Ammonia artificial photosynthesis

Blank experiments are commonly referred to in the literature on artificial photosynthesis of ammonia, and no ammonia is often given as an analytical result from such experiments. In our papers we have given concentrations of synthesized ammonia, concentrations in blank experiments, and reported the difference. We point out here that the chemical analytical procedures used for detection of ammonia constitute zero-inertia meters and must always give a result for ammonia concentration which only coincidentally might be null. In all cases the amount of ammonia found in both preparation and control experiments must be reported along with uncertainties and units. A result of no ammonia is meaningless and, in fact, cannot be obtained. 

Examination of the thermodynamics and kinetics of proposed chemical reactions for the artificial photosynthesis of ammonia presents several problems, not the least of which is the logical and rhetorical one of discussing mechanisms for a process while suggesting that it does not occur. The latter problem can be largely resolved by understanding beforehand that the purpose of the present section is to call into question and to dispute the proposition that ammonia is synthesized photocatalytically by irradiation of N2 and H20 by the artificial methods described already. We can examine the application in reported ammonia photosynthesis reactions of both categories of catalyst discussed in Section IV.A. 

Often when a discovery is made it is at or near the limit of detection by existing methods, as would be the case with artificial photosynthesis of ammonia. If the discovery is important enough to warrant a major new effort on its basis, as was the case with artificial photosynthesis of ammonia, then most of that effort needs to be concentrated on removal of any equivocation from the results. The concept of a major discovery that remains forever on the borderline of detectability is internally contradictory. Our considered opinion is that artificial photosynthesis of ammonia is such a concept and that it has not been discovered. The major effort reviewed here, though fully justified, has been improperly conducted in that such a small part of it has been directed toward experiments that would remove ambiguity about the discovery, for example, appropriate l5N-labeling experiments or production of high yields. 

Despite many studies there is available, at this time, no unequivocal report of artificial photocatalytic synthesis of ammonia from nitrogen and water on heterogeneous catalysts. The chemical reaction 1, shown at the beginning of this chapter, remains speculative 17 years after it was initially reported. No rational start has yet been made on determining a mechanism for the reported nitrogen fixation process, despite the fact that a clear demonstration and understanding of any such process would be of great importance. Despite 17 years of research, the reported yields of ammonia from artificial photosynthesis remain at or near the limits of detection by routine analytical methods. As we stated earlier in this chapter, the concept of a major discovery that remains forever on the borderline of detectability is internally contradictory. The current state of the field is one where serious scientific skepticism is appropriate. 

There is no doubt that ammonia has been detected in many experiments intended to investigate the artificial photosynthesis of ammonia from nitrogen and water. It is probable that in many cases the ammonia was present as a contaminant and was not synthesized during the process studied. In other cases it is possible that ammonia was synthesized. As we have mentioned earlier (Section III.C), the generation of a low-valent metal center capable of reducing nitrogen stoichiometrically is entirely reasonable and such reactions have been known for years (Section I.D). The production of ammonia in such a reaction is far removed both in concept and in... 

The Question of Artificial Photosynthesis of Ammonia on Heterogeneous Catalysts 235... 

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