RESUMEN
Transition metal dichalcogenides (TMDs), such as MoS2 and WS2, are promising alternative non-noble metal catalysts to drive the electrocatalytic H2 evolution reaction (HER). However, their catalytic performance is inherently limited by the small number of active sites as well as their poor electrical conductivity. Here, we grow vertically aligned 2H-WS2 on different substrates to expose their edge sites for the HER and introduce a scalable approach to tune these active sites via defect engineering. In a thermal hydrogen treatment procedure, sulfur vacancies and metallic tungsten nanoparticles are formed. The extent of desulfurization, and thus the HER activity, can be tuned via controlling the H2 annealing conditions. The obtained W/WS2-x electrocatalysts are evaluated experimentally and theoretically to arrive at a better understanding of how to modify the inherently inert 2H-WS2 for more efficient HER.
RESUMEN
In this work, we developed a novel strategy to synthesize porous (alumino)silicate materials using a single structure-directing agent composed of an imidazole unit with a hydrophobic tail, namely, 1,2-dimethyl-3-hexadecyl-1H-imidazol-3-ium bromide (C16dMImz). A wide range of products such as ordered mesoporous silicas, layered silica-alumina, and hierarchically porous mordenite zeolite were obtained by varying synthesis parameters such as temperature and aluminum concentration. By changing crystallization temperature, we could control the degree of silica condensation and tune the textural and morphological properties of the final materials. By varying the aluminum concentration in the gel, we can obtain mesoporous amorphous silica-alumina or crystalline mordenite zeolite with, respectively, weak and strong Brønsted acid sites. Obtained acidic silica-alumina materials displayed promising performance in catalytic reactions of linear paraffin hydroisomerization and Friedel-Crafts alkylation of benzene with benzyl alcohol.
RESUMEN
Molybdenum disulfide (MoS2) is a highly promising catalyst for the hydrogen evolution reaction (HER) to realize large-scale artificial photosynthesis. The metallic 1T'-MoS2 phase, which is stabilized via the adsorption or intercalation of small molecules or cations such as Li, shows exceptionally high HER activity, comparable to that of noble metals, but the effect of cation adsorption on HER performance has not yet been resolved. Here we investigate in detail the effect of Li adsorption and intercalation on the proton reduction properties of MoS2. By combining spectroscopy methods (infrared of adsorbed NO, 7Li solid-state nuclear magnetic resonance, and X-ray photoemission and absorption) with catalytic activity measurements and theoretical modeling, we infer that the enhanced HER performance of Li x MoS2 is predominantly due to the catalytic promotion of edge sites by Li.
RESUMEN
The restructuring of a silver catalyst during ethylene epoxidation under industrially relevant conditions was investigated without and with vinyl chloride (VC) promotion. During non-VC-promoted ethylene epoxidation, the silver particles grow and voids are formed at the surface and in the bulk. Electron tomography highlighted the presence of voids below the Ag surface. A mechanism is proposed involving reconstruction of the silver lattice and defect sites induced by oxygen adsorption on the external surface and grain boundaries, which finally create pores. Promotion of the catalytic reaction by VC suppresses to a significant extent void formation. The use of VC also redisperses silver particles, initially grown during ethylene epoxidation without VC. This process is rapid as the average size decreased from 172 to 136 nm within 2 h. These insights emphasize the dynamic nature of the silver particles during the ongoing ethylene epoxidation reaction and indicate that particle size and morphology strongly depend on reaction conditions.
RESUMEN
The catalytic activity of metal nanoparticles can be altered by applying strain, which changes the crystalline lattice spacing and modifies the electronic properties of the metal. Understanding the role of elastic strain during catalytic reactions is thus crucial for catalyst design. Here, we show how single highly faceted Pt nanoparticles expand or contract upon interaction with different gas atmospheres using in situ nano-focused coherent X-ray diffraction imaging. We also demonstrate inter-particle heterogeneities, as they differ in development of strain under CO oxidation reaction conditions. The reported observations offer new insights into the design of catalysts exploiting strain effects.