Transient mechanistic studies

PD Dr. Evgenii Kondratenko

Transient techniques are very helpful for unraveling complex reaction networks in terms of near to elementary reaction steps. Such a deep fundamental understanding of catalytic reactions is of prime importance for catalyst development or even for optimization of reactor operation. The Temporal Analysis of Products (TAP) reactor and Steady-State Isotopic Transient Kinetic Analysis (SSITKA) method belong to this group of techniques.

The TAP method is a pulse technique operating at sub-milliseconds time resolution. This important feature distinguishes this transient technique from another ones in terms of deeper understanding reaction mechanisms, micro kinetics, and transport phenomena of gas-solid reactions. For example, by using the TAP technique in combination with isotopic traces, we developed an advanced mechanistic scheme of high-temperature (> 1000 K) ammonia oxidation over industrially applied noble metal gauzes [1, 2]. The scheme considers the formation of N2, N2O, and N2O and identifies the origins of the loss of NO selectivity.

The SSITKA method is based upon the inclusion of one or more stable isotopic labels in a reactant flow and can operate in a broad range of pressures (from vacuum to elevated pressures). These experiments provide information on concentration of different types of adsorbed reaction intermediates, coverages and lifetimes of surface species. For the first time, a combined in-situ UV/Vis-SSITKA set up has been developed in our group and applied for identifying selectivity- and activity-determining factors of the oxidative dehydrogenation of propane over supported vanadium-based catalysts [3, 4]. This work was performed in the frame of the competence network (Sonderforschungsbereich 546) “Structure, dynamics and reactivity of transition metal oxide aggregates”

References

  1. J. Pérez-Ramírez, E.V. Kondratenko, V.A. Kondratenko, and
    M. Baerns, J. Catal., 227 (2004) 90–100.
  2. E.V. Kondratenko, and J. Pérez-Ramírez, Appl.Catal. A, 289 (2005) 97-103.
  3. E.V. Kondratenko , O. Ovsitser, J. Radnik, M. Schneider, R. Kraehnert, U. Dingerdissen, “Influence of reaction conditions on catalyst composition and selective/non-selective reaction pathways of the ODP reaction over V2O3, VO2 and V2O5 with O2 and N2O”, Applied Catalysis A, 319 (2007) 98-110.
  4. O. Ovsitser, M. Cherian, and E.V. Kondratenko, ”In-situ UV/Vis and transient isotopic analysis of the role of oxidizing agent in the oxidative dehydrogenation of propane over silica supported vanadia catalysts”, J.Phys.Chem.C, 2007, in press.