Diphosphure de trirhodium, Rh3P2: premier exemple d'une structure lacunaire ordonnée de type anti-PbFCl

Current State of the Art of the Solid Rh-Based Catalyzed Hydroformylation of Short-Chain Olefins

The hydroformylation of olefins is one of the most important homogeneously catalyzed processes in industry to produce bulk chemicals. Despite the high catalytic activities and selectivity’s using rhodium-based homogeneous hydroformylation catalysts, catalyst recovery and recycling from the reaction mixture remain a challenging topic on a process level. Therefore, technical solutions involving alternate approaches with heterogeneous catalysts for the conversion of olefins into aldehydes have been considered and research activities have addressed the synthesis and development of heterogeneous rhodium-based hydroformylation catalysts. Different strategies were pursued by different groups of authors, such as the deposition of molecular rhodium complexes, metallic rhodium nanoparticles and single-atom catalysts on a solid support as well as rhodium complexes present in supported liquids. An overview of the recent developments made in the area of the heterogenization of homogeneous rhodium catalysts and their application in the hydroformylation of short-chain olefins is given. A special focus is laid on the mechanistic understanding of the heterogeneously catalyzed reactions at a molecular level in order to provide a guide for the future design of rhodium-based heterogeneous hydroformylation catalysts.

Platinum Group Metal Phosphides as Efficient Catalysts in Hydroprocessing and Syngas-Related Catalysis

Platinum group metal phosphides are reviewed as catalytic materials for hydroprocessing and syngas-related catalysis. Starting from synthetic procedures leading to highly disperse nano-particular compounds, their properties in the applications are discussed and compared with relevant benchmarks, if available. Regarding their mode of action, two confronting mechanistic scenarios are presented: (i) a cooperative scenario in which catalytic sites of different functionalities are active in hydroprocessing and (ii) single site catalysis, which appears to be the relevant mode of action in syngas-related catalysis and which occurs over “frustrated” active sites.

The Cu2Sb and related structures

It is observed that neither inspection of z values, consideration of near-neighbour coordination, nor chemical considerations show in all cases which atom occupies site 2 (c I) and which site 2 (c II) of the Cu2Sb tP6 structure. Calculation of the Wirkungsbereiche by the Dirichlet construction shows indisputably which site is which. Assignments are made for all phases whose z values have been determined. Separation of phases with the Cu2Sb structure into two groups is effected on chemical considerations and observed physical properties.

Wirkungsbereiche, near-neighbour coordination, and framework descriptions of the structure are discussed, as well as related derived structure types. Stability and availability of the structure is discussed in relation to the number of valency electrons provided by the component atoms.

Thermodynamic and mechanical stabilities of tantalum nitride

We perform first-principles density functional calculations on a newly discovered tantalum nitride with an orthorhombic U2S3 structure to assess its thermodynamic and mechanical stabilities. Our random search unveils a tetragonal Ta2N3 structure that is energetically more favorable than an orthorhombic Ta2N3 at zero pressure. We predict that the tetragonal Ta2N3 transforms into the orthorhombic phase above a relatively low pressure of 7.7 GPa. Single-crystal elastic constant calculations reveal that orthorhombic Ta2N3 is mechanically unstable because of a negative c66. Our calculations suggest that minor oxygen substitution for nitrogen plays an important role in stabilizing the orthorhombic Ta2N3 structure.