Transition state and product diffusion control by polymer–nanocrystal hybrid catalysts

Abstract

Effective catalysts stabilize specific transition states and control the transport of species to and from catalytically active sites. Enzymes show these traits thanks to their diverse amino acid functional groups encapsulating metal centres, but are limited in the reaction conditions in which they can operate. Realizing a catalyst with this kinetic and transport control that can be used under demanding industrial conditions is challenging. Here, we show a modular approach for the systematic synthesis of polymer–nanocrystal hybrids, where palladium nanocrystals are encapsulated within tunable microporous polymer layers. The polymer chemistry and morphology control the catalytic performance of the metal sites, affecting the transition state for CO oxidation and controlling the transport of CO2 away from the active site. This approach can be applied to other polymer–nanocrystal compositions and catalytic applications, and is therefore expected to have an impact in many areas of catalysis.

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Fig. 1: Modular synthesis of the Pd/polymer composites.
Fig. 2: Characterization of POF-encapsulated Pd NCs.
Fig. 3: Kinetic studies of the mechanism of CO oxidation on several Pd-based materials prepared in this study.
Fig. 4: Oscillations in activity.
Fig. 5: Diffusion limitations.

Data availability

All data are available from the authors upon reasonable request.

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Acknowledgements

Support for this work was provided by a seed grant through the Natural Gas Initiative at Stanford University. The authors thank E. Goodman (Stanford University) for help with microscopy, L. Kunz (Stanford University) for help with elemental analysis, A.-C. Yang and A. Aitbekova (Stanford University) for help with synthesis of the materials and O. Müller (SLAC National Laboratory) for help with X-ray absorption experiments. M.C. acknowledges further support from the School of Engineering at Stanford University and from a Terman Faculty Fellowship. A.R.R. acknowledges support from the National Science Foundation Graduate Research Fellowship Program. Characterization of the hybrid materials was performed at the Stanford Nano Shared Facilities (SNSF) at Stanford University supported by the National Science Foundation under award ECCS-1542152. XAS measurements were collected at SSRL beam lines 9-3 and 7-3. A.S.H., A.B. and S.R.B. acknowledge support from the Department of Energy, Basic Energy Sciences funded Consortium for Operando and Advanced Catalyst Characterization via Electronic Spectroscopy and Structure (Co-ACCESS) at SLAC.

Author information

A.R.R. and M.C. conceived the idea for the study. A.R.R. synthesized the materials and performed structural and catalytic characterization. C.J.W. contributed to structural characterization. A.A.H. performed tomography characterization. A.S.H. and A.B. contributed to XAS characterization supervised by S.R.B. A.M. and M.V. contributed to the synthesis of materials. M.C. supervised the entire project. A.R.R. and M.C. wrote the manuscript with contributions from all authors.

Correspondence to Matteo Cargnello.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–11

Supplementary Video

HAADF–STEM tomography reconstruction of a POF/Pd/POF, initially shown as cross-sections of a single microparticle and later as a tilt series to create the 3D reconstruction followed by the surface generated after segmentation of the POF and the Pd particles. Finally, the same surface, but with 60% transparency of the POF material.

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