Research Interests and Equipment
Catalytic Performance, Steady-state and Transient Kinetic Studies
In situ investigation of gas/solid interactions using step-gas concentration switches and temperature-programmed techniques to study kinetics and mechanistic aspects of heterogeneous catalytic reactions and adsorption/desorption processes are conducted in this home-made apparatus. Techniques used in our laboratory are as follows:
• SSITKA-Mass Spectrometry (Balzers, Quadrupole 1-300 amu) methodology for the quantification of the active reaction intermediates and inactive (spectator) species.
• H₂ or CO-TPD and gas-pulse chemisorption for the determination of the particle size and dispersion of metal in supported metal catalysts.
• NH₃- and CO₂-TPD determination of surface acidity and basicity of solids
• Temperature-programmed (TPR) and Transient Isothermal Reduction (TIR) to investigate redox properties/kinetics of solids.
• ¹⁶O/¹⁸O Transient Isothermal Isotopic Exchange (TIIE) for the estimation of transient kinetic rates of surface and bulk oxygen exchange/diffusion along with the estimation of important kinetic parameters of the exchange process (e.g. Deff (cm²/s), Eₐₚₚ).
• Steady state kinetic experiments free of mass/heat transport effects allow detailed micro-kinetic modeling or kinetic rates coupled with apparent activation energies and orders of reaction.
Transient Techniques
Steady-State Isotopic Transient Kinetic Analysis (SSITKA)
This technique aims at the use of stable isotopes in heterogeneous gas/solid catalytic reactions that permits in a direct way the in situ evaluation of forward and reverse reaction rates of individual elementary reaction steps and the surface concentration, mean life-time of truly active reaction intermediates. A more accurate site activity determination, TOFITK (s⁻¹) based on the concentration of these active intermediates is then possible. A step-gas concentration switch from the non-isotopic to the equivalent isotopic feed gas or vice versa is made at constant T, P and flow rate. Based on the recorded reactants/products gas responses by mass spectrometry and appropriate mass balance relationships, the above-mentioned kinetic quantities can be estimated.
In the graph shown, a SSITKA switch ¹²CO₂/¹²CH₄ → ¹³CO₂/¹²CH₄ during Dry Reforming of Methane over a supported Ni catalyst allows to follow the CO₂ activation path towards CO formation, where active carbon (CO₂ + C ↔ 2 CO) and inactive adsorbed CO₂ can be estimated.
