Exchange between H2 and

This reaction is much too slow to play any role in catalytic hydrogenation. In the presence of D2, the ortho positions of the phenyl rings are deuterated.4 H-D exchange between H2 and D2 and between D2 and solvent ethanol is also catalyzed by (2) and (3).20... 

Burstein (145) in an extensive study of the exchange between H2 and Da on charcoal found that this process is governed by the dissociative adsorption of hydrogen in the range of temperatures between 500°K. and... 

Blank runs demonstrated that the reactants and final products caused no exchange between H2 and D2. 

The acidification of H2 may also be involved in hydrogenase action, where H2 is beheved to bind to an Fe(II) center. Isotope exchange between H2 and D2O is catalyzed by the enzyme see Nickel Enzymes Cofactors Nickel Models of Protein Active Sites Iron-Sulfur Proteins). Similar isotope exchange can also occur in H2 complexes. Oxidative addition to give a classical dihydride is also a common reaction. [W(H2)(CO)3(PCy3)2] is in equilibrium with about 20% of the dihydride in solution. This can lead to subsequent hydrogenolysis of M-C bonds as in the case of a cyclometallated phenylpyridine complex of Ir(III). ... 

Non-catalyzed gaseous systems. There are some systems whose isotopic exchange rates are not enhanced by the presence of catalysts. Deuterium-hydrogen exchange between H2 and either H20(v) or CH4 may exemplify such systems (Lecluse and Robert... 

---