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.