What Overall Nitrogen Kinetics can Teach us about Optimizing Catalytic NO Abatement Reactors

Abstract

Due to the competition of chemical reactions, respectively favorable or defavorable to appropriate performance of finite size catalytic converters, optimum NO conversion may become noticeably dependent on the residence time (or GHSV) of the gaseous reactants. Model computations, required then to assess the optimum temperature-concentrations-residence time relationship, need an appropriate kinetic subroutine. In the present default of detailed, intrinsic catalytic kinetics, it is shown that overall experimental rates, suitably chosen to match the experimental observations, constitute a promising bias as a surrogate chemical subroutine, since, provided they have been determined at conditions identical to the industrial application, (i) they implicitely account for co-controlling physical transport phenomena and (ii) they allow for very acceptable trend predictions even with simple, one dimensional modeling calculations. This is illustrated for three typical cases: (i) NO reduction in gasoline engine exhaust by three-way catalysts, (ii) selective catalytic NO reduction with ammonia (SCR) and (iii) selective NO reduction by hydrocarbons on ZSM5-Cu catalysts in the presence of excess oxygen.

Keywords:

• Catalytic NO control
• modeling of catalytic converters
• overall catalytic rates
• three-way catalytic NO reduction
• SCR
• catalytic NO reduction by hydrocarbons