An outstanding challenge in the field of heterogeneous catalysis is the synthesis of catalysts (typically clusters of metal atoms or metal ions in combination with oxo, hydroxo, and/or aqua ligands) with single-atom control over the catalyst/cluster composition and structural configuration. A related challenge is to avoid sintering and maintain the catalyst structure over the course of a catalytic reaction. Satisfying these conditions can enormously facilitate the discovery of meaningful structure/reactivity relationships and greatly aid the hypothesis-driven and computationally guided development of desired new catalysts. Clusters can be highly catalytic on a per-atom basis because essentially all atoms are accessible to reactants. The catalytic activity and chemical selectivity of clusters in the few-to-several atom size range can be highly sensitive to the exact cluster size and configuration – thus the need to pursue single-atom precision. In favorable cases, desired arrays of catalytic clusters of uniform size and composition can be obtained by employing zeolites as catalyst supports. A complementary approach is to employ chemically and thermally robust, high-surface area, mesoporous metal-organic frameworks (MOFs), of appropriate design, as crystallographically well-defined templates and supports for cluster assembly and use as heterogeneous catalysts. This presentation will explore this complementary and conceptually new approach to catalytic materials design, synthesis, and utilization. “AIM” or ALD In MOFs has been used to synthesize uniform, high-density arrays of catalytic clusters. ALD is atomic layer deposition. AIM and a closely related solution-based technique termed “SIM” have proven effective for the synthesis of scores of new catalysts, including metal-oxides, metal-sulfides, and mixed-metal clusters. These have been extensively characterized, typically via synchrotron-based methods, and several have been explored as catalysts. These early studies reveal that: a) composition control at the level of single metal atoms is often achievable, b) sintering can be shut down, c) appropriately chosen MOF supports are typically stable even under fairly harsh conditions (e.g. oxygen-rich atmosphere at 350oC), d) chemically interesting catalytic activity can be observed, and e) virtuous cycles of experiment and theory can be started and then used to leverage mechanistic understanding and uncover transferrable rules for nanoscale catalyst design.

AIM-ing for catalyst synthesis with single-atom precision

255th National Meeting (2018)

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