Reaction Mechanism Of Hydrogenation Research Articles

Theory study on catalytic hydrogenation of CO2 to formic acid over Si, N‐doped modified graphene quantum dots supported single atom Fe

AbstractExploring suitable catalysts to catalyze the chemical transformation of CO2 molecules is essential to reduce CO2 levels. In this article, catalyst models of Fe‐C4, Fe‐N4, and Fe‐Si4 were constructed using the density functional theory (DFT) calculations, and the reaction mechanisms of CO2 hydrogenation over these three catalysts were calculated and analyzed. The results showed that the doping of N atoms lowered the energy barrier of the second hydrogenation step compared with that of Fe‐C4 catalyst, while the doping of Si atoms changed the electron distribution on the surface of the catalyst and formed new Si adsorption sites. And the Fe‐Si4 catalyst had a stronger ability to activate CO2 molecules as well as stronger catalytic performance compared with the Fe‐C4 and Fe‐N4 catalysts, which was mainly attributed to the synergistic catalytic effect between the doped Si atoms and the Fe metal atom.

Theoretical study on CO production mechanism from CO2 reduction on Cu–catalyst surface with different oxidation states

The rational design of copper (Cu)-based catalysts with different oxidation states is essential to achieve highly selective and efficient CO2 electroreduction. However, the effect of different oxide states of Cu-based catalysts has rarely been studied. Herein, the reaction mechanism of CO2 hydrogenation into CO on Cu-based catalysts with different oxidation states, such as Cu(111), Cu2O(111) and CuO(111), was studied using the density functional theory. The most favored pathway for CO production and the rate-controlling step on the three catalyst models were determined. The results show that, Cu2O (111) shows the best catalytic activity among the three catalysts due to the lowest activation barrier. The electronic structure analysis shows that Cu2O has the proper electronic structure to activate CO2 which is further reduced to CO. This work provides an important insight on the effect of oxidation state of Cu-based catalysts on the reduction of CO2 to CO.

First-principles study of CO2 hydrogenation to methanol on In-Ru alloys: Revealing the influence of surface In/Ru ratio on reaction mechanism and catalyst performance

Designing high-performance catalyst is vital in the field of CO2 methanolization. In this study, two In3Ru surfaces (In3Ru_i and In3Ru_r) were employed as computational models and the density functional theory was applied to study the influence of surface In/Ru ratio on their surface morphologies, reaction mechanisms and catalysis performance for methanol synthesis. Surface characterization reveals that In3Ru_i is higher in surface In/Ru ratio than In3Ru_r, and such difference facilitates CO2 adsorption on In3Ru_r. Being different in surface In/Ru ratio, two surfaces exhibit distinct variations in the reaction mechanism of methanol formation. For In3Ru_i, the “Formate” pathway dominates the first CO2 activation step which leads to methanol production. On the other hand, In3Ru_r prefers the “reverse water-gas shift” pathway (RWGS) in the initial step of CO2 activation, but this mechanism is unable to generate CH3OH due to the kinetic limitation of CO* hydrogenation. Based on the microkinetic modeling, In3Ru_i is superior in both CO2 production rate and CH3OH selectivity than the other one, suggesting higher surface In/Ru ratio benefits methanol formation, which complies well with the experiment. Overall, our study offers a new perspective with respect to how surface morphology of the bimetallic catalyst influences the reaction mechanisms of CO2 hydrogenation.

Investigating the catalytic activity of Mgn (n = 4–8) clusters for the hydrogen evolution reaction using density functional theory

AbstractTo efficiently desorb H2, pure Mgn (n = 4–8) clusters were chosen for the hydrogen evolution reaction with H2O. At the PBE0/def2‐TZVP level and the PBE0‐D3/def2‐TZVP level, the lowest energy structures of Mgn (n = 4–8) clusters and the most stable structures of Mgn@H2O (n = 4–8) complexes were searched in the local region. The transition state was predicted, and then the hydrogen evolution reaction channel was obtained by using the intrinsic reaction coordinate (IRC) to confirm the transition state. To better analyze the hydrogen reaction mechanism, the character of Mgn@H2O (n = 4–8) complexes and MgnO (n = 4–8) clusters, as well as the atomic charge change trend, were investigated using interaction region indicator function analysis (IRI) and natural population analysis (NPA). The reaction effect of Mg4 cluster and H2O is the worst. The energy barrier does, however, progressively lower as the cluster atom count rises, improving the reaction effect.

