Hydrogen Transfer Process Research Articles

Effect of ZnCl2-activated biochar on catalytic pyrolysis of mixed waste plastics for producing aromatic-enriched oil

ZnCl2-activated biochar produced by one-step (impregnated by a 40% ZnCl2 solution, defined as Zn/C-I) and two-step (impregnated by a 40% ZnCl2 solution and microemulsion, defined as Zn/C-II and Zn/C-III, respectively) methods was used to catalyze the pyrolysis of mixed waste plastics (polyethylene, polyethylene, and polystyrene) to comparatively study their catalytic effect on aromatic-enriched oil production. The catalytic mechanism was discussed. The results show that ZnCl2-activated biochar showed high catalytic selectivity to aromatics during the pyrolysis of plastics at 500 °C, and the content of aromatics was increased to 47.5, 46.8, and 42.4% when respectively catalyzed by Zn/C-I, Zn/C-II, and Zn/C-III. Two-ring aromatics were significantly enriched, which accounted for 90.7, 73.1, and 87.7% of the aromatics in Zn/C-I, Zn/C-II, and Zn/C-III catalytic pyrolysis oils. 1,3-Diphenylpropane was the major component of the oils, and its proportion was 19.4, 11.5, and 15.9% in Zn/C-I, Zn/C-II, and Zn/C-III catalytic pyrolysis oils, respectively. The introduced Zn species could increase the surface acidity by forming Lewis acid sites (Zn-L), which increased aromatic yields by promoting the Diels–Alder reaction, hydrogen transfer, and dehydrogenation processes. Zn-L also promoted the condensation reaction of aromatics. Compared with Zn/C-I, Zn/C-III treated by ZnCl2 microemulsion could reduce 41.8% of coke on the catalysts owing to its larger pore size, while maintaining a relatively high oil quality.

Laser ionization of solid RDX: a density functional theory study

Structural changes induced via ionization in an RDX lattice have been studied by using optimized [(RDX)2]0 conformers comprising eight combinations of four RDX isomers using DFT. Structures, dissociation enthalpy, and free energies of the resulting [(RDX)2]·+ clusters are calculated. The gas-phase and medium polarizable continuum model (PCM) calculations of the most stable [(RDX)2]·+ cluster produced similar structural results. Electron removal caused 75% of the [(RDX)2]·+ conformers to be unstable in their neutral isomeric composition and orientation. Charge distributions and structural factors indicate that [(RDX)2]·+ are in the general form RDX·+·RDX. Ionization causes charge polarization, hydrogen transfer, N-N dissociation, and assisted HONO formation in solid RDX. The assisted HONO formation occurs via and suggests hydrogen mobility within [(RDX)2]·+, causing a stabilization by a minimum of 114 kJ/mol more than the other conformers. The RDX conformational identity is a determining factor in the emerging dissociation pathways. The energy costs of ion-neutral dissociation are comparable to the hydrogen transfer and NO2 loss processes. Ionization of the RDX surface is expected to produce NO2 and HONO precursors of the NO+ ion observed previously.

Mechanistic Insights into the Nickel-Catalyzed Cross-Coupling Reaction of Benzaldehyde with Benzyl Alcohol via C–H Activation: A Theoretical Investigation

With the aid of density functional theory (DFT) calculations, mechanistic investigations have been carried out for the nickel-catalyzed dehydrogenative cross-coupling reaction of benzaldehyde with benzyl alcohol in the presence of N-heterocyclic carbene (NHC) ligand. The overall Ni(0)/Ni(II) catalytic cycle consists of four basic steps: ligand exchange, oxidative addition, hydrogen transfer, and reductive elimination. Considerable interests are paid on detecting the transition state of the rate-determining step, with particular emphasis on the structural and electronic properties, together with clarifying the important roles of external oxidant and hydrogen acceptor. The hydrogen transfer process in the oxidative addition step is rate-determining in the whole catalytic cycle, which is accomplished by C-Ha (active Ha) activation without generating the high energy nickel hydride intermediate. Such process could be understood as the direct hydrogen transfer, instead of general concerted oxidative addition to low valent transition metal. The analysis of the bond distances, electrondistributions, and orbital interactions highlights the direct hydrogen transfer mechanism. Furthermore, by exploring the influences from the electronic effect of different substrates on the reaction energy barriers, the a,a,a-trifluoroacetophenone could accelerate the direct hydrogen transfer with low activate energy.

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

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

Selective Transfer Hydrogenation of Furfural into Furfuryl Alcohol on Zr-Containing Catalysts Using Lower Alcohols as Hydrogen Donors.

