Catalytic Transfer Hydrogenation Research Articles

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.

Pd-Catalyzed Transfer Hydrogenation of Alkenes Using Tetrahydroxydiboron as the Sole Hydrogen Donor

Tetrahydroxydiboron-mediated catalytic transfer hydrogenations have typically involved co-additives that, like tetrahydroxydiboron itself, are H atom donors. Herein we report an alkene transfer hydrogenation method with tetrahydroxydiboron as the sole source of H atoms. The reaction uses Pd(OAc)2 as a convenient putative colloid pre-catalyst, and cyclic monoethers are competent solvents. Highly efficient alkene deuteration is demonstrated using tetradeuteroxydiboron.

Low-Temperature Catalytic Transfer Hydrogenation of Biomass-Derived Furfural over Irreversibly Adsorbed and Highly Dispersed Zr(IV) Species.

Developing pure inorganic catalysts for low-energy transfer hydrogenation of biomass-derived furfural and alcohols below 100 °C is still challenging. This work reports highly dispersed Zr(IV) species catalysts prepared by irreversible adsorption of different solvent-dissolved Zr(IV) cations such as Zr4+ or [Zr4(OH)8(H2O)16]8+ on/in SBA-15 through Zr-O coordination, without adding an alkaline precipitant and calcination treatment. In the transfer hydrogenation of furfural to furfuryl alcohol, the Zr(IV) species catalysts exhibited unexpectedly outstanding transfer hydrogenation activity at low temperatures of 70 and 85 °C, superior to other transition-metal (Zr4+, Hf4+, Fe3+, etc.)- and main-group metal (Al3+, etc.)-based inorganic catalysts, which need high reaction temperatures above 100 °C, and comparable to the best-performing metal-organic hybrid catalysts with precise defect engineering modification or specific macromolecular ligands, and had negligible Zr leaching amounts (<0.01%) in water and in the collected liquid reaction medium from 7 cycles of reactions. In addition, the large strong Lewis acidic site amount rather than the large total acidic amount is a crucial condition for the catalysts to obtain high transfer hydrogenation activity, and basic sites were also involved in catalysis, and their absence would induce the acetalization side reaction. Furthermore, the catalysts were universal for low-temperature transfer hydrogenation of other aldehydes.

Acid-base synergistic effect towards catalytic transfer hydrogenation reactions

Catalytic transfer hydrogenation (CTH) of aldehydes/ketones by using alcohols as hydrogen donors is an attractive and environmentally friendly hydrogenation technology, which has evoked widespread attention in synthesis of fine chemicals from biomass resources. In this work, a Co-Al mixed metal oxide catalyst (Co1Al2-MMO-200) was obtained through structural topological transformation process of layered double hydroxides, which was used in the CTH reaction of furfural with isopropanol. Notably, the reaction rate achieves 0.023 mol g−1 h−1, which is preponderate to acid-base catalysts earlier reported. The joint research based on CO2-TPD, NH3-TPD and poisoning experiment substantiates that the synergy effect of acid-base sites plays an essential role in this catalytic system. Isotopic labelling MS, in-situ FT-IR and DFT studies further verify that the CTH reaction of furfural occurs via the Meerwein-Ponndorf-Verley (MPV) route, in which the basic site promotes the deprotonation of isopropanol whilst the acid site facilitates the formation of a six-membered ring transition state. This work demonstrates an acid-base synergetic catalysis for the CTH reaction by revealing the structure-property correlation and exploring reaction route, which is instructive for designing high-performance heterogenous catalysts.

Iridium(III) complexes with cyclometalated imidazolylidene ligands: sp2 phenyl C[sbnd]H activation vs sp2 benzyl C[sbnd]H activation and catalytic transfer hydrogenation reactions

Cyclometalated N-heterocyclic carbene (NHC) complexes possess fascinating electronic and catalytic properties. A series of cyclometalated iridium(III) complexes have been synthesized from the corresponding imidazolium salts via the aryl sp2 CH bond activation at the N1-phenyl/N3-benzyl wingtips of the imidazolylidene moiety. The electronic tuning towards the competitive formation of cyclometalated complexes (sp2 phenyl CH activation vs sp2 benzyl CH activation) has been discussed. These complexes have been utilized for the transfer hydrogenation (TH) reaction of 4-bromobenzaldehyde and 4-bromoacetophenone. These complexes showed excellent yields of the aryl-alcohols from 4-bromobenzaldehyde or 4-bromoacetophenone.

