Role of Clay Minerals in Oil-Forming Reactions

Mineral-catalyzed decarboxylation reactions are important in both crude oil formation and, increasingly, biofuel production. In this study we examined decarboxylation reactions of a model fatty acid, propionic acid, C2H5COOH, to an alkane, C2H6, in a model of pyrophillite with an isomorphic substitution of aluminum in the tetrahedral layer. We model a postulated reaction mechanism (Almon, W. R.; Johns, W. D. 7th International Meeting on Organic Geochemistry 1975, Vol. 7) to ascertain the role of Al substitution and a counterion in decarboxylation reactions. We employ a periodic cell, planewave, ab initio DFT computation to examine the total energies and the frontier orbitals of different model sets, including the effects of charge on the reaction, the effect of Al substitution, and the role of Na counterions. The results show that an uncharged system with a sodium counterion is most feasible for catalyzing the decarboxylation reaction in an Al-substituted pyrophillite and, also, that analysis of the orbitals is a better indicator of a reaction than charge alone

DFT+U investigation of the catalytic properties of ferruginous clay

The formation of fossil oil within clay minerals i.e., mineral-catalyzed decarboxylation, is a mechanism awaiting a thorough chemical explanation. To contribute to such an explanation, the study presented here investigates this mechanism at the level of first-principles, electronic structure computations, employing density functional theory (DFT plus Hubbard-U), planewaves, pseudopotentials, and periodic cells of two types of ferruginous clay minerals, specifically two types of nontronite [Fe2 (Si,Al)4O10(OH)2]. The formation of the fossil oil is modeled as a decarboxylation pathway, converting the fatty acid propionic acid, C2H5COOH to an alkane, C2H6 and the intermediate stages along this conversion pathway are represented by five configurations of interlayer species within the clay minerals. In this study, we test both the effect of the presence of iron on the theoretical stages of decarboxylation, together with the effect of two different density functionals: with and without strong correlations of the d-orbital electrons of iron. We have found that inclusion of the d-orbital electron correlations in the guise of a Hubbard parameter results in the introduction of three new intermediate configurations (one of which is potentially a new transition state), alters the location of the occupied Fermi level orbitals, and changes the band gaps of the clay mineral/interlayer species composites, all of which serves to inform the chemical interpretation of mineral-catalyzed decarboxylation

An ab initio characterization of the electronic structure of LaCo x Fe 1- x O 3 for x ≤ 0.5

Solid oxide fuel cells are an important class of energy conversion devices in the search to replace fossil fuels. Their electrodes’ materials mostly belong to the perovskite family, which in their versatile composition are numerous; here we focus on the perovskite LaCoxFe1−xO3 and examine its electronic structure for x ≤ 0.5 using density functional theory with a plane wave basis and pseudopotentials. The resulting lattice parameters show good agreement with experiment, and the Mulliken and Bader charges show that iron and cobalt mostly remain as Fe3+ and Co3+ throughout an increasing Co:Fe ratio. The charge and spin magnitudes of oxygen ions is determined by their local, cation neighbors with the largest charge and spin magnitudes found on oxygen ions sandwiched between two Fe ions. Density of states and partial density of states analyses reveal that increasing the ratio of Co to Fe in oxygen stoichiometric materials decreases their relative, semi‐conducting nature toward insulating, by virtue of the decrease in the number of (conducting) O–Fe–O bonds and the increase in (insulating) O–Co–O bonds. The appearance of an intermediate spin state of Co and examination of its PDOS confirms the hypothesis that Co–O, d–p hybridization is a necessary factor for its occurrence

An ab initio characterization of the electronic structure of LaCo x_{x} Fe 1−x_{1- x} O 3_{3} for x ≤ 0.5 (Phys. Status Solidi B 9/2016)

Simple perovskite-type materials have the general chemical formula ABO3. While that already offers a broad variability in choosing A and B, additional tuning of the properties can be achieved by partial substitution of the A and/or B site. As such, this class of materials has found widespread use in chemical and electrochemical applications, e.g. in catalytic conversions, electrolysers and fuel cells. Calculating the changes in lattice parameters and electronic structure (oxidation and spin states, density of states) caused by the A and/or B site substitutions, deepens the understanding and enables prediction of the associated experimental trends, thereby increasing the potential applicability of these perovskite-type materials. Geatches et al. (pp. 1673–1687) have focused on the elaboration of the electronic structure of LaCoxFe1-xO3 with varying ratios of Fe/Co, revealing that increasing the ratio of Co to Fe changes their rather semiconducting nature toward insulating. This behaviour can be related to the decrease in the number of (conducting) O–Fe–O bonds and the increase in (insulating) O–Co–O bonds

Understanding cationic polymer adsorption on mineral surfaces: kaolinite in cement aggregates

