ABSTRACT
Metal-organic frameworks (MOFs) are playing a key role in developing the next generation of heterogeneous catalysts. In this work, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is applied to study in operando the CO oxidation on Pt@MOFs (UiO-67) and Pt@ZrO2 catalysts, revealing the same Pt surface dynamics under the stoichiometric CO/O2 ambient at 3â mbar. Upon the ignition at ca. 200 °C, the signature Pt binding energy (BE) shift towards the lower BE (from 71.8 to 71.2â eV) is observed for all catalysts, confirming metallic Pt nanoparticles (NPs) as the active phase. Additionally, the plug-flow light-off experiments show the superior activity of the Pt@MOFs catalyst in CO oxidation than the control Pt@ZrO2 catalyst with ca. 28 % drop in the T 50% light-off temperature, as well as high stability, due to their sintering-resistance feature. These results provide evidence that the uniqueness of MOFs as the catalyst supports lies in the structural confinement effect.
ABSTRACT
A quantitative method for assessment of defects in metal-organic framework (MOF) is presented based on isotherms calculated using Grand Canonical Monte Carlo (GCMC) simulations. Defects in MOF structures generated during the synthesis and sample preparation can lead to large variations in experimentally measured adsorption isotherms but are difficult to quantify. We use as a case study CO2 adsorption on Cu3(BTC)2 MOF (BTC = benzene-1,3,5-tricarboxylic acid) to show that different samples reported in the literature have various proportions of principal pores blocked or side pores blocked, resulting in isotherms with different capacity and affinity toward CO2. The approach presented is easily generalized to other materials, showing that simulation results combined with experimentally measured gas adsorption isotherms can be used to quantitatively identify key defective features of the material.
