AVS 60th International Symposium and Exhibition
    Atom Probe Tomography Focus Topic Wednesday Sessions
       Session AP+AS+MI+NS+SS-WeA

Paper AP+AS+MI+NS+SS-WeA11
NO2 Reduction over Pt and Rh Single Nanoparticles: Imaging with Nanometric Lateral Resolution

Wednesday, October 30, 2013, 5:20 pm, Room 203 A

Session: APT and FIM Analysis of Catalysts and Nanoscale Materials
Presenter: C. Barroo, Université Libre de Bruxelles, Belgium
Authors: C. Barroo, Université Libre de Bruxelles, Belgium
S. Lambeets, Université Libre de Bruxelles, Belgium
Y. De Decker, Université Libre de Bruxelles, Belgium
F. Devred, Université Libre de Bruxelles, Belgium
T. Visart de Bocarmé, Université Libre de Bruxelles, Belgium
N. Kruse, Université Libre de Bruxelles, Belgium
Correspondent: Click to Email
Nitric oxides (NOx) emissions from vehicles are harmful to human beings and may cause severe health issues. NOx abatement is therefore highly desirable, but the development of viable solutions still represents a major challenge for catalyst makers, especially in the case of lean-driven vehicles. NO is known to be oxidized to NO2 under lean-burn conditions in automotive engines, and subsequently reduced into N2 during the rich-burn regime. In this work, we have investigated the catalytic reduction of NO2 over platinum and rhodium field emitter tips by means of Field Emission Microscopy (FEM). Real-time FEM is a powerful method for studying the dynamics of catalytic reactions that take place on the surface of the top of a nanosized metal tip, which acts as a catalytic particle. These studies are performed during the ongoing catalytic reaction which can be imaged in real time and space. Nanoscale resolution is achieved, providing a local indication of the instantaneous surface composition. Reaction-induced structural changes of the catalyst’s surface can also be assessed with step-site resolution. FEM is based on the emission of electrons from the sample which can be affected by the presence of various adsorbates. Local variations of the work function are reflected in the form of a brightness pattern and the surface composition of the sample can be qualitatively investigated during the ongoing catalytic process, allowing for the determination of the elementary processes involved.

The microscope is run as an open nanoreactor, through a constant supply of gaseous reactants and constant gas-phase pumping of the reaction chamber, ensuring that the system is kept far from thermodynamic equilibrium. This may lead to non-linear dynamics. Among others, oscillating phenomena observed during the NO2 reduction by H2 over both Pt and Rh nanocrystal (whose diameter is ≈40 nm) are presented.

Data have been characterized by Fourier transforms, temporal autocorrelations and dynamical attractors that demonstrate the existence and robustness of the kinetic oscillations. Furthermore, the optimal parameters obtained for the reconstruction of the dynamical attractor from the experimental time series, give important information that can lead to a better understanding of the mechanism of the catalytic reduction of NO2 over PGM nanoparticles.