High-Throughput Catalyst Characterization

A.4. Mossbauer Spectroscopy and High-Throughput Catalyst Characterization... 

The implementation of combinatorial chemistry and automated methods for rapid synthesis, testing, and characterization of catalysts, has opened a wide range of new opportunities in catalysis. However, so far, Mossbauer spectroscopy has not been introduced into this methodology. Two hurdles must be overcome for Mossbauer spectroscopy to become important in high-throughput catalyst characterization the system for recording spectra must be scaled down, and the data acquisition and exploitation systems must be adapted. 

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. 

Although the library of catalysts was actually very small, this combinatorial approach was shown to work surprisingly well. It remains to be seen if truly high throughput can be put into practice, which would require on-line methods for the detection and characterization of the particles bearing the polymers. 

Most of the techniques discussed above are typically used ex situ for catalyst characterization before and after reaction. This is normally the easiest way to carry out the experiments, and is often sufficient to acquire the required information. However, it is known that the reaction environment plays an important role in determining the structure and properties of working catalysts. Consequently, it is desirable to also try to perform catalytic studies under realistic conditions, either in situ [113,114,157, 191-193] or in the so-called operando mode, with simultaneous kinetics measurements [194-196], In addition, advances in high-throughput (also known as combinatorial) catalysis call for the fast and simultaneous analysis of a large number of catalytic samples [197,198], This represents a new direction for further research. 

Fig. 11.8 Schematic of the automated primary high-throughput electrochemical workflow employed at Symyx Technologies for the combinatorial development of new fuel cell catalysts. Individual steps of the workflow include choice of catalyst concept, design of appropriate materials library using Library Studio [31], synthesis of electrocatalyst library on electrode array wafer, XRD and EDX characterization of individual electrocatalysts before screening, high-throughput parallel electrochemical screening of library, XRD and EDX characterization of catalysts after screening, data processing and evaluation.

Flego [1] recommends the use of micro devices for automated measurement and microanalysis of high-throughput in situ characterization of catalyst properties. Murphy et al. [5] stress the importance of the development of new reactor designs. Micro reactors at Dow were described for rapid serial screening of polyolefin catalysts. De Bellefon ete al. used a similar approach in combination with a micro mixer [6], Bergh et al. [7] presented a micro fluidic 256-fold flow reactor manufactured from a silicon wafer for the ethane partial oxidation and propane ammoxidation. 

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). 

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