Heterogeneous catalysis is essential to many industrial applications. These catalysts are often comprised of supported nanoparticles, which contain various different surface sites. For some... Show moreHeterogeneous catalysis is essential to many industrial applications. These catalysts are often comprised of supported nanoparticles, which contain various different surface sites. For some reactions, the presence of specific surface sights dominates the overall reactivity. Fundamental insight into the influence of different surface sites on the surface reaction dynamics may lead to better catalyst design in the future. In this thesis, we combine ultra-high vacuum techniques and (curved) single crystal surfaces to study surface structure effects relevant to heterogeneous catalysis. We study how step edges on a platinum surface affect (elementary) reactions that occur in oxygen reduction: hydrogen dissociation, hydrogen recombination, and oxygen reduction. Show less
Cao, K.; Lent, R. van; Kleyn, A.W.; Juurlink, L.B.F. 2018
Dissociative chemisorption is an important reaction step in many catalytic reactions. An example of such a reaction is the Haber-Bosch process, which is used commercially to produce ammonia... Show more Dissociative chemisorption is an important reaction step in many catalytic reactions. An example of such a reaction is the Haber-Bosch process, which is used commercially to produce ammonia, an important starting material in the production of fertilisers. In theoretical descriptions of such chemical processes often approximations need to be made in order to keep the computational cost feasible, such as fixing the surface atoms in place, rather than allowing them to vibrate. In this work, several example systems (hydrogen dissociation on different metal surfaces) are used in order to test to what extent such approximations work well. Show less
The study of gas-surface interaction dynamics is important both for the fundamental knowledge it provides and also to aid the development of applications involving processes such as sputtering,... Show moreThe study of gas-surface interaction dynamics is important both for the fundamental knowledge it provides and also to aid the development of applications involving processes such as sputtering, plasma etching and heterogeneous catalysis. Elementary steps in the interactions, such as chemical reactions, adsorption and scattering are prototypical of more complex processes and better understanding of them deepens our knowledge of such processes. In addition, experimental measurements of specific interactions can be used to validate advanced computer models. Hence the experiments in this thesis have been carried out under well-defined condition, namely in ultrahigh vacuum and using high-purity single-crystal samples. The thesis is primarily focussed on understanding the interaction of hyperthermal Ar and N (~4-6 eV) with Ru(0001) and Ag(111) via scattering studies. Ar is very inert and its interaction with surfaces is primarily repulsive in nature, while N atoms probe the surface chemisorption well. From the study of Ar scattering dynamics, surface properties have been probed. From N scattering studies, chemisorption dynamics have been investigated. It is found that the electronic state of the incident particle may play an important role in the gas-surface interaction. Separately, the influence of pre-adsorbed CO on Ru(0001) on D2 dissociation have been unravelled. Show less
We have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those... Show moreWe have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those sites. Under UHV conditions OH groups can be formed on Pt(111) by pre-covering the surface with O adatoms, causing water to dissociate. We have shown that on stepped platinum surfaces OHad might not be as readily formed as one would assume based on the energetics of OH adsorption alone. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on D/Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on D/Pt(553). Under electrochemical conditions we show that in spite of the similar looking cyclic voltammograms, the kinetics of underpotential deposited hydrogen are significantly different in acidic and alkaline media. In alkaline media the ad- and desorption process is slow, whereas it is very fast in acidic media. We have pointed out three discrepancies in the current interpretation of the blank cyclic voltammetry of stepped platinum surfaces and propose a co-adsorption model that accounts for these discrepancies. Show less
As nickel and platinum are in the same group of the periodic table, the Ni(111) and Pt(111) surfaces may be expected to show similar interaction with water and hydrogen. However in this thesis, we... Show moreAs nickel and platinum are in the same group of the periodic table, the Ni(111) and Pt(111) surfaces may be expected to show similar interaction with water and hydrogen. However in this thesis, we show these interactions for Ni(111) are quite different from those of Pt(111). Moreover, our results show that the Ni(111) surface is a unique surface with regards to its chemistry of water and hydrogen. Show less
