Controlled release of hydrogen isotope compounds and tunneling effect in the heterogeneously-catalyzed formic acid dehydrogenation

Kohsuke Mori,Hiromi Yamashita,Yuya Futamura,Shinya Masuda,Hisayoshi Kobayashi

doi:10.1038/s41467-019-12018-7

Kohsuke Mori, Hiromi Yamashita + Show 3 more

Open Access

https://doi.org/10.1038/s41467-019-12018-7

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Abstract

The hydrogen isotope deuterium is widely used in the synthesis of isotopically-labeled compounds and in the fabrication of semiconductors and optical fibers. However, the facile production of deuterium gas (D2) and hydrogen deuteride (HD) in a controlled manner is a challenging task, and rational heterogeneously-catalyzed protocols are still lacking. Herein, we demonstrate the selective production of hydrogen isotope compounds from a combination of formic acid and D2O, through cooperative action by a PdAg nanocatalyst on a silica substrate whose surface is modified with amine groups. In this process, D2 is predominantly evolved by the assist of weakly basic amine moieties, while nanocatalyst particles in the vicinity of strongly basic amine groups promote the preferential formation of HD. Kinetic data and calculations based on semi-classically corrected transition state theory coupled with density functional theory suggest that quantum tunneling dominates the hydrogen/deuterium exchange reaction over the metallic PdAg surfaces.

Highlights

The hydrogen isotope deuterium is widely used in the synthesis of isotopically-labeled compounds and in the fabrication of semiconductors and optical fibers
The presence of the amine groups was confirmed by the analysis of each specimen by Fourier transform-infrared (FT-IR) spectroscopy (Supplementary Fig. 1) and N 1s X-ray photoelectron spectroscopy (XPS) (Supplementary Fig. 2)
The long-range ordering of hexagonally packed mesoporous structures in these materials was demonstrated on the basis of low-angle X-ray diffraction (XRD) patterns (Supplementary Fig. 3)

Summary

Introduction

The hydrogen isotope deuterium is widely used in the synthesis of isotopically-labeled compounds and in the fabrication of semiconductors and optical fibers. We demonstrate the selective production of hydrogen isotope compounds from a combination of formic acid and D2O, through cooperative action by a PdAg nanocatalyst on a silica substrate whose surface is modified with amine groups. Kinetic data and calculations based on semi-classically corrected transition state theory coupled with density functional theory suggest that quantum tunneling dominates the hydrogen/deuterium exchange reaction over the metallic PdAg surfaces. The use of homogeneous catalysts on an industrial scale is extremely challenging due to the difficulties involved in recovering the precious metals and ligands from the reaction mixture For these reasons, systems based on heterogeneous catalysts in association with undeuterated FA and D2O would be highly beneficial, but such processes have not yet been researched, in spite of the obvious practical advantages. The H/D exchange reactions between FA and D2O is found to involve a quantum tunneling effect, as evidenced by the large kinetic isotope effect (KIE) value, and based on semiclassically corrected transition state theory (SC-TST) coupled with density functional theory (DFT) calculations

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Conclusion