Spectroscopic Characterization of Rocksalt-Type Aluminum Nitride

Starting from nanocrystalline and submicron wurtzite-aluminum nitride (w-AlN) powder rocksalt structure (rs-AlN) samples were synthesized by two different methods of shock wave recovery experiments. The resulting samples contained up to 86% rs-AlN, stable at room temperature, giving for the first time the possibility to comprehensively characterize the material by powder X-ray diffraction, Fourier transform infrared (IR), Raman, and ²⁷Al NMR spectroscopy. Raman and IR modes were calculated by density functional theory, allowing for the interpretation of the respective experimental spectra. By ²⁷Al NMR the chemical shift of rs-AlN was determined, and the quadrupolar coupling constant was estimated

Automating the Optimization of Catalytic Reaction Mechanism Parameters Using Basin-Hopping: A Proof of Concept

Parameter estimation is a crucial step for successful microkinetic modeling in catalysis. However, the large number of parameters to be optimized in order to match the experimental data is a bottleneck. In this regard, the global optimization algorithm Basin-Hopping is utilized to automate the typically time-extensive and error-prone task of manual fitting of kinetic parameters for a heterogeneous catalytic system. The stochastic approach of the Basin-Hopping algorithm to explore the kinetic parameter solution space coupled with local search methods makes it possible to screen the high-dimensional space for an optimal set of kinetic parameters giving the least residual between the simulated and the experimentally measured catalytic performance data. Our approach also ensures that only thermodynamically consistent solution candidates are explored at each optimization step. We utilize two example case studies in heterogeneous catalysis, namely, methane oxidation over a palladium catalyst and carbon monoxide methanation over a nickel catalyst, with corresponding detailed kinetic models to illustrate the applicability of the algorithm to efficiently fine-tune detailed kinetic models