Catalytic transfer hydrogenation with methanol over Pt/C catalyst for synergistic hydrothermal hydrogenation of palmitic acid

Achieving hydrothermal hydrogenation and deoxygenation of bio-oil with high water content such as microalgae-based bio-oil still faces significant challenges. Traditional upgrading processes require a large amount of H2. The objective of current research uses methanol and formic acid as a hydrogen donor to achieve the hydrothermal hydrodeoxygenation of palmitic acid (a model of microalgae-based bio-oil) to prepare pentadecane over Pt/C catalyst without the need for additional H2 supply. The research findings have shown that the H2 supply mechanism of methanol and formic acid in synergy with palmitic acid hydrothermal hydrodeoxygenation is obviously different. Formic acid is directly decomposed to produce H2, while methanol undergoes aqueous steam reforming to produce H2 in synergy with palmitic acid hydrodeoxygenation. More importantly, methyl palmitate, a typical model compound of the first-generation biodiesel, achieved efficient deoxygenation without the addition of H2 and hydrogen donors. At 300 °C, the yield of pentadecane reached 91.25 % within 150 min. The hydrothermal stability test shows that the decrease in Pt content and specific surface area (SBET), as well as the destruction of pore structure, are the main reasons for the decrease in activity of the Pt/C catalyst after cycling. The H2 production efficiency of hydrogen donors possesses a significant impact on the hydrodeoxygenation of palmitic acid and therefore more efficient catalysts need to be developed.

Production of isopropyl levulinate from furfural catalyzed by zirconium phosphate supported on nanosponge MFI zeolite through catalytic transfer hydrogenation

Alkyl levulinate is a kind of high value chemicals derived from biomass. Here, a nanosponge ZSM-5 supporting zirconium phosphate (ZrPO/NPZ) catalyst is prepared and used for catalytic transfer hydrogenation of furfural (FUR) to produce isopropyl levulinate (IPL) using isopropanol as H-donor. ZrPO specie provides Lewis acid sites together with additional Brønsted acid sites by ZSM-5 zeolite. Using the hierarchical ZSM-5 with exposed surface area as support, the dispersion of ZrPO active species increases, which facilitates the adsorption and conversion of FUR with the generation of 2-(isopropoxymethyl)furan (IPMF). The moderate Brønsted acid sites by zeolite promote the adsorption and activation of isopropanol, thus increasing the conversion rates of intermediate IPMF with formation of IPL. Furthermore, improved proportions of Brønsted/Lewis was detected with the increase of P/Zr ratios in the prepared catalysts, which is adverse for conversion of FUR. The optimized ZrPO/NPZ catalyst with P/Zr of 1 gives the best catalytic performance with IPL yield of ∼69 wt% after 3 h reaction at 200 °C (TOF of 6.98 mmol g−1 h−1), which provides an essential catalyst to produce IPL from FUR.

Catalytic transfer hydrogenation of α-angelica lactone over Nickel(II) modified UiO-66 metal organic framework under mild conditions

In the realm of biomass valorization, catalysts play a pivotal role, and UiO-66(Zr), a type of metal organic framework (MOF), emerges as a promising heterogeneous catalyst. This study focuses on incorporating Ni2+ into UiO-66(Zr) for application in catalytic transfer hydrogenation (CTH) of bio-derived α-angelica lactone (a-AL) to ɣ-valerolactone (GVL). The synthesis of UiO-66(Zr) occurs through a solvothermal process at 120 °C for 24 h. Ni(II) modification, achieved through wet impregnation with loadings of 2.5 and 5.0 wt%, results in no observable diffraction peaks associated with Ni particles in XRD analysis. FTIR analysis indicates significant shifts, suggesting deprotonation of the carboxylic moiety from the ligand and coordination with Zr4+ metal ion. Nitrogen sorption isotherms show a reduction in surface area and pore volume upon Ni(II) incorporation. FESEM analysis reveals particle agglomeration and increased size with Ni(II) introduction. EDX and HRTEM confirm the presence of 0.9 and 1.8 wt% Ni(II) on UiO-66(Zr). TG/DTA analysis affirms that Ni(II) does not affect the thermal stability of UiO-66(Zr). Ultimately, the introduction of Ni(II) enhances the catalytic performance of UiO-66(Zr), increasing the conversion and selectivity towards ɣ-valerolactone from 67 to 83.3 % and 71.6 % to 97.4 %, respectively, under mild reaction conditions.

