Carbon deactivation

Carbon Deactivation Postulated for Industrial Cobalt Catalysts... 

Agrawal, P. K., Katzer, J. R., and Manogue, W. H. 1981. Methanation over transition metal catalysts. II. Carbon deactivation of cobalt/alumina in sulfur-free studies. J. Catal. 69 312-26. 

Palladium catalysts are more often modified for special selectivities than platinum catalysts. Palladium prepared by reduction of palladium chloride with sodium borohydride Procedure 4, p. 205) is suitable for the reduction of unsaturated aldehydes to saturated aldehydes [i7]. Palladimn on barium sulfate deactivated with sulfur compounds, most frequently the so-called quinoline-5 obtained by boiling quinoline with sulfur [34], is suitable for the Rosenmund reduction [i5] (p. 144). Palladium on calcium carbonate deactivated by lead acetate Lindlar s catalyst) is used for partial hydrogenation of acetylenes to cw-alkenes [36] (p. 44). 

The turnover numbers and activation energies for methanation over all four metals