RESUMEN
Absorption in amine solutions is a well-established advanced technology for CO2 capture. However, the fundamental aspects of the chemical reactions occurring in solution still appear to be unclear. Our previous investigation of aqueous monoethanolamine (MEA) and 2-amino-2-methyl-1,3-propanediol (AMPD), based on ab initio molecular dynamics simulations aided with metadynamics, provided new insights into the reaction mechanisms leading to CO2 capture and release with carbamate formation and dissociation. In particular, the role of water-strongly underestimated in previous computational studies-was established as essential in determining the development of all relevant reactions. In this article, we apply the same simulation protocol to other relevant primary amines, namely, a sterically hindered amine (2-amino-2-methyl-1-propanol (AMP)) and an aromatic amine (benzylamine (BZA)). We also discuss the case of CO2 capture with the formation of bicarbonate. New information is thus obtained that extends our understanding. However, quantitative predictions obtained using molecular simulations suffer from several methodological problems, and comparison among different chemical species is especially demanding. We clarify these problems further with a discussion of previous attempts to explain the different behaviors of AMP and MEA using other types of models and computations.
RESUMEN
We combine classical empirical potentials and density functional theory (DFT) calculations to characterize the catalyst/electrode interface of a promising device for artificial photosynthesis. This system consists of inorganic Ru-polyoxometalate (Ru-POM) molecules that are supported by a graphitic substrate functionalized with organic dendrimers. The experimental atomic-scale characterization of the active interface under working conditions is hampered by the complexity of its structure, composition, as well as by the presence of the electrolyte or solvent. We provide a detailed atomistic model of the electrode/catalyst interface and show that the catalyst anchoring is remarkably dependent on water solvation. A tight host-guest binding geometry between the surface dendrimers and the Ru-POM catalyst is predicted under vacuum conditions. The solvent destabilizes this geometry, leads to unfolding of the dendrimers and to their flattening on the graphitic surface. The Ru-POM catalyst binds to this organic interlayer through a stable electrostatic link between one POM termination and the charged terminations of the dendrimers. The calculated dynamics and mobility of the Ru-POM catalyst at the electrode surface are in fair agreement with the available high-resolution transmission electron microscopy data. In addition, we demonstrate that the high thermodynamic water-oxidation efficiency of the Ru-POM catalyst is not affected by the binding to the electrode, thus rationalizing the similar electrochemical performances measured for homogeneous and heterogeneous Ru-POM catalysts.
RESUMEN
This work assesses the predictive power and capabilities of classical interatomic potentials for describing the atomistic structure of a fully inorganic water-oxidation catalyst in the gas phase and in solution. We address a Ru-polyoxometalate molecule (Ru-POM) that is presently one of the most promising catalysts for water oxidation due to its efficiency and stability under reaction conditions. The Ru-POM molecule is modeled with two interatomic potentials, the rigid ion model and the shell model potentials, which are used to perform molecular dynamics simulations. The predictions of these two approaches are discussed and compared to the available ab-initio data. These results allow us to establish the suitable level of theory to model complex heterogeneous interfaces between the Ru-POM and electrodes in solution.
RESUMEN
The synthesis of relevant renewable aromatics from bio-based furfural derivatives and cheap alkenes is carried out by using a Diels-Alder/aromatization sequence. The prediction and the control of the ortho/meta selectivity in the Diels-Alder step is an important issue to pave the way to a wide range of renewable aromatics, but it remains a challenging task. A combined experimental-theoretical approach reveals that, as a general trend, ortho and meta cycloadducts are the kinetic and thermodynamic products, respectively. The nature of substituents, both on the dienes and dienophiles, significantly impacts the feasibility of the reaction, through a modulation on the nucleo- and electrophilicity of the reagents, as well as the ortho/meta ratio. We show that the ortho/meta selectivity at the reaction equilibrium stems from a subtle interplay between charge interactions, favoring the ortho products, and steric interactions, favoring the meta isomers. This work also points towards a path to optimize the aromatization step.
RESUMEN
The production of amine intermediates from biomass is capturing increasing attention. Herein, a simple and efficient preparation of l furan-derived amines was developed [e.g., 1-(furan-2-yl)-4-methylpentan-2-amine] with high yield (up to 95 %) from (E)-1-(furan-2-yl)-5-methylhex-1-en-3-one. The catalyst used was Ru/C, and it was recyclable up to the fourth cycle. To further realize cost-efficiency, a one-reactor tandem concept was attempted. To this aim direct reaction from furfural was investigated. A high yield (74 %) towards 1-(furan-2-yl)-4-methylpentan-2-amine could be achieved starting directly from furfural in the presence of methyl isobutyl ketone, NH3 , H2 , and Ru/C catalyst.
RESUMEN
We report here that C-C coupling in tertiary amines for the synthesis of long chain and hindered amines might be efficiently performed over Pt and Pd catalysts. The mechanism study confirms similarity with the Guerbet reaction through dehydrogenation of the alkyl group and subsequent attack of the α-carbon atom by an alkyl group of another molecule. Finally, secondary amines and tertiary amines with longer alkyl chains are formed.
RESUMEN
Aqueous monoethanolamine (MEA) solution is commonly used for post-combustion carbon capture via chemical absorption. Extensive research has been carried out to characterize both uptake and release of carbon dioxide (CO2), with the aim of improving process performance. However, an intensive research is still needed on fundamental aspects of the key chemical reactions, to achieve a comprehensive understanding of the cyclic process at the microscopic level and a quantitative assessment. We present several ab initio simulations of MEA solutions at a concentration of 30 wtâ¯%-the current standard in the industry-and study the dynamics of key multistep chemical reactions, using the metadynamics technique. Pathways for the entire cycle are investigated and characterized in terms of related free-energy and enthalpy barriers, and of the accompanying variations in both structural and electronic properties. The results of this study lead us to propose, among competing processes, an unforeseen scenario in which the zwitterion acts as sn intermediate not only of CO2 uptake, in the form of carbamate, but also of its release. Rate-limiting steps are the formation of the zwitterion for the former and MEAH(+) deprotonation for the latter. Water is shown to play a multifaceted role, which is crucial in determining the development and the energetics of each step of the reactions. The level of comprehension here achieved for MEA should help defining a strategy for solvent optimization.
RESUMEN
Chemical absorption in amine aqueous solutions is a widespread technology for postcombustion carbon capture, and a large effort is ongoing to improve their performance. Characterization of the "reactant" and "product" solutions at the microscopic level is highly desirable for process optimization. Recently X-ray scattering experiments and "in situ" infrared spectroscopy have been applied to this aim, but a complete and convincing interpretation is missing. We present large-scale ab initio molecular dynamics simulations of monoethanolamine solutions at experimental concentration and temperature and analyze how structural and vibrational properties change after carbamate formation. An exhaustive account of the experimental data is obtained. Fingerprints of the reaction products and specific interactions are unravelled. Hydration effects are specific to each component of the solution and are essential for a correct assignment of the experimental data.