Hydrogenation Reactions Research Articles

One-pot conversion of xylose to 1,2-pentanediol catalyzed by an organic acid-assisted Pt/NC in aqueous phase.

The direct synthesis of 1,2-pentanediol (1,2-PeD) from renewable xylose and its derivatives derived from hemicellulose is appealing yet challenging due to its low selectivity for the target product. In this study, one-pot catalytic conversion of xylose to 1,2-PeD was performed by using nitrogen-doped carbon (NC) supported Pt catalysts with the assistance of organic acids. A remarkable yield of 49.3% for 1,2-PeD was achieved by reacting 0.1869 g xylose in 30 mL water at 200 °C under a hydrogen pressure of 3 MPa for 8 h in the presence of 0.1 g of 2.5Pt/NC600 catalyst and 0.1869 g propanoic acid co-catalyst. The presence of vicinal Pt-acid pair sites on the surface of the 2.5Pt/NC600 catalyst exhibited a synergistic effect in promoting the hydrogenation of furfural to furfuryl alcohol intermediate and subsequent hydrogenation and ring-opening reactions leading to the formation of 1,2-PeD. The addition of organic acids, may serve as both acid catalyst for dehydration of xylose and hydrogen donor for hydrogenation of furfural and furfuryl alcohol, thereby promoting the one-pot conversion of xylose to 1,2-PeD. Remarkably, the 2.5Pt/NC600 catalyst demonstrated outstanding catalytic performance and good reusability over five consecutive cycles without significant deactivation.

Influence of Ga doped CoMo/Al2O3 catalysts on the selective hydrogenation performance of polycyclic aromatic hydrocarbons

It is a challenge to effectively control the intermediate ring hydrogenation products in tricyclic aromatic hydrocracking reactions in order to further increase the selectivity of BTX. A series of doped gallium modified CoMo/Al2O3 catalysts were prepared, the effect of gallium on the catalyst's physicochemical properties, active phase structure and hydrogenation reaction pathway was studied. The study revealed that the doping of gallium species promoted the sulfidation of Mo species and improved the catalytic activity of the catalyst. The 1 % Ga-modified catalyst showed the best selective hydrogenation performance, in which the conversion rate of phenanthrene was up to 83.75 % and the selectivity for dihydrophenanthrene reached 28.60 %. In addition, DFT calculations show that the introduction of Ga into the active phase between the Co and Mo atoms results in a higher differential charge density in the middle ring, which is more conducive to hydrogen adsorption.

Highly efficient Zn-MOF derived Carbon-Nitrogen material based catalyst for nitroaromatic Hydrogenation: The role of Zn-O-C bond and Pyridinic-N

Zn-based catalysts have great feature of environmental friendliness and developmental potential to replace precious metals in heterogeneous catalytic hydrogenation. In this work, a porous CN material-based catalysts containing trace Zn were prepared by high-temperature pyrolysis using zeolitic imidazolate framework (ZIF-8) material as precursor. The result shows that (Zn)NC-800 and (Zn)NC-600–700 exhibit outstanding hydrogenation ability and good stability in nitro compounds hydrogenation reaction. Based on the results of characterization and DFT calculations, two hydrogenation active sites complete the hydrogenation of nitro compounds in (Zn)NC-800 and (Zn)NC-600–700: the residual trace Zn in the form of Zn-O-C bond can activate the CN structure and promote the conversion of nitrobenzene; the pyridinic-N is confirmed to accelerate the electron transfer and enhance the selectivity to aniline. This work has an enlightening significance for the efficient development of heterogeneous catalytic hydrogenation catalysts.

