Microkinetic analysis for the reduction of nitric oxide by hydrogen over palladium under lean-burn conditions

Utilizing the stochastic simulation, a microkinetic model that quantitatively describes the reduction of no by h-2 on the i'd catalyst under the lean-burn conditions was developed. the parameters of elementary reaction steps were calculated by the transition state theory along with the unity bond index-quadratic exponential potential method. the rate-limiting step of the reaction is the generation of h* from h-2 (* denotes an active site and h* means an adsorbed h atom). when reaction temperature is below 270 degrees c, h* is formed by the process o* + h-2(*) reversible arrow oh* + h*. when temperature rises to 310 degrees c, the generation of h* prefers to occur via the reaction h-2(*) + * reversible arrow 2h*. no adsorbs on the pd surface in a dimer form of (no)(2)(*) instead of no*. the re ducing product n2o comes from two routes, decomposition of (no)(2)(*) and combination of adjacent no*. n-2 comes from the decomposition of n2o* or the combination of n-* and no*. when temperature is above 230 degrees c, little amount of n2 is formed through combination of neighboring n*. nh3 is produced by the gradual hydrogenation of hno*. during the reduction process, there is a competition between no and 02 in adsorption as well as reduction. no favors to adsorb on pd, while 02 prefers to be reduced. at low temperature, the adsorption influences the reaction predominantly, so no can be reduced by h2 selectively. with the increase in reaction temperature, the adsorption of no decreases gradually, and the side reaction between h2 and 02 becomes predominant. from 150 degrees c to 310 degrees c, the simulation results are in accordance with the experimental data.