An attempt to correlate surface physics with chemical properties: molecular beam and Kelvin probe investigations of Ce_1−xZr_xO₂ thin films

Abstract

What is the correlation between physical properties of the surfaces (such as surface potential, electronic nature of the surface), and chemical and catalysis properties (such as chemisorption, sticking probability of surface)? An attempt has been made to explore any correlation that might exist between the physical and chemical properties of thin film surfaces. Kelvin probe microscopy (KPM) and the molecular beam (MB) methods were employed to carry out the surface potential, and oxygen adsorption and oxygen storage capacity (OSC) measurements on CeZrO thin films. A sol-gel synthesis procedure and spin-coating deposition method have been applied to make continuous nanocrystalline CeZrO (x = 0-1) (CZ) thin films with uniform thickness (35-50 nm); however, surface roughness and porosity inherently changes with CZ composition. MB studies of O adsorption on CZ reveal high OSC for CeZrO, which also exhibits highly porous and significantly rough surface characteristics. The surface potential observed from KPM studies varied between 30 and 80 mV, with Ce-rich compositions exhibiting the highest surface potential. Surface potential shows large changes after reduction or oxidation of the CZ film demonstrating the influence of Ce/Ce on surface potential, which is also a key to catalytic activity for ceria-based catalysts. The surface potential measured from KPM and the OSC measured from MB vary linearly and they depend on the Ce/Ce ratio. More and detailed studies are suggested to arrive at a correlation between the physical and chemical properties of the surfaces.

Subtle interaction between Ag and $$\hbox {O}_{2}$$ O 2 : a near ambient pressure UV photoelectron spectroscopy (NAP-UPS) investigations

“…This cationic nature creates a space charge layer on the Ag surface and possibly induces a semiconductor-like character. 41 As predicted by van Santen et al, 15 Ag δ+ character is expected to change the repulsive behaviour of alkenes toward Ag to an attractive one ≥ 390 K. In fact, a decrease in the O 2p antibonding character and a shift towards lower BE ( Figure 2) hints an imminent enhancement in reactivity. A comparison between Figures 2b and 2c shows an apparent inverse correlation among them.…”

“…It is also to be noted that industrial epoxidation catalysts employ silver supported on alumina with promoters and few other ingredients at high pressures (10-30 bar). Hence, we suggest for detailed work function measurements on model surfaces 41 as well as on industrial catalysts with Kelvin probe force microscopy under reaction conditions. This is expected to give more information about the formation of the space charge layer and the role of surface charge in the reaction.…”

Sustainable CO2 Reduction on In2O3 with Exclusive CO Selectivity: Catalysis and In Situ Valence Band Photoelectron Spectral Investigations

“…The 1:1 ratio also shows very similar changes and is hence not presented here. More interesting results are observed with 1:0.67, and the following points are worth underscoring: (i) The entire VB broadened up to 0.6 eV toward the Fermi level highlighting a possible electron filling of VB; it is to be noted that a similar VB shift was observed on reduction of ceria, 41,42 and this leads to a change in the work function too; (ii) although the VB changes observed resemble that of the changes seen with 1:3 up to 573 K, a drastic change occurs at 673 K and above; (iii) the first and low BE VB feature gains in intensity at ≥673 K and shift to low BE by 0.7 eV (indicated by dot-dash arrow), at the expense of the second VB feature; (iv) unlike 1:3, the VB reverts back to the spectral pattern observed at 295 K on cooling in the reaction atmosphere. The last point suggests that the changes observed with the VB are fully reversible and it can be observed exclusively with in situ spectral methods; no postreaction analysis would reveal these changes.…”

New Strategy toward a Dual Functional Nanocatalyst at Ambient Conditions: Influence of the Pd–Co Interface in the Catalytic Activity of Pd@Co Core–Shell Nanoparticles

“…Although Pd is more electronegative than Co, metallic Co observed in PC catalysts even under oxidizing conditions reiterates that electron transfer does occur from Pd to Co through possible Fermi level equilibration. It is worth investigating the changes in the surface work function of these catalysts, possibly under in situ conditions, to understand the electronic state of surfaces in detail , by relevant methods. Significantly different DOS metals may be combined to create new and/or tunable activity/conversion/selectivity regime for different reactions.…”