Layered carbon encapsulated CuOx nanopaticles for selective hydrogenation of furfural to furfuryl alcohol

Furfuryl alcohol (FOL) is commercially available by selective hydrogenation of furfural (FAL). A variety of catalysts have been developed for such purpose, among which Cu-based catalysts show superior catalytic performance. However, copper nanoparticles with complex valence states are easy to agglomerate during hydrogenation reaction, which might have a negative influence on the catalytic performance. The carbon coating is an efficient strategy to prevent the sintering of Cu-based catalysts. Herein, a strategy based on the thermal decomposition of Cu-EDTA complex was designed to prepare carbon encapsulated Cu-based catalysts. The prepared catalysts were applied in the selective hydrogenation of FAL to FOL in the batch reactor. The results showed that a nearly quantitative conversion of FAL with a selectivity of 98.7 % towards FOL was achieved using CuOx@NC-150 (molar ratio of Cu: Na4EDTA·4H2O=2:1; obtained by oxidative activation at 150 °C) under 140 °C, 3 MPa in 4 h. The performance was comparable to that of the commercial CuCr2O4 catalyst under the identical conditions. In addition, the developed carbon encapsulated Cu-based catalysts exhibited a slightly better stability than CuCr2O4 catalyst in terms of FOL yield in five consecutive cycles. XPS and XAES characterizations implied that the presence of a suitable surface ratio of Cu+/(Cu++Cu0) of the prepared catalyst may contribute to the selective hydrogenation of FAL to FOL.

Lewis Acid-Tethered (cAAC)-Copper Complexes: Reactivity for Hydride Transfer and Catalytic CO2 Hydrogenation.

We present a series of borane-tethered cyclic (alkyl)(amino)carbene (cAAC)-copper complexes, including a borane-capped Cu(I) hydride. This hydride is unusually hydridic and reacts rapidly with both CO2 and 2,6-dimethylphenol at room temperature. Its reactivity is distinct from variants without a tethered borane, and the underlying principles governing the enhanced hydricity were evaluated experimentally and theoretically. These stoichiometric results were extended to catalytic CO2 hydrogenation, and the borane-tethered (intramolecular) system exhibits ~3-fold enhancement relative to an intermolecular system.

Unraveling the Solvent Regulation in the Heteroatom-Doped Endohedral Gold Clusters: A Theoretical Study on the Electronic Properties and O2 Activation.

Liquid-phase synthesis of atomically precise nanoclusters has experienced rapid development recently, where polar solvents are indispensable in such a process. However, the regulation effect of solvents on the structural and electronic properties of different metal clusters and cluster assembly materials is still not well understood. Herein, a comprehensive density functional theory calculation has been performed to explore the solvation effect on heteroatom-doped endohedral gold clusters that always have remarkable stabilities and tunable electronic structures. The solvation free energy of the M@Au12 clusters (M = Cr, Mo, W, Co, Rh, Ir, Cu, Ag, and Au) was found to be related to the charge distribution of the central doped-atom M and the outer Au12 cage. Moreover, the aqueous solvent was observed to be able to increase the adsorption capacity of M@Au12 to O2 following the activation of O2 through the charge transfer from M@Au12 to O2, in which the transferred electrons occupy the π antibonding orbital of O2. In addition, the water solvent can also improve the hydrogenation reaction of O2 to form OOH over M@Au12, where the activation energy barrier for this process is very low with the participation of the solvent. Considering the importance of solvents in the liquid-phase synthesis of atomically precise clusters, these findings highlighted here could provide valuable theoretical guidance in potential applications of functional gold nanoclusters, especially in the liquid-phase cluster catalysis.

Electrocatalytic hydrogen evolution coupled with dye hydrogenation reactions for sustainable wastewater treatment using transition-metal (Fe, Co, Ni, Cu) nanoparticles with ZnO nanowire supports

A water electrolysis coupled with chemical reduction strategy is proposed to realize sustainable wastewater treatment. Correspondingly, a series of transition-metal (e.g., iron, cobalt, nickel and copper) nanoparticles anchored on zinc oxide nanowire array (ZnO NA) with bifunctional catalytic activity for hydrogen evolution reaction together with dye hydrogenation reaction (HER/DHR) are developed, while their catalytic activity are comparatively investigated at the same time. This renewable strategy with environmental and economic benefits exhibits high-efficiency treatment capability towards various dye wastewaters. For example, a typical system based on nickel nanoparticles with ZnO NA supports, which exhibits higher catalytic activity towards the HER/DHR than those of other three counterparts under the same conditions, can transform waste 4-nitrophenol into valuable 4-aminophenol with an apparent rate constant of 36.95 × 10-3 min−1 and a conversion rate of 98.32 %, thereby achieving dye decolorization and resource regeneration simultaneously. Its efficiency is significantly superior to that of chemical method dependent on traditional reducing agents and commercial nickel materials, demonstrating its stronger competitiveness. It is mainly benefited from the interface synergistic effect of nickel nanoparticles and zinc oxide nanowires. This novel system is expected to replace conventional sewage remediation technologies for efficient, inexpensive, and eco-friendly dye degradation, and thus is very important for energy and environmental sustainability.

