Models Facilitating the Design of a New Metal‐Organic Framework Catalyst for the Selective Decomposition of Formic Acid into Hydrogen and Carbon Dioxide

Abstract

Here we describe a new conceptual approach for the design of a heterogeneous metal‐organic framework (MOF) catalyst based on UiO‐67 for the selective decarboxylation of formic acid, a reaction with important applications in hydrogen storage and in situ generation of H2. Models for the {CuH} reactive catalytic site at the organic linker are assessed. In the first model system, gas‐phase mass spectrometry experiments and DFT calculations on a fixed charge bathophen ligated copper hydride complex, [(phen*)Cu(H)]2−, were used to demonstrate that it acts as a catalyst for the selective decomposition of formic acid into H2 and CO2 via a two‐step catalytic cycle. In the first step liberation of H2 to form the carboxylate complex, [(phen*)Cu(O2CH)]2− occurs, which in the second step selectively decomposes via CO2 extrusion to regenerate the hydride complex. DFT calculations on four other model systems showed that changing the catalyst to neutral [(LCu(H)] complexes or embedding it within a MOF results in mechanisms which are essentially identical. Thus catalytic active sites located on the organic linker of a MOF appear to be close to a gas‐phase environment, thereby benefitting from the favorable characteristics of gas‐phase reactions and validating the use of gas‐phase models to design new MOF based catalysts.

Spectroscopy and photochemistry of copper nitrate clusters

“…Well-defined gasphase experiments can provide valuable insight into reaction mechanisms on a molecular level, [30][31][32] while spectroscopy based experiments can yield detailed insight into the molecular and electronic structure. 33,34 In the gas phase, many molecular mechanisms involving the activation of methane, 35,36 carbon dioxide [37][38][39][40] and elementary steps of hydrogen storage applications [41][42][43] have successfully been studied. Ultraviolet/visible/near-infrared (UV/vis/NIR) photodissociation spectroscopy is a very powerful tool to characterize the complex electronic structure of transition metal complexes and clusters in the gas phase.…”

Organometallic Gas‐phase Ion Chemistry and Catalysis: Insights Into the Use of Metal Catalysts to Promote Selectivity in the Reactions of Carboxylic Acids and Their Derivatives

“…The experimental challenges of developing these zeolite-based "ship in a bottle" catalysts (Ozin&Gil, 1989), focused our attention on metal organic frameworks (MOFs) (Hoskins&Robson 1989;Hoskins&Robson 1990), which offer three types of potential catalytic sites, as illustrated for the UiO-67 MOF (Scheme 25c) (Huang et al, 2017). Of these, the organic linker, which can be functionalized to introduce a catalytic site, provides an attractive target for our gas-phase model studies (O'Hair et al, 2019).…”

“…The experimental challenges of developing these zeolitebased "ship in a bottle" catalysts (Ozin & Gil, 1989), focused our attention on metal-organic frameworks (MOFs) (Hoskins & Robson 1989, which offer three types of potential catalytic sites, as illustrated for the UiO-67 MOF (Scheme 25c) (Huang et al, 2017). Of these, the organic linker, which can be functionalized to introduce a catalytic site, provides an attractive target for our gas-phase model studies (O'Hair et al, 2019). Experiments on the fixed-charge model 36d revealed that the same two-step catalytic cycle (Scheme 25a) operates, while DFT calculations showed that the mechanisms and energetics associated with the two-step catalytic cycle of simple gas-phase catalysts 36d-36f (Scheme 25d) are very similar to those of the models 36g and 36h of UiO-67 MOF (Scheme 25e).…”

Controlling Cation‐Cation Interactions in Uranyl Coordination Dimers by Varying the Length of the Dicarboxylate Linker

“…The general utility and versatility of gasphase studies has been established in many realms, such as organometallic chemistry and C-H bond activation. [60][61][62][63][64][65][66][67] Examples of gas-phase contributions to uranium chemistry include oxo-exchange of uranyl with water, [68] a nitrosyl complex, [69] a peroxide dimer, [70] and an "extreme" CCI. [71] Stand-alone com-putational studies have assessed stabilities of elementary CCIs in gas-phase uranyl dimers.…”