Substituted Heterocycles As New Candidates for Liquid Organic Hydrogen Carriers: in Silico Design from DFT Calculations
Total Page：16
File Type：pdf, Size：1020Kb
international journal of hydrogen energy xxx (xxxx) xxx Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he Substituted heterocycles as new candidates for liquid organic hydrogen carriers: In silico design from DFT calculations * Rodolfo Izquierdo a, ,Nestor Cubillan b, Mayamaru Guerra c, Merlı´n Rosales d a Laboratorio de Quı´mica Teorica y Computacional, Departamento de Quı´mica, Facultad Experimental de Ciencias, Universidad Del Zulia, Maracaibo, Venezuela b Programa de Quı´mica, Facultad de Ciencias Basicas, Universidad Del Atlantico, Barranquilla, Colombia c Laboratorio de Optica y Procesamiento de Imagenes, Facultad de Ciencias Basicas, Universidad Tecnologica de Bolı´var, Turbaco, Colombia d Laboratorio de Quı´mica Inorganica, Departamento de Quı´mica, Facultad Experimental de Ciencias, Universidad Del Zulia, Maracaibo, Venezuela highlights graphical abstract DFT calculations for hydrogena- tion/dehydrogenation of heterocy- cles was examined. Thermodynamic calculations with M06HF are consistent with those of the G3(MP2) one. The thermodynamic parameters for reactions of N-andS-hetero- clycles are discussed. Pyrrole and thiophene could be key structures for the develop- ment of new LOHCs. It is the first report on the poten- tiality of allyl- and thienyl-pyrrole as LOHCs. article info abstract Article history: A new set of compounds based on N- and S-heterocycles were investigated through Density Received 15 December 2020 Functional Theory (DFT) for their use as liquid organic hydrogen carriers (LOHCs). The Received in revised form hydrogenated forms of these compounds could release hydrogen within the most impor- 6 February 2021 tant technical requirements in mobile and stationary applications. In this work, the po- Accepted 24 February 2021 tential of the 1H-pyrrole/tetrahydro-1H-pyrrole and thiophene/tetrahydrothiophene pairs Available online xxx as possible leader structures to synthesize more sustainable LOHCs from costless oil- refining and oil-hydrotreating by-products is shown. According to DFT-M06-HF results, * Corresponding author. E-mail address: [email protected] (R. Izquierdo). https://doi.org/10.1016/j.ijhydene.2021.02.201 0360-3199/© 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Izquierdo R et al., Substituted heterocycles as new candidates for liquid organic hydrogen carriers: In silico design from DFT calculations, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2021.02.201 2 international journal of hydrogen energy xxx (xxxx) xxx the 3-allyl-1H-pyrrole/3-allyl-tetrahydro-1H-pyrrole pair presented an adequate theoretical Keywords: hydrogen storage capacity (3.6 %wt H) and a high theoretical dehydrogenation equilibrium Liquid Organic hydrogen carriers yields (% ε ¼ 67.8%) at 453 K. Therefore, this pair is recommended for hydrogen storage (LOHCs) d stationary applications. On the other hand, the 2-(thiophen-2-yl)-1H-pyrrole/2-(2,3- Heterocycles dihydrothiophen-2-yl)tetrahydropyrrole pair proved to be suitable for both mobile and Pyrrole stationary applications; the storage capacity of this pair was 3.9 %wt H and the theoretical Thiophene dehydrogenation equilibrium yields at 453 K (% ε ¼ 28.1%) was considered moderate. Density functional theory (DFT) d © 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. M06-HF The LOHCs basic theory indicates that these substances Introduction can be found in two chemical states. The first is an energy-rich 2n state (ERh), in which a LOHC stores hydrogen atoms (where In the continuing transition to use renewable energy, the n is an integer number) through an exothermic reaction. The intermittent energy sources (solar and wind power) will need second state corresponds to an energy-lean state (ELd) where new methods to store and transport energy in order to balance n the hydrogen-loaded LOHC releases H2 molecules through the world supply and demand [1,2]. Hydrogen is widely an endothermic reaction. Subsequently, the hydrogen pro- considered an ideal energy carrier from the sustainability duced by ERh-ELd interchange is used for energy production, point of view due to the following reasons: (i) ideally, it could and the LOHC is regenerated [20e22]. be produced entirely from renewable energy sources [3,4], (ii) The LOHCs can be easily integrated to applications with the hydrogen energy cycle is based on non-toxic species portable power (on-board), stationary power (off-board), and e interconversion: water, oxygen, and hydrogen [5 7] and (iii) energy transportation [18,21,23,24]. According to Mu¨ ller et al. molecular hydrogen is the lightest molecule (molecular [25], the LOHCs