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 na nocrystalline Group IIIB metal oxides was investigated between 400 deg rees C and 675 degrees C. Scandium oxide and yttrium oxide are better catalysts than lanthanum oxide because they have a greater specific ac tivity and selectivity. The activity of yttrium oxide is 75% of that o f Co-ZSM-5 at 600 degrees C and yttrium oxide was also found to have e xcellent hydrothermal stability, with only a small reversible inhibiti on 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 I IIB metal oxide catalysts, with approximate values of -0.5, 0.5 and 0. 8, respectively. A nanocrystalline grain size and high surface area im prove the conversion of NO to N-2 by shifting the light-off curve for methane activation to a lower temperature, where the methane selectivi ty is higher. (C) 1998 Elsevier Science B.V. All rights reserved.