a much higher selectivity to ethylene than the gas phase process.

High-Entropy Alloy Al0.2Co1.5CrFeNi1.5Ti0.5 Prepared from High-Entropy Oxide (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a Deoxidation Process via a CaH2-Assisted Molten Salt Method

High-entropy alloys (HEAs) have attracted a great deal of research interest these days because of their attractive properties. Low-temperature chemical synthesis methods are being developed to obtain nanoscale HEAs with low energy consumption. In this study, we prepared HEA Al0.2Co1.5CrFeNi1.5Ti0.5 nanoparticles from high-entropy oxide (HEO) (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a deoxidation process via a CaH2-assisted molten salt method at 600 °C. X-ray diffraction measurements demonstrated that the oxide precursor and the reduced product have single-phases of spinel structure and face-centered cubic structures, indicating the formation of HEO and HEA, respectively. The HEA nanoparticles exhibited superior catalytic performance in the liquid-phase hydrogenation of p-nitrophenol at room temperature with little leaching of the component elements. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX) exhibited a good distribution of constituent elements over the HEA nanoparticles in a micro-sized range. However, transmission electron microscopy (TEM) with EDX revealed a slight deviation of elemental distributions of Al and Ti from those of Co, Cr, Fe, and Ni in a nano-sized range, probably due to the incomplete reduction of aluminum and titanium oxides. The elemental homogeneity in the HEA nanoparticles could be improved by taking advantage of the HEO precursor with homogeneous elemental distributions, but the experimental results suggested the importance of the total reduction of oxide precursors to prepare homogeneous HEAs from HEOs.

Liquid-phase hydrogenation of sunflower oil over platinum and nickel catalysts: Effects on activity and stereoselectivity

This study presents the results of comparative hydrogenation of sunflower oil over a platinum catalyst supported on activated diatomite and an industrial nickel catalyst (Pricat-9910). Catalysts are characterized using physical methods, such as transmission electron microscopic, temperature programmed hydrogen desorption, Brunauer–Emmett–Teller and inductively coupled plasma atomic emission spectrometry, enabling the determination of the size of catalyst particles, forms of adsorbed hydrogen, and specific surface area. Depending on the process conditions, hydrogenation reaction rates on platinum catalysts have been found to be 2–5 times higher than cis-trans isomerization reaction rates. Using a nickel catalyst, the hydrogenation and isomerization rates at low temperatures (110°C-130 °C) and 0.5 MPa pressure are almost similar, while, the hydrogenation rate is 1.4–1.8 times lower than the isomerization rate at high temperatures and pressures, leading to the formation of a large number of trans isomers. The difference in catalysts selectivity may be attributed the speciation and different adsorption energies of surface hydrogen, leading to the possibility of simultaneous hydrogenation of linoleic and oleic acids on the nickel catalyst.

Construction of Synergistic Co/CoO Interface to Enhance Hydrogenation Activity of Ethyl Lactate to 1,2-Propanediol.

The development of effective and stable non-precious catalysts for hydrogenation of ester to diols remains a challenge. Herein, the catalytic hydrogenation of ethyl lactate (EL) to 1,2-propanediol (1,2-PDO) with supported Co catalysts derived from layered double hydroxides (LDHs) is investigated. Catalytic tests reveal that LDH-derived Co catalysts exhibit the best catalytic performance with 98 % of EL conversion and >99 % of 1,2-PDO selectivity at mild conditions, compared with other Co catalysts (supported on Al2O3, and TiO2) and LDH-derived Cu catalysts. Due to the strong interaction among Co and Al matrix, the main composition is metallic Co0 and CoO after reduction at 600 °C. Besides, the catalyst shows good recyclability in the liquid phase hydrogenation. The superior catalytic performance can be attributed to the synergistic effect between Co0 and CoO, in which H2 molecule is activated on Co0 and EL is strongly adsorbed on CoO via hydroxyl groups.

