Steam reforming of CH4 and microstructure of BaTi(1-x)RhxO3

Kurzfassung

Rh-doped perovskites BaTi0.9Rh0.1O3 and Rh-BaTiO3 were prepared by a new synthesis method and analyzed by XRD and FE-SEM. The effect of HCl for sol-formation was studied, but chlorine remains in the catalyst even after calcination treatment at 1000°C. Cl-free catalysts were prepared and analyzed on model reaction mixtures of the H2O-reforming of CH4. The Rh-integrated perovskite BaTi0.9Rh0.1O3 displayed better catalytic performance compared to Rh-BaTiO3 and Rh-TiO2 under the studied reaction conditions. Carefull XRD analysis was carried out to demonstrate the incorporation of Rh in the perovskite lattice. Rhodium reacts with the tetragonal perovskite BaTiO3 to stabilize the hexagonal modification. Mainly the hexagonal perovskite was found in the catalyst BaTi0.9Rh0.1O3. The hexagonal modification appears only after Rh-impregnation and calcination of the tetragonal BaTiO3 thus coexisting the hexagonal perovskite BaTi(1-x)RhxO3 and the tetragonal BaTiO3. The catalysts were reduced in diluted H2 containing gas mixtures to cause the segregation of Rh° out of the perovskite crystal lattice as stated in the literature. In the present case the hexagonal modification in both perovskites appears to decompose at a first instance into probably an orthotitanate Ba2TiO4 and the Rh°. But, after atmospheric exposition of the reduced samples the orthotitanate disappeared upon time.