Surface Compositions of Oxide Supported Bimetallic Catalysts: A Compared Study by High‐Sensitivity Low Energy Ion Scattering Spectroscopy and X‐Ray Photoemission Spectroscopy

Abstract

It is well known that there is a critical relationship between the surface composition and catalytic performance for a bimetallic catalyst. However, in most cases, the surface composition is obviously different from that of the bulk. Moreover, the surface is normally reconstructed under reaction conditions. In this personal account, our recent progresses in determining the surface compositions of oxide supported bimetal catalysts by high‐sensitivity low energy ion scattering spectroscopy (HS‐LEIS) and X‐ray photoemission spectroscopy (XPS) are summarized. Phase diagrams of the surface compositions under various conditions as a function of the bulk composition are established and compared. It is found that oxidation induces de‐alloying and enrichment of PdO, CuO, SnO2 on the surface, while H2 reduction results in re‐alloying. The addition of the second component not only modifies the nature of the active site, but also varies the dispersion of the active components. The support effects are discussed. The compared studies reveal that HS‐LEIS can achieve a more reliable surface composition for oxide supported catalysts.

Promotion Effect of Cu for CO Oxidation on Ceria Supported PdxCuy Bimetallic Catalysts

“…For Pd/CeO 2 , the binding energy of Pd 3d5/2 is about 337.4 eV after oxidation at 400 °C (Figure S4), which is higher than the typical values of the bulk PdO, for example, 336.6 eV for Pd-Au/TiO 2 and 337 eV for Pd/TiO 2 . 30 The difference of Pd 3d5/2 between the oxidized and reduced Pd/CeO 2 is 2 eV, which is close to those of the above-mentioned Pd/TiO 2 catalysts. Moreover, the Pd 3d5/2 for Pd 2+ in the PdCeO x solid solution was reported to be 338 eV.…”

“…Surface-sensitive characterizations were mainly performed with high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS) and X-ray photoelectron spectroscopy (XPS) combined with a homemade ambient pressure ex-situ reaction cell, and more details have been reported previously. , The catalysts were pretreated in an ex-situ continuous-flow reactor under atmospheric pressure, which can mimic the experimental conditions to be the same as the realistic reaction enviornment. Oxidation and reduction treatments were conducted with 20 vol % O 2 /N 2 and H 2 (99.999%).…”

Selective and Stable In-Promoted Fe Catalyst for Syngas Conversion to Light Olefins

“…This suggested that the In concentration near the surface layers can be increased by increasing the In loading in the catalyst. This phenomenon was also observed in a range of bimetallic materials, intermetallic compounds, and transition metal ceramics. ,− …”