Chapter One - Analysis of Catalyst Surface Structure by Physical Sorption

Abstract

Abstract Heterogeneous catalysis usually takes place by sequences of reactions involving fluid-phase reagents and the exposed layer of the solid catalyst surface. Estimation of the total catalyst surface area, its potential accessibility to gas- or liquid-phase reactants, and general catalytic activity are initially based on the morphology of the catalyst. Universally, measurements of adsorption and their interpretation are used to estimate the surface area and porosity relevant to catalytic reactions. We provide here a description of many traditional and recent techniques in adsorption-based catalyst characterization intended for experimental practitioners of adsorption. Our chapter includes descriptions of which regions of the isotherm correspond to micropore filling, mesopore filling, surface coverage, and saturation, supplemented by discussions of model isotherms, from the Langmuir isotherm and the Brunauer–Emmett–Teller theory to the Halsey equation. Pore size distribution methods include the Barrett–Joyner–Halenda and related methods for mesopores, empirical methods developed for micropores, and simulation-based methods that have finally resolved the differences between adsorption (increasing loading) and desorption (decreasing loading). This chapter also includes a discussion of hysteresis and metastability, both of which “trip up” experimentalists from time to time. We finish with a description of data acquisition methods and equipment, which are often obscured behind the facade of automation, and a discussion of what users should be aware of and what can go wrong.