Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives

The catalytic behavior of metal-organic frameworks of different structures (Fe(BTC), MIL-100(Fe), MIL-100(Cr) and Cu-3(BTC)(2)) was investigated in annulation reaction between 2-methyl-3-buten-2-ol and phenols differing in size (phenol, 2-naphthol). MIL-100(Fe) possessing intermediate Lewis acidity, perfect crystalline structure, and the highest S-BET surface area showed the highest activity (TOF = 0.7 and 1.4h(-1) for phenol and 2-naphthol, respectively) and selectivities to target benzopyran (45% and 65% at 16% of phenol and 2-naphthol conversion, respectively). The increasing strength of Lewis acid centers for MIL-100(Cr) was found to result in the dramatically decreased activity of the catalyst, while negligible conversion of phenols was found over Fe(BTC), characterized by a less ordered framework.M.O. and J.C. acknowledge the Czech Science Foundation for the support (14-07101S) and RNDr. Libor Brabec, CSc. for SEM images.Shamzhy, MV.; Opanasenko, MV.; García Gómez, H.; Cejka, J. (2015). Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives. Microporous and Mesoporous Materials. 202:297-302. doi:10.1016/j.micromeso.2014.10.003S29730220

Electronic structure of porphyrin-based metal-organic frameworks and their suitability for solar fuel production photocatalysis

Metal-organic frameworks (MOFs) can be exceptionally good catalytic materials thanks to the presence of active metal centres and a porous structure that is advantageous for molecular adsorption and confinement. We present here a first-principles investigation of the electronic structure of a family of MOFs based on porphyrins connected through phenyl-carboxyl ligands and AlOH species, in order to assess their suitability for the photocatalysis of fuel production reactions using sunlight. We consider structures with protonated porphyrins and those with the protons exchanged with late 3d metal cations (Fe2+, Co2+, Ni2+, Cu2+, Zn2+), a process that we find to be thermodynamically favorable from aqueous solution for all these metals. Our band structure calculations, based on an accurate screened hybrid functional, reveal that the bandgaps are in a favorable range (2.0 to 2.6 eV) for efficient adsorption of solar light. Furthermore, by approximating the vacuum level to the pore center potential, we provide the alignment of the MOFs’ band edges with the redox potentials for water splitting and carbon dioxide reduction, and show that the structures studied here have band edges positions suitable for these reactions at neutral pH

Tuneable nature of metal organic frameworks as heterogeneous solid catalysts for alcohol oxidation

[EN] Selective benzyl alcohol oxidation (BA) to benzaldehyde has been frequently used as a benchmark reaction to evaluate the catalytic activity of metal organic frameworks (MOFs) as oxidation catalysts. Substituted BAs, and aliphatic and allylic alcohols have also been often used as substrates in these studies. In the present review, the current state of the art of MOFs as heterogeneous catalysts for the oxidation of BA and other alcohols is described, grouping the reports according to the nature of the active sites present on the MOFs. Thus, MOFs in which the catalytic centres are located at the ligands, at metallic nodes, or at metal nanoparticles (MNPs) incorporated within the MOF pores and photoassisted oxidations have been commented on. The aim of this review is to stress the current limitations encountered in the use of MOFs, particularly with respect to MOF stability and activity and propose new targets in the area.AD thanks the University Grants Commission (UGC), New Delhi, for the award of an Assistant Professorship under its Faculty Recharge Programme. AD also thanks the Department of Science and Technology, India, for the financial support through Extra Mural Research Funding (EMR/2016/006500). Financial support from the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2015-69153-CO2-1) is gratefully acknowledged.Dhakshinamoorthy, A.; Asiri, AM.; García Gómez, H. (2017). Tuneable nature of metal organic frameworks as heterogeneous solid catalysts for alcohol oxidation. Chemical Communications. 53(79):10851-10869. https://doi.org/10.1039/c7cc05927bS1085110869537

Encapsulation of bimetallic metal nanoparticles into robust zirconium-based metal-organic frameworks : evaluation of the catalytic potential for size-selective hydrogenation

The realization of metal nanoparticles (NPs) with bimetallic character and distinct composition for specific catalytic applications is an intensively studied field. Due to the synergy between metals, most bimetallic particles exhibit unique properties that are hardly provided by the individual monometallic counterparts. However, as small‐sized NPs possess high surface energy, agglomeration during catalytic reactions is favored. Sufficient stabilization can be achieved by confinement of NPs in porous support materials. In this sense, metal–organic frameworks (MOFs) in particular have gained a lot of attention during the last years; however, encapsulation of bimetallic species remains challenging. Herein, the exclusive embedding of preformed core–shell PdPt and RuPt NPs into chemically robust Zr‐based MOFs is presented. Microstructural characterization manifests partial retention of the core–shell systems after successful encapsulation without harming the crystallinity of the microporous support. The resulting chemically robust NP@UiO‐66 materials exhibit enhanced catalytic activity towards the liquid‐phase hydrogenation of nitrobenzene, competitive with commercially used Pt on activated carbon, but with superior size‐selectivity for sterically varied substrates