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. 2023 Oct 27;24(21):15643.
doi: 10.3390/ijms242115643.

XPS and HR TEM Elucidation of the Diversity of Titania-Supported Single-Site Ir Catalyst Performance in Spin-Selective Propene Hydrogenation

Anna V Nartova  1 , Ren I Kvon  1 , Larisa M Kovtunova  1 , Ivan V Skovpin  2 , Igor V Koptyug  2 , Valerii I Bukhtiyarov  1
Affiliations

XPS and HR TEM Elucidation of the Diversity of Titania-Supported Single-Site Ir Catalyst Performance in Spin-Selective Propene Hydrogenation

Anna V Nartova et al. Int J Mol Sci. .

Abstract

Immobilized [Ir(COD)Cl]2-Linker/TiO2 catalysts with linkers containing Py, P(Ph)2 and N(CH3)2 functional groups were prepared. The catalysts were tested via propene hydrogenation with parahydrogen in a temperature range from 40 °C to 120 °C which was monitored via NMR. The catalytic behavior of [Ir(COD)Cl]2-Linker/TiO2 is explained on the basis of quantitative and qualitative XPS data analysis performed for the catalysts before and after the reaction at 120 °C. It is shown that the temperature dependence of propene conversion and the enhancement of the NMR signal are explained via a combination of the stabilities of both the linker and immobilized [Ir(COD)Cl]2 complex. It is demonstrated that the N(CH3)2-linker is the most stable at the surface of TiO2 under used reaction conditions. As a result, only this sample shows a rise in the enhancement of the NMR signal in the 100-120 °C temperature range.

Keywords: NMR; XPS; heterogeneous catalysis; hydrogenation; single-site catalysts.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Results of catalytic tests in propene hydrogenetion reaction (a) conversion; (b) NMR signal enhancement.
Figure 2
Figure 2
XPS atomic ratios (left panel) (blue bars are for ‘as is’ sample, red bars are for sample after reaction at 120 °C) and spectra (right panel) (points) of the Ir 4f line and spectrum deconvolutions (solid lines, different chemical states are marked by color and with references with binding energy) before (top blue spectrum) and after (bottom red spectrum) the propene hydrogenation reaction at 120 °C for the Ir-Py-TiO2 sample.
Figure 3
Figure 3
XPS atomic ratios (left panel) (blue bars are for ‘as is’ sample, red bars are for sample after reaction at 120 °C) and spectra (right panel) (points) of the Ir 4f line and spectrum deconvolutions (solid lines, chemical states are marked with reference with binding energy) before (top blue spectrum) and after (bottom red spectrum) the propene hydrogenation reaction at 120 °C for the Ir-P-TiO2 sample.
Figure 4
Figure 4
TEM data with Ir clusters. (a) ‘as is’ Ir-P-TiO2 sample; (b) Ir-P-TiO2 after reaction at 120 °C.
Figure 5
Figure 5
EDX data. (a) ‘as is’ Ir-P-TiO2 sample; (b) Ir-P-TiO2 after reaction at 120 °C.
Figure 6
Figure 6
XPS atomic ratios (left panel) (blue bars are for ‘as is’ sample, red bars are for sample after reaction at 120 °C) and spectra (right panel) (points) of the Ir 4f line and spectrum deconvolutions (solid lines, different chemical states are marked by color and with references with binding energy) before (top blue spectrum) and after (bottom red spectrum) the propene hydrogenation reaction at 120 °C for the Ir-N-TiO2 sample.
Figure 7
Figure 7
TEM data for the Ir-N-TiO2 sample after the reaction at 120 °C.
Figure 8
Figure 8
Chemical structures of the linkers: (a) 2-(4-pyridylethyl)triethoxysilane; (b) 2-(diphenylphosphino)ethyltriethoxysilane; (c) (3-N,N-dimethylaminopropyl)triethoxysilane.
Figure 9
Figure 9
XPS survey spectra of studied samples.
See this image and copyright information in PMC

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