Operando fluorescence spectroscopy for evaluating the activity of fatty acid hydrogenation catalysts

Here, we report for the first time on operando fluorescence spectroscopy for liquid-phase reaction monitoring at elevated temperature and pressure. We show that it is a powerful tool for studying the hydrogenation of branched unsaturated fatty acids with zeolite and palladium catalysts. During the reaction, fluorescent impurities reacted with the zeolite, leading to a redshift of the fluorescence spectrum, which could be suppressed by hydrogenation. A strong correlation was found between the redshift of the spectrum and the hydrogenation activity of the catalysts, which can be used as a proxy. We discovered that unsaturated fatty acids were not responsible for the redshift, but that it was likely caused by fluorophores reacting on the zeolite. Experiments using a model fluorophore showed that the feedstock fluorophores are likely polycyclic aromatic hydrocarbons. We believe that this tool can be used in industrial fatty acid hydrogenation reactors to predict the endpoint of the hydrogenation.