Abstract
The effect of gases on the surface composition of Cu-Pt bimetallic catalysts has been tested by in situ infrared (IR) and x-ray absorption spectroscopies. Diffusion of Pt atoms within the Cu-Pt nanoparticles was observed both in vacuum and under gaseous atmospheres. Vacuum IR spectra of CO adsorbed on CuPtx/SBA-15 catalysts (x = 0-∞) at 125 K showed no bonding on Pt regardless of Pt content, but reversible Pt segregation to the surface was seen with the high-Pt-content (x ≥ 0.2) samples upon heating to 225 K. In situ IR spectra in CO atmospheres also highlighted the reversible segregation of Pt to the surface and its diffusion back into the bulk when cycling the temperature from 295 to 495 K and back, most evidently for diluted single-atom alloy catalysts (x ≤ 0.01). Similar behavior was possibly observed under H2 using small amounts of CO as a probe molecule. In situ x-ray absorption near-edge structure data obtained for CuPt0.2/SBA-15 under both CO and He pointed to the metallic nature of the Pt atoms irrespective of gas or temperature, but analysis of the extended x-ray absorption fine structure identified a change in coordination environment around the Pt atoms, from a (Pt-Cu):(Pt-Pt) coordination number ratio of ∼6:6 at or below 445 K to 8:4 at 495 K. The main conclusion is that Cu-Pt bimetallic catalysts are dynamic, with the composition of their surfaces being dependent on temperature in gaseous environments.
| Original language | English |
|---|---|
| Article number | 234706 |
| Journal | Journal of Chemical Physics |
| Volume | 157 |
| Issue number | 23 |
| DOIs | |
| State | Published - Dec 21 2022 |
| Externally published | Yes |
Funding
T.H. and F.Z. acknowledge financial support from the U.S. National Science Foundation, Division of Chemistry (Grant No. NSF-CHE1953843). A.I.F. acknowledges support from the U.S. National Science Foundation, Division of Chemistry (Grant No. NSF-CHE2203858). This research used the 8-ID (ISS) beamline of the National Synchrotron Light Source, a U.S. DOE Office of Science User Facilities operated for the DOE Office of Science by Brookhaven National Laboratory (BNL) under Contract No. DE-SC0012704. The authors thank the beamline scientist E. Stavitski at the 8-ID beamline of the NSLS-II for support during the beamline experiments.