Bi-functional VPP catalyst for both ethanol ammoxidation to acetonitrile and β-picoline oxidation to nicotinic acid: investigation of reaction mechanisms and the role of acidic and redox sites for the optimization of the selectivity to target products. Display omitted •Vanadyl pyrophosphate VPP is a bi-functional catalyst used in oxidation reactions.•Selective oxidations may require a multifunctional approach.•Acetonitrile is synthesized by ethanol ammoxidation.•Nicotinic acid is synthesized by β-picoline oxidation.•VPP features may be either favourable or detrimental depending on reaction mechanism. This study investigates the catalytic activity of vanadyl pyrophosphate (VPP) for both gas-phase ethanol ammoxidation to acetonitrile and β-picoline oxidation to nicotinic acid. Both reactions may be alternative processes to the industrial technologies used to produce these two chemicals. The reaction networks were investigated, also by feeding possible intermediates; in-situ DRIFT spectroscopy was used to monitor the interaction of ethanol and ammonia with the catalyst. VPP bi-functionality features played an important role in the two reactions; specifically, acidity was detrimental either because it catalyzed undesired reactions, such as ethanol dehydration to ethylene during ethanol ammoxidation, or because it caused a strong interaction with reactants – especially those containing N atoms, ammonia and β-picoline – thus giving rise to some surface saturation phenomena which inhibited the consecutive reactions leading to the final desired compounds, acetonitrile and nicotinic acid. The co-feeding of steam helped product desorption, thus enhancing selectivity in β-picoline oxidation.