A combo Zr–zeolite and Zr(OH)4 mixture composition for one–pot production of γ–valerolactone from furfural

The one–pot cascade transformation of biomass–derived furfural (FUR) to γ–valerolactone (GVL) has attracted great attention but always facing relative low reaction rates. In this work, a combo ZrO2 supported on ZSM–5 nanosheet (ZrO2/NS) and Zr(OH)4 were mixed as a hybrid catalysts system, which was prepared by impregnation and precipitation, respectively. Then the catalytic system was used for conversion of FUR to produce GVL through catalytic transfer hydrogenation in isopropanol. NS zeolite with hierarchical pores promoted the dispersion of ZrO2 and exposed surface assisted the conversion of FUR to isopropyl levulinate (IPL). Moreover, the addition of Zr(OH)4 facilitated the cascade transformation of the intermediate IPL to GVL through the enhanced adsorption of IPL and isopropanol with the cooperation of basic sites. The ZrO2/NS and Zr(OH)4 catalyst system with optimized proportion delivers >90 wt% yield of GVL at 180 °C after 2h reaction, with generation rates of GVL (RGVL) up to 9.2 mmol g−1 h−1.

In-cell Catalysis by Tethered Organo-Osmium Complexes Generates Selectivity for Breast Cancer Cells.

Anticancer agents that exhibit catalytic mechanisms of action offer a unique multi-targeting strategy to overcome drug resistance. Nonetheless, many in-cell catalysts in development are hindered by deactivation by endogenous nucleophiles. We have synthesised a highly potent, stable Os-based 16-electron half-sandwich ('piano stool') catalyst by introducing a permanent covalent tether between the arene and chelated diamine ligand. This catalyst exhibits antiproliferative activity comparable to the clinical drug cisplatin towards triple-negative breast cancer cells and can overcome tamoxifen resistance. Speciation experiments revealed Os to be almost exclusively albumin-bound in the extracellular medium, while cellular accumulation studies identified an energy-dependent, protein-mediated Os accumulation pathway, consistent with albumin-mediated uptake. Importantly, the tethered Os complex was active for in-cell transfer hydrogenation catalysis, initiated by co-administration of a non-toxic dose of sodium formate as a source of hydride, indicating that the Os catalyst is delivered to the cytosol of cancer cells intact. The mechanism of action involves the generation of reactive oxygen species (ROS), thus exploiting the inherent redox vulnerability of cancer cells, accompanied by selectivity for cancerous cells over non-tumorigenic cells.

Alkaline modified Zr-loading on nanosheet zeolite towards production of γ-valerolactone from levulinic acid through catalytic transfer hydrogenation

A self-pillared nanosheet ZSM-5 zeolite (SP) loading Zr catalyst is prepared for conversion of levulinic acid (LA) to produce γ-valerolactone (GVL). The hierarchical pore by nanosheet aggregates promotes Zr dispersion with establishment of strong interaction between Zr and zeolite. Moreover, Na ions are introduced to modify the chemical environment of Zr on nanosheet zeolite (Zr/NaSP). In catalytic transfer hydrogenation of LA using isopropanol as H-donor, uniformly dispersed Zr species on SP zeolite is conducive for both conversion of LA as well as production of GVL, in comparison with samples using conventional microporous ZSM-5 as supports (Zr/CZ). More importantly, different from protonated zeolite sample (Zr/HSP), the introduction of alkali sites could attract protons in hydroxyl groups of isopropanol, which accelerates the generation rates of GVL. The as-designed Zr/NaSP catalyst delivers GVL generation rates of 31.9 mmol·g-1·h-1, which provides a potential catalyst for GVL production.

Methyl Formate, an Alternative Transfer Hydrogenating Agent for Chemoselective Reduction of N-Heteroarenes and Azoarenes.

The search for efficient molecular hydrogen precursors and their catalytic exploration is necessary for the evolution of catalytic transfer hydrogenation. Methyl formate (MF) having high hydrogen content still remains unexplored for such transformations. Herein, we disclosed a bifunctional Ir(III)-complex catalyzed chemoselective TH protocol for N-heteroarenes and azoarenes using MF. A variety of substrates including ten bioactive molecules have been synthesized under mild reaction conditions. A probable mechanistic pathway was proposed based on control experiments and mechanistic studies.

