Atomic scale simulations of the interactions of plasma species on nickel catalyst surfaces.

Date: 15 September 2015

Venue: UAntwerp - Campus Drie Eiken - Building R - Auditorium R1 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk

Time: 2:15 PM

Organization / co-organization: Department of Chemistry

PhD candidate: Wesley Somers

Principal investigator: Annemie Bogaerts & Erik Neyts

Short description: PhD defence Wesley Somers - Faculty of Science, Department of Chemistry



Abstract

The increased greenhouse gas concentrations compared to the pre-industrial values have led to an enhanced greenhouse effect and, as a consequence, global warming. One of the possibilities to mitigate the climate change is to increase the energy efficiency of industrial processes. This is particularly interesting for the methane reforming processes, since CH4 (and CO2 in the case of dry reforming) is converted into syngas, a valuable chemical mixture of H2 and CO. These processes have a large energy cost under conventional conditions, due to the high temperatures that are required.

A promising alternative to the conventional procedure is the use of plasma catalysis, i.e. the combination of plasma technology and catalysis. However, this technology is very complex and there is little fundamental knowledge on the operative interaction mechanisms between plasma and catalyst.

Therefore, reactive molecular dynamics (MD) simulations are used in this doctoral study to investigate the interactions of plasma species on different nickel catalyst surfaces. The plasma species under study are CHx radicals (x={1,2,3}) and vibrationally excited CH4. These particles impinge on a total of six different nickel surfaces, to study the influence of crystallinity on the reactivity.

At a temperature of 400 K, different reaction mechanisms are observed, dependent on the nickel surface. The reactivity of impinging CH2 and CH radicals is high, however little H2 is formed at this temperature. A temperature study within the range of 400 K – 1600 K showed that high H2 yields are obtained at temperatures above 1400 K. However, at these temperatures the crystallinity of the nickel surface is reduced due to the continuous C-diffusion into the surface. Therefore, the role of the surface structure seems to become limited.

Afterwards, the motion of vibrationally excited CH4 is included in the MD simulations. This is done by first calculating the normal coordinates of the vibrational modes. These are then linked to the vibrational velocities, keeping into account the mode specific vibrational energy. Finally, the reaction behavior of vibrationally excited CH4 is investigated. Despite the correct vibrational motion, the reactivity is not as predicted in literature. Even after applying several corrections, MD simulations are not capable to accurately predict the reaction behavior of all vibrational modes.