Aim of Catalyst Characterization

The catalytic properties of a surface are determined by its composition and structure on the atomic scale. Hence, it is not sufficient to know that a surface consists of a metal and a promoter, say iron and potassium, but it is essential to know the exact structure of the iron surface, including defects, steps, etc., as well as the exact locations of the promoter atoms. Thus, from a fundamental point of view, the ultimate goal of catalyst characterization should be to look at the surface atom by atom, and under reaction conditions. The well-defined surfaces of single crystals offer the best likelihood of atom-by-atom characterization, although occasionally atomic scale information can be obtained from real catalysts under in situ conditions as well, as the examples in Chapter 9 show. 

The industrial view on catalyst characterization is different. Here the emphasis is mainly on developing an active, selective, stable and mechanically robust catalyst. In order to accomplish this, tools are needed which identify those structural properties that discriminate between efficient and less efficient catalysts. All spectroscopic information that helps to achieve this is welcome. Establishing empirical relationships between the factors that govern catalyst composition, particle size and shape and pore dimensions on the one hand and catalytic performance on the other are extremely useful in the process of catalyst development, although such relationships may not give much fundamental insight into how the catalyst operates in molecular detail. 

Van Santen [13] identifies three levels of research in catalysis. The macroscopic level is the world of reaction engineering, test reactors and catalyst beds. Questions concerning the catalyst deal with such aspects as activity per unit volume, mechanical strength and whether it should be used in the form of extrudates, spheres or loose powders. The mesoscopic level comprises kinetic studies, activity per unit surface area, and the relationship between the composition and structure of a catalyst and its 

Simplifying, one could say that catalyst characterization in industrial research deals with the materials science of catalysts on a more or less mesoscopic scale, whereas the ultimate goal of fundamental catalytic research is to characterize the surface of a catalyst at the microscopic level, i.e. on the atomic scale. 

Catalyst characterization is a lively and highly relevant discipline in catalysis. A literature survey identified over 4000 scientific publications on catalyst characterization in a period of two years [14]. The desire to work with defined materials is undoubtedly present. No less than 78% of the 143 papers presented orally at the 1 llh International Congress on Catalysis [15] contained at least some results on the catalyst(s) obtained by characterization techniques, whereas about 20% of the papers dealt with catalytic reactions over uncharacterized catalysts. Another remarkable fact from these statistics is that about 10% of the papers contained results of theoretical calculations. The trend is clearly to approach catalysis from many different viewpoints with a combination of sophisticated experimental and theoretical tools. 

---

What are the aims of catalyst characterization in the context of (a) industrial catalysis and (b) fundamental research ... 

Heterogeneous Catalysis Aim of Catalyst Characterization Spectroscopic Techniques Research Strategies... 

Heterogeneous catalysis The aim of catalyst characterization Spectroscopic techniques Research strategies... 

We have already mentioned that fundamental studies in catalysis often require the use of single crystals or other model systems. As catalyst characterization in academic research aims to determine the surface composition on the molecular level under the conditions where the catalyst does its work, one can in principle adopt two approaches. The first is to model the catalytic surface, for example with that of a single crystal. By using the appropriate combination of surface science tools, the desired characterization on the atomic scale is certainly possible in favorable cases. However, although one may be able to study the catalytic properties of such samples under realistic conditions (pressures of 1 atm or higher), most of the characterization is necessarily carried out in ultrahigh vacuum, and not under reaction conditions. 

In this study butyl acetate (AcOBu) was hydrogenolysed to butanol over alumina supported Pt, Re, RePt and Re modified SnPt naphtha reforming catalysts both in a conventional autoclave and a high throughput (HT) slurry phase reactor system (AMTEC SPR 16). The oxide precursors of catalysts were characterized by Temperature-Programmed Reduction (TPR). The aim of this work was to study the role and efficiency of Sn and Re in the activation of the carbonyl group of esters. 

The aim of this study is to develop model reaction for the characterization of the acidity and basicity of various transition aluminas, the experimental conditions being close to that for catalysis use. Among various model reactions, the transformation of cyclopentanol and cyclohexanone mixture was chosen for this work. Indeed, this reaction was well known for estimating simultaneously the acid-base properties of oxide catalysts [1], Two reactions take place the hydrogen transfer (HT) on basic sites and the alcohol dehydration (DEH) on acid sites. The global reaction scheme is shown in Figure 1. 

Spectroscopy in Catalysis is an introduction to the most important analytical techniques that are nowadays used in catalysis and in catalytic surface chemistry. The aim of the book is to give the reader a feeling for the type of information that characterization techniques provide about questions concerning catalysts or catalytic phenomena, in routine or more advanced applications. 

In this chapter we present four case studies to illustrate catalyst characterization from a problem-oriented approach. The intention is to show what can be achieved by using combinations of techniques. The selected studies all have the aim of determining the composition and the structure of a catalyst or a catalytic surface in atomic detail. 

With the ability to obtain information about the concentrations of various types of metal surface sites in complex metal nanocluster catalysts, HRTEM provides new opportunities to include nanoparticle structure and dynamics into fundamental descriptions of the catalyst properties. This chapter is a survey of recent HRTEM investigations that illustrate the possibilities for characterization of catalysts in the functioning state. This chapter is not intended to be a comprehensive review of the applications of TEM to characterize catalysts in reactive atmospheres such reviews are available elsewhere (e.g., 1,8,9 )). Rather, the aim here is to demonstrate the future potential of the technique used in combination with surface science techniques, density functional theory (DFT), other characterization techniques, and catalyst testing. 

The author of this book has been permanently active during his career in the held of materials science, studying diffusion, adsorption, ion exchange, cationic conduction, catalysis and permeation in metals, zeolites, silica, and perovskites. From his experience, the author considers that during the last years, a new held in materials science, that he calls the physical chemistry of materials, which emphasizes the study of materials for chemical, sustainable energy, and pollution abatement applications, has been developed. With regard to this development, the aim of this book is to teach the methods of syntheses and characterization of adsorbents, ion exchangers, cationic conductors, catalysts, and permeable porous and dense materials and their properties and applications. 

---