Dehydration of various alcohols over H-ZSM-5 is studied using density functional theory. The activation energies are shown to scale linearly with the van der Waals interaction with the zeolite framework. The van der Waals interaction itself is shown to be a simple function of the number of atoms of the involved alcohol. Consequently, activation barriers for the dehydration of primary alcohols are now easily derived directly from the number of atoms of these alcohols through the obtained scaling relations.

Methylation of aromatic molecules in H-SSZ-13 is studied from benzene to hexamethylbenzene via all possible isomers. Both methylations with methanol (MeOH) and dimethyl ether (DME) are investigated via both stepwise and concerted mechanisms. Calculations are carried out using periodic density functional theory corrected by high-level DLPNO-CCSD­(T) calculations on cluster models. While we find little selectivity between the methylations of different aromatics, our calculations indicate that isomerization via methyl shifts between different isomers is a viable mechanism with barriers comparable to methylation. The generally observed trend is that MeOH methylation barriers are smaller than those using DME, with the difference between MeOH and DME increasing with the level of methylation of the aromatic molecule.

The side-chain mechanism of the methanol-to-olefins process over the H-SSZ-13 acidic zeolite was investigated using periodic density functional theory with corrections from highly accurate ab intio calculations on large cluster models.

The influence of the confinement imposed by eight different zeotypes on the formation of the alkoxides of 13 primary alcohols is studied using dispersion corrected density functional theory calculations with the PBE-D3 functional. Adsorption energies of the alcohols are computed along with barriers for formation of the alkoxides, which is the first step of the stepwise dehydration mechanism. We find that variations in the adsorption and transition state energies are largely governed by van der Waals interactions between substrates and the zeolite framework. Trends between different reactants, on the other hand, are largely due to the size of the molecules, which can be described quantitatively by the number of atoms constituting them. We find that the stabilization of adsorbates is largest for frameworks that are neither too small, leading to repulsive interaction, nor too spacious leading only to weak interaction.

Chemical reactions and phase stabilities in the Si− Te system at high pressures were explored using in situ angledispersive synchrotron powder diffraction in a large-volume multianvil press together with density functional theory-based calculations. Cubic and rhombohedrally distorted clathrates, with the general formula Te 8 @(Si 38 Te 8 ) and wide compositional range, preceded by a hexagonal phase with the composition Si 0.14 Te, are formed for different mixtures of Si and Te as starting materials. Si 0.14 Te, with the structural formula Te 2 (Te 0.74 Si 0.26 ) 3 (Te 0.94 Si 0.06 ) 3 , is the very first chalcogenide with the Mn 5 Si 3 -type structure. Silicon sesquitelluride α-Si 2 Te 3 decomposes into a mixture of phases that includes the clathrate and hexagonal phases at high pressures and high temperatures. The higher the pressure, the lower the temperature for the two phases to occur. Regardless of the starting compositions, only the clathrate is quenched to atmospheric conditions, while the hexagonal phase amorphizes on decompression. The rhombohedral clathrates Te 8 @(Si 38 Te 8 ) form on quenching of the cubic phases to ambient conditions. There is a high degree of interchangeability of Si and Te not only in the clathrates but also in the Mn 5 Si 3 -type structure. The theoretical calculations of enthalpies indicate that the reported decomposition of α-Si 2 Te 3 is energetically favorable over its transformation to another polymorph of the A 2 X 3 type at extreme conditions.