No abstract

No abstract

We find that exposure of the MoS2 basal plane to methanol leads to the formation of adsorbed methoxy and coincides with sulfur vacancy generation. The conversion of methanol to methoxy on MoS2 is temperature dependent. Density functional theory simulations and experiment indicate that the methoxy moieties are bound to molybdenum, not sulfur, while some adsorbed methanol is readily desorbed near or slightly above room temperature. Our calculations also suggest that the dissociation of methanol via O–H bond scission occurs at the defect site (sulfur vacancy), followed subsequently by formation of a weakly bound H2S species that promptly desorbs from the surface with creation of new sulfur vacancy. Photoluminescence and scanning tunneling microscopy show clear evidence of the sulfur vacancy creation on the MoS2 surface, after exposure to methanol.

The dynamic motion, within the lattice of single crystal CH 3 NH 3 PbBr 3 (001) hybrid halide perovskite, was investigated using powder and single crystal x-ray diffraction, and x-ray photoemission spectroscopy. Single crystal x-ray diffraction studies indicate the methylammonium cation adopts multiple orientations within the crystal, at room temperature, evidence of a disordered methylammonium sublattice within a rigid and ordered PbBr 3 matrix lattice. From the Br 3d 5/2 core level photoemission temperature dependence, an effective Debye temperature of 160 ± 22 K can be estimated, while the Pb 4f 7/2 core-level Debye-Waller factor plots suggest an effective Debye temperature of 202 ± 131 K, indicative of a very rigid lattice along the (001) direction. The combination of x-ray diffraction with temperature dependent x-ray photoemission spectroscopy for bromine and lead core level peaks support the characterization of CH 3 NH 3 PbBr 3 as a lattice polar liquid crystal, as CH 3 NH 3 PbBr 3 does not meet the criteria required for a ferroelectric material.

Homogenous single-layer MoS2 films coated with sub-single layer amounts of gold are found to isolate the reaction of methanol with carbon monoxide, the fundamental step toward higher alcohols, from an array of possible surface reactions. Active surfaces were prepared from homogenous single-layer MoS2 films coated with sub-single layer amounts of gold. These gold atoms formed clusters on the MoS2 surface. A gas mixture of carbon monoxide (CO) and methanol (CH3OH) was partially converted to acetaldehyde (CH3CHO) under mild process conditions (308 kPa and 393 K). This carbonylation of methanol to a C2 species is a critical step toward the formation of higher alcohols. Density functional theory modeling of critical steps of the catalytic process identify a viable reaction pathway. Imaging and spectroscopic methods revealed that the single layer of MoS2 facilitated formation of nanoscale gold islands, which appear to sinter through Ostwald ripening. The formation of acetaldehyde by the catalytic carbonylation of methanol over supported gold clusters is an important step toward realizing controlled production of useful molecules from low carbon-count precursors.