Energy Level Shifts at the Silica/Ru(0001) Heterojunction Driven by Surface and Interface Dipoles

Abstract

Charge redistribution at heterogeneous interfaces is a fundamental aspect of surface chemistry. Manipulating the amount of charges and the magnitude of dipole moments at the interface in a controlled way has attracted tremendous attention for its potential to modify the activity of heterogeneous catalysts in catalyst design. Two-dimensional ultrathin silica films with well-defined atomic structures have been recently synthesized and proposed as model systems for heterogeneous catalysts studies. R. Wlodarczyk et al. (Phys. Rev. B, 85, 085403 (2012)) have demonstrated that the electronic structure of silica/ Ru(0001) can be reversibly tuned by changing the amount of interfacial chemisorbed oxygen. Here we carried out systematic investigations to understand the underlying mechanism through which the electronic structure at the silica/Ru(0001) interface can be tuned. As corroborated by both in situ X-ray photoelectron spectroscopy and density functional theory calculations, the observed interface energy level alignments strongly depend on the surface and interfacial charge transfer induced dipoles at the silica/ Ru(0001) heterojunction. These observations may help to understand variations in catalytic performance of the model system from the viewpoint of the electronic properties at the confined space between the silica bilayer and the Ru(0001) surface. The same behavior is observed for the aluminosilicate bilayer, which has been previously proposed as a model system for zeolites.Jian-Qiang Zhong and Mengen Wang contributed equally to this work.

Immobilization of single argon atoms in nano-cages of two-dimensional zeolite model systems

“…On the basis benchmark calculations on constituents of the system (bulk ruthenium and silica)28, the consistent exchange van der Waals density functional (vdW-DF-cx)3637 was used to describe the non-local vdW interactions in the Ar-silica/O/Ru(0001) system. The Ru(0001) substrate was modelled by a five-layer Ru slab.…”

Selective Catalytic Transfer Hydrogenolysis of Glycerol to 2-Isopropoxy-Propan-1-Ol over Noble Metal Ion-Exchanged Mordenite Zeolite

“…The enhanced catalytic performance of the RuMOR(cal) and RhMOR(cal) catalysts relative to that of PdMOR(cal) was attributed to the strong coordination of Ru and Rh with MOR (due to the +3 oxidation state of Ru and Rh, whereas Pd remains in the divalent state in PdMOR(cal)). The highest catalytic efficiency exhibited by the RuMOR(cal) catalyst can be correlated to the XPS data, which indicates the presence of chemisorbed oxygen (O-Ru) with a binding energy of 529.3 eV [29]. The chemisorbed oxygen would lead to strong interaction between MOR and Ru metal, thereby augmenting the stability of the catalyst.…”

“…The major peak at 532.8 eV and a smaller peak at ~531.4 eV can be assigned to Si-O-Si and Si-O-Al linkages, respectively. The shoulder peak at 529.3 eV was assigned to the chemisorbed oxygen (O-Ru) in the RuMOR catalyst [29]. Figure 3h−j present the Si2p spectra for all catalysts.…”

Model systems in heterogeneous catalysis: towards the design and understanding of structure and electronic properties

“…2(a)), in agreement with previous studies. 40,[51][52][53] For hydroxylation of the silica surface, the lm was pre-covered with a thin "ice" layer formed upon water adsorption at 100 K and subsequently irradiated with low energy (200 eV) electrons, as described in detail in ref. 46.…”

“…In principle, the shis could be explained by the loss of oxygen at the Ru-silica interface and respective changes in the work function of the substrate underneath the silica. [51][52][53] Since the shi in the O(Si) core level is substantially different 310 | Faraday Discuss., 2018, 208, 307-323 This journal is © The from the Si 2p one (0.4 vs. 0.8 eV), it is more plausible, however, that the observed shis are, to a large extent, due to chemical changes in the silica framework caused by the formation of silanol bonds. 43,46 Cr deposition onto hydroxylated lms was carried out at low temperatures in order to prevent the migration of adsorbed metal atoms to the silica/support interface as previously observed for Pd.…”