Atmosphere-Dependent Structures of Pt–Mn Bimetallic Catalysts

Abstract

Pt−Mn bimetallic catalysts exhibit high activity in many heterogeneous catalytic and electrocatalytic reactions. However, the surface structure of Pt−Mn catalysts under different reaction conditions remains less explored. This work describes the construction of different surface structures of the Mn/Pt(111) model system via controlling atmospheres at variable temperatures. Our results suggest that the Pt−Mn surface alloy and nearsurface alloy can be obtained upon low-temperature and high-temperature annealing in ultrahigh vacuum, respectively. With high-temperature oxidation, near-surface Mn atoms under the Pt-skin surface segregate outwards to form MnO on the Pt(111) surface. Structural transformation between MnO/ Pt(111) and Pt−Mn near-surface alloy can be repeated by alternate hightemperature oxidative and reductive treatments. CO adsorption sites change from Mn sites to Pt sites with the surface structure transformed from Mn/Pt(111) to Pt−Mn surface alloy. CO vibrational peaks shift to lower wavenumbers when the surface structure changes from Pt−Mn surface alloy to near-surface alloy. CO desorbs more easily on the surfaces of Pt−Mn surface alloy and Pt−Mn near-surface alloy compared with the clean Pt(111) surface because of the downshift of d-band center of surface Pt atoms. The feasible modulation of Pt−Mn surface structure provides a guidance for the rational design of Pt−Mn bimetallic catalysts.

Operando Surface Studies on Metal-Oxide Interfaces of Bimetal and Mixed Catalysts

“…Namely, small gas molecules such as hydrogen (H 2 ), carbon monoxide (CO), oxygen (O 2 ), and carbon dioxide (CO 2 ) would make dramatic alterations to catalyst structures in working conditions. Metal nanoparticles (NPs) supported by oxide catalysts can create active interfaces during catalytic reactions. − Bimetallic catalysts may rearrange its morphologic structures by selective surface segregations in oxygen environments. − Such an adsorbate-induced structural complexity has been also introduced by various operando techniques: X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), infrared reflection absorption spectroscopy (IRRAS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under reaction conditions. These characterization tools can be used for a wide range of catalysts in ex situ or in situ measurement mode. , As reported in the literature for bimetallic catalysts (Table ), the summarized characterization results deal with metastable alterations of nanocatalysts under various gas environments.…”

Carbon‐Coated Magnetic Fly Ash Modified with Guanylthiourea and Polydopamine for Simultaneous Removal of Cu(II) and Pb(II) in Acidic Aqueous Solutions

“…The constituent groups of guanylthiourea were À NH and C=S, confirming that guanylthiourea was successfully grafted onto PC-MFA . [23] The XRD patterns of MFA, C-MFA, and GPC-MFA are shown in Figure 3. The five peaks of MFA at the XRD diffraction peaks 2θ = (30°-65°) were in accordance with the diffraction peaks of the spinel structure of pure Fe 3 O 4 .…”

Promoting n-Butane Dehydrogenation over PtMn/SiO2 through Structural Evolution Induced by a Reverse Water-Gas Shift Reaction

“…The catalysts were also investigated using quasi in situ X-ray photoelectron spectroscopy (XPS), and the results are shown in Figure d. The main peak of Mn 2p 3/2 located at 641.6 eV and the additional satellite peak located at 644.7 eV are assigned to MnO, indicating most Mn stays oxidized; the peak at 639.4 eV is attributed to Mn 0 , consistent with the formation of PtMn alloy. , After RWGS, MnO and Mn 0 were also observed, and the proportion of the latter decreased from 3.8% to 2.3% (Table S2), which indicates that the Mn 0 atoms of Pt 3 Mn NPs are partially removed/oxidized to MnO, consistent with the results of XAS. The profiles of H 2 temperature-programmed reduction (H 2 -TPR) also showed that excess manganese oxide was reduced to MnO, consistent with the XPS results (Figure S3).…”