(570m) Non-Steady-State Catalyst Characterization with Thin Zone TAP Experiments | AIChE

(570m) Non-Steady-State Catalyst Characterization with Thin Zone TAP Experiments

Authors 

Redekop, E. - Presenter, Washington University in Saint Louis
Yablonsky, G. S. - Presenter, Washington University in Saint Louis
Constales, D. - Presenter, Ghent University
Zheng, X. - Presenter, University of Houston
Veith, G. - Presenter, Oak Ridge National Laboratory
Gleaves, J. T. - Presenter, Washington University in Saint Louis


Fundamental understanding of the physicochemical processes on the surface of the industrial heterogeneous catalysts under working conditions is still a major challenge in chemical engineering science. To develop more efficient catalytic materials, and to better understand, design, and operate catalytic reactors, the kinetics of the catalytic reactions must be investigated. Non-steady-state kinetic studies complemented by catalyst surface characterization can provide valuable information about the reaction mechanism and its relation to the surface composition. Kinetic models of the steady-state and non-steady-state complex catalytic processes, that are the foundations of catalyst development and reactor design, must be based on experimental rate data extraction of which often involves preliminary theoretical assumptions. The kinetically ?model-free approach?, i.e. extracting the values of chemical transformation rates with no assumptions about the kinetic model, have been successfully applied by Temkin (1979). Temkin used a model free approach in the analysis of steady-state kinetic data, particularly of CSTR-data. However, the kinetically ?model-free? approach for the extraction of non-steady-state chemical transformation rate is still in the development stage. The limiting factor step is the lack of an efficient computation procedure to extract the rate of chemical transformation. The concept of the kinetically model free procedure (so called Y-procedure) and its realization have been described recently by Yablonsky et al (2007) regarding the non-steady-state data obtained in the Thin Zone TAP-reactor (TZTR) which is shown on Figure 1. Recently, the Y-Procedure was developed as a method for the reconstruction of the gas concentrations and the surface reaction rates from the exit flux measured in a TZ TAP experiment. Mathematically, the Y-Procedure is based on the Laplace domain solution of the diffusion equation for the inert zones in the TZ TAP reactor. The numerical algorithm utilizes the equivalent of this solution in the Fourier domain. The key feature of the Y-Procedure is that the gas concentrations and the reaction rates are extracted from the experimental data without any a priory assumptions about the reaction mechanism. Previously, the Y-Procedure was introduced and illustrated by just one example - the first order reaction on the surface. In this paper the Y-Procedure methodology for non-steady-state catalyst characterization was developed beyond the simplest case of first order irreversible reaction and illustrated by the applications to the model mechanisms as well as experimental data. For the model mechanisms, irreversible adsorption and reversible adsorption, the characteristic patterns in the non-steady-state rate/concentration data were identified and explained in terms of model parameters. The application of the Y-Procedure to the experimental data, CO adsorption and oxidation over silica supported gold nanoparticles showed that the real reactions exhibit complex behavior much different from the ideal systems (see Figure 2 a,b). The Y-Procedure analysis of real experimental data accomplished in this project is a first of its kind to the best of our knowledge.

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