Supporting Nano Catalysts for the Selective Hydrogenation of Biomass-derived Compounds.

The selective hydrogenation of biomass derivatives presents a promising pathway for the production of high-value chemicals and fuels, thereby reducing reliance on traditional petrochemical industries. Recent strides in catalyst nanostructure engineering, achieved through tailored support properties, have significantly enhanced the hydrogenation performance in biomass upgrading. A comprehensive understanding of biomass selective upgrading reactions and the current advancement in supported catalysts is crucial for guiding future processes in renewable biomass. This review aims to summarize the development of supported nanocatalysts for the selective hydrogenation of the US DOE's biomass platform compounds derivatives into valuable upgraded molecules. The discussion includes an exploration of the reaction mechanisms and conditions in catalytic transfer hydrogenation (CTH) and high-pressure hydrogenation. By thoroughly examining the tailoring of supports, such as metal oxide catalysts and porous materials, in nano-supported catalysts, we elucidate the promoting role of nanostructure engineering in biomass hydrogenation. This endeavor seeks to establish a robust theoretical foundation for the fabrication of highly efficient catalysts. Furthermore, the review proposes prospects in the field of biomass utilization and address application bottlenecks and industrial challenges associated with the large-scale utilization of biomass.

The Mechanism of Guerbet Reaction by Metal Ligand Cooperation Catalyst Mn-PCP.

The Guerbet reaction is important for the synthesis of longer-chain monoalcohols like isobutanol through catalytic transfer hydrogenation from short-chain methanol and ethanol. However, the mechanism becomes complicated, especially considering the variations in the different metal-ligand cooperation (MLC) catalysts used. In order to further understand the Guerbet reaction, DFT studies were performed to figure out the detailed mechanism initiated by the unique Mn-PCP MLC Catalyst. Our results suggest that even with the assistance of the carbanion site of the PCP ligand, the direct substitution mechanism is less favored than the condensation-reduction mechanism. The key step of the reaction is the final reduction of the carbonyl, in which the 1,4-reduction of the unsaturated aldehyde is prior to the 3,4-reduction or 1,2-reduction due to the stronger interaction between the catalyst and the substrate. It is found that the production of isobutanol is preferred over n-butanol because of the lower total free energy barrier and lower relative free energy of the product. Finally, by changing the electronic effect of the carbanion site of the catalyst, we found that the relation between the electronic effect and the highest free energy span was not monotonous and a point with optimal electronic effect exists numerically.

Tandem hydrogenation/hydrogenolysis of furfural to 2-methylfuran over multifunctional metallic Cu nanoparticles supported ZIF-8 catalyst

Catalytic transfer hydrogenation (CTH), that employs protic solvents as hydrogen sources to alleviate the use of molecular hydrogen H2, has gained great attention. This work, reports multifunctional, metallic Cu nanoparticles supported ZIF-8 material for CTH of furfural to a highly valued fuel additive, 2-methylfuran (2-MF) using 2-propanol. Of all as-synthesized xCu(yM)/ZIF-8 catalysts with varied NaBH4 concentration (yM) and Cu loading (x), 11Cu(1.5 M)/ZIF-8 exhibited higher catalytic activity with > 99 % FAL conversion and 93.9 % 2-MF selectivity. This is ascribed to its high specific surface area, and existence of optimum amount of Lewis acid-base sites along with Cu0 species, which are responsible for hydrogenation of furfural to furfuryl alcohol and subsequent hydrogenolysis to produce 2-MF. The present work reports a highly efficient and stable, metal-MOF hybrid material for CTH of FAL to 2-MF, which is one among the best reports available in literature, therewith suggests a promising approach for bio-oil upgradation.

Heteropolyacid promoted lignin-MOF derived spherical catalyst for catalytic hydrogen transfer of 5-hydroxymethylfurfural

Catalytic conversion of biomass-derived value-added chemicals was of great significance for the utilization of renewable biomass resources to instead of fossil chemicals. Biomass-derived lignin was regarded as an important support and 5-hydroxymethylfurfural (HMF) was a vital platform chemical derived from cellulose. Herein, a series of lignin-MOF hybrid catalysts were prepared and modified with different heteropolyacids (HPAs), which were then successfully introduced into the selective conversion of HMF to 5-hydroxymethylfurfuryl alcohol (MFA). The effect of different HPA, calcination temperature, etc. were all studied, and all catalysts were well characterized. It was confirmed that silicotungstic acid modified catalyst (Ni3Co-MOF-LS@HSiW) exhibited the best catalytic performance, while the highest conversion of HMF was up to 100%, with the best MFA yield of 86.5%. The finding in this study could provide novel insights for the utilization of lignin and preparation of value-added biomass-derived chemicals.