Theoretical Insights into the Reaction Mechanism of Direct Hydrogenation of Maleic Anhydride to Produce 1,4-Butanediol on the Cu–ZnO Surface

Theoretical Insights into the Reaction Mechanism of Direct Hydrogenation of Maleic Anhydride to Produce 1,4-Butanediol on the Cu–ZnO Surface

Multiscale Investigation of the Mechanism and Selectivity of CO2 Hydrogenation over Rh(111).

CO2 hydrogenation over Rh catalysts comprises multiple reaction pathways, presenting a wide range of possible intermediates and end products, with selectivity toward either CO or methane being of particular interest. We investigate in detail the reaction mechanism of CO2 hydrogenation to the single-carbon (C1) products on the Rh(111) facet by performing periodic density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations, which account for the adsorbate interactions through a cluster expansion approach. We observe that Rh readily facilitates the dissociation of hydrogen, thus contributing to the subsequent hydrogenation processes. The reverse water-gas shift (RWGS) reaction occurs via three different reaction pathways, with CO hydrogenation to the COH intermediate being a key step for CO2 methanation. The effects of temperature, pressure, and the composition ratio of the gas reactant feed are considered. Temperature plays a pivotal role in determining the surface coverage and adsorbate composition, with competitive adsorption between CO and H species influencing the product distribution. The observed adlayer configurations indicate that the adsorbed CO species are separated by adsorbed H atoms, with a high ratio of H to CO coverage on the Rh(111) surface being essential to promote CO2 methanation.

Hierarchical porous Pt/Hβ catalyst with controllable acidity for efficient hydrogenation of naphthalene

A series of hierarchical porous Pt/Hβ catalysts with different mesopores-acidity were synthesized without using secondary template. The pore structures of the catalysts were altered by constructing mesopores through alkali etching to reduce the mass transfer resistance. Moreover, the metal-support interaction (MSI) was optimized to improve the dispersion of the Pt metal particles. The smaller metal species could expose more active sites during the hydrogenation process, along with a more pronounced electron-deficiency effect. Furthermore, the effect of acid sites distribution on the hydrogenation reaction path and product distribution were also investigated. The strong acid-mesopores-metal factor (X) was defined to describe the relationship with the yield of decalin. The yield of decalin was well correlated with a high R2 value of 0.97. The Pt/Hβ-75 catalyst showed the best synergistic effect between acidity, mesopore and Pt species, leading to the optimal naphthalene conversion (96.7%) and higher yield of decalin (76.7%) at a relatively low temperature, which exhibited a better activity than other catalysts reported in literature for hydrogenation of naphthalene at a similar reaction condition. Besides, the hydrogenation reaction mechanism of naphthalene over Pt supported catalysts was further investigated by density functional theory, and the effect of Pt NPs size on the catalytic reaction process and activity was preliminarily revealed.

Characteristics and catalytic behavior of Ru-Sn bimetallic catalysts for TMCB hydrogenation to CBDO.

A series of Ru-Sn/γ-Al2O3 catalysts were prepared by the immersion method for tetramethylcyclobutane-1,3-dione (TMCB) hydrogenation to prepare 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO). The effect of the preparation method and reaction technology on TMCB hydrogenation activity was discussed. The catalysts were analyzed by means of XRD, BET, H2-TPR, XPS, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and it was found that the synthesized Ru was distributed on the surface of the carrier in the form of nanoparticles, showing a good catalytic effect. The results showed that when Ru loading was fixed at 5%, Sn was used as an auxiliary agent, and Ru/Sn = 1 : 1 as the catalyst, the reaction conditions were 120 °C, 4 MPa, and 1 h, and the catalytic hydrogenation effect of TMCB on CBDO was the best. The selectivity was as high as 73.5%, and the cis-trans ratio was 1.11. It may be the strong interaction between Ru and Sn under this ratio condition, which leads to the largest number of nano-active centers of elemental Ru. Finally, the reaction mechanism of TMCB hydrogenation to CBDO is discussed.

