Making sense of parameter estimation and model simulation in bioprocesses.

Most articles that report fitted parameters for kinetic models do not include meaningful statistical information. This study demonstrates the importance of reporting a complete statistical analysis and shows a methodology to perform it, using functionalities implemented in computational tools. As an example, alginate production is studied in a batch stirred-tank fermenter and modeled using the kinetic model proposed by Klimek and Ollis (1980). The model parameters and their 95% confidence intervals are estimated by nonlinear regression. The significance of the parameters value is checked using a hypothesis test. The uncertainty of the parameters is propagated to the output model variables through prediction intervals, showing that the kinetic model of Klimek and Ollis (1980) can simulate with high certainty the dynamic of the alginate production process. Finally, the results obtained in other studies are compared to show how the lack of statistical analysis can hold back a deeper understanding about bioprocesses.

Platinum Inhibits Low-Temperature Dry Lean Methane Combustion through Palladium Reduction in Pd-Pt/Al2 O3 : An In†Situ X-ray Absorption Study.

Palladium-platinum bimetallic catalysts supported on alumina with palladium/platinum molar ratios ranging from 0.25 to 4 are studied in dry lean methane combustion in the temperature range of 200 to 500 °C. Platinum addition decreases the catalyst activity, which cannot be explained by the decrease in dispersion or the structure sensitivity of the reaction. In situ X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopy measurements have been conducted for monometallic Pd, Pt, and 2:1 Pd-Pt catalysts. Monometallic palladium is fully oxidized in the full temperature range, whereas platinum addition promotes palladium reduction, even in a reactive oxidizing environment. The Pd/PdO weight ratio in bimetallic Pd-Pt 2:1 catalysts decreases from 98/2 to 10/90 in the 200-500 °C temperature range under the reaction conditions. Thus, platinum promotes the formation of the reduced palladium phase with a significantly lower activity than that of oxidized palladium. The study sheds light on the effect of platinum on the state of the active palladium surface under low-temperature dry lean methane combustion conditions, which is important for methane-emission control devices.