A series of zirconium-based catalysts were prepared for the selective transfer hydrogenation of biomass-derived furfural (FFR) into furfuryl alcohol with lower alcohols as hydrogen sources. The sample structures were clearly characterized using various methods, such as X-ray powder diffraction, thermogravimetric analysis, scanning electron microscope, NH3-temperature-programmed desorption (TPD), CO2-TPD, and nitrogen physisorption. Excellent furfuryl alcohol yield of 98.9 mol % was achieved over Zr(OH)4 using 2-propanol as a hydrogen donor at 447 K. The poisoning experiments indicated that basic centers displayed pronounced effect for FFR transfer hydrogenation. Moderate monoclinic phase content in ZrO2-x enhanced the conversion rate and furfuryl alcohol selectivity, whereas acid–basic site density ratio had slight influence on FFR conversion. Besides, Zr(OH)4 revealed good performance and stability after being repeated four times. The possible mechanism for this transfer hydrogenation process over Zr(OH)4 catalyst with 2-propanol as the hydrogen source was proposed.

Furfural to Furfuryl Alcohol: Computational Study of the Hydrogen Transfer on Lewis Acidic BEA Zeolites and Effects of Cation Exchange and Tetravalent Metal Substitution

The hydrogen transfer of furfural to furfuryl alcohol with i-propanol as the hydrogen source over cation-exchanged Lewis acidic BEA zeolite has been investigated by means of density functional calculations. The reaction proceeds in three steps. First the O-H bond of i-propanol is broken to form a propoxide intermediate. After that, the furylmethoxy intermediate is formed via hydrogen transfer process, and finally furylmethoxy abstracts the proton to form the furfuryl alcohol product. The second step is rate-determining by requiring the highest activation energy (23.8 kcal/mol) if the reaction takes place on Li-Sn-BEA zeolite. We find that the catalytic activity of various cation-exchanged Sn-BEA zeolites is in the order Li-Sn-BEA > Na-Sn-BEA > K-Sn-BEA. The lower activation energy for Li-Sn-BEA compared to Na-Sn-BEA and K-Sn-BEA can be explained by the larger charge transfer from the carbonyl bond to the catalyst, leading to its activation and to the attraction of the hydrogen being transferred. The larger charge transfer in turn is due to the smaller gap between the energies of furfural HOMO and the zeolite LUMO in Li-Sn-BEA, compared to both Na-Sn-BEA and K-Sn-BEA. In a similar way, we also compare the catalytic activity of tetravalent metal centers (Sn, Zr, and Hf) substituted into BEA and find in the order Zr ≥ Hf > Sn, based on activation energies. Finally we investigate statistically which property of the reactants is a suitable descriptor for an approximative prediction of the reaction rate in order to be able to quickly screen promising catalytic materials for this reaction.

An interactive chemical enhancement of CO2 capture in the MEA/PZ/AMP/DEA binary solutions

Chemical absorption is an effective method for CO2 capture. Due to their high absorption/desorption efficiency, amines have been used in single or blended form. Compared with the single ones, blended solvents usually show better absorption/desorption performance because of their interactive enhancement effect, however the mechanism is still unclear. In this study, the chemical interactive reaction is assumed to be one of the key factors for the enhancement. Based on this, the reactions of CO2 absorption in binary amine solvents (the binary mixtures of monoethanolamine (MEA)/piperazine (PZ)/2-amino-2-methyl-1-propanol (AMP)/diethanolamine (DEA)) have been investigated. The ab initio method with Density Functional Theory (DFT) is adopted in the simulations. Compared with other amines, numerical results showed that PZ presents the lowest forward energy barrier and the second lowest backward energy barrier in zwitterion formation. During the intermolecular hydrogen transfer processes, PZ shows a significant enhancement effect on MEA/DEA/AMP in the interactive reactions. For MEA, it shows an enhancing effect on AMP but hindering effect on PZ and DEA. Moreover, it was found that the MEA+COO− based reactions have good absorption property while the AMP+COO− based ones have good desorption performance. These findings reveal the interactive effect between different amines during the interactive reactions, which may provide theoretical instructions for solvent screening of blended solutions.

