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The final activation under H2 was realized after determination of the experimental conditions by temperature programmed reduction (TPR). The samples were characterized by XPS and ZD6474 manufacturer TEM after the catalytic test. Afterwards, small particles were still observed but with the concomitant presence of small agglomerates (5�C10 nm) probably due to sintering during the catalytic test (see Figure S4 in Supporting Information File 1). The same TEM observations were made for the five catalysts. Table 2 Description of catalysts prepared for ammonia synthesis. The catalytic tests were realized at different temperatures and the results are presented in Supporting Information File 1. Table 3 summarizes the best results obtained for each catalyst. From these results, it can be concluded that the presence of Pt and particularly of Au is negative for the production of NH3. It is known that Pt easily dissociates H2 which would cover the Ru surface by H making it inaccessible for N2 dissociation. These results (ammonia synthesis rate, mmol NH3 h?1g?1 Ru) are as good as or better than some results obtained on inorganic oxides supports [54�C55] but less (��10��) than some results reported with carbon nanotubes and nanofibers in the literature [43,56�C57] check details using different experimental catalytic testing conditions. This allows for a benchmark for our systems and shows that they are not yet highly performing. It is remarkable that significant activity was obtained although such a low temperature and at atmospheric pressure with very low Ru loading was used. The maximum Ru percentage anchored was between 2 and 3 wt %, while a higher percentage (5�C10 %) of Ru was used in reported studies to guarantee high performance. In addition, it has been shown that ultrasmall particles (1�C2 nm) are less active in ammonia synthesis than larger ones (3�C4 nm) [58]. In our catalysts the majority of particles have a diameter of TRIB1 8 and 9 are characterized by a higher decomposition temperature. Therefore, the selected low activation temperature could adversely influence their catalytic activity together with residues from the functionalization arm (Cl, S, O, P) [59]. Thus, there is room for improvement of the catalytic performance by optimizing the thermal activation pretreatment. Table 3 Ammonia production (%) and ammonia synthesis rate (mmol NH3 h?1g?1 cat or mmol NH3 h?1g?1 Ru) for catalysts prepared on functionalized carbon nanofibers (see Table 2). Conclusion Samples of carbon nanofibers and nanotubes were functionalized with chelating phosphine groups. Ru-based clusters were covalently anchored onto the modified carbon surfaces by ligand exchange. The characterization of the materials demonstrated the molecular nature of grafted fragments.