Surface science approach to catalyst preparation

In this work, results of surface science studies related to the preparation of supported metal catalysts on well-defined oxide surfaces applying procedures used in real-world catalysis are presented. Specifically, a thin Fe3O4(111) film grown on Pt(111) was chosen as support and its surface was exposed to solutions of PdCl2 in order to deposit a Pd precursor. Scanning Tunneling Microscopy (STM) combined with X-ray Photoelectron Spectroscopy (XPS) have been applied to track both morphological and chemical changes that come along with the transformation of the adsorbed Pd precursor into nanoparticles in the early stages of catalyst preparation. The chemical properties of the prepared Pd model catalyst have been investigated by Temperature Programmed Desorption (TPD) and Infrared Reflection Absorption Spectroscopy (IRAS). For the supported Pd model catalyst prepared by impregnation of Fe3O4(111) films with acidic (pH 1.3) PdCl2 solution, STM and XPS results provide evidence for homogeneous nucleation of Pd particles out of a monolayer of adsorbed precursor, and an enhancement of the particle-support interaction with increasing annealing temperature. Chlorine, which remains on the model catalyst surface after vacuum annealing, could be removed by oxidation/reduction. However such a treatment leads to particle sintering. A Pd sample prepared through deposition-precipitation using a pH 10 PdCl2 solution shows a different particle evolution behavior as compared to the pH 1.3 sample because of the different precursor speciation and chemical decomposition mechanism. A comparison of Pd/Fe3O4 samples created via Pd evaporation under UHV conditions and that resulting from the solution deposition of Pd-hydroxo complexes reveals that changes in the interfacial functionalization of the support surface govern the differences in Pd nucleation behavior observed. The effect of solution pH on Pd loading and particle size during preparation has been studied. Homogeneously distributed Pd particles with narrow size distribution are formed on Fe3O4(111) from low and high pH PdCl2 solutions. Post-preparation treatment by oxidation and CO reduction leads to CO chemisorptive features characteristic of Pd nanoparticles. H2 reduction of a Pd/Fe3O4 sample, however, induces the strong metal support interaction (SMSI) with Pd-Fe alloy formation.

Author dc:creator

• Wang, Huifeng

• catalyst preparation
• surface science
• palladium
• iron oxide
• thin film
• nanoparticle
• model catalyst,
• wet chemical
• PVD

Licence dc:rights.uri

• http://www.fu-berlin.de/sites/refubium/rechtliches/Nutzungsbedingungen

Language dc:language

eng

Identifier URI

http://dx.doi.org/10.17169/refubium-7773

OAI record oai:identifier

https://refubium.fu-berlin.de/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Arefubium.fu-berlin.de%3Afub188%2F3573