SCR of NO by CH4 on Pt/ZrO2-TiO2 sol-gel catalysts

ZrO2-TiO2 mixed oxides with various ZrO2/ZrO2 + TiO2 composition (0.9, 0.5 and 0.1) were prepared by the sol-gel method and used as catalytic support for Pt. As a function of the support composition the surface area of ZrO2-TiO2 oxides goes through a maximum (552 m2/g) for the (ZT0.5) support whose surface area was almost nine times higher than that of the single oxides (around 60 m2/g). Also, different reducibility properties of the platinum oxide were observed. The catalytic performance of the solids was studied using the selective reduction of NO with CH4. The steady-state activity of the catalysts was also dependent on the support composition. The reactivity of the catalysts (TON) in the range 573-773 K follows the order: Pt/ZT(0.9) > Pt/ZrO2 ≈ Pt/ZT(0.5) ≈ Pt/ZT(0.1) > Pt/TiO2. The Pt/ZT(0.9) catalyst which includes in the support formulation 10 mol% of TiO2 showed the highest catalytic activity with TON values 2.5 times higher than those found in Pt/ZrO2. Also the selectivity for N2 production was slightly higher for this catalyst. The addition of N2O as an oxygen source for NO oxidation was also evaluated. All catalysts improved their performance in the presence of N2O. The combination of acid properties, particle size and the presence of stable isocyano type intermediates which characterize the Pt/ZT(0.9) catalyst could explain its performance.