Applied Catalysis B: Environmental 150–151 (2014) 446–458 Contents lists available at ScienceDirect Applied Catalysis B: Environmental jo ur nal home p ag e: www.elsevier.com/locate/apcatb Prediction of diffusivity and conversion of n-decane and CO in coated Pt/-Al 2 O 3 catalyst depending on porous layer morphology Michal Dudák a , Vladimír Novák a,b , Petr Koˇ cí a,c,∗ , Miloˇ s Marek a,c , Patricia Blanco-García b , Glenn Jones b a Institute of Chemical Technology, Prague, Department of Chemical Engineering, Technická 5, Prague 166 28, Czech Republic b Johnson Matthey Technology Centre, Blounts Court Road, Sonning Common, Reading RG4 9NH, United Kingdom c New Technologies Research Centre, University of West Bohemia, Univerzitní 8, Pilsen 306 14, Czech Republic a r t i c l e i n f o Article history: Received 30 September 2013 Received in revised form 10 December 2013 Accepted 11 December 2013 Available online 20 December 2013 Keywords: Diffusion Exhaust gas aftertreatment Diesel oxidation catalyst CO and n-decane oxidation Multi-scale modeling a b s t r a c t The conversion in monolith reactors for automotive exhaust gas aftertreatment can be limited by dif- fusion in the catalytic layer. This is particularly important for monolith reactors with multiple coated layers. In this paper, we present detailed modeling methodology for prediction of effective diffusivity based on the actual structure of a porous coating (particle and pore size distributions). We demonstrate the approach on diffusion and oxidation of n-decane and CO in Pt/-Al 2 O 3 layers typically used in diesel oxidation catalysts. To validate the model predictions experimentally, several layers were coated with uniform thickness on flat metal foils, and their macroporous structure was controlled by alumina particle size distribution, pore templates and compaction techniques. A multi-scale modelling approach was then applied to predict effective diffusivity and impact of the internal diffusion limitations on the achieved con- versions. Diffusion of CO and n-decane was simulated on a micro-scale together with oxidation reactions in a 3D digitally reconstructed porous layer structure. The results were combined with a macroscopic 1D plug-flow model to calculate the reactor outlet conversions. Good agreement was achieved between the predicted and the measured conversions both for n-decane and CO oxidation. The predicted effective diffusion coefficients D eff through the tested Pt/-Al 2 O 3 layers were 1.4, 3.6 and 6.4 × 10 -6 m 2 s -1 for CO at T = 298 K in compact, standard and macropore-templated sample, respectively. The corresponding diffusivities for n-decane were 0.53, 1.2 and 2.0 × 10 -6 m 2 s -1 , respectively. The model quantified rela- tive contributions of volume and Knudsen diffusion regimes to overall transport as well as temperature dependence of D eff . © 2013 Elsevier B.V. All rights reserved. 1. Introduction The catalytic layer deposited on the walls of monolith channels in automotive exhaust gas converters consists of meso- or micro- porous particles (e.g., -Al 2 O 3 , CeO 2 , zeolites) with internal pore sizes below 50 nm and high specific surface area that allows dis- persion of active metal sites. Macropores are present between the support particles as shown in schematic Fig. 1 and their typical size ranges from 0.1 m up to several microns. The particle size distribution (PSD) of the supporting material influences the result- ing macroporosity [1]. The conversion of reactants can be limited by transport both in flowing gas phase [2] and inside porous cat- alytic coating [1,3,4]. The internal transport is particularly relevant to monoliths with multiple coated layers, where the active sites ∗ Corresponding author. Tel.: +420 22044 3293; fax: +420 22044 4320. E-mail addresses: petr.koci@vscht.cz (P. Koˇ cí), gjones@matthey.com (G. Jones). URL: http://www.vscht.cz/monolith (P. Koˇ cí). in the bottom layer are accessible only by the diffusion through the top layer [5–7]. Volume diffusion in macropores is essential for efficient transport of reactants through the layer, because Knud- sen diffusion regime in small pores is significantly slower (Fig. 1). Understanding and quantification of the internal diffusion effects are thus pre-requisites for design of optimum catalytic coating in monolith reactors. A common approach to prediction of the internal diffusion effects used in the automotive industry relies on 1D + 1D (or 1D + effectiveness factor) simulations of a monolith channel, where the coated catalytic layer is considered to have uniform thick- ness and transport properties are represented by an effective diffusion coefficient [8]. This effective diffusivity is typically cal- culated from random pore model correlation [9] that combines contributions of small meso/micro-pores (intrinsic nanostructure of the used material, slow Knudsen diffusion) and larger macro- pores (microstructure influenced by the coating procedure, faster volume diffusion). More complex computational strategies for non- uniform distribution of washcoat are available as well [10,11]. 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.12.018