must meet six ideal requirements in order to ¼ weight (MW) 2.016) with the highest known energy content be used in the hydrogen distribution alongside the develop- D ¼ À1 ( rH298:15K 241.8 kJ mol , reaction 1) [2,8]. ment for on-board applications [25]: (i) non-toxicity, the acceptable toxicity limit is the octane lethal dose þ / À H2 O2 H2O (1) ¼ 1 (LD50rat,oral 1297 mg kg )[17], (ii) easiness to handle solid or liquid with low vapor pressure (below 0.1 bar), (iii) low prices In this sense, energy suppliers need different storage or desirably obtained from by-products or residues of indus- technologies. Currently, hydrogen storage technologies (HSTs) trial chemical processes (ecofriendly LOHCs) [26], (iv) high are identified as a key challenge and the largest barrier to- gravimetric storage density, which is conventionally wards the hydrogen economy [8e15]. HSTs include both measured in theoretical [4,27,28] and experimental [29,30] physical (compression/liquefaction) and chemical storages investigations from the theoretical hydrogen weight per- [16]. Among the chemical storage technologies, the liquid centage (% wt H) for completed hydrogenation reaction of ELd organic hydrogen carriers (LOHCs) are highlighted by loading to ERh, (substances with % wt H superior to 5.5 are considered and unloading considerable amounts of hydrogen (H )ina 2 efficient hydrogen container [31]; however, currently, a lower sustainable cyclical process (Scheme 1). The LOHCs are liquids minimum storage capacity of 4.5% wt H has been established or solids of low melting point that can be reversibly hydro- special on-board applications [32]), (v) thermally stable sub- genated and dehydrogenated under moderate reaction con- stance, i.e. low melting points (mp < 273 K) and high boiling ditions in presence of a catalyst [17e19]. points (bp), and (vi) hydrogenation as well as dehydrogena- tion can be performed at reasonable technical conditions; hydrogenation reaction must be selective, meanwhile dehy- drogenation reaction must occur easily and reversibly. The main strategy to achieve this goal is based on reducing the temperature of dehydrogenation by modification of the LOHC molecule to reduce the enthalpy of the reaction [11]. One starting point for modeling hydrogen storage consists of carrying out the theoretical equilibrium calculations at 453 K. Jessop et al. [33] suggested that this temperature should be limited for operating conditions onboard a fuel cell vehicle and stationary applications such as stand-alone energy sys- Scheme 1 e Illustration of the LOHC concept according to tems, back-up systems [17]. Aakko-Saksa et al. [22]: (a) LOHC is hydrogenated to a state Finally, in addition to these requirements, a seventh aspect ERh, (b) hydrogenated LOHC is transported to end-user (c) should be included: there must be at least one efficient cata- H2 is released and used as useful energy (d) LOHC is lyst for the hydrogenation/dehydrogenation of the ELd/ERh dehydrogenated to a state ELd and dehydrogenated form is pair [18,34]. In fact, several researchers have studied the transported to the hydrogenation site. possibility to use catalytic systems for the reversible Please cite this article as: Izquierdo R et al., Substituted heterocycles as new candidates for liquid organic hydrogen carriers: In silico design from DFT calculations, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2021.02.201 international journal of hydrogen energy xxx (xxxx) xxx 3 hydrogenation/dehydrogenation reactions employing organic Administration (FDA), N- and S-heterocycles occupy an hydrogen carriers. Recently, Shimbayashi and Fujita [18] important place as raw materials for drug development reviewed a series of works on the use of catalysts for this [47,48], therefore their toxicities must be manageable. Addi- purpose, which are promising to application to hydrogen tionally, N- and S-heterocycles are by-products from oil- storage. refining [49,50] and this fact represents a challenge for There are different materials commonly considered as hydrotreating [51]. Consequently, from the green chemistry LOHCs or pairs ELd/ERh. Initially oil-derivatives cyclic hy- perspective, the use of by-products as LOHCs are economi- drocarbons were the simplest candidates. Two emblematic cally attractive and sustainable [52]. Among the N-heterocy- examples are the pairs toluene/methylcyclohexane [35]and cles compounds previously studied, the following ELd/ERh dibenzyltoluene/perhydrodibenzyltoluene [36], which pre- pairs can be featured: 1-phenylpyrazole/tetrahydropyrazole sented stationary and energy transport applications with [53], 4-aminopyridine/4-aminopiperidine [33], quinoline/ high technology readiness levels (TRL) [37]. Despite their 1,2,3,4-tetrahydroquinoline