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Chemical reactivity and sorption in zeolites are coupled to confinement and—to a lesser extent—to the acid strength of Brønsted acid sites (BAS). In presence of water the zeolite Brønsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Brønsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1–2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents (n > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape. The structure of water around Brønsted acid sites in zeolites is shown to influence their catalytic activity. Here the authors shed light on confinement effects in different pores zeolites/water interfaces acidic strength by means of ab-initio molecular dynamics and enhanced sampling metadynamics techniques. [ABSTRACT FROM AUTHOR]

Concrete is a very common material consisting of a mixture of aggregates (sand, gravel, crashed rock) and paste (cement, water and additives). The paste component, made up mainly of cement and water, degrades with time. Despite this shortcoming, research toward the next-generation cement and concrete materials has intensified in the past 10–15 years. Self-healing cementitious materials, in particular, are a research area that has attracted a great deal of attention. A number of novel formulations have demonstrated an increase in mechanical and chemical stability with respect to conventional Portland cement, through the addition of inorganic, organic, and even biological additives. This review reports on the latest developments in cement research related to the synthesis of cement and concrete materials with autogenous healing and/or self-healing capability. These include geopolymers, engineered cementitious materials, bacterial cement composites, microencapsulated self-healing materials, self-healing assisted by shape-memory alloys, and polymer–cement composites. This work describes the performance of each cementitious material and the mechanism responsible for healing, including a section on atomistic simulations and modeling of cementitious materials. A detailed understanding of various cement technologies with autogenous healing and self-healing properties, including their strengths and weaknesses, is critical to determine the areas where new development is needed to enable novel, energy-efficient, and environmentally responsible cement and concrete solutions. To this end, molecular simulations can play a significant role and have already demonstrated promise in achieving an atomic level view of interactions between cementitious materials and other add-on compounds, such as carbon nanotubes or polymers for enhanced reinforcement or autonomous healing properties. Next-generation construction materials are led by self-healing cement and concrete. With a wide range of autonomous healing strategies based on smart polymers and alloys, biotechnology, and molecular modeling, advanced cementitious materials are becoming part of our daily lives. This work represents a comprehensive review on progress, challenges, and opportunities in the development of these materials for infrastructure and beyond. [ABSTRACT FROM AUTHOR]

The composition of the reaction medium near photoactive catalytic sites can be inferred from the solvatochromism of the absorption and emission spectra of the wetted sites, which depend on the polarizability of the fluid. In brief, solvatochromism measures the interaction of the dipole moments of the ground and excited states with the electric field imposed by the solvent shell: a field, which does not relax on the time scale of the absorption or emission events. To establish the utility of the technique for inorganic catalysts that operate in complex reaction media, such as encountered in the upgrading of biogenic fuels, we have measured the solvatochromism of a common, structural feature of metal oxide catalysts, mono-oxide or dioxide of a transition metal prepared by incorporating the OM or O2M moiety into the framework of a polyhedral oligomeric silsesquioxane (POSS). In toluene, cyclohexene, chloroform and tetrahydrofuran, POSS-ligated oxometalates exhibit strong ligand-to-metal charge-transfer bands in their UV-visible absorption and emission spectra. From the solvatochromism of the chromophores dissolved in toluene-chloroform mixtures we inferred an unexpectedly strong, preferential solvation of the chromophore even when all three components (oxometalate and the two solvents) were highly miscible. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Transition metal modified Rh-catalysts can be used for converting syngas (CO + H) into C oxygenates. It has been found that Mn has a favorable effect in the selectivity towards oxygenates, while addition of Ir to the binary Rh-Mn catalysts significantly increases the space-time-yield (STY) of C oxygenates, mainly by formyl formation at the early stages of conversion. Quantum mechanical calculations used to investigate the distribution of promoter sites in Rh-rich nanoparticles show that moderately high Mn/Ir ratios result in particles with all 3 metals on the surface, and that Ir atoms act as co-adsorption sinks of CO and H leading to HCO in the initial stages. [ABSTRACT FROM AUTHOR]

We investigate the solvation structure of aqueous potassium ions, using a combination of electronic structure calculations, statistical mechanical simulations with a derived polarizable empirical potential and experimental measurement of the extended X-ray absorption fine structure (EXAFS) spectra. The potassium K-edge (at 3,608 eV) EXAFS spectra were acquired on the bending magnet of sector 20 at the Advanced Photon Source, at ambient conditions and for the concentrations of 1 and 4 m KCl. We focus on the coordination distances and the degree of disorder of the first hydration shell as determined by electronic structure calculations, molecular dynamics simulations and experimental measurement. Finally, we characterize the changes of the structure in the first hydration shell with increasing temperature as predicted by molecular simulation [ABSTRACT FROM AUTHOR]