The selective catalytic reduction of nitric oxide with methane over scandium oxide, yttrium oxide and lanthanum oxide

The selective catalytic reduction of nitric oxide with methane over nanocrystalline Group IIIB metal oxides was investigated between 400 degrees C and 675 degrees C. Scandium oxide and yttrium oxide are better catalysts than lanthanum oxide because they have a greater specific activity and selectivity. The activity of yttrium oxide is 75% of that of Co-ZSM-5 at 600 degrees C and yttrium oxide was also found to have excellent hydrothermal stability, with only a small reversible inhibition of activity in the presence of water vapor. In an excess of oxygen, the reaction orders in O-2, NO and CH4 are similar over these Group IIIB metal oxide catalysts, with approximate values of -0.5, 0.5 and 0.8, respectively. A nanocrystalline grain size and high surface area improve the conversion of NO to N-2 by shifting the light-off curve for methane activation to a lower temperature, where the methane selectivity is higher. (C) 1998 Elsevier Science B.V. All rights reserved.