In situ DRIFTS and DFT study of CO2 hydrogenation over the In2O3 catalyst.

The pressure dependent reaction mechanism of CO2 hydrogenation over In2O3 was investigated. CO2 hydrogenation on In2O3 can produce methanol only at high pressure, while the atmospheric pressure operation leads to the formation of CO. The conversion from HCOO* to H3CO* is accelerated at high pressure, leading to the formation of methanol with the formate route (CO2* → HCOO* → H3CO* → H3COH).

Phenol hydrogenation over H-MFI zeolite encapsulated platinum nanocluster catalyst.

The development of catalysts with high activity and selectivity is of paramount importance for the industrial conversion of biomass. One crucial reaction in this process is the hydrogenation of phenol, a key component of phenolic resins in biomass, into cyclohexanone and cyclohexanol. In this study, density functional theory (DFT) calculations were utilized to examine phenol hydrogenation reaction mechanisms over a platinum (Pt) nanocluster encapsulated in the H-MFI zeolite, e.g., Pt6@H-MFI. Various anchoring positions of the Pt6 nanocluster on the H-MFI framework and the adsorption configurations of phenol on the Pt6@H-MFI were firstly determined. DFT calculation results demonstrate that, compared to the Pt surface, the Pt6@H-MFI catalyst shows high hydrogenation activity with a notable selectivity towards cyclohexanol. The pathway leading to the formation of cyclohexanol is both kinetically and thermodynamically more favorable over the pathway leading to the formation of cyclohexanone. The present work offers significant contributions to the strategic development of catalysts consisting of metal nanoclusters encapsulated within zeolite frameworks.

Enhancing CO2 Hydrogenation Using a Heterogeneous Bimetal NiAl-Deposited Metal-Organic Framework NU-1000: Insights from First-Principles Calculations.

The hydrogenation of CO2 to high-value-added liquid fuels is crucial for greenhouse gas emission reduction and optimal utilization of carbon resources. Developing supported heterogeneous catalysts is a key strategy in this context, as they offer well-defined active sites for in-depth mechanistic studies and improved catalyst design. Here, we conducted extensive first-principles calculations to systematically explore the reaction mechanisms for CO2 hydrogenation on a heterogeneous bimetal NiAl-deposited metal-organic framework (MOF) NU-1000 and its catalytic performance as atomically dispersed catalysts for CO2 hydrogenation to formic acid (HCOOH), formaldehyde (H2CO), and methanol (CH3OH). The present results reveal that the presence of the NiAl-oxo cluster deposited on NU-1000 efficiently activates H2, and the facile heterolysis of H2 on Ni and adjacent O sites serves as a precursor to the hydrogenation of CO2 into various C1 products HCOOH, H2CO, and CH3OH. Generally, H2 activation is the rate-determining step in the entire CO2 hydrogenation process, the corresponding relatively low free energy barriers range from 14.5 to 15.9 kcal/mol, and the desorption of products on NiAl-deposited NU-1000 is relatively facile. Although the Al atom does not directly participate in the reaction, its presence provides exposed oxygen sites that facilitate the heterolytic cleavage of H2 and the hydrogenation of C1 intermediates, which plays an important role in enhancing the catalytic activity of the Ni site. The present study demonstrates that the catalytic performance of NU-1000 can be finely tuned by depositing heterometal-oxo clusters, and the porous MOF should be an attractive platform for the construction of atomically dispersed catalysts.

