Heterogeneous catalytic reactions involving molecular hydrogen are central to many industrial processes. One of the major challenges in such processes is to achieve high activity, but also high selectivity for one product over all other potential products, which would avoid wasting starting materials and minimize the generation of undesirable byproducts. A detailed understanding of the reaction mechanism and rate limiting step is thus necessary in order to design and implement improved catalytic processes. For example, a common feature for most hydrogenation and dehydrogenation catalysts is the presence of a highly active site that is either favorable for dissociation of hydrogen molecules into atoms, or for the recombination of atoms into hydrogen molecules. This kind of activity occurs in varying degree for nearly all hydrogenation catalysts, and the nature of the activity is often associated with the presence of metal atoms, clusters or nanoparticles on the surface of the catalyst. We previously showed that Metal-Organic Frameworks (MOFs) are promising hydrogenation catalysts, and in some cases high selectivity may be achieved, opening new avenues for the design of highly desirable industrial processes. The nature of the catalytic activity of MOFs in hydrogenation reactions, however, remains unclear. Here, the versatile IRMOF-74(n) series is used as a platform for studying hydrogen activation through hydrogen-deuterium exchange reactions. Residual Gas Analysis experiments demonstrate that the H-D exchange reaction of equimolar H2/D2 mixtures occurs at a high rate in the presence of IRMOF-74(Mg, Co and Ni) under mild conditions of temperature and pressure (≤120 °C, ≤1 atm H2). Detailed in situ vibrational experiments demonstrate that the IRMOF-74 open metal sites are the active sites for the H-H and D-D molecule activation. The MOF catalysts are recyclable and retain their crystallinity and framework structure after the isotope exchange reaction. These studies represent the first step toward gaining a molecular-level understanding of the factors controlling hydrogenation reactions within MOFs and their relationship to MOF structure.

Rapid hydrogen–deuterium exchange in metal-organic frameworks

255th National Meeting (2018)

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