Experimental characterization techniques catalyst

The development of modern surface characterization techniques has provided means to study the relationship between the chemical activity and the physical or structural properties of a catalyst surface. Experimental work to understand this reactivity/structure relationship has been of two types fundamental studies on model catalyst systems (1,2) and postmortem analyses of catalysts which have been removed from reactors (3,4). Experimental apparatus for these studies have Involved small volume reactors mounted within (1) or appended to (5) vacuum chambers containing analysis Instrumentation. Alternately, catalyst samples have been removed from remote reactors via transferable sample mounts (6) or an Inert gas glove box (3,4). 

The most informative characterization techniques used to determine Ti species inside dehydrated TS-1 catalysts are described in Sects. 3.1-3.7. The discussion is supported by the experimental data reported in Fig. 2. 

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. 

Characterization is an integral tool for the development of new zeolites and for the development and commercialization of zeolitic catalysts and adsorbents. Single techniques are not sufficient as they rarely provide full details of the system. A combination of selective characterization techniques is required. As suggested by Deka [1] even a single acidity characterization method may be insufficient to provide the necessary detailed information to understand the zeolite acid sites. Thus according to Deka the combination of different experimental techniques is required to shorten the time of development for a new catalyst. 

Table I lists the major characterization techniques which have been applied to the molybdena catalyst. They may be grouped into two broad categories nonspectroscopic and spectroscopic methods. Space does not permit a full discussion of the theory, experimental techniques, or interpretation of results of these techniques—we give here only the author s interpretations of their results. The reader is referred to any number of standard texts or reviews on the specific technique for a more complete description.

The role of infrared spectroscopic characterization of catalysts should become increasingly important in catalyst development, but present problems, both experimental and theoretical must be recognized and overcome before reliable information can be routinely obtained using infrared methods. Techniques and understanding will improve as more information becomes available, but detailed interpretation of spectra will continue to present problems for some time. Partial interpretation and "fingerprinting can still be... 

The characterization technique of CO Temperature-Programmed Desorption has been studied with Pt reforming catalysts. Critical factors in the experimental procedure and the catalyst pretreatment conditions were examined. The CO desorption spectrum consists mainly of two peaks which are probably combinations of other peaks and the result of various binding energy states of CO to Pt. These in turn could be due either to the interaction between Pt and the alumina support or the results of high and low coordination sites on the Pt crystallites. No significant relationship between the character of the CO desorption profile and the activity of commercial catalysts was observed. 

The characterization of catalysts has become the object of high-throughput screening. Experimental arrays employing microsystems techniques are now available. The area is promising, at least to identify relative data of catalyst activity and selectivity [102]. Combinatorial catalysis, as the field is called, will not replace the innovative chemical idea, as amply shown in this book (cf. Section 3.1.3). 

To check the behavior of SCR elements they have to be tested at regular intervals. For this purpose a test programme was developed which includes catalyst activity and selectivity tests in a bench-scale system with surface analysis and characterization of catalysts using highly sensitive surface techniques. By combining these experimental techniques valuable information on ageing and fouling processes on the catalysts is obtained. 

Experimental. Characterizations of a heterogeneous surface by means of surface group titration utilizing visible and ultraviolet chemical indicators to define the titration end point have frequently been employed with white solid catalysts(7-12), (17-20). Aspects of the surface acid group distribution have often correlated with the catalytic activity of the solid(2-9), (21-25). An adaptation of the technique appears to be suitable for studying the interactions between the surface acid groups in mixtures of carbon black and white reference solids. 

Table 1 Experimental Techniques for Characterization of Catalysts and Adsorbed Species...

Furthermore, with the advent of improved instriunentation and experimental techniques interesting in-situ investigations became possible which were related, for instance, to the synthesis of and heterogeneous catalysis on zeofites, catalyst deactivation, diffusion or solid-state ion exchange as well as other postsynthesis modifications. Combinations of IR spectroscopy with various characterization techniques such as, e.g., temperature-programmed desorption of probe molecules (TPD/IR, cf.[223,224]), electron spin resonance spectroscopy (ESR/IR, cf.[225,226]), UV-Vis spectroscopy [227,228], etc. were developed. 

According to the different thermal techniques and the selection of the experimental parameters, a large selection of applications is available for the characterization of catalysts and related materials, and also the simulation of the catalytic processes. The Table 2.1 provides a brief overview of the main applications that have been developed. 

The thermal analysis and calorimetric techniques provide a very large variety of possibilities of experimentations, of combinations with other analytic techniques that make unlimited the number of applications, especially in the field of characterization of catalysts and evaluation of catalytic processes. 

The same Maya crude oil was used as feedstock. More details of Maya crude oil properties and its classification respect to other crudes according to the content of metals, sulfur, and API gravity were reported by Rana et al. (2007). The same NiMo/ AI2O3 commercial catalyst, loading and sulfiding procedures, as well as characterization techniques were also used. Other experimental details were reported previously (Ancheyta et al., 2001). Experiments were conducted at the following conditions pressure of 6.9, 8.3, and 9.8 MPa, temperature of 380°C-420°C, 5000 standard cubic feet per barrel of H2/oil ratio, and 1.5,0.5, and 0.33 h EHSV in the same isothermal bench-scale unit mentioned in the previous section. 

This review starts with an introduction to the principles and techniques of solid-state NMR spectroscopy and the description of the most important experimental approaches for NMR investigations of solid catalysts in the working state (Sections II and III). Section IV is a summary of experimental approaches to the characterization of transition states of acid-catalyzed reactions under batch reaction conditions. 

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