The influence of phase purity on the stability of Pt/LaAlO3 catalysts in the aqueous phase reforming of glycerol

Aqueous phase reforming (APR) of waste oxygenates offers the potential for sustainable hydrogen production. However, catalyst stability remains elusive, due to the aggressive hydrothermal conditions employed. Herein, we show that the catalytic performance and stability of Pt supported on LaAlO₃ catalysts for glycerol APR is strongly influenced by the phase purity of LaAlO₃. Calcination of the support at 700 °C produces the LaAlO₃ perovskite phase and an amorphous lanthanum carbonate phase, which can be removed by calcination at higher temperature. Catalysts comprised of phase pure LaAlO₃ were notably more active, with a support calcination temperature of 1100 °C resulting in 20.4% glycerol conversion (TOF 686 h−1) in a 2 h batch reaction. Interestingly, all the catalysts, regardless of LaAlO₃ phase purity, eventually transform into Pt/LaCO₃OH-AlO(OH) during reaction, but only in the presence of evolved carbon dioxide, itself produced from glycerol reforming. Studies using simulated reaction products showed that organic acid products (lactic acid), in the absence of CO₂, facilitated La leaching and loss of crystallinity. A carbonate source (CO₂) is essential to limit La leaching and form stable Pt/LaCO₃OH. Pt supported on LaCO₃OH and AlO(OH) are stable and active catalysts during APR reactions. Yet, the rate of perovskite phase decomposition strongly influences the final catalyst performance, with the initially phase impure LaAlO₃ decomposing too quickly to facilitate Pt redistribution. LaAlO₃ calcined at higher temperatures evolved more slowly and consequently produced more active catalysts.