Porous Zr‐Bibenzyldiphosphonate Nanohybrid with Extra Hydroxy Species for Enhancive Upgrading of Biomass‐Based Levulinates

AbstractLewis acidic and/or basic sites are typically clarified to play a positive role in the cascade hydrogen transfer and lactonization process, while the influence of Brønsted acid species on the catalyst activity and stability is rarely studied. In this work, a new acid‐base bifunctional hybrid BPhZr with augmented average pore diameter was prepared from the assembly of ([1, 1’‐biphenyl]‐4,4’‐diylbis(methylene))diphosphonic acid with zirconium via a facile solvothermal method. The effects of reaction parameters, substrate scope, and metal ion type were investigated. Besides the promotional effect of moderate Lewis acid/base sites and improved texture properties, the presence of Brønsted acidic species (e. g., –OH) in BPhZr was demonstrated to positively promote the synthesis of γ‐valerolactone (GVL; ca. 95% yield) from levulinates via cascade transfer hydrogenation and lactonization. In comparison with previously reported catalysts, the BPhZr hybrid exhibited a superior activity in terms of TOF (3.2 h−1) and activation energy (21 kJ/mol) for the reaction. Moreover, BPhZr was found to be highly stable and recyclable in five consecutive cycles, showing no significant decrease in GVL yield and selectivity.

(Invited) Chiral-at-Metal Fullerene Hybrids for Catalysis

Fullerenes have found their main application in organic photovoltaic devices thanks to their ability to give rise a high efficient photo-induced electron transfer process and to their behaviour as n-type charge carriers.[1] On the other hand, in face of the great interest for carbon based materials in catalysis, the use of fullerenes in this field has been completely neglected as probably due to the difficult to endow fullerene cages with suitable active sites. In this regards, as a first step to address this issue, we have reported recently a wide range of asymmetric metal mediated or organocatalytic methodologies for a precise stereocontrol in the fullerenes functionalizations.[2]Herein, we present the enantioselective catalytic synthesis of fullerene hybrids where C60 is endowed with metal atoms such us iridium, rhodium and ruthenium with high enantiomeric excesses. A complete control on the stereochemistry of all the asymmetric centers was achieved, even on the stereogenic metal center.[3]The catalytic and photo-electrocatalytic properties of these new fullerene derivatives will be discussed together with their ability to transfer chirality in hydrogen transfer processes.[4][1] (a) B. C. Thompson, J. M. J. Fréchet, Angew. Chem. Int. Ed. 2008, 47, 58; (b) J. L. Delgado, P.-A. Bouit, S. Filippone, M. A. Herranz, N. Martin, Chem.Commun. 2010, 46, 4853. [2] (a) Maroto, E. E.; Izquierdo, M.; Reboredo, S.; Marco-Martínez, J.; Filippone, S.; Martín, N. Acc. Chem. Res. 2014, 47, 2660. (b) Filippone, S.; Maroto, E. E.; Martín-Domenech, A.; Suárez, M.; Martín, N. Nat. Chem. 2009, 1, 578. (c) Maroto, E. E.; Mateos, J.; Garcia-Borràs, M.; Osuna, S.; Filippone, S.; Herranz, M. Á.; Murata, Y.; Solà, M.; Martín, N. J. Am. Chem. Soc. 2015, 137, 1190. (d) Marco-Martínez, J.; Reboredo, S.; Izquierdo, M.; Marcos, V.; López, J. L.; Filippone, S.; Martín, N. J. Am. Chem. Soc. 2014, 136, 2897. (e) Marco-Martínez, J.; Marcos, V.; Reboredo, S.; Filippone, S.; Martín, N. Angew. Chem. Int. Ed. 2013, 52, 5115. [3] J. Marco-Martínez, S. Vidal, I. Fernández, S. Filippone and N. Martín, Angew. Chem. Int. Ed., 2017, 56, 2136. [4] R. Maria Giron, J. Marco-Martinez, S. Bellani, A. Insuasty, H. Comas Rojas, G. Tullii, M. R. Antognazza, S. Filippone and N. Martin, J. Mater. Chem. A, 2016, 4, 14284. Figure 1

Hantzsch ester triggered metal-free cascade approach to isoindolinones

Disclosed herein is an expedient synthesis of biologically important isoindolinone derivatives from reactions of 2-formylbenzoic acids with various amines. This method operates via a deliberately designed catalyst-free tandem reductive amination/cyclization cascade event triggered by a transfer hydrogenation process with easily available Hantzsch ester as the organic hydride source. The ease of operation, mild reaction conditions, facile accessibility of the starting materials, and easy scalability of the current method distinguish it from the other precedent protocols, thus enable it a practical approach to the syntheses of valuable isoindolinone-incorporated drugs.

Quantum Chemical Calculations of Amine-Catalyzed Polymerization of Silanol

Because of the technical importance of organosilicon materials, insight into the related synthetic processes is significantly essential. In this paper, the amine-catalyzed polymerization of silanol has been investigated by the density functional theory (DFT) method. Our data have shown that amines can catalytically promote the hydrogen transfer process by substantially reducing the energy barrier. The activation barrier via hydrogen transfer with catalysis is 38.32 kJ/mol, much lower than that of catalysis-free process (120.88 kJ/mol). The lower energy barrier is in agreement with the much more intense polymerization of silanols with amine catalysts. Based on the above results, amines and other catalysts capable of assisting hydrogen transfer are expected to be used as catalysts for silanol polymerization.

