Understanding the catalyst-reactants interaction in heterogeneous catalysis: two examples of industrial interest

Understanding the mechanism by which reactants interact with catalysts is the key-tool for optmize reaction conditions and achieve the best process performance. In this context, it may be surprising that for some processes, implemented at an industrial level and used since many years, still the reaction mechanism is far from being fully understood. I would like to examine here two emblematic examples, namely the gas-phase synthesis of 2,6-xylenol by means of the base-catalyzed methylation of phenol with methanol, and the gas-phase selective oxidation of n-butane into maleic anhydride, catalyzed by vanadyl pyrophosphate. In the former case, the process mechanism has been revealed only in recent times, despite the production of 2,6-xylenol, an important monomer for technical polymers, is carried out in the industry since several years. In the case of n-butane selective oxidation catalyzed by vanadyl pyrophosphate, the wide and discordant literature dealing with the nature of the catalytically active phase has been recently rationalised. This allowed us providing a clear picture of the catalyst requirements, needed to obtain the best process performance in n-butane oxidation. In both cases, combining reactivity measurements with in-situ spectroscopic methods was crucial in the aim of understanding the key-steps of the catalytic process.