Knowledge of the reaction mechanism is key for rational catalyst improvement. Traditionally mechanistic studies focus on structure and the reaction conditions like temperature, pH, pressure, etc., whereas the time dimension is often overlooked. Here, we demonstrate the influence of time on the mechanism of a catalytic reaction. A dual catalytic mechanism was identified for the CO oxidation over Au/TiO2 by time‐resolved infrared spectroscopy coupled with modulation excitation spectroscopy. During the first seconds, CO on the gold particles is the only reactive species. As the reaction proceeds, the redox properties of TiO2 dominate the catalytic activity through electronic metal‐support interaction (EMSI). CO induces the reduction and reconstruction of TiO2 whereas oxygen leads to its oxidation. The activity of the catalyst follows the spectroscopic signature of the EMSI. These findings demonstrate the power of studying short‐time kinetics for mechanistic studies.
Knowledge of the reaction mechanism is key for rational catalyst improvement. Traditionally mechanistic studies focus on structure and the reaction conditions like temperature, pH, pressure, etc., whereas the time dimension is often overlooked. Here, we demonstrate the influence of time on the mechanism of a catalytic reaction. A dual catalytic mechanism was identified for the CO oxidation over Au/TiO2 by time‐resolved infrared spectroscopy coupled with modulation excitation spectroscopy. During the first seconds, CO on the gold particles is the only reactive species. As the reaction proceeds, the redox properties of TiO2 dominate the catalytic activity through electronic metal‐support interaction (EMSI). CO induces the reduction and reconstruction of TiO2 whereas oxygen leads to its oxidation. The activity of the catalyst follows the spectroscopic signature of the EMSI. These findings demonstrate the power of studying short‐time kinetics for mechanistic studies.
Carbamate is an emerging class of polymer backbone for constructing sequence-defined, abiotic polymers. It is expected that new functional materials can be de novo designed by controlling the primary polycarbamate sequence. While amino acids have been actively studied as building blocks for protein folding and peptide self-assembly, carbamates have not been widely investigated from this perspective. Here we combined infrared (IR), vibrational circular dichroism (VCD) and nuclear magnetic resonance (NMR) spectroscopy with density functional theory (DFT) calculations to understand the conformation of carbamate monomer units in a non-polar, aprotic environment (chloroform). Compared with amino acid building blocks, carbamates are more rigid, presumably due to the extended delocalization of π-electrons on the backbones. Surprisingly, cis configurations can be energetically stable for carbamates while peptides typically assume trans configurations at low energies. This study lays an essential foundation for future developments of carbamate-based sequence-defined polymer material design.
Carbamate is an emerging class of polymer backbone for constructing sequence-defined, abiotic polymers. It is expected that new functional materials can be de novo designed by controlling the primary polycarbamate sequence. While amino acids have been actively studied as building blocks for protein folding and peptide self-assembly, carbamates have not been widely investigated from this perspective. Here we combined infrared (IR), vibrational circular dichroism (VCD) and nuclear magnetic resonance (NMR) spectroscopy with density functional theory (DFT) calculations to understand the conformation of carbamate monomer units in a non-polar, aprotic environment (chloroform). Compared with amino acid building blocks, carbamates are more rigid, presumably due to the extended delocalization of π-electrons on the backbones. cis configurations can be energetically stable for carbamates while peptides typically assume trans configurations at low energies. This study lays an essential foundation for future developments of carbamate-based sequence-defined polymer material design.
The front cover artwork for issue 23/2018 is provided by an international group of scientists from the University of Geneva (Switzerland), the Technical University of Vienna (Austria), the Universitat Politècnica de Catalunya and ALBA Synchrotron Light Facility (Spain), and the University of Bialystok (Poland). The image shows the thiol ligand migration from the gold nanocluster to the surface once it has been supported, forming sulfur oxide species. See the Communication itself at https://doi.org/10.1002/cctc.201801474.
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