Long Zhang

Research Project – Emiel Hensen/Long Zhang

Background

Automotive exhaust gases are very harmful to both environment and public health. The three-way catalyst (TWC) was developed to clean up these toxic gases. Recently, Studies show that ceria is important components in TWC which rely on their excellent capability of releasing and storing oxygen. Besides, it can contribute to maintain high dispersion of the noble metal atoms, clusters and nanoparticles which are very helpful to increase the catalytic centers [Science, 2010, 329, 933-936].  That’s make the ceria a promising material for efficient TWC. In this project, we plan to study the behaviors of ceria based catalysts on automotive exhaust gas cleaning, e.g. NO and CO.

Project and objective

Our initial results indicate that the direct NO dissociation on Pd clusters/CeO2 is very difficult due to the high energy barrier, see figure 1. And this calculated result is in line with the NO reduction on Pd (111) [J. catal. 2014. 11. 011]. Earlier works have paid attention on the selective catalytic reduction of NO with H2 over the noble metal-based catalysts both experimentally and theoretically [J. catal. 2006. 237. 381]. Given the green environmental factor and commercial interest, the ceria based three-way catalysts will be investigated, aiming to decrease noble metal and rare earth elements content. Density functional theory (DFT) calculations will be carried out to understand the catalytic mechanisms for NO reduction and CO oxidation at the interface between ceria and the supported transition metal atoms (Pd, Pt, Rh, Fe, Co, Mn…) or clusters. To rationally design the catalyst, a kinetic parameters database is very necessary to be constructed. Here, the micro-kinetic model will be involved into study the elementary reaction and predict the reaction rates.

Methodology

We will perform DFT calculations by using the projector augmented wave (PAW) method as implemented in VASP. The exchange and correlation potential is PBE and will be treated using the generalized gradient approximation (GGA) with considering spin-polarization. A Hubbard Ueff = 4.5 eV is added to the PBE potential. The vacuum space is 15 Å to avoid the spurious interactions between CeO2(111) surface images. A K-point sampling of 1x1x1 for the Brillouin Zone integration of (4x4) surface unit cell. In order to study the reaction mechanism we will calculate the transition states by climbing-image nudged elastic band (CI-NEB) approach.

For further information:

Emiel Hensen (Helix, STW 3.35, Tel 5178, e.j.m.hensen@tue.nl)

ong Zhang (Helix, STW 4.37, Tel 3769, l.zhang3@tue.nl)