Infrared studies of unsteady-state processes during oxidation reactions over supported catalysts.

摘要

The spatio-temporal dynamic behavior of CO oxidation over supported catalysts is studied using infrared thermography and Fourier transform infrared spectroscopy. A novel experimental technique is developed to measure the concentration of adsorbed CO with spatial resolution. A Monte Carlo simulation is formulated to simulate the spatio-temporal behavior of auto-oscillations.; Auto-oscillations on the supported catalysts are affected by many parameters including reactor temperature, reactant concentration, catalyst activity and characteristics, sizes and distributions of crystallites, and properties of the support. It does not appear however, that spatial thermal effect is a necessary condition for auto-oscillatory states but rather the consequence of changes occurring on a non-uniform reaction environment.; Spatio-temporal dynamics of a distributed thermal hot spot system is successfully suppressed by video feedback control. The technique requires an empirical eigenfunction analysis of the IR video images. Properly vibrating the feed suppresses the large amplitude chaotic auto-oscillations with an increase in the average CO{dollar}sb2{dollar} production. Feed vibrations also lower the ignition and extinction temperatures. The results indicate that the feed vibrations drive the oscillations of oxygen and CO coverage on the catalyst surface which periodically interrupt the gradual formation and propagation of the CO adlayer on the catalyst surface which inhibits the reaction. In situ FTIR studies confirm that vibrating the feed decreases the coverage of linearly bonded CO and bridged CO during the reaction.; A novel in-situ IR technique (SRIR) that measures the spatial distribution of the CO surface concentration on supported catalysts is also developed. The experimental system built in this work is the first one capable of measuring the spatial distributions of both the temperature and the adsorbate concentration under atmospheric pressure on a supported catalyst.; A non-isothermal Monte Carlo model is developed which successfully predicts the major results observed in the experiments. The model includes an oxidation-reduction trigger mechanism at the catalyst surface and it combines the Monte Carlo simulation with the partial different equation of heat transfer in a distributed system to simulate CO oxidation on supported catalysts.