Hydroformylation is an industrial process for the production of aldehydes from alkenes1,2. Regioselective hydroformylation of propene to high-value n-butanal is particularly important, owing to a wide range of bulk applications of n-butanal in the manufacture of various necessities in human daily life3. Supported rhodium (Rh) hydroformylation catalysts, which often excel in catalyst recyclability, ease of separation and adaptability for continuous-flow processes, have been greatly exploited4. Nonetheless, they usually consist of rotationally flexible and sterically unconstrained Rh hydride dicarbonyl centres, only affording limited regioselectivity to n-butanal5-8. Here we show that proper encapsulation of Rh species comprising Rh(I)-gem-dicarbonyl centres within a MEL zeolite framework allows the breaking of the above model. The optimized catalyst exhibits more than 99% regioselectivity to n-butanal and more than 99% selectivity to aldehydes at a product formation turnover frequency (TOF) of 6,500 h-1, surpassing the performance of all heterogeneous and most homogeneous catalysts developed so far. Our comprehensive studies show that the zeolite framework can act as a scaffold to steer the reaction pathway of the intermediates confined in the space between the zeolite framework and Rh centres towards the exclusive formation of n-butanal.
We report a general route to decipher the apportionment of metal ions in bulk metal-organic frameworks (MOFs) by solid-state nuclear magnetic resonance spectroscopy. We demonstrate this route in Mg1-xNix-MOF-74, where we uncover all eight possible atomic-scale Mg/Ni arrangements through identification and quantification of the distinct chemical environments of 13C-labeled carboxylates as a function of the Ni content. Here, we use magnetic susceptibility, bond pathway, and density functional theory calculations to identify local metal bonding configurations. The results refute the notion of random apportionment from solution synthesis; rather, we reveal that only two of eight Mg/Ni arrangements are preferred in the Ni-incorporated MOFs. These preferred structural arrangements manifest themselves in macroscopic adsorption phenomena as illustrated by CO/CO2 breakthrough curves. We envision that this nondestructive methodology can be further applied to analyze bulk assembly of other mixed-metal MOFs, greatly extending the knowledge on structure-property relationships of MOFs and their derived materials.
Experimentally observed magnetic properties are usually statistically averaged from bulk materials and information associated with the local chemical environment cannot be specified. Against this backdrop, we propose a theoretical strategy to provide an in-depth understanding of the multi-role for metrics that may contribute to the apparent magnetic moment of iron borides. In particular, we demonstrate this strategy through systematic manipulation of the iron/boron stoichiometry of six prototype iron borides to tune their associated local structural and electronic environment to further modulate the resultant magnetic moment. The local coordinative structures of the six iron borides were resolved utilizing bond valence analysis by taking the different coordination shells into account. Furthermore, the local electronic properties of each Fe atom in these iron borides, such as charge transfer, electronic distribution, bonding feature and orbital energy level, were carefully analyzed by Bader analysis, density of states analysis and Crystal Orbital Hamilton Population analysis. From the combination of analyses of both the coordinative and electronic properties of the prototype iron borides, a linear relationship between the local magnetic moment and the bond valence as well as the average energy of the Fe 3d orbitals has been confirmed.
