Measurement of the effective diffusivity for a vanadia-tungsta-titania/sepiolite catalyst for SCR of NO x

Abstract

Experimental measurement of the effective diffusion coefficient for a vanadia-tungsta-titania/sepiolite catalyst, as employed for SCR of NO x , was carried out using a chromatographic technique in a packed column (under inert conditions) employing helium as carrier and nitrogen, argon and oxygen as tracers. Measurements were carried out at temperatures 298 and 473 K with particle sizes 0.4 and 0.5 mm. The values obtained for D e are from 0.6 · 10 −6 to 0.94 · 10 −6 for the gas tracers and temperature range employed. Adsorption constant for the gas tracers above quoted have been also determined giving values of K a around, 1.3, thus, a light adsorption strength existed. Because D e depends on the gas temperature and composition, different structure models for the solid have been applied to calculate from D e the corresponding structural parameters: τ (in pore models) or Z (in percolation model), which only depends on the solid structure and can be employed for other gases and temperatures. The τ values obtained from the bundle pore model (around 3) are smaller than calculated applying the cross linked pore model (τ between 5 and 6). The coordination number, Z, has a meaningless value when catalyst is analyzed as unimodal ( Z < 3). On the other hand, if the experimental pore size distribution was taken into account Z yields appropriate values were between 5 and 6.