Copper promoter effect on acid–base and redox sites of Fe/Al2O3 catalysts and their role in ethanol–acetone mixture conversion

The redox site properties favours the hydride transfer.

Kinetic Characteristics of Hydrogen Transfer Through Palladium-Modified Membrane

The paper deals with hydrogen transfer through Pd-23%Ag alloy membrane, the surface of which is modified by the electrolytic deposition of highly dispersed palladium. The dependence between the density of hydrogen flow and its excess pressure on the input surface of membrane is well approximated by the first-order curve. This fact indicates that the process of hydrogen permeability is defined by its dissociation on the input surface. Activation energy of this process is 47.9 kJ/mol which considerably exceeds that of the process of hydrogen transfer through palladium (22–30 kJ/mol). This confirms the fact that the chemisorption is a rate-controlling step of the hydrogen transfer through membrane.

Thermodynamic Analysis of Two Stage Metal Hydride Based Hydrogen Compressor

A pair of high pressure metal hydrides La0.9Ce0.1Ni5Hx and La0.8Ce0.2Ni5Hx were used for the thermodynamic analysis of two stage metal hydride based hydrogen compressor (MHHC). The PCIs of these metal hydrides were measured at different temperatures and thermodynamic properties were estimated using van’t Hoff plots. Later, the performance of MHHC was determined based on the driving pressure differential, and the rate of hydrogen transfer between coupled metal hydride beds using PCIs and thermodynamic property data. In addition, the actual variation in pressure difference during hydrogen transfer processes of MHHC was studied by plotting thermodynamic cycle with pressure variations.

Mononuclear thorium halide clusters ThX4 (X = F, Cl): gas-phase hydrolysis reactions.

Density functional theory (DFT) calculations have been performed to explore the gas-phase hydrolysis reaction of mononuclear thorium halide clusters ThX4 (X = F, Cl). We have found that the hydrolysis of ThCl4 is easier than that of ThF4. Furthermore, their hydrolysis reactions favor pathways of direct dehydration of Th(OH)4 instead of further hydrolysis of ThOX2. There are some differences between the hydrolysis of ThCl4 and that of MCl4 (M = Ti, Zr and Hf). The X-HY (X = F, Cl; Y = F, Cl and OH) hydrogen bonds play an important role in the hydrogen transfer process of the hydrolysis reaction. The differences in the steric effects and bonding may be important factors that are related to the disparities in the hydrolysis of the above-mentioned metal halides.

A computational study of energy barriers of structural transformations and hydrogen transfer in boehmite

The crystal structure of boehmite (γ-AlOOH) contains a large amount of hydrogen bonds that are joined into chains by sharing hydrogen-bond donor and acceptor oxygen atoms. The hydrogen ions in the hydrogen-bond chains are highly mobile and have complicated structural characterizations, and this feature may well be utilized for proton-conducting applications, but the mechanism is unknown without the dynamic parameters of the hydrogen-transfer processes. We propose probable hydrogen-transfer paths and compute their energy barriers using density functional theory with van der Waals density functionals, on both perfect and vacancy-containing crystal structures. It is revealed that the energy barriers are generally below 21 kJ mol−1 in a perfect crystal, and 14 kJ mol−1 in a vacancy-containing structure. The low energy barriers are indicators of the high proton conductivity of boehmite even at room temperature.

Efficient and Adaptive Methods for Computing Accurate Potential Surfaces for Quantum Nuclear Effects: Applications to Hydrogen-Transfer Reactions.

