HTFFR kinetics studies of Al+CO2→AlO+CO from 300 to 1900 K, a non-Arrhenius reaction

High-temperature fast-flow reactors (HTFFR) were used to obtain the rate coefficients k1 (and their accuracies) for the reaction Al +CO2→AlO+CO. At 310, 490, 750, 1500, and 1880 K, k1 is found to be (1.5±0.6) ×10−13, (6.9±2.7) ×10−13, (1.6±0.7) ×10−12, (9.0±3.8) ×10−12, and (3.8±1.5) ×10−11, respectively (all in ml molecule−1 s−1 units). For this temperature range k1(T) may be expressed by the curve fitting equation k1(T) =2.5 ×10−13 T1/2 exp(−1030/T)+1.4×10−9 T1/2 exp(−14 000/T). The data also indicate a wall-oxidation process of zeroth order in [CO2] with γAl of 10−3 to 10−2, not measurably dependent on T. Factors affecting the accuracy of the measurements are discussed. Over the 310–750 K range k1(T) obeys an Arrhenius expression, with an activation energy of 2.6±1.3 kcal mole−1, which implies D(Al–O) ?122 kcal mole−1. Above 750 K, k1(T) increases much more rapidly with T. This behavior cannot be described on the basis of simple transition state theory alone; the most probable additional factors involved are the opening of a second reaction channel leading to AlO(A 2Π) and preferential reaction of Al with CO2 in bending modes.