Ruthenium potassium promoted catalysts

Rarog W, Kowalczyk Z, Sentek, J, Skadonowski D, Szmigiel D, Zielinski J (2001), Decomposition of ammonia over potassium promoted ruthenium catalyst supported on carbon , Appl. Catal. A Gen., 208, 213-216. 

The effectiveness of the promoter in the nitrogen exchange reaction can be further extended by supporting ruthenium/potassium on basic oxides such as BeO, CaO, and MgO in place of the more usual acidic and neutral oxides. A steady increase in the nitrogen exchange TON with support basicity is seen but, surprisingly, there is no effect on the ammonia synthesis TON relative to that observed on the carbon-supported catalysts. This may reflect a marked shift in the overall synthesis kinetics, which are strongly dependent on both the support and the promoter. 

Catalyst for ammonia synthesis containing a transition metal, especially ruthenium on a graphite-containing carbon with rubidium or potassium promoter. A. M. Lear, J. J. McCarroll, D. A. Pippard, and S. R. Tennison (British Petroleum Ltd). GB 2087746 (1982). 

Ammonia synthesis catalyst consisting of ruthenium on a pretreated carbon support with barium and/or potassium promoters. J. J. McCarroll, S. R. Tennison, and N. P. Wilkinson (British Petroleum Ltd). GB 2136704 (1984) EP 120655 (1984) US 4600571 (1986). 

The compounds K2[Ru4(CO)i3], K4[Ru4(CO)i2], and K6[Ru4(CO)n] have received attention as catalysts in ammonia synthesis.The compounds act as precursors for both the catalytically active ruthenium particles and the potassium promoter. The rate of the ammonia synthesis at 300 °C over these catalysts increases with the increase in the K Ru ratio in the starting carbonyl metallate. ... 

Where the Fischer-Tropsch process has been used on an industrial scale, iron or cobalt are the essential catalyst components. Technical catalysts also contain oxidic promoters, such as alumina and potassium oxide. Ruthenium and nickel are most attractive for academic research since they produce the simplest product packages. Nickel is used for methanation (production of substitute natural gas and removal of carbon monoxide impurities from hydrogen). 

Research with an alkali-promoted (potassium or K2O) ruthenium catalyst has demonstrated that ammonia synthesis can be effected at lower temperatures and pressures than those required by the Haber process. As the price of energy increases, ruthenium catalysis might become increasingly important, because the energy-expensive compression process could be avoided. Another advantage of ruthenium if its diminished susceptibility to poisoning by H2O and CO. Ruthenium catalysts can carry out the direct synthesis of ammonia from N2, CO, and H2O ... 

Potassium is considered to be electron donor for the iron catalysts. For ruthenium catalysts, electronic effect of support and promoter is very important. According to the eletronegativity, the electronic effect of support and promoter are summarized and shown in Fig. 6.15 and Table 6.8. ... 

There are optimum content proportion between promoter and ruthenium. Figures 6.22 and 6.23 show the effect of the content of potassium and barium independently as single promoter on the activity of the ruthenium catalysts. It can... 

The effect of the types of alkah metal and alkaline earth metal salts on the activity for Ru-M (promoter)/AC with 4% of Ru is shown in Fig. 6.25. When the anions of metal salts are ah NO3 the effect of promoters follows the descending order as Ba(N03)2 >KNOs >Sr(NOs)2. When potassium as promoter and anion is SOJ, CO, N03 and OH, respectively, except for K2SO4 significantly reduces the activity due to the introduction of the sulfur, the influence of the rest anions on activity have little difference wherein nitrate salts are a few better. Obviously, sulfur is also a serious poison for ruthenium catalyst (Fig. 6.26). 

Promoter effect. Potassium (K) and barium (Ba) are good promoters for Ru/AC, while barium can increase not only the catalytic activity, but also the dispersion of ruthenium, as well as prevent the sintering of Ru crystallite, reduce the methanation reaction of activated carbon, improve the thermal stabUity of the catalyst. The role of electronic promoter about K is more evident, but it can only increase the catalytic activity, and it cannot prevent the sintering of Ru crystallite and the methanation of activated carbon. 

Of the platinum group metals only ruthenium and osmium show significant ammonia synthesis activity, though only in the presence of alkali promoters. This can be seen from the performance of the potassium metal promoted carbon-supported catalysts in Table Although osmium was one of the earliest and... 

Figure 9.12. Pulsed nitrogen adsorption on potassium nitrate promoted ruthenium-carbon catalysts. denotes normalized peak width. This is a function of the heat of adsorp> tion of the more weakly bonded species. The increase in peak width above 520 K indicates the onset of an activated adsorption/desorption process. A denotes moles of irreversibly adsorbed nitrogen. The rapid increase above 700 K is possibly due to the formation of the N2—Ru—K bulk complex.

Catalysts for ammonia synthesis containing ruthenium together with potassium and barium as promoters. R. M. Elofson and F. F. Cadallah. US 4142993 (1979). 

---