We present two sampling measures to gauge critical regions of potential energy surfaces. These sampling measures employ (a) the instantaneous quantum wavepacket density, an approximation to the (b) potential surface, its (c) gradients, and (d) a Shannon information theory based expression that estimates the local entropy associated with the quantum wavepacket. These four criteria together enable a directed sampling of potential surfaces that appears to correctly describe the local oscillation frequencies, or the local Nyquist frequency, of a potential surface. The sampling functions are then utilized to derive a tessellation scheme that discretizes the multidimensional space to enable efficient sampling of potential surfaces. The sampled potential surface is then combined with four different interpolation procedures, namely, (a) local Hermite curve interpolation, (b) low-pass filtered Lagrange interpolation, (c) the monomial symmetrization approximation (MSA) developed by Bowman and co-workers, and (d) a modified Shepard algorithm. The sampling procedure and the fitting schemes are used to compute (a) potential surfaces in highly anharmonic hydrogen-bonded systems and (b) study hydrogen-transfer reactions in biogenic volatile organic compounds (isoprene) where the transferring hydrogen atom is found to demonstrate critical quantum nuclear effects. In the case of isoprene, the algorithm discussed here is used to derive multidimensional potential surfaces along a hydrogen-transfer reaction path to gauge the effect of quantum-nuclear degrees of freedom on the hydrogen-transfer process. Based on the decreased computational effort, facilitated by the optimal sampling of the potential surfaces through the use of sampling functions discussed here, and the accuracy of the associated potential surfaces, we believe the method will find great utility in the study of quantum nuclear dynamics problems, of which application to hydrogen-transfer reactions and hydrogen-bonded systems is demonstrated here.

Thermodynamic simulation of hydrogen based solid sorption heat transformer

The hydrogen absorption and desorption pressure-concentration isotherms (PCI) of La0.9Ce0.1Ni5 and LaNi4.6Al0.4 alloys are measured by static and dynamic method. The hydrogen absorption and desorption kinetics of the alloys also measured. The measured properties are used to study the performance of hydrogen based solid sorption heat transformer (MHHT). The thermodynamic simulation of MHHT is conducted using statically and dynamically measured PCI and thermodynamic properties. Due to variation in statically and dynamically measured metal hydride properties, significant variations in coefficient of performance (COP) and heat transformation capacity of MHHT are observed. In case of thermodynamic analysis using dynamically measured properties the heat transformation capacity and COP are decreased by 42.6% and 22.2% respectively, compared to statically measured data. This is due to the decrease in amount of hydrogen transmission and pressure differential between paired metal hydride reactors, and increase in reaction enthalpies. Later, the actual thermodynamic cycle for MHHT is constructed by considering the variation in pressure during hydrogen transfer processes between the metal hydride reactors.

Ag-Cu bimetallic nanocatalysts for p-nitrophenol reduction using a green hydrogen source

The quest for new nanomaterials that can efficiently catalyze reduction reactions using green transfer hydrogenation process is an important current area of research. Conventionally, NaBH4, which is both expensive and toxic, has been the reducing agent for the model catalytic reduction of p-nitrophenol (Nip) to p-aminophenol (AP). The present communication studies the application of Ag-Cu bimetallic nanoparticles (Ag-Cu BNPs) stabilized by poly-vinylpyrollidone (PVP) as catalysts for this reaction with glycerol as the green hydrogen source. Bimetallic nanoparticles with different compositions were prepared using three different ratios (1:1, 2:1 and 4:1) of precursor silver and copper salts in appropriate amount of ethylene glycol and PVP. While the XRD patterns of these nanomaterials clearly show the formation of both pure silver and copper phases, the analysis of the data obtained from their LSPR and SEM EDX elemental mapping point to the formation of phase-separated nanostructures with adjacent Ag and Cu domains. The catalytic activity of these nanomaterials with glycerol and NaBH4 as the reducing agents are investigated. Catalytic activities of these bimetallic nanoparticles in terms of turnover frequency changes with composition variation. Synergistic catalytic activity with respect to composition was observed whether NaBH4 or glycerol was used as the reductant.

Nonadiabatic dynamics simulation of photoisomerization mechanism of the second stablest isomer of N-salicilydenemethylfurylamine

The photoisomerization processes of the second stablest isomer in the aromatic Schiff base, N-salicilydenemethylfurylamine, in the gas phase have been studied by static electronic structure calculations and surface-hopping dynamics simulations based on the Zhu-Nakamura theory. Various stable structures are obtained in the optimization because of different orientations of methyl-furyl part with respect to the salicylaldimine part and different orientations of hydroxy group with respect to the benzene ring. Upon photoexcitation into the first excited state, bond isomerization in the salicylaldimine part is completely suppressed until the strong excited-state hydrogen bond is broken. The decay pathway involves two excited-state minima, one in cis-enol form and the other in cis-keto form. After the excited-state proton transfer, twists of bonds lead to a conical intersection between the ground and excited states. After internal conversion around a conical intersection, the molecule is stabilized in cis- or trans-keto form. If the reverse hydrogen transfer process occurs in the ground state, the molecule will finally end up in the cis-enol region. The cis-keto and trans-keto isomers are observed as photoproducts. According to our full-dimensional nonadiabatic dynamics simulations, we find the excited-state intramolecular proton transfer and torsions of three single bonds in the chain to be responsible for photoisomerization of the second stablest isomer of N-salicilydenemethylfurylamine.