Demonstrating the applicability of Raman spectroscopy for the characterization of hydrogen loading of bicyclic liquid organic hydrogen carriers (LOHCs) under process-relevant conditions

During hydrogenation and dehydrogenation reactions of liquid organic hydrogen carriers (LOHC), their thermophysical properties change significantly as a function of the degree of hydrogenation (DoH). Compared with conventional techniques, Raman spectroscopy offers a contactless methodology for online process monitoring without the need of sampling. This work demonstrates the application of Raman spectroscopy for the determination of the DoH under process-relevant conditions for LOHC systems based on diphenylmethane (DPM) and benzyltoluene (BT) up to 473 K. For the DPM-based system, a previous study is extended by examining the influence of process-like disturbances. For the BT-based system, a novel approach using indirect hard modeling of the unpolarized Raman spectra is applied, which results in strongly reduced uncertainties and insensitivity towards process-like disturbances, e.g. reaction by-products. For a corresponding testing set exhibiting a pronounced fluorescent background in the Raman spectra, the DoH is determined with an average absolute deviation of 0.0057.

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.

Expedited Synthesis of Metal Phosphides Maximizes Dispersion, Air Stability, and Catalytic Performance in Selective Hydrogenation

AbstractMetal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation substantially lower the appeal and performance of metal phosphides in catalysis. We show here that a 1‐step procedure that relies on safe and cheap precursors can furnish an air‐stable Ni2P/Al2O3 catalyst containing 3.2 nm nanoparticles. Ni2P/Al2O3 1‐step is kinetically competitive with the palladium‐based Lindlar catalyst in selective hydrogenation catalysis, and a loading corresponding to 4 ppm Ni was sufficient to convert 0.1 mol alkyne. The 1‐step synthetic procedure alters the surface ligand speciation of Ni2P/Al2O3, which protects the nanoparticle surface from oxidation, and ensures that 85 % of the initial catalytic activity was retained after the catalyst was stored under air for 1.5 years. Preparation of Ni2P on a variety of supports (silica, TiO2, SBA‐15, ZrO2, C and HAP) as well as Co2P/Al2O3, Co2P/TiO2 and bimetallic NiCoP/TiO2 demonstrates the generality with which supported metal phosphides can be accessed in a safe and straightforward fashion with small sizes and high dispersion.

Expedited Synthesis of Metal Phosphides Maximizes Dispersion, Air Stability, and Catalytic Performance in Selective Hydrogenation.

Metal phosphides have been hailed as potential replacements for scarce noble metal catalysts in many aspects of the hydrogen economy from hydrogen evolution to selective hydrogenation reactions. But the need for dangerous and costly phosphorus precursors, limited support dispersion, and low stability of the metal phosphide surface toward oxidation substantially lower the appeal and performance of metal phosphides in catalysis. We show here that a 1-step procedure that relies on safe and cheap precursors can furnish an air-stable Ni2P/Al2O3 catalyst containing 3.2 nm nanoparticles. Ni2P/Al2O3 1-step is kinetically competitive with the palladium-based Lindlar catalyst in selective hydrogenation catalysis, and a loading corresponding to 4 ppm Ni was sufficient to convert 0.1 mol alkyne. The 1-step synthetic procedure alters the surface ligand speciation of Ni2P/Al2O3, which protects the nanoparticle surface from oxidation, and ensures that 85 % of the initial catalytic activity was retained after the catalyst was stored under air for 1.5 years. Preparation of Ni2P on a variety of supports (silica, TiO2, SBA-15, ZrO2, C and HAP) as well as Co2P/Al2O3, Co2P/TiO2 and bimetallic NiCoP/TiO2 demonstrates the generality with which supported metal phosphides can be accessed in a safe and straightforward fashion with small sizes and high dispersion.

