H2 D2 Exchange

The H2 + D2 isotopic exchange is interesting as one of the simplest chemical reactions of H2 on the catalyst surface. 

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Fig. 19. Rate of H2-D2 exchange (at -40°C) divided by nickel content as a function of composition for Cu-Ni alloy films deposited at 300°C and sintered at 400°C 84).

As discussed in the previous section, metal oxides have both acidic and basic properties. The acid-base properties of metal oxides have led to many interesting catalytic reactions. Catalytic reactions such as H2-D2 exchange, hydrogenation, isomerization, dehydrogenation, dehydrohalo-genation, and benzylation can be considered as examples of acid-base catalysis reactions.31-36 These reactions will be briefly discussed in the following section. The remarkable properties of MgO as a catalyst have been well documented in the literature and we shall discuss some of these unique catalytic properties. 

The analogy goes further if the activity of NiO as an oxidation catalyst is examined closely. In the case of the H2-D2 exchange reaction on ZnO, there was an activation period corresponding to a surface reduction. For NiO, there is a deactivation period also corresponding to surface reduction during the catalytic oxidation of carbon monoxide. 

Just as in the case of the H2-D2 exchange on ZnO, two mechanisms are also discernible for the carbon monoxide oxidation [stage (b)] on nickel oxide below 300°C. There is a low-temperature mechanism operative between 100° and 180°C. characterized by a low activation energy of 2 kcal./mole and a high-temperature mechanism, above 180°C., with a higher activation energy of 13 kcal./mole. The kinetics are different and are respectively ... 

Massoth (21) also found less H on an Mo/Al catalyst than on the A1203 support alone by an H2-D2 exchange technique. 

The photochemically produced PtCPEt fragment, stabilized as the cis- and trans-PtH (PEt- )2 complexes, has proved (54,55,56) to be an efficient and long lived homogeneous catalyst for H2/D2 exchange (Equation 17), deuteration of acetone or acetontrile (Equations 18 and 19), decomposition of formic acid (Equation 20), and hydrolysis of acetonitrile (Equation 21). Because of the catalytic promise... 

A few solutions have been found to possess the unusual property of activating molecular hydrogen so as to bring about reduction of organic or inorganic compounds or to cause H2-D2 exchange or ortho-para-hydrogen interconversion. Such catalytic systems have been termed homo-... 

The H2-D2 exchange occurs to an appreciable extent only under conditions when H (or D2) is not being absorbed rapidly in a chemical reaction such as the reduction of quinone or cupric acetate. This is consistent with the idea that the rate-determining step in the reduction is the activation of hydrogen by cuprous acetate (reaction (11)], the activated hydrogen being rapidly removed by reaction with quinone or Cu before it can return to the gas phase. 

The results for Pt(5 3 3) (Figs. 11 and 26) are consistent with the increased sticking probability observed for a Maxwellian source of H2 on Pt(9 9 7) over Pt(l 1 1) [81]. It also provides direct evidence for an additional channel to dissociative adsorption through step sites which was invoked to explain the enhanced rate of H2 + D2 exchange reaction at Pt(3 3 2) over that observed on Pt(l 1 1) surfaces investigated using a Maxwellian beam source [82]. 

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