The non-isothermal catalytic effectiveness factor for monolith supported catalysts

Abstract

Catalytic effectiveness factor relationships expressed in terms of laboratory observables are derived for monolith supported catalysts in instances in which (a) a nonporous monolith sustains an n th order ( n ⪌ 1) reaction in the presence of external temperature and concentration gradients, and (b) an isothermal diffusion affected porous monolith sustains first order reaction in the presence of external temperature and concentration gradients. Further, a simple relationship is presented which testifies to the validity of the isothermal pellet assumption, hence the derived effectiveness for the porous monolith is applicable to muffler systems composed of pelleted catalysts. Finally, for the case of negative order kinetics, as found in CO oxidation over Pt, Pd, Rh and Ru, multiple steady states and regimes of instability are cited which combined with the rate-enhancing effects of axial dispersion, tend to clarify the noted thermal instability of noble metal catalyst systems.