Effect of copper cluster on reaction pathways of carbon dioxide hydrogenation on magnesium hydride surface

Understanding the reaction mechanism of CO2 hydrogenation to produce value-added chemicals is essential for the rational design of catalysts to improve reaction activity and product selectivity. In this work, the first-principles calculations based on density functional theory were employed to study the effect of copper cluster on product selectivity in CO2 hydrogenation utilizing magnesium hydride as hydrogen source. The results show that on pristine MgH2 (0 0 1), CO2 molecule adsorbs on the surface with an O atom close to Mg atom, and the hydrogenation reaction follows formate pathway to yield CH3OH with an energy barrier only 1.09 eV for the rate-limiting step; however, the production of the most accessible C2-based product (CH2OH)2 needs to overcome an energy barrier up to 1.94 eV. On MgH2 (0 0 1) with Cu7 cluster, the C atom of CO2 molecule can strongly adsorb on a Cu atom of Cu7 cluster, and the hydrogenation more likely proceeds through reverse water-gas shift pathway, in which it is easy to generate C2 product C2H4 by the coupling of intermediate H2C*, with an energy barrier only 1.53 eV for the rate-limiting step. The findings utilizing transition metal cluster to change the reaction pathway and product selectivity of CO2 hydrogenation on magnesium hydride can provide novel perspectives for the design of catalysts.

Ionic Liquids Boost Anthraquinone Hydrogenation over Pd‐based Bimetallic Pincer Catalysts

AbstractA series of bimetallic‐ionic liquid (IL) pincer catalysts Pd−M@IL were synthesized using low Pd‐loading amount (0.3 %) and adopting six kinds of ion liquids with the cation containing the imidazole ring, and then evaluated the catalytic activities toward 2‐ethylanthraquinone hydrogenation reaction with the purpose to produce H2O2. Under the reaction conditions of 60 °C, 0.30 MPa and 15 min reaction time, over the catalysts Pd−La@[BMIm]Ac/alu and Pd−La@[VBIM]Br/alu achieved high hydrogenation efficiency(9.4 g/L and 8.5 g/L) but also high selectivity toward the active anthraquinone (98.9 % and 99.6 %). Through characterizations of STEM, TPD, in‐situ XPS, etc., it illustrates that the pincer catalysts Pd−La@[BMIm]Ac/alu and Pd−La@[VBIM]Br/alu have much better dispersity than the bimetallic Pd−La/alu, these two ionic liquids of [BMIm]Ac and [VBIM]Br provide different local environment around Pd−La sites, which in turn modulate the catalytic activity of the pincer‐catalysts toward anthraquinone hydrogenation. DFT calculations disclose the unique electron transfer between ILs ([BMIm]Ac and [VBIM]Br) and Pd−La clusters and subsequent changes of energy barriers for anthraquinone hydrogenation. The work illuminates a facile strategy to design novel hydrogenation catalysts through combining the pincer microenvironment partially encapsulated by the cation and the anion of ionic liquids with the internal bimetallic sites.

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis.

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

Pd-N-doped carbons for chemoselective hydrogenation of cinnamaldehyde: Unravelling the influence of particle size and support in multiphase batch and continuous-flow systems

