(616d) Chemical Engineering at the Stanford Synchrotron Radiation Lightsource (SSRL) XAS Beamlines

In-situ X-ray absorption spectroscopy (XAS) is frequently used to determine structure-activity relationships of catalysts. However, designing an in-situ XAS experiment is complicated by many factors such as (i) micromolar quantities of the active metal in the quantity of the catalyst in the experimental cell, (ii) catalyst particle sizes vary compared to lab based experiments, (iii) the time it takes to purge out a reactive environment, and (iv) the quantity of impurities found in dead volumes of the flow system are on the same order magnitude as the active metal. To determine how the factors above may influence the dynamics of our system, we have evaluated how our flow system and reactor that is installed at the beamline compares from a mass transport and gas purity standards to reactors set up in labs for catalyst kinetics characterization allowing us to improve operations and better design in-situ XAS experiments. External and internal particle diffusion were calculated for some example catalysts. Mass transport equations were solved, and the result was used to predict the concentration of gas impurities throughout the Co-ACCESS flow system as a function of number of flow controllers used. Modeling of our 6-gas ambient pressure flow system in its basic operation (6 lines sequentially connected to form one outlet), we have investigated what type of flow regimes we have for the process gas feed entering the cell, and how long it takes to purge different sections of the system to reach desired gas purities. Based upon these results we have developed new flow patterns to reduce the effects of time associated with switching gas streams, low Reynolds numbers, and minimizing effects of dead volumes while also investigating causes of subtle changes in the XAS spectra based upon time on stream.