Abstract
Metal ions exchanged on zeolites represent a unique bridge between heterogeneous solid materials and homogeneous inorganic chemistry. The complexing of exchanged metal ions with H2O or NO, is of particular relevance for a number of reactions, including the ubiquitous presence of both gases in pollution remediation technologies. Here, we interrogate the molecular structure of Pd cations in SSZ-13 zeolites and their interaction with H2O and NO using experimental and computational analyses. Density functional theory (DFT) and spectroscopic characterization establish that Pd cations preferentially populate two Al (2Al) sites in the six-membered ring as PdII. In situ spectroscopic and kinetic analyses follow the Pd coordination environment and reactivity as a function of environmental conditions, and molecular structures are rationalized through ab initio molecular dynamics and first-principles thermodynamic modeling. Experiment and computational modeling together reveal that, at temperatures <573 K, Pd ions are solvated and mobilized by H2O molecules, promoting catalytic CO oxidation, and form molecular complexes akin to their Pd homogeneous analogues. Exposure to NO promotes transformation from 2Al → 1Al charge-compensated H2O-solvated Pd-nitrosyl complexes, which desorb NO at higher temperatures and inhibit CO adsorption and oxidation. A comparison with Pd-BEA and Pd-ZSM-5 zeolites demonstrates a heterogeneous distribution of Pd-NO complexes under dry conditions that coalesce into homogeneous H2O-solvated Pd-nitrosyl complexes upon exposure to H2O.
| Original language | English |
|---|---|
| Pages (from-to) | 12801-12818 |
| Number of pages | 18 |
| Journal | ACS Catalysis |
| Volume | 10 |
| Issue number | 21 |
| DOIs | |
| State | Published - Nov 6 2020 |
Funding
The authors acknowledge financial support by the Department of Energy Office of Energy Efficiency & Renewable Energy (DE-EE0008233) (W.S.E., L.C.G.). Collaboration with Oak Ridge National Laboratory was funded by the U.S. Department of Energy Vehicle Technologies Office (W.S.E., Y.G.), and the UVA Engineering Research and Innovation Award (C.P., K.M.). S.L. acknowledges financial support by a PLS-Postdoctoral Grant of the Lawrence Livermore National Laboratory during the preparation of this manuscript. This manuscript has been authored in part by UT-Battelle (J.A.P.), LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). This research used beamline 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. The authors thank Prof. Jeffrey T. Miller, Matthew A. Conrad, Nicole J. Libretto, and Christopher K. Russell for their assistance with the XAS experiments. The authors acknowledge Research Computing at the University of Virginia for providing computational resources and technical support that have contributed to the results reported within this publication.
Keywords
- adsorption
- catalytic reactions
- ions
- nitric oxide
- zeolites