Infrared and kinetic studies were conducted for NiO-Al₂O₃ aerogel catalysts to determine the types and relative numbers of Ni sites responsible for catalytic activity and selectivity in the nitroxidation of propene to 2-propenenitrile. The evaluated catalysts had Ni to Al ratios of 0.04/1.0, 0.4/1.0 and 1.0/1.0. The effect of catalyst preparation on active Ni sites was determined by studying pairs of catalysts with the same Ni/Al ratio. The infrared studies were carried out using CO and NO as molecular probes, and by varying the temperature of pretreatment ( calcination and reduction). Bands for adsorbed CO were seen for all catalysts corresponding to weakly held CO on Ni^{2+ and Ni}1+ sites. Both linear and bridged adsorption of CO on reduced Ni^O sites were also evident on catalysts reduced in H₂ at 550°C. All catalysts showed bands arising from NO strongly held on Ni sites. The CO and NO bands varied in intensity depending on the temperature of pretreatment. Catalytic activity depends on both the number of exposed Ni sites and a catalyst's ability to be easily oxidized and reduced without loss of sites. Ni crystal size was found to affect selectivity as well as activity