Selective Catalytic Hydrogenation

Final purification of argon is readily accompHshed by several methods. Purification by passage over heated active metals or by selective adsorption (76) is practiced. More commonly argon is purified by the addition of a small excess of hydrogen, catalytic combustion to water, and finally redistiHation to remove both the excess hydrogen and any traces of nitrogen (see Fig. 5) (see Exhaust control, industrial). With careful control, argon purities exceed 99.999%. 

Carbonyl groups may be hydrogenated catalytically, as carbon-carbon unsaturated linkages were (p. 191). It is, however, normally more difficult to effect the catalytic reduction of C=0 than of C=C, C=C, C=N, or C N, so that selective reduction of the former—in the presence of any of the latter—cannot normally be achieved catalytically. This can, however, be done with various, usually complex, metal hydrides. 

NExSELECT A catalytic, selective hydrogenation process developed by Neste Oy. Operated inPorvoo, Finland, since 1996. 

Stirbar stirred vials Catalytic oxidation with hydrogen peroxide selective oxidation of methylcyclohexene6... 

An attempt will be made to correlate primary adsorption (consequently the reactions expected) with two main factors the nature of the metal and the amount of hydrogen available during the catalytic process. The latter may be of paramount importance the amount of surface hydrogen may govern which type of chemisorbed species is formed and, by doing so, determine catalytic selectivity. 

Table 1 Recommended reaction conditions for catalytic hydrogenation of selected types of...

Catalytic hydrogenation may selectively reduce the double bond, or reduce the aromatic ring as well depending on the reaction conditions used [430,463, 464]. Only exceptionally has the benzene ring been hydrogenated in preference to the pyrrole ring [463,46S. ... 

The structure of Ni3Os3(CO)9( /5-C5H5)3 has been established by X-ray diffraction.3 The complex behaves as an homogeneous catalyst for selective hydrogenation Hydrogenating catalytic activity is observed also when adsorbed on alumina.4... 

Thus, the Pd layer serves multiple purposes its surface catalyzes the dissociation of molecular hydrogen, it selectively forms palladium hydride, and it can be used as the metal gate of the field-effect devices. The scheme in Fig. 6.34 also shows the catalytic reaction involving oxygen. If both oxygen and hydrogen are present, the steady-state response of the Pd IGFET includes the surface-catalyzed oxidation. 

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