The chemoselective hydrogenation of the CC bond of cinnamaldehyde (CAL) was investigated under batch and continuous flow conditions, by comparing the performance of two ad-hoc prepared palladium-based catalysts supported on N-doped carbons to that of a commercial Pd/C system. An impregnation (I) and a solution-mediated (S) protocols were used for the synthesis of the catalytic materials, Pd-N/Ci and Pd-N/Cs, respectively, in the presence of chitin as a precursor of the support. The S method afforded palladium nanoparticles of 2.0±0.5 nm, while by impregnation, a wider size distribution was achieved with particles mostly belonging to two groups displaying a mean radius of 3.0±0.5 nm and 8.4±0.5 nm, respectively. A parametric analysis of the hydrogenation reaction showed that both the reaction conditions and the nature of the catalysts played a role to steer the selectivity towards the formation of the desired product, 3-phenylpropanal (hydrocinnamaldehyde, HCAL). At 50 °C and 1 bar H2, in a triphasic (liquid-liquid-liquid) batch reactor where the catalyst was compartmentalized in an ionic liquid layer, Pd-N/Ci and commercial Pd/C were almost equally active and allowed to obtain HCAL in a 90–96 % selectivity at complete conversion. On the other hand, at the same T and p (50 °C/1 bar), Pd-N/Cs was more effective in the continuous-flow mode: the process was quantitative yielding HCAL with a selectivity and a productivity of 91 % of 16 mmol (gcat h)−1, respectively, while the catalyst proved highly stable showing no loss of activity over 300 min of time on-stream. The reaction environment, the size and dispersion of the metal active sites, and the nature of the catalyst support were major contributors to such results, acting synergistically to each other to tune the energetics of adsorption/desorption of reactants/products, of the interfacial interactions/ barriers, and in the last analysis, of the process kinetics/selectivity.

La doped-Fe2(MoO4)3 with the synergistic effect between Fe2+/Fe3+ cycling and oxygen vacancies enhances the electrocatalytic synthesizing NH3

The electrocatalytic nitrogen reduction reaction (NRR) is a crucial process in addressing energy shortages and environmental concerns by synthesizing the NH3. However, the difficulty of N2 activation and fewer NRR active sites limit the application of NRR. Therefore, the NRR performance can be improved by rapid electron transport paths to participate in multi-electron reactions and N2 activation. Doping with transition metal element is a viable strategy to provide electrons and electronic channels in the NRR. This study focuses on the synthesis of Fe2(MoO4)3 (FeMo) and x%La-doped FeMo (x = 3, 5, 7, and 10) using the hydrothermal method. La-doping creates electron transport channels Fe2+-O2−-Fe3+ and oxygen vacancies, achieving an equal molar ratio of Fe2+/Fe3+. This strategy enables the super-exchange in Fe2+-O2−-Fe3+, and then enhances electron transport speed for a rapid hydrogenation reaction. Therefore, the synergistic effect of Fe2+/Fe3+ cycling and oxygen vacancies improves the NRR performance. Notably, 5%La-FeMo demonstrates the superior NRR performance (NH3 yield rate: 29.6 μg h−1 mgcat−1, Faradaic efficiency: 5.8%) at −0.8 V (vs. RHE). This work analyzes the influence of the catalyst electronic environment on the NRR performance based on the effect on different valence states of ions on electron transport.

Surfactant Directionally Assembled at the Electrode-Electrolyte Interface for Facilitating Electrocatalytic Aldehyde Hydrogenation.

Electrocatalytic hydrogenation of unsaturated aldehydes to unsaturated alcohols is a promising alternative to conventional thermal processes. Both the catalyst and electrolyte deeply impact the performance. Designing the electrode-electrolyte interface remains challenging due to its compositional and structural complexity. Here, we employ the electrocatalytic hydrogenation of 5-hydroxymethylfurfural (HMF) as a reaction model. The typical cationic surfactant, cetyltrimethylammonium bromide (CTAB), and its analogs are employed as electrolyte additives to tune the interfacial microenvironment, delivering high-efficiency hydrogenation of HMF and inhibition of the hydrogen evolution reaction (HER). The surfactants experience a conformational transformation from stochastic distribution to directional assembly under applied potential. This oriented arrangement hampers the transfer of water molecules to the interface and promotes the enrichment of reactants. In addition, near 100 % 2,5-bis(hydroxymethyl)furan (BHMF) selectivity is achieved, and the faradaic efficiency (FE) of the BHMF is improved from 61 % to 74 % at -100 mA cm-2. Notably, the microenvironmental modulation strategy applies to a range of electrocatalytic hydrogenation reactions involving aldehyde substrates. This work paves the way for engineering advanced electrode-electrolyte interfaces and boosting unsaturated alcohol electrosynthesis efficiency.