Synthesis, characterisation, and catalytic application of a soluble molecular carrier of sodium hydride activated by a substituted 4-(dimethylamino)pyridine

Recently main group compounds have stepped into the territory of precious transition metal compounds with respect to utility in the homogeneous catalysis of fundamentally important organic transformations. Inspired by the need to promote more sustainability in chemistry because of their greater abundance in nature, this change of direction is surprising since main group metals generally do not possess the same breadth of reactivity as precious transition metals. Here, we introduce the dihydropyridylsodium compound, Na-1,2-tBu-DH(DMAP), and its monomeric variant [Na-1,2-tBu-DH(DMAP)]·Me6TREN, and demonstrate their effectiveness in transfer hydrogenation catalysis of the representative alkene 1,1-diphenylethylene to the alkane 1,1-diphenylethane using 1,4-cyclohexadiene as hydrogen source [DMAP = 4-dimethylaminopyridine; Me6TREN = tris(N,N-dimethyl-2-aminoethyl)amine]. Sodium is appealing because of its high abundance in the earth’s crust and oceans, but organosodium compounds have been rarely used in homogeneous catalysis. The success of the dihydropyridylsodium compounds can be attributed to their high solubility and reactivity in organic solvents.

Zn Single-Atom Catalysts Enable the Catalytic Transfer Hydrogenation of α,β-Unsaturated Aldehydes.

Highly active nonprecious-metal single-atom catalysts (SACs) toward catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes are of great significance but still are deficient. Herein, we report that Zn-N-C SACs containing Zn-N3 moieties can catalyze the conversion of cinnamaldehyde to cinnamyl alcohol with a conversion of 95.5% and selectivity of 95.4% under a mild temperature and atmospheric pressure, which is the first case of Zn-species-based heterogeneous catalysts for the CTH reaction. Isotopic labeling, in situ FT-IR spectroscopy, and DFT calculations indicate that reactants, coabsorbed at the Zn sites, proceed CTH via a "Meerwein-Ponndorf-Verley" mechanism. DFT calculations also reveal that the high activity over Zn-N3 moieties stems from the suitable adsorption energy and favorable reaction energy of the rate-determining step at the Zn active sites. Our findings demonstrate that Zn-N-C SACs hold extraordinary activity toward CTH reactions and thus provide a promising approach to explore the advanced SACs for high-value-added chemicals.

Cover Feature: Influence of Charge Delocalization on Manganese Catalyzed Transfer Hydrogenation (ChemCatChem 7/2024)

Cover Feature: Influence of Charge Delocalization on Manganese Catalyzed Transfer Hydrogenation (ChemCatChem 7/2024)

Efficient synthesis of γ-valerolactone from ethyl levulinate via catalytic transfer hydrogenation in supercritical isopropanol over nickel aluminum oxide nanosheets

This study reports a novel method for γ-valerolactone (GVL) production from ethyl levulinate (EL) utilizing non-noble metal catalysts within a supercritical isopropanol (IPA) system. Nickel-loaded nickel–aluminum oxide nanosheets (NiXAl-R) were fabricated via hydrothermal treatment of Ni–Al layered double hydroxide precursors, followed by hydrogen reduction at 550 °C for 1.5 h. Using NiXAl-R as the catalyst and IPA as the hydrogen donor, we achieved notable results: 82.7% EL conversion, 73.6% GVL yield, and 1.178 molGVL g−1 h−1 reaction efficiency after 1.5 h in supercritical IPA. The catalytic activity of NiXAl-R remained stable over five catalytic cycles. The surface of NiXAl-R exhibits abundant oxygen vacancies and unsaturated Al species (Alx+), which promote the initial transfer hydrogenation of EL to form the ethyl 4-hydroxypentanoate (4-HPE) intermediate. Simultaneously, the supercritical IPA environment overcomes mass transfer limitations at the solid–liquid interface between 4-HPE and the catalyst, thereby facilitating the Alx+-catalyzed intramolecular esterification of 4-HPE into GVL.