Abstract <p>The interaction of hydrazine monohydrate with nickel on various carriers has been investigated using a set of physicochemical methods. Hydrazine monohydrate was adsorbed on catalysts in forms both active and inactive in the IR region of the spectrum. The adsorption sites of hydrazine monohydrate particles were localized on the carrier. No correlation was found between the spectral manifestations of a number of catalysts under study and their catalytic activity in hydrogen formation. The surface hydrazine complexes activated by adsorption on the carrier diffused onto metal clusters, where the main reactions of hydrogen formation occurred. It was found that the reaction energy decreased the size and, apparently, rearranged the structure of the clusters with the appearance of centers suitable for efficient intramolecular dehydrogenation of hydrazine. This process was most effective on smaller clusters, possibly because a stronger Me−H bond was formed on them. Adsorption of hydrazine monohydrate through hydrogen atoms was possible on these clusters. These conditions ensured the predominant formation of hydrogen at low temperatures. An increase in temperature promoted a competing reaction of ammonia formation associated with the N–N bond rupture in the adsorption complex, which led to the formation of NH₂ complexes and then ammonia.</p>