1,721,013 research outputs found
Graphitised carbon as support for Ru/C ammonia synthesis catalyst
Full text linkIn the present work, we compared the catalytic activity and mainly the stability under the usual ammonia synthesis conditions, of some carbon supports, differing as for their nature, purity and temperature of pretreatment. The effect of catalyst composition (metal and promoters loading) on stability was also investigated. XRD and N-2 adsorption/desorption analysis helped in elucidating the effect of carbon treatment. It was found that only after the support has been heated at least at 1900 degrees C the stability of the tri-promoted catalyst becomes fully satisfactory and virtually independent of Ru loading. For practical purposes such high temperature treatment must be compatible with the preservation of a sufficiently high surface area
Ru loading effect on Ru/C ammonia synthesis catalyst
No full textThis work deepens the study of the formulation of Ru/C catalysts for ammonia synthesis. The focus is posed on the optimisation of the content of Ru in order to achieve a competitive cost of the catalyst
Promoters effect in Ru/C ammonia synthesis catalyst
No full textA series of carbon-supported, ruthenium-based catalysts, variously promoted with alkali and alkali-earth compounds, were prepared, aiming at investigating the effect of such promoters on catalyst activity and stability. It was found that a simultaneous action of three promoters (K+Ba+Cs) maximised both activity and thermal resistance of the catalyst. In particular, Ba is very effective in providing catalyst activity and resistance to methanation, while Cs strongly improves resistance to metal sintering. A further activity improvement is given by K as third promoter. Through a XPS study, the promoter effect was confirmed to be essentially of electronic nature. The optimal catalyst composition, in terms of activity, thermal resistance in the reaction environment and cost, corresponds to Ru ca. 5 wt.%, Ba/Ru=0.6, Cs/Ru=1 and K/Ru=3.5 atomic ratios
Kinetic study of ammonia synthesis on a promoted Ru/C catalyst
No full textA set of kinetic tests on a promoted Ru/C catalyst for ammonia synthesis has been carried out under industrially relevant reaction conditions (T= 370-460 DegC, P= 50-100 bar). The results have been elaborated by using some kinetic models either derived from literature or here-developed. The best results, as for fitting and consistency of the optimized parameters, were obtained by simply modifying the Temkin equation with the addn. of H2 and NH3 adsorption terms, to take into account their inhibiting effect on catalyst performance. Such an equation can be advantageously applied for better design and operation of ammonia synthesis reactors using Ru/C catalysts. The activation energy for the synthesis reaction was 23 kcal/mol, much lower than that previously found for Fe-based catalysts. From a practical point of view, it has been shown that the working pressure can be decreased, with the same plant productivity, by 40-50% when using the present Ru/C catalyst. Likewise, the ammonia concn. in the exit gas can be increased by about the same value if the working pressure is not decreased
Characterisation of Ru/C catalysts for ammonia synthesis by oxygen chemisorption
Full text linkA standard chemisorption procedure has been set up for the determination of Ru dispersion in Ru/C catalysts. Pulse chemisorption of oxygen was carried out at 0 °C, after having proved that no corrosive chemisorption phenomena are present. An average chemisorption stoichiometry was experimentally determined through measurements on Ru black. The procedure was applied to the investigation of promoted and unpromoted Ru/C catalysts for ammonia synthesis, supported on two different carbon supports. The main factor influencing Ru dispersion showed to be Ru loading, while the addition of even large amounts of Ba–Cs–K promoters has practically no influence. It is also briefly discussed how such results can help in elucidating several aspects of the behaviour of Ru/C as catalyst for ammonia synthesis
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