Interpretations of NMR chemical shifts via theoretical calculations in catalytic selective hydrogenation system of CO2 to methanol
Title: Interpretations of NMR chemical shifts via theoretical calculations in catalytic selective hydrogenation system of CO2 to methanol
DNr: SNIC 2019/3-582
Project Type: SNIC Medium Compute
Principal Investigator: Niklas Hedin <niklas.hedin@mmk.su.se>
Affiliation: Stockholms universitet
Duration: 2019-11-01 – 2020-03-01
Classification: 10403 10407
Homepage: https://www.su.se/english/profiles/nhedi-1.187310
Keywords:

Abstract

In our parallel and current studies, we aim at studying the CO2 selective reduction into methanol in Ru-based molecular catalyst by quantum chemical calculations, and importantly the reaction channels depend on the various captured-CO2 species on amine-grafted silica surface. In the lab work, we have involved the solid-state NMR technique and isotope enrichment to explore the species before and after the catalytic reductions. Some informative NMR signals have been detected that need to be interpreted theoretically to solidify the interpretation of the experimental findings. This project proposal will expand on our parallel studies, in which we calculate the hydrogenation reaction channels of CO2 to methanol. In this project, we will focus on the NMR properties of different captured-CO2 species in our reaction systems. Recently, density function theory (DFT) methods have been developed that can precisely describe the 13C NMR chemical shifts. The NMR chemical shift is a second-derivative property of the electrons surrounding the nuclei and closely related to the geometric structures. Therefore, the interesting geometries will be accurately optimized at the relatively high calculation level. After the test of methods, we decided to use the OLYP/cc-pVTZ for the optimization calculations, as a high precision of the predicted 13C NMR chemical shifts is needed. The molecular descriptions of the geometries include the carbamate, zwitterionic carbamic acid and bicarbonate species on amine-functionalized SiO2 support in the presence/absence of water molecules. These relevant moieties contain dozens of atoms and even the partially relaxed optimization takes a lot of computing time. However, it is very meaningful to theoretically rationalize in which forms the captured-CO2 exits on the amine-functionalized SiO2 systems and what is the role of H2O. The captured or preconcentrated CO2 have a rich chemistry, and we have to study both theoretically and experimentally in which forms that chemisorbed CO2 is present to control the formation of competitive species and to promote the high selective hydrogenation reaction to methanol. Even if we have a good experimental setup with solid-state NMR data accessible, we still need further computations to conclude on the specifics of the preconcetrated CO2 captured on the amines grafted on silica. There is indee a relevant publication (https://pubs.acs.org/doi/10.1021/acs.est.8b05978) about the structure of chemisorbed CO2 species in mesoporous aminosilicas, however, the calculation method used in their study is not sufficiently robust and accurate especially for the 13C NMR chemical shift property. In this project, the Gaussian software will be mainly used. We hope to get access to the increased resources with this new proposal for the period of November 1, 2019 until the end of June, 2020. This new project should be viewed as an addition to our running project, and during the overlapping time period we will run the two project simultaneously.