Influence of homogeneous decane oxidation on the catalytic performance of lean NO_x catalysts

Extensive homogeneous gas-phase reactions were observed when decane was used as the hydrocarbon reductant for the selective reduction of NO_x. The catalytic performance of a SnO₂/CoO_x/Al₂O₃ catalyst was found to be strongly dependent on the extent of the homogeneous reaction in the pre-catalytic volume. The effect of the homogeneous reaction on the catalytic performance also depended on whether SO₂ was present in the feed. By filling the pre-catalytic volume with 25-35 mesh irregularly shaped quartz chips, gas-phase reaction was suppressed significantly. This methodology was used to evaluate the inherent catalytic performance of SnO₂/CoO_x/Al₂O₃ and SnO₂/Al₂O₃ catalysts with decane as a reductant. It was found that in the absence of SO₂, SnO₂/Al₂O₃ was a better catalyst than SnO₂//CoO_x/Al₂O₃, but in the presence of 30 ppm of SO₂ the latter was a far better catalyst.