Ni@C nanocatalysts for the highly efficient hydrogenation of maleic anhydride to γ-butyrolactone

Core-shell Ni@C catalysts with a uniform grain size distribution were synthesised via a simple hydrothermal method followed by pyrolysis carbonisation, and their catalytic performance for the liquid-phase hydrogenation of maleic anhydride (MA) was investigated herein. When the pyrolysis temperature was 350 °C, the resulting Ni@C catalyst (Ni@C-350) possessed abundant Ni/NiO heterostructures and a carbon surface layer. Among the analysed catalysts, Ni@C-350 demonstrated the lowest apparent activation energy for the hydrogenation of CC bonds (Ea = 34.3 KJ/mol) and CO bonds (Ea = 65.18 KJ/mol), yielding an MA conversion of 100 % and a γ-butyrolactone (GBL) selectivity of 99.89 % under mild reaction conditions (200 °C, 3 MPa hydrogen pressure, and 0.05 g catalyst). Furthermore, the Ni@C-350 catalyst exhibited high stability, with the yield of GBL above 95 % after five consecutive usage cycles. Ni@C-350 significantly outperformed other previously reported catalysts for the liquid-phase hydrogenation of MA.

Effects of alloying palladium with gold in furfural hydrogenation:An in situ ATR-IR spectroscopy and density functional theory study

Furfural is a versatile platform molecule and a model compound to explore the key factors influencing activity and selectivity in heterogeneous catalysis. In this study, Pd and AuPd nanoparticles (average size 3.5–4 nm) were deposited on TiO2 by sol immobilization method and were evaluated for liquid-phase furfural hydrogenation. Alloying Au and Pd caused a decrease in activity, an enhancement in stability, and a change in selectivity, favouring the complete hydrogenation of furfural over the decarbonylation reaction. These variations in catalytic performance were elucidated by combining in situ attenuated total reflectance infrared spectroscopy and density functional theory studies.

Influence of binder selection on the catalytic performance of zeolite-based bifunctional catalysts for biomass catalysis

The impact of binder selection on catalytic performance of real catalyst extrudates is still limitedly shown in biomass catalysis. Herein, we have prepared two zeolite-based bifunctional extrudates (Ni/LaY-Al2O3 and Ni/LaY-SiO2). Compared with Ni/LaY-Al2O3, Ni/LaY-SiO2 shows a markedly enhanced durability and sustained performance for 936 h in the continuous liquid-phase hydrogenation of γ-valerolactone into methyl pentanoate. Complementary characterization studies reveal that choosing SiO2 as binder could efficiently mitigate metal agglomeration, coke formation and support dealumination during catalysis. These findings showcase that binder selection is essential for catalyst durability in the development of the industrial-level bifunctional catalysts for biomass valorization.

A Kinetic Model of Furfural Hydrogenation to 2-Methylfuran on Nanoparticles of Nickel Supported on Sulfuric Acid-Modified Biochar Catalyst

Lignocellulosic biomass can uptake CO2 during growth, which can then be pyrolysed into three major products, biochar (BC), syngas, and bio-oil. Due to the presence of oxygenated organic compounds, the produced bio-oil is not suitable for direct use as a fuel and requires upgrading via hydrodeoxygenation (HDO) and hydrogenation. This is typically carried out over a supported metal catalyst. Regarding circular economy and sustainability, the BC from the pyrolysis step can potentially be activated and used as a novel catalyst support, as reported here. A 15 wt% Ni/BC catalyst was developed by chemically modifying BC with sulfuric acid to improve mesoporous structure and surface area. When compared to the pristine Ni/BC catalyst, sulfuric activated Ni/BC catalyst has excellent mesopores and a high surface area, which increases the dispersion of Ni nanoparticles and hence improves the adsorptive effect and thus catalytic performance. A liquid phase hydrogenation of furfural to 2-methylfuran was performed over the developed 15 wt% Ni/BC catalyst. Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic type models for adsorption of dissociative H2 were screened based on an R2 value greater than 99%, demonstrating that the experimental data satisfactorily fit to three plausible models: competitive (Model I), competitive at only one type of adsorption site (Model II), and non-competitive with two types of adsorption sites (Model III). With a correlation coefficient greater than 99% between the experimental rates and the predicted rate, Model III, which is a dual-site adsorption mechanism involving furfural adsorption and hydrogen dissociative adsorption and surface reaction, is the best fit. The Ni/BC catalyst demonstrated comparative performance and significant cost savings over previous catalysts; a value of 24.39 kJ mol−1 was estimated for activation energy, −11.43 kJ mol−1 for the enthalpy of adsorption for H2, and −5.86 kJ mol−1 for furfural. The developed Ni/BC catalyst demonstrated excellent stability in terms of conversion of furfural (96%) and yield of 2-methylfuran (54%) at the fourth successive experiments. Based on furfural conversion and yield of products, it appears that pores are constructed slowly during sulfuric acid activation of the biochar.