Effect of the Second-Shell Coordination Environment on the Performance of P-Block Metal Single-Atom Catalysts for the Electrosynthesis of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is an important chemical with a diverse range of industrial applications in chemical synthesis and medical disinfection. The traditional anthraquinone oxidation process, with high energy consumption and complexity, is being replaced by cost-effective and environmentally friendly alternatives. In order to explore suitable catalysts for the electrocatalytic synthesis of H2O2, the stability of B,N-doped graphene loaded with various p-block metal (PM) single atoms (i.e., PM-NxBy: x and y represent the number of atoms of N and B, respectively) and the effects of different numbers and positions of B dopants in the second coordination shell on the catalytic performance were studied by density functional theory (DFT) calculations. The results show that Ga-N4B6 and Sb-N4B6 exhibit enhanced stability and 2e− oxygen reduction reaction (ORR) activity and selectivity. Their thermodynamic overpotential η values are 0.01 V, 0.03 V for Ga-N4B6’s two configurations and 0.02 V, 0 V for Sb-N4B6’s two configurations. Electronic structure calculations indicate that the PM single atom adsorbs OOH* intermediates and transfers electrons into them, resulting in the activation of the O-O bond, which facilitates the subsequent hydrogenation reaction. In summary, Sb-N4B6 and Ga-N4B6 exhibit extraordinary 2e− ORR performance, and their predicted activities are comparable to those of known outstanding catalysts (such as PtHg4 alloy). We propose effective strategies on how to enhance the 2e− ORR activities of carbon materials, elucidate the origin of the activity of potential catalysts, and provide insights for the design and development of electrocatalysts that can be used for H2O2 production.

Hydrogen splitting at a single phosphorus centre and its use for hydrogenation.

Catalytic processes are largely dominated by transition-metal complexes. Main-group compounds that can mimic the behaviour of the transition-metal complexes are of great interest due to their potential to substitute or complement transition metals in catalysis. While a few main-group molecular centres were shown to activate dihydrogen via the oxidative addition process, catalytic hydrogenation using these species has remained challenging. Here we report the synthesis, isolation and full characterization of the geometrically constrained phosphenium cation with the 2,6-bis(o-carborano)pyridine pincer-type ligand. Notably, this cation can activate the H-H bond by oxidative addition to a single PIII cationic centre, producing a dihydrophosphonium cation. This phosphenium cation is also capable of catalysing hydrogenation reactions of C=C double bonds and fused aromatic systems, making it a main-group compound that can both activate H2 at a single molecular main-group centre and be used for catalytic hydrogenation. This finding shows the potential of main-group compounds, in particular phosphorus-based compounds, to serve as metallomimetic hydrogenation catalysts.

First-Principles Insights into the Mechanism of CO2 Hydrogenation Reactions by Fe-PNP Pincer Complex.

Using the state of the art theoretical methods, we have provided a comprehensive mechanistic understanding of the CO2 hydrogenation into HCOOH, H2CO, and CH3OH by 2,6-bis(diisopropylphosphinomethyl)pyridine (PNP)-ligated Fe pincer complex, featuring one CO and two H as co-ligands. For the computational investigation, a verified structural model containing methyl groups in place of the experimental isopropyl groups was used. Three catalytic conversions involving hydrogenation of CO2 into formic acid (HCOOH), HCOOH into formaldehyde and methanol were studied in different solvent medium. Our modelled complex appears to be a viable base-free catalyst for the conversion of CO2 into HCOOH and HCOOH into H2CO, based on the free energy profiles, which show apparent activation energy barriers of 16.28 kcal/mol and 23.63 kcal/mol for the CO2 to HCOOH and HCOOH to H2CO conversion, respectively. However, the computed results show that, due to the huge energy span of H2CO to CH3OH conversion, complete hydrogenation of CO2 into methanol could not occur under moderate conditions. Morpholine co-catalyst, which can lower the hydrogenation barrier by taking part in a simultaneous H-atom donation-acceptance process, could have assisted in completing this step.