No abstract

Although rhenium may not be the most common choice of active species in catalysis, it has been reported as a highly active and selective catalyst over a wide range of reactions. Its applications include hydrogenation reactions of great relevance in the field of renewable materials and bio‐derived platform molecules, such as valorization of lignin, CO2, and carboxylic acids. Different from several transition metals, rhenium presents oxidation numbers varying from −3 to +7. Such diversity in the coordination chemistry of rhenium is reflected in the variety of known rhenium compounds, since this metal can form stable structures such as ligand‐bridged multinuclear and organometallic compounds as well as inorganic oxides, metal‐organic frameworks, and clusters. The exceptional flexibility in rhenium speciation yields numerous selective catalysts; however, it also makes the characterization of rhenium catalysts challenging, and its influence on the catalytic activity is not trivial. This review will outline the most established rhenium‐based materials used in hydrogenation catalysis and shed some light on the relation of rhenium species to catalyst selectivity based on advanced characterization techniques. Finally, our perspectives on the use of rhenium catalysts to produce value‐added products will be given.

No abstract

No abstract

Hydrogen (H2) has emerged as a sustainable energy carrier capable of replacing/complementing the global carbon-based energy matrix. Although studies in this area have often focused on the fundamental understanding of catalytic processes and the demonstration of their activities towards different strategies, much effort is still needed to develop high-performance technologies and advanced materials to accomplish widespread utilization. The main goal of this review is to discuss the recent contributions in the H2 production field by employing nanomaterials with well-defined and controllable physicochemical features. Nanoengineering approaches at the sub-nano or atomic scale are especially interesting, as they allow us to unravel how activity varies as a function of these parameters (shape, size, composition, structure, electronic, and support interaction) and obtain insights into structure–performance relationships in the field of H2 production, allowing not only the optimization of performances but also enabling the rational design of nanocatalysts with desired activities and selectivity for H2 production. Herein, we start with a brief description of preparing such materials, emphasizing the importance of accomplishing the physicochemical control of nanostructures. The review finally culminates in the leading technologies for H2 production, identifying the promising applications of controlled nanomaterials.

The conversion of CO 2 into CO is an important step in CO 2 utilization to achieve clean fuels and value-added chemicals. Herein, we explored the pyrolysis of zeolitic imidazolate framework-8 (ZIF-8) loaded with different amounts of Ni 2 + to obtain NiÀ Zn carbide (Ni 3 ZnC) embedded in N-doped carbon. Ni is present in the intermetallic compound, while Zn excess remains on the N-doped carbon. The Ni 3 ZnC phase catalyzes the selective hydrogenation of CO 2 into CO via the reverse water gas shift reaction, reaching 100 % CO selectivity at ~30 % CO 2 conversion at 450 °C and atmosphere pressure (CO 2 : H 2 = 1 : 4, GHSV = 30000 mL g cat À 1 h À 1 ). The methanation reaction of CO 2 / CO, which is usually favored over Ni catalysts, is suppressed. The selectivity to CO at the expense of CH 4 is related to the stability of chemisorbed CO in the Ni 3 ZnC surface, which is lower compared to Ni surfaces. The Ni 3 ZnC@NC catalyst is selective towards CO over a wide range of conditions, including high pressure, that is usually required for the conversion of CO to hydrocarbons and alcohols via the Fisher-Tropsch synthesis (FTS) process. Contrarily, a classical Ni/SiO 2 catalyst prepared by impregnation produces CH 4 under high pressure.

The Cover Feature shows the catalyst production process starting from a mixture of zeolitic imidazolate framework‐8 (ZIF‐8) and Ni2+ precursor, which is then pyrolyzed to yield the intermetallic Ni3ZnC catalyst. This intermetallic compound catalyzes the selective hydrogenation of CO2 into CO via the reverse water gas shift reaction pathway, while the most common methanation reaction pathway is suppressed, even at high pressure. The gain in selectivity is represented by the catalyst's being able to move the railway switch control towards CO. Image credit: Eliana R. de Almeida. More information can be found in the Full Paper by L. M. Rossi and co‐workers.

No abstract