Formic acid, dehydrogenation

This is the reason why, for example, the zero order formic acid dehydrogenation may easily be measured on bulk metal catalysts at 200-300°C. whereas the approximately first order ethanol dehydrogenation requires highly activated porous metals of large specific surface in order to become measurable under the same conditions. The same has been shown for the decomposition of formaldehyde, acetic acid, and hydrazine hydrate. In these cases, the fractional surface coverage is simply 1000 times lower than in the case of a zero order reaction. 

Activiation Energies of Model Catalysis and Alloys for Formic Acid Dehydrogenation... 

The results with magnesia led us to a planned series of experiments with doped aluminas. Nickel was evaporated in vacuo onto the surface of grains of undoped or doped alumina or, alternatively, onto compact nickel. These preparations were then used as catalysts for the donor model reaction of formic acid dehydrogenation as above. Table II shows the results. 

Encouraged by these results, we used the donor test (or model) reaction of formic acid dehydrogenation for the study of the well-known ammonia... 

Flo. 2. Activation energy of formic acid dehydrogenation over silver on doped silicon carhide (19). (Copyright by the Universite de Liege. Reprinted with permission.)... 

Figure 2 Volcano plots illustrating how catalytic activities depend on the nature of the metal used as catalyst, (a) Correlation between catal)hic activity for formic acid dehydrogenation and enthalpy of formation of metal formates. (Ref 10. Reproduced by permission of John Wiley Sons, Inc.) (b) Correlation between catal)hic activity for ammonia synthesis and degree of d-band fiUing in the metal used as catalyst. (Ref 12. Reproduced by permission of John Wiley Sons, Inc.) ...

Figure 27.14 shows how the binding increases with the affinity K, and the release rate decreases, leading to the overall result (c) that there is an optimal binding affinity for catalytic effectiveness. Figure 27.16 shows a plot of the rate of formic acid dehydrogenation as a function of the type of metal surface that is used as a catalyst. Such plots are sometimes called volcano curves... 

Figure 27.16 A volcano curve shows the catalytic activities of metal surfaces in formic acid dehydrogenation, as a function of the enthalpy AH of formation of the metal formates. The enthalpies represent the strength of the substrate-surface interaction. Source BC Gates, Catalytic Chemistry, Wiley, New York, 1992. Data are from WJM Rootsaert and WMH Sachtler, Z Phys Chem NF 26, 16 (1960).

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