Enhancing the Catalytic Activity of Palladium Nanoparticles via Sandwich-Like Confinement by Thin Titanate Nanosheets.

Daniel R Wagner,Thomas Götsch,Takayuki Kikuchi,Takayoshi Sasaki,Jutta Kröhnert,Annette Trunschke,Josef Breu,Thomas Lunkenbein,Kevin Ament

doi:10.1021/acscatal.1c00031

Abstract

As atomically thin oxide layers deposited on flat (noble) metal surfaces have been proven to have a significant influence on the electronic structure and thus the catalytic activity of the metal, we sought to mimic this architecture at the bulk scale. This could be achieved by intercalating small positively charged Pd nanoparticles of size 3.8 nm into a nematic liquid crystalline phase of lepidocrocite-type layered titanate. Upon intercalation the galleries collapsed and Pd nanoparticles were captured in a sandwichlike mesoporous architecture showing good accessibility to Pd nanoparticles. On the basis of X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) Pd was found to be in a partially oxidized state, while a reduced Ti species indicated an electronic interaction between nanoparticles and nanosheets. The close contact of titanate sandwiching Pd nanoparticles, moreover, allows for the donation of a lattice oxygen to the noble metal (inverse spillover). Due to the metal–support interactions of this peculiar support, the catalyst exhibited the oxidation of CO with a turnover frequency as high as 0.17 s–1 at a temperature of 100 °C.

Highlights

Are supporting materials important to disperse and stabilize catalytically active nanoparticles and extensive research gave convincing evidence for an active role of the support in the catalytic processes.[1]
Was 2 g L−1.24 Upon mechanical shaking a nematic phase was obtained with individual nanosheets separated to 59 nm according to small-angle X-ray scattering (SAXS; Figure S1)
4-dimethylaminopyridine (DMAP) was applied as the capping ligand for the Pd nanoparticles, which in turn were synthesized by reduction of Na2[PdCl4] with NaBH4.32 The as-synthesized nanoparticles showed a narrow size distribution of 3.4 ± 0.4 nm, as determined by transmission electron microscopy (TEM; Figure S2a)

Summary

INTRODUCTION

Are supporting materials important to disperse and stabilize catalytically active nanoparticles and extensive research gave convincing evidence for an active role of the support in the catalytic processes.[1]. Two-dimensional (2D) layered lepidocrocite-type titanates with a nominal formula of AxTi2−yO4My (A = K+, Cs+, Rb+, M = Li+; vacancy; x = 0.7−0.8; abbreviated as L-titanate)[22,23] appear promising in the context sketched above. These can be converted into a protonated form by acid treatment. In a later step of the catalytic cycle this vacancy is refilled by O2 from the gas phase The resulting catalyst was highly active in the oxidation of CO

RESULTS AND DISCUSSION

■ CONCLUSION

■ REFERENCES

■ ACKNOWLEDGMENTS