May 22, 2019 | Updated: 05:48 PM EDT

Cultivating Defective Porous Materials for Robust and Selective Heterogeneous Catalysis

May 06, 2019 08:08 AM EDT

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Cultivating Defective Porous Materials for Robust and Selective Heterogeneous Catalysis
(Photo : Manuel A. Ortuño (ICIQ))

One of the few industrial processes that employ homogeneous catalysis due to their high selectivity is the production of 1-butene via ethylene dimerization, despite the massive amounts of activators and solvents required. Recently, a new paper by the University of the Basque County (UPV/EHU), in collaboration with the Lopez group at the Institute of Chemical Research of Catalonia (ICIQ) and RTI International, shows a more substantial alternative via metal-organic frameworks (MOFs), a family of porous materials formed by metallic nodes connected through organic ligands.

In the study, the scientists demonstrate that tailored MOFs under condensation regimes catalyze the ethylene dimerization to 1-butene with high selectivity and stability in the absence of activators and solvent. The researchers published the study in Nature Communications, and it opens new avenues to develop robust heterogeneous catalysts for a wide variety of gas-phase reactions.

The scientists have engineered defects in the MOF (Ru) HKUST-1 without compromising the framework structure via two strategies, a conventional ligand exchange approach during MOF synthesis and a pioneering post-synthetic thermal approach. Then, the researchers characterized the defects, which have been shown to be catalytically active for ethylene dimerization.

The computational resources of the Barcelona Supercomputing Center (BSC) proved to be invaluable to the researchers. BSC belongs to the "Red Espanola de Supercomputacion" (RES), and the researchers were able to simulate realistic MOF systems to characterize the defects and compute the reaction mechanism. Also, they discovered that unsaturated metal centers induced by defects drive activity while the bimetallic nature of the node controls selectivity. When the researchers finished testing the catalytic performance of the system, then, they improved the recyclability and robustness of the catalyst through one critical condition, intrapore condensation.

Through the gas-phase, this is when the production of 1-butene via ethylene dimerization occurs. When the reaction happens at low reactant pressure, some catalytic sites get deactivated due to the coordination of oligomers. But when the pressure increases, the reactant molecules can condensate inside the pores of the material. This kind of concentration effect avoids deactivation thus enhancing the stability of the catalyst.

For the researchers, the next steps of the project would involve the use of MOF catalysts based on first-row transition metals as well as the application of the novel intrapore condensation strategy to other gas-phase reactions.

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