We present a joint experimental and theoretical investigation into the adsorption of polycationic quaternary ammonium polymers on the clay mineral kaolinite. Within the cement and concrete manufacturing industries such polymers are used to improve the final product by inerting the adsorption capacity of the clay minerals for more expensive additives. The adsorption of the presently used polymer (FL22) was compared with both a similar variant, but without a hydroxyl group (Fl22mod) and uncharged polyvinyl alcohol (PVA). Experimental results show that adsorption of FL22 is higher than that of FL22mod at both pH 6 and at pH > 10 and that the adsorption of PVA is the highest. Theoretical density functional theory (DFT) results and simplified models consisting of the basal surfaces of kaolinite, with monomers of FL22, FL22mod and PVA gave monomer coverage per unit surface area of kaolinite, a comparison of the configurations of the relaxed models, formation energies and Mulliken charges. These results show that the polycationic polymers interact with the basal surfaces of kaolinite electrostatically, explaining the high affinity of these polymers for kaolinite surfaces in the experimental results. The hydroxyl groups of FL22 and PVA form hydrogen bonds with the basal surfaces of kaolinite in conditions of pH 6. The joint experimental and theoretical results suggest that, due to the presence of the hydroxyl group, the conformation of FL22 changes under pH, where at neutral pH it lies relatively flat to the kaolinite surfaces, but at higher pH, conformational changes of the polymer occur, thereby increasing the adsorbed quantity of FL2

Insights into the Behaviour of Biomolecules on the Early Earth: The Concentration of Aspartate by Layered Double Hydroxide Minerals

The role of mineral surfaces in concentrating and facilitating the polymerisation of simple protobiomolecules during the Hadean and Archean has been the subject of much research in order to constrain the conditions that may have led to the origin of life on early Earth. Here we examine the adsorption of the amino acid aspartate on layered double hydroxide minerals, and use a combined computer simulation – experimental spectroscopy approach to gain insight into the resulting structures of the host-aspartate material. We show that the uptake of aspartate occurs in alkaline solution by anion exchange of the dianion form of aspartate, rather than by surface adsorption. Anion exchange only occurs at values of pH where a significant population of aspartate has the amino group deprotonated, and is then highly efficient up to the mineral anion exchange capacity

Methylene Blue Adsorption on the Basal Surfaces of Kaolinite: Structure and Thermodynamics from Quantum and Classical Molecular Simulation

Abstract—Organic dyes such as methylene blue (MB) are often used in the characterization of clays and related minerals, but details of the adsorption mechanisms of such dyes are only partially understood from spectroscopic data, which indicate the presence of monomers, dimers, and higher aggregates for varying mineral surfaces. A combination of quantum (density functional theory) and classical molecular simulation methods was used to provide molecular detail of such adsorption processes, specifically the adsorption of MB onto kaolinite basal surfaces. Slab models with vacuum-terminated surfaces were used to obtain detailed structural properties and binding energies at both levels of theory, while classical molecular dynamics simulations of aqueous pores were used to characterize MB adsorption at infinite dilution and at higher concentration in which MB dimers and one-dimensional chains formed. Results for the neutral MB molecules are compared with those for the corresponding cation. Simulations of the aqueous pore indicate preferred adsorption on the hydrophobic siloxane surface, while charge-balancing chloride ions adsorb at the aluminol surface. At infinite dilution and in the gas-phase models, MB adsorbs with its primary molecular plane parallel to the siloxane surface to enhance hydrophobic interactions. Sandwiched dimers and chains are oriented perpendicular to the surface to facilitate the strong hydrophobic intermolecular interactions. Compared with quantum results, the hybrid force field predicts a weaker MB adsorptio

Methylene Blue Adsorption on the Basal Surfaces of Kaolinite: Structure and Thermodynamics from Quantum and Classical Molecular Simulation

Abstract—Organic dyes such as methylene blue (MB) are often used in the characterization of clays and related minerals, but details of the adsorption mechanisms of such dyes are only partially understood from spectroscopic data, which indicate the presence of monomers, dimers, and higher aggregates for varying mineral surfaces. A combination of quantum (density functional theory) and classical molecular simulation methods was used to provide molecular detail of such adsorption processes, specifically the adsorption of MB onto kaolinite basal surfaces. Slab models with vacuum-terminated surfaces were used to obtain detailed structural properties and binding energies at both levels of theory, while classical molecular dynamics simulations of aqueous pores were used to characterize MB adsorption at infinite dilution and at higher concentration in which MB dimers and one-dimensional chains formed. Results for the neutral MB molecules are compared with those for the corresponding cation. Simulations of the aqueous pore indicate preferred adsorption on the hydrophobic siloxane surface, while charge-balancing chloride ions adsorb at the aluminol surface. At infinite dilution and in the gas-phase models, MB adsorbs with its primary molecular plane parallel to the siloxane surface to enhance hydrophobic interactions. Sandwiched dimers and chains are oriented perpendicular to the surface to facilitate the strong hydrophobic intermolecular interactions. Compared with quantum results, the hybrid force field predicts a weaker MB adsorptio