A switchable hydrogenation chemoselectivity of biomass platform compounds based on solvent regulation

Selective catalytic conversion of biomass-derived compounds to fuels and fine chemicals serves as a renewable energy pathway for the partial substitution of fossil resources, in which reaction pathway and selectivity control are key issues. Herein, we report a fully exposed Pt clusters immobilized on CoAl mixed metal oxides catalyst (denoted as Ptn/CoAl-MMOs), which exhibits prominent catalytic performance towards liquid phase hydrogenation reaction of furfural (FAL). Noteworthily, the hydrogenation chemoselectivity can be switched among four products via using four different solvents: tetrahydrofurfuryl alcohol (THFA; yield: 91.4%), furfuryl alcohol (FA; yield: 97.7%), 2-methylfuran (2-MF; yield: 92.1%) and furan (FU; yield: 90.8%) are obtained in ethanol, dioxane, isopropanol and n-hexane solvent, respectively. Experimental studies (in situ FT-IR and TPSR-Mass) combined with theoretical calculations (DFT) reveal that solvent molecules exert an essential influence on the adsorption configuration of FAL via changing the solvent-catalyst and/or substrate-catalyst interaction, which ultimately determines the hydrogenation pathway, key intermediate and final product. This work demonstrates a facile solvent-dependent product-switching strategy within one catalytic system, which opens up potential opportunities for tailoring hydrogenation selectivity in liquid-solid catalytic reactions towards biomass upgrading.

Hydrogenation of Cinnamaldehyde Using Carbon Dots Reduced Palladium Nanoparticles

Carbon dots (CDs) with a size range of 0.2 to 2 nm were prepared using a hydrothermal treatment of sucrose and oleic acid. The as-synthesized CDs were used to reduce H2PdCl4 to metallic Pd nanoparticles with dPd = 9.3 ± 3.7 nm, as confirmed by PXRD and HRTEM data. Pd particles were made to be larger than the CDs, to observe any inverse support effects, however, TEM data revealed that the CDs were transformed to carbon sheets in the reduction reaction at 100 °C. The synthesized Pd-CDs catalysts (0.81 wt. % loading) and CDs were both tested for the liquid phase hydrogenation of cinnamaldehyde. The influence of mass, temperature, and hydrogen flow rate on the activity and selectivity of the CDs and Pd-CDs catalyst on the hydrogenation of cinnamaldehyde was investigated. The CDs gave a cinnamaldehyde conversion (40%, 4 h) with selectivity towards the reduction of the C = O bond (cinnamyl alcohol) while the Pd-carbon catalyst was only selective to the reduction of the C = C bond (conversion 78%) indicating the dominance of Pd in the reaction. Post analysis of the deactivated catalysts indicated formation of carbon sheets and sintering of the Pd nanoparticles. It is thus shown that the presence of Pd induces the CDs to carbon sheet formation and thus indicates the limited use of CDs as a support for the olefin hydrogenation reaction with the CDs produced carbon support. This finding has implications for other studies using CDs as supports.Graphical abstract

Design of hollow structured nanoreactors for liquid-phase hydrogenations.

Inspired by the attractive structures and functions of natural matter (such as cells, organelles and enzymes), chemists are constantly exploring innovative material platforms to mimic natural catalytic systems, particularly liquid-phase hydrogenations, which are of great significance for chemical upgrading and synthesis. Hollow structured nanoreactors (HSNRs), featuring unique nanoarchitectures and advantageous properties, offer new opportunities for achieving excellent catalytic activity, selectivity, stability and sustainability. Notwithstanding the great progress made in HSNRs, there still remain the challenges of precise synthetic chemistry, and mesoscale catalytic kinetic investigation, and smart catalysis. To this extent, we provide an overview of recent developments in the synthetic chemistry of HSNRs, the unique characteristics of these materials and catalytic mechanisms in HSNRs. Finally, a brief outlook, challenges and further opportunities for their synthetic methodologies and catalytic application are discussed. This review might promote the creation of further HSNRs, realize the sustainable production of fine chemicals and pharmaceuticals, and contribute to the development of materials science.