Molybdena characterization

A differential flow microreactor was used for the preparation of the nitrided catalyst and the TPD, TPR, and NH3-TPD measurements. Nitriding of the molybdena-alumina and alumina was carried out by temperature-programed reaction with NH3 (NH3-TPR).1719 The MoCV A1203 precursor was oxidized at 723 K for 24 h, cooled to 573 K, reacted with NH3 at 49.6 (xmols-1 from 573 to 773, 973 or 1173 K at a rate of 0.0167 Ks-1, held at the nitriding temperature for 3 h, and then cooled to room temperature (RT) in flowing NH3. The catalysts were characterized by TPD, TPR, and NH3-TPD under in situ conditions, while BET and diffuse reflectance FTIR measurements were carried out after passivation. For the diffuse reflectance FTIR study, the catalysts after NH3 treatment... 

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 individual techniques used to characterize molybdena catalysts are now considered. Table II presents a listing of articles concerning the characterization of molybdena catalysts. Unless otherwise specified, we implicitly refer to Mo and/or Co supported on an activated alumina, commonly y-AlaOs. Most work has been done on the calcined (oxidized) state of the catalyst because of ease of sample handling. Reduced and sulfided catalysts are more difficult to work with since for meaningful results, exposure of these samples to air or moisture should be rigorously avoided. Therefore, sample transfer or special in situ treatment facilities must be provided. 

Barry Gorewit and Minoru Tsutsui Characterization of Molybdena Catalysts F. E. Massoth... 

Another degree of modification of the catalysts can be achieved by introduction of components which on one hand affect the dispersion of the noble metal similarly to the ceria discussed earlier, but also possess catalytic activities of their own. One example of such an additive explored in depth at Ford Research is molybdenum oxide. Molybdena, similar to ceria, forms a two-dimensional phase on 7-AI2O3 and thereby also affects the Pt dispersion and its catalytic properties. Platinum, in turn, affects strongly the reducibility of molybdena, as shown in Fig. 4, using ESCA to characterize the oxidation state after reduction in the absence and presence of Pt [7]. 

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