Cation-doping strategies for tuning of zirconia acid-base properties

The role of Y-, Ca- and Ce-doping of cubic zirconia (c-ZrO₂) (111) surface on its acidity, basicity and the interplay between surface acid-base pairs is investigated by computational methods. The most stable surface structures for this investigation were initially determined based on previous studies of Y-doped c-ZrO₂ (111) and by a detailed exploration of the most stable configuration for Ca-doped c-ZrO₂ (111) and Ce-doped c-ZrO₂ (111). Next, surface mapping by basic probe molecules (NH₃ and pyridine) revealed a general reduction of the acidity of the surface sites, although a few exceptions were observed for zirconium ions at next nearest neighbour (NNN) positions to the oxygen vacancy and at the nearest neighbour (NN) position to the dopants. Adsorption of CO₂ over basic sites revealed a cooperative interplay between acid-base groups. In this case, the overall effect observed was the decrease of the calculated adsorption energies when compared with the pristine surface. Moreover, spontaneous formation of η ³-CO₂ systems from initial η ²-CO₂ configurations indicates a decrease in the required energy for forming oxygen vacancies in the doped ZrO₂ systems at NNN positions or further away from the existing vacancy site.

Structural, electronic, and magnetic properties of Ni nanoparticles supported on the TiC(001) surface

Metals supported on transition metal carbides are known to exhibit good catalytic activity and selectivity, which is interpreted in terms of electron polarization induced by the support. In the present work we go one step further and investigate the effect that a titanium carbide (TiC) support has on the structural, electronic, and magnetic properties of a series of Ni nanoparticles of increasing size exhibiting a two- or three-dimensional morphology. The obtained results show that three-dimensional nanoparticles are more stable and easier to form than their homologous two-dimensional counterparts. Also, comparison to previous results indicates that, when used as the support, transition metal carbides have a marked different chemical activity with respect to oxides. The analysis of the magnetic moments of the supported nanoparticles evidences a considerable quenching of the magnetic moment that affects mainly the Ni atoms in close contact with the TiC substrate indicating that these atoms are likely to be responsible for the catalytic activity reported for these systems. The analysis of the electronic structure reveals the existence of chemical interactions between the Ni nanoparticles and the TiC support, even if the net charge transfer between both systems is negligible.

Ab initio investigation of the formation mechanism of nano-interfaces between 3d-late transition-metals and ZrO2 nanoclusters

Understanding the formation of nano-interfaces between metallic clusters and nanoscale metal-oxides is an important step towards using such systems for catalytic applications. Thus, in this work, we employ density functional theory calculations to study the TMn-(ZrO2)13 interactions, for TM = Fe, Co, Ni, or Cu, and n = 1, 4, and 8. We found a general trend for adsorption and interaction energies (ad/int) for all cluster sizes, with . In terms of size effects, both adsorption and interaction (frozen adsorbed structures) energies become stronger with increasing cluster sizes due to the increase in the number of TM atoms in direct contact with the (ZrO2)13 nanocluster. The structural and electronic properties change for each TMn/(ZrO2)13 system, indicating that these properties could be tuned through variables like the TM species, cluster size and morphology (isomers with different structures). The results also indicate that, from the studied TMs, Ni (Cu) should form the smallest (largest) clusters when supported on the (ZrO2)13 nanoclusters. These and other results discussed here help understand the formation of the nano-interface in the TM-ZrO2 systems, which can be useful in the development of new catalysts.

Perspectives on the design of nanoparticle systems for catalysis

An overview of the Faraday Discussion, "Designing Nanoparticle Systems for Catalysis", is presented. Examples are taken from the papers presented at the meeting and from the literature to illustrate the main discussion points.