| AVS 64th International Symposium & Exhibition | |
| Fundamental Discoveries in Heterogeneous Catalysis Focus Topic | Thursday Sessions |
| Session HC+SA+SS-ThM |
| Session: | Mechanisms and Reaction Pathways in Heterogeneously Catalyzed Reactions |
| Presenter: | Aart Kleyn, Center of Interface Dynamics for Sustainability, PR China |
| Authors: | Q. Huang, Center of Interface Dynamics for Sustainability, Chengdu, PR China D.Y. Zhang, Center of Interface Dynamics for Sustainability, Chengdu, PR China E. Schuler, van 't Hoff Institute for Molecular Sciences, Amsterdam, The Netherlands M. Ronda Lloret, van 't Hoff Institute for Molecular Sciences, Amsterdam, The Netherlands G. Rothenberg, van 't Hoff Institute for Molecular Sciences, Amsterdam, The Netherlands N.R. Shiju, van 't Hoff Institute for Molecular Sciences, Amsterdam, The Netherlands A.W. Kleyn, Center of Interface Dynamics for Sustainability, PR China |
| Correspondent: | Click to Email |
Endothermic catalytic reactions require operation at elevated temperatures. The heating required is usually obtained by combustion of hydrocarbons and contributes to CO2 emission. Instead electricity obtained in a sustainable should drive the reaction. In addition, it is desirable that the energy transfer involved is done in a bond specific manner. Plasma excitation and dissociation of molecules can serve this purpose. In plasma, all molecular degrees of freedom are not in equilibrium and dissociation of CO2 can be realized much more efficiently than in thermodynamic equilibrium. There is a preferential vibrational excitation of CO2.
In Chengdu we use a plasma chemical reactor with mass spectroscopy, infrared spectroscopy, optical emission spectroscopy and a Langmuir probe to study the characteristics of the plasma, reaction products and the catalyst. In Amsterdam we use a thermal reactor and gas chromatography to study reaction products. The reactions are carried out at pressures of several hundreds of Pa up to atmospheric in Ar buffergas. Catalysts are prepared in the usual way.
The simplest reaction studied in the plasma reactor is the dissociation of CO2 into CO and O2. We find energy efficiencies higher than 45%, indicating that the system is not in thermodynamic equilibrium and plasma favors vibrational excitation to translational heating. Adding a catalyst like AgO or NiO on Al2O3 does not enhance the yield. However, a purely metallic catalyst does significantly enhance the yield.
Optical emission spectroscopy shows that the radiofrequency (RF) and microwave (MW) plasma behave quite different. In the MW plasma predominantly emission from the C2 Swann-band is seen, whereas the RF plasma shows mainly chemiluminescence from excited CO. This is due to a different electron excitation mechanism.
In the case of dry reforming of CH4 with CO2 in the plasma reactor we find that addition of an oxidic catalyst does not enhance the yield of CO + H2. In the case of dry reforming of butane (C4H10) to yield butene (C4H8), plasma reforming with or without catalyst does shows only small conversion. Mainly cracking of butane into C2Hx is seen and polymerization. However, running the same reaction under high temperature conditions in a thermal reactor yields a satisfactory conversion. A Co based catalyst has the best performance.
These studies allow us to obtain mechanistic information on the conversion of simple molecules, pretreated by plasma, on various catalysts. We are exploring to what extend direct Eley-Rideal reactions are relevant in the plasma reactor. This reaction mechanism is very unlikely under thermal conditions.