Selective Catalytic Chemistry at Rhodium(II) Nodes in Bimetallic Metal–Organic Frameworks

Abstract

We report the first study of a gas‐phase reaction catalyzed by highly dispersed sites at the metal nodes of a crystalline metal–organic framework (MOF). Specifically, CuRhBTC (BTC3−=benzenetricarboxylate) exhibited hydrogenation activity, while other isostructural monometallic and bimetallic MOFs did not. Our multi‐technique characterization identifies the oxidation state of Rh in CuRhBTC as +2, which is a Rh oxidation state that has not previously been observed for crystalline MOF metal nodes. These Rh2+ sites are active for the catalytic hydrogenation of propylene to propane at room temperature, and the MOF structure stabilizes the Rh2+ oxidation state under reaction conditions. Density functional theory calculations suggest a mechanism in which hydrogen dissociation and propylene adsorption occur at the Rh2+ sites. The ability to tailor the geometry and ensemble size of the metal nodes in MOFs allows for unprecedented control of the active sites and could lead to significant advances in rational catalyst design.

Bimetallic metal–organic frameworks and their derivatives

“…[129][130][131][132][133][134][135] For example, Chen and coworkers prepared (Cu x Ru 1Àx ) 3 -(BTC) 2 (CuRhBTC) for propylene hydrogenation. 136 CuRh(33%)BTC exhibited an activity of 1600 mmol g catalyst À1 min À1 for propane production. The CuBTC MOF showed no activity under the reaction conditions, and RhBTC was unstable upon exposure to air.…”

Catalysis in Confined Spaces of Metal Organic Frameworks

“…The catalytic activity of CuRhBTC was tested in the room-temperature gas-phase hydrogenation of propylene. [68] Hydrogenation of propylene was facilely observed with CuRhBTC, while CuBTC and analogous CuMBTC solids (M=Co, Ir, Ni, Ru ions) showed no activity ( Figure 5). These catalytic data clearly indicate the unique role of Rh 2 + in the CuBTC framework.…”

“…Recently, Cu‐BTC was post‐synthetically exchanged with Rh 3+ , followed by chemical reduction, resulting in the formation of CuRhBTC. The catalytic activity of CuRhBTC was tested in the room‐temperature gas‐phase hydrogenation of propylene . Hydrogenation of propylene was facilely observed with CuRhBTC, while CuBTC and analogous CuMBTC solids (M=Co, Ir, Ni, Ru ions) showed no activity (Figure ).…”

A Metal‐Organic Framework (MOF)‐Based Multifunctional Cargo Vehicle for Reactive‐Gas Delivery and Catalysis

“…One possible hypothesis for such behavior is that the Rh 3 (BTC) 2 framework degraded and resulted in the formation of metal particles that could catalyze the Suzuki–Miyaura coupling reaction. To test this hypothesis, we prepared a more robust heterometallic isostructural analog, Cu 2.38 Rh 0.62 (BTC) 2 , using a literature procedure, [64] that could maintain its crystallinity after the reaction (Figure S8). Indeed, PXRD analysis revealed that Cu 2.38 Rh 0.62 (BTC) 2 could be isolated after the reaction and retained its structural integrity (Figure S8).…”