Multiscale reactor modelling using a microkinetic approach for the Water-Gas Shift (WGS) reaction over catalysts supported on carbon nanotubes

Abstract

Most of the catalytic reactor design projects use macrokinetic models to describe the reaction process, in which the rate is generally represented in terms of power-law expressions or Langmuir-Hinshelwood models with parameters estimated from experimental macroscopic data. However, such models are limited to specific catalysts and provide little information for catalyst design. As a result, the progress of microkinetic models, on the other hand, allowed the understanding of fundamental catalyst surface phenomena in terms of reaction elementary steps, yielding a more accurate reaction rate. This approach takes into account physical and chemical catalyst properties in the model formulation, known as catalyst descriptors, which can be computed from chemistry theory methods, thus assisting in the search of new or improved catalysts for a certain process. Thereby, this work aims to develop a microkinetic model that best describes the underlying mechanisms of the Water-Gas Shift (WGS) reaction, considered one of the major routes for hydrogen production - a clean valuable energy source and keystone of the new energy economy - over catalysts supported on carbon nanotubes. The use of carbon nanotubes as supports for catalysts has been shown to be advantageous due to their high surface area and the low availability of some oxides for this purpose. Furthermore, the incorporation of such a microkinetic model into a multiscale fixed-bed reactor model - which considers a porous solid phase and a fluid one - can provide further insights regarding the impact of catalytic elementary surface reactions and intermediate transport limitations on the overall process performance.