Two-Nozzle Flame Synthesis of Pt/Ba/Al₂O₃ for NO_x Storage

A novel two-nozzle flame spray pyrolysis (FSP) process has been developed for one-step preparation of Pt/Ba/Al 2 O 3 particles as used for NO x storage-reduction (NSR) catalysts. The materials were characterized by transmission electron microscopy, CO chemisorption, nitrogen adsorption, X-ray diffraction, and temperature programmed decomposition and tested for their NO x storage behavior. The use of two separate nozzles, one as aluminum and the other as a barium/platinum source, resulted in individual Al 2 O 3 and monoclinic BaCO 3 nanoparticles, exhibiting good NO x storage activity. In contrast, using a single-nozzle process resulted in Al 2 O 3 particles with amorphous Ba species with negligible NO x storage capacity. Increasing the internozzle distance resulted in late mixing of the two flame products and increased the amount of crystalline BaCO 3 . At ambient conditions, as-prepared monoclinic BaCO 3 transformed into orthorhombic BaCO 3 . Independent of the Ba loading, nanocrystalline BaCO 3 showed a low thermal stability (decomposition below 900 °C, LT-BaCO 3 ) that was distinctly different from its “bulk” behavior (decomposition above 900 °C).