SCR of NO by CH 4 on Pt/ZrO 2–TiO 2 sol–gel catalysts

Abstract

ZrO 2–TiO 2 mixed oxides with various ZrO 2/ZrO 2 + TiO 2 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 ZrO 2–TiO 2 oxides goes through a maximum (552 m 2/g) for the (ZT0.5) support whose surface area was almost nine times higher than that of the single oxides (around 60 m 2/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 CH 4. 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/ZrO 2 ≈ Pt/ZT(0.5) ≈ Pt/ZT(0.1) > Pt/TiO 2. The Pt/ZT(0.9) catalyst which includes in the support formulation 10 mol% of TiO 2 showed the highest catalytic activity with TON values 2.5 times higher than those found in Pt/ZrO 2. Also the selectivity for N 2 production was slightly higher for this catalyst. The addition of N 2O as an oxygen source for NO oxidation was also evaluated. All catalysts improved their performance in the presence of N 2O. 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.