Low-temperature hydrogenation of butanal proceeding via keto-enol tautomerization

Hydrogenation of carbonyl-containing compounds to alcohols is a crucial step in various technological processes, including reversible green hydrogen storage. Activation of the highly stable C=O bond, however, is highly challenging and typically proceeds under harsh reaction conditions. Recent theoretical predictions on low-barrier hydrogenation pathway of carbonyl compounds suggest that this step proceeding over a high activation barrier can be overcome in an alternative low barrier process, which comprises two steps: keto-enol tautomerization followed by hydrogenation of the C=C bond in the newly formed enol. The major challenge of this predicted pathway is the low stability of enol species, which would readily convert to ketone if not intentionally stabilized.In this study, we performed atomistic-level investigation on keto-enol tautomerization and low-temperature hydrogenation of butanal over well-defined Pd(111) model catalyst by combination of surface sensitive infrared reflection absorption spectroscopy (IRAS) and molecular beam techniques. Specifically we show that different types of enol species can be formed on the H-containing Pd(111) surface, whose appearance and abundance strongly dependent on the surface temperature. Importantly, the evolution of the partly hydrogenated product of butanal – C-butoxy species attached to Pd via C atom – was detected already at cryogenic temperatures, which points to a possibility of low temperature hydrogenation. A very clear correlation between the abundance of the enol species and the C-butoxy hydrogenated product was detected: the growing concentration of enol species was found to result in the formation of the C-butoxy product. In contrast, strong decrease in the abundance of enol adsorbates lead to full vanishing of the hydrogenation product C-butoxy. With this, we experimentally show a strong link between the population of the enol species and hydrogenation of butanal at cryogenic temperatures. Finally, we discuss the chemical nature of different enol species, which appear to be stabilized on the surface in different ways via hydrogen bonding, and propose the reaction mechanisms of low-barrier butanal hydrogenation that are consistent with all experimental observations.Obtained atomistic-level insights in low-barrier hydrogenation of carbonyl compounds provide important information on the elementary reaction steps of this potentially highly promising class of reactions for green hydrogen storage. Related phenomena can be employed for controlling keto-enol tautomerization and enol stabilization via mutual lateral interactions on functionalized catalytic surfaces for the broad range of aldehydes and ketones to enable their low-barrier hydrogenation.

Interfacial synergistic catalysis of Cun single-cluster catalysts anchored on α-Al2O3(0001) for promoting hydrogenation of CO2 to methanol

The size-selected copper single-cluster catalysts(SCCs) play a crucial role in catalyzing of CO2 hydrogenation. However, nature of size effect and hydrogenation mechanism is still unclear. Here, Density functional theory(DFT) calculations were performed to investigate activation and reaction mechanism of CO2 hydrogenation to methanol over copper single-clusters catalyst anchored on α-Al2O3(0001). Our results show that Cun(n = 1–9)/Al2O3 catalysts significantly promote activation of CO2 in a bent configuration due to the synergistic interaction associated with Cun-Al2O3(0001) interfacial site. Bader charge analysis suggested electron transfer occurring from Cun-Al2O3(0001) interface to CO2, leading to negatively charged CO2. We find descriptors of deviation of CO2 bonds length and bonds angle, d-band center of Cun(n = 1–9) cluster that can well descript for determining activation degree of CO2. Especially, the Cu5/α-Al2O3(0001) has the best activity for CO2 hydrogenation among them. Furthermore, reaction mechanism of CO2 hydrogenation at Cu5/Al2O3 interface have been explored. Methanol synthesis takes formate route and direct CO bond cleavage route competitive with rate-dominant step of HCOO* and HO* hydrogenation, respectively. While CO-hydrogenation produced by RWGS route is not feasible because of high activation barrier of formed CO intermediate(1.95 eV). This study will provide insight into designing and application of ultrahigh-performance Cu-based single-cluster catalysts for CO2 hydrogenation.

Hard kinetic modeling of the industrial reaction of hydrogenation of soybean oil optimized by heuristic problem-solving techniques

Partial hydrogenation of vegetable oils is an important process for generating fats with particular characteristics. In this study, the hard kinetic modeling of the nickel-catalyzed soybean oil hydrogenation reaction was optimized by three algorithms considering five reaction mechanisms. In three mechanisms, it was considered to have a formation of half-hydrogenated intermediate compounds, and two did not consider this possibility. The Particle Swarm Optimization (PSO) algorithm allowed for achieving lower errors between the experimental and modeled values compared to the Simulated Annealing (SA) and Sequential Simplex (SP) algorithms for the five evaluated reaction mechanisms. In addition, the optimized apparent rate constants values indicated that in these reactional conditions, the industrial reaction mechanism of hydrogenation follows some preferred reaction pathways, such as a preliminary isomerization of cis to trans fatty acids to be then hydrogenated to other fatty acids less unsaturated. These optimization algorithms proved to be efficient tools for investigating the kinetics of the partial hydrogenation reaction of soybean oil and offer promising perspectives for other industrial processes.

CO2 hydrogenation using MOFs encapsulated PdAg nano-catalysts for formate production

Catalytic hydrogenation of CO2 for the production of formic acid/formate, a valuable commodity and renewable hydrogen carrier, is a promising strategy to achieve an economic andsustainable CO2-mediated hydrogen energy cycle. The rational design of highly active and stable heterogeneous catalysts for CO2 hydrogenation in gas–liquid-solid phase still remains challenging. In this work, we report a series of dual-function catalysts namely PdAg@MIL-101-PEI, where PdAg alloy nanoparticles (NPs) for hydrogen activation and dissociation are encapsulated into MIL-101 supports tethered with CO2 adsorption agent polyethyleneimine (PEI). The optimal PdAg@MIL-101-PEI catalyst displays exceptional performance for CO2 hydrogenation, affording a high turnover number (TON) of 4968 at 120 °C under 8 MPa in 2 h. Thermodynamic and kinetic studies illustrate that Ag incorporation and PEI functionalization dramatically reduce the activation energy barrier of PdAg@MIL-101-PEI catalyst for CO2 hydrogenation. Furthermore, the optimal PdAg@MIL-101-PEI catalyst demonstrates outstanding structural stability and reusability over multiple catalytic cycles. We also propose a reaction mechanism for CO2 hydrogenation through in situ DRIFTS study.

Mechanistic study of CO2 hydrogenation to C1 products on molybdenum step site

The catalytic conversion of CO2 into fuel is an ideal solution to the energy and environment crisis in the context of carbon neutrality, while the design of high-performance catalysts is the key. Unfortunately, the complicated reaction mechanism makes the rational catalyst design with simulations challenging. Herein, we employed density functional theory (DFT) calculations to systematically analyze the complex reaction mechanism of CO2 hydrogenation to C1 products on the stepped metal active sites using molybdenum as the model catalyst, while the established mean-field microkinetic model (MKM) identified the more favorable production of carbon monoxide (CO) than formic acid (HCOOH), methanol (CH3OH) and methane (CH4). Our results not only provide the energetics of all elementary steps during CO2 hydrogenation to C1 products on metallic Mo but also propose the directions to steering the activity and selectivity of Mo in CO2 conversion.

Hydrogen storage properties and reaction mechanism of the Mg-Li-Na-Al ternary hydride system

This research uses the ball milling technique to study the preparation of the MgH2-LiAlH4-NaAlH4 with a molar ratio of 4:1:1 ternary-hydride system. The hydrogen storage behavior and reaction mechanisms have been carefully explored. The result demonstrates a reduction in the onset decomposition temperature of the 4MgH2-LiAlH4-NaAlH4 ternary composite compared to the as-milled MgH2, LiAlH4, and NaAlH4 components. Four substantial dehydrogenation processes, corresponding to the decomposition of LiAlH4, NaAlH4, and MgH2 were detected in a system with a total hydrogen capacity of 8.4 wt%. The onset decomposition temperature of LiAlH4 in this system is around 110 °C, while NaAlH4-relevant decomposition began releasing hydrogen at 153 °C, approximately 52 °C lower than the as-milled NaAlH4. Meanwhile, the destabilized system modifies the reaction route of MgH2, where MgH2-relevant decomposition begins around 270 °C, 82 °C lower than the as-milled MgH2. The apparent activation energy, Ea, for the decomposition of MgH2 in the composite was lowered to 124 kJ/mol based on the Kissinger analysis. It is believed that the enhancement of the dehydrogenation properties was attributed to the formation of intermediate compounds, including Li-Mg, Mg-Al and Li-Al alloys, upon dehydrogenation, which improved the thermodynamics properties by altering the de/rehydrogenation pathway.

An investigation of the catalytic performance of Fe–Mn/Al2O3 nanocatalyst for light olefins production using RSM method and kinetic study

AbstractThe Fe–Mn/Al2O3 nanocatalysts were manufactured via the sol‐gel procedure and were evaluated for Fischer–Tropsch synthesis. The impact of different operational parameters of T, P, and H2/CO ratio on the catalytic performance for light olefins production has been studied using response surface methodology (RSM). Furthermore, the optimization and modeling of selected responses were also carried out via RSM and historical data design type of DOE; and the best process conditions were found to be T = 365°C, H2/CO = 1.50, and P = 1.50 bar. The mechanism of CO hydrogenation reaction over the Fe–Mn/Al2O3 nanocatalysts was also investigated using the non‐linear regression method. It was found that the mechanism of the CO hydrogenation reaction is based on the Eley–Rideal type and the best‐fitted equation for this mechanism was found to be −rCO = KPCOPH2/1+αPCO. The obtained value of activation energy (85.20 kJ mol−1) affirmed the absence of internal mass transfer limitations. The physico‐chemical properties of the samples were investigated by various techniques of XRD, BET, TPR, TGA, and DSC.

Hydrogenation of Carbon Dioxide to Methanol over Non-Noble Catalysts: A State-of-the-Art Review

The malignant environmental changes caused by the ever-increasing amount of anthropogenic CO2 emissions have been particularly prominent in recent years. To achieve carbon mitigation and carbon neutrality, CO2 hydrogenation to methanol is regarded as a promising and sustainable route. However, the development of catalysts with exceptional performance and the establishment of a clear structure–activity relationship remain formidable challenges. Considering the lack of a state-of-the-art review on the catalytic progress of CO2 hydrogenation to methanol over non-noble catalysts, we conducted a detailed review in terms of the thermodynamic analysis, catalytic development, and reaction mechanism. In this work, we mainly reviewed the latest research progress of different catalysts including Cu-based, In2O3-based, bimetallic, solid solution, and other catalysts. Meanwhile, we summarized the effects of the support materials, promoters, and preparation methods on the catalytic performance. In addition, we also summarized the possible reaction mechanisms of direct hydrogenation of CO2 to methanol. Overall, this work would be of importance for the researchers to obtain a comprehensive understanding of the design and development of efficient catalysts for CO2 hydrogenation to methanol.

Selective hydrogenation of crotonaldehyde over Ir/TiO2 catalysts: Unraveling the metal-support interface related reaction mechanism

For the supported catalysts for the selective hydrogenation of α, β - unsaturated aldehyde with H2, tailoring of metal - support interfacial effect to improve reaction performance is a significant but challenging subject. In this work, we regulated both the size regimes of the Ir deposits (single atom, nanocluster and nanoparticle) and the crystal plane of anatase TiO2 (TiO2(101), TiO2(100) and TiO2(001)) so as to alter the Ir-TiOx interfacial properties, in order to unravel reaction mechanism of selective hydrogenation of crotonaldehyde over the Ir/TiO2 catalysts. Both the activity and selectivity to crotyl alcohol increased as the Ir size grew from single atom to nanoparticle, ascribed to high Ir0 content, high concentration of surface defects and prominent H-spillover effect on the Ir nanoparticles. Moreover, the in situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations demonstrated that an end-on CO adsorption mode for crotonaldehyde molecule was favored at the Ir-TiOx interface particularly at high H coverage, which thus facilitated the hydrogenation of CO bond to form crotyl alcohol. Moreover, the highest reactivity of the Ir nanoparticles was evidenced by the lowest reaction barrier. These results explicitly demonstrate that larger metal nanoparticles and adsorption geometry of the reactant at the metal - support interface are vital for improved catalytic performance, which would shed light on the ingenious catalyst design.