Platinum aluminophosphate oxynitride (Pt-AlPON) catalysts. Consequences of surface hydrolysis and heating processes ore the structure

Consecutive heating/cooling cycles over a platinum aluminophosphate oxynitride (Pt-AlPON) catalyst with a high nitrogen content (17.8 wt %) have been studied by diffuse reflectance infrared spectroscopy (DRIFTS). Heating steps to 500 degrees C produces the desorption of part of the nitrogenous species of the catalyst (NE4+, NH3, -NH2, -NH-) as gaseous ammonia. During the treatment at room temperature, N-2 saturated with water produces a hydrolysis reaction that transforms part of the bulk nitride ions into NH4+ surface species. These species are easily removed from the catalyst surface during the next heating step. As a result of combined successive hydrolysis/heating processes, the catalyst loses practically all its nitrogen content, reaching a structure similar to that of its AlPO4 precursor.