Bauer Udo, Späth Florian, Düll Fabian, Bachmann Phillip, Steinhauer Johann, Steinrück Hans-Peter, Papp Christian
Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058, Erlangen, Germany.
Erlangen Catalysis Resource Center (ECRC), Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058, Erlangen, Germany.
Chemphyschem. 2018 Jun 19;19(12):1432-1440. doi: 10.1002/cphc.201800044. Epub 2018 Apr 19.
We have investigated the adsorption and thermal reactivity of CO and C H on well-defined bimetallic Pt Ag /Pt(111) surface alloys (with x=0.67, 0.50, 0.38 and 0.32) using in situ synchrotron-based high-resolution X-ray photoelectron spectroscopy. During low-temperature (140 K) adsorption of CO, we find population of the energetically more stable Pt on-top site followed by the Pt bridge site, as known from clean Pt(111); CO does not adsorb on Ag facets under the applied conditions. The total CO coverage linearly decreases with Ag surface content. Upon heating, CO and CO desorb at higher temperatures than on bare Pt(111), for example, by ∼65 K for CO for an Ag content of 33 %. This shift is due to the well-known electronic ligand-effect of Ag atoms surrounding Pt atoms/clusters. For C H adsorption on the AgPt alloys at low temperature (120 K), we find two species in the C1s XP spectrum, each displaying a vibrational fine structure; this contrasts the situation on clean Pt(111), where only one species is found. Upon heating, ethylene reacts with ethylidyne being the dominant intermediate; in contrast to clean Pt(111), on the alloy surfaces the reaction to CCH occurs at much lower temperatures, e. g. by ∼60 K for the alloy with 68 % Ag, and no ethylene desorption is found.
我们使用基于同步加速器的原位高分辨率X射线光电子能谱，研究了CO和CH在定义明确的双金属PtAg/Pt(111)表面合金（x = 0.67、0.50、0.38和0.32）上的吸附和热反应性。在CO的低温（140K）吸附过程中，我们发现能量上更稳定的Pt顶位被占据，随后是Pt桥位，这与清洁的Pt(111)情况相同；在施加的条件下，CO不会吸附在Ag面上。总CO覆盖率随Ag表面含量线性降低。加热时，CO和CO的脱附温度比在裸露的Pt(111)上更高，例如，对于Ag含量为33%的情况，CO的脱附温度高出约65K。这种位移是由于围绕Pt原子/团簇的Ag原子的著名电子配体效应。对于在低温（120K）下CH在AgPt合金上的吸附，我们在C1s XP光谱中发现了两种物种，每种都显示出振动精细结构；这与清洁的Pt(111)情况形成对比，在清洁的Pt(111)上只发现一种物种。加热时，乙烯与乙基乙炔反应，乙基乙炔是主要中间体；与清洁的Pt(111)不同，在合金表面上，向CCH的反应在低得多的温度下发生，例如，对于含68%Ag的合金，反应温度低约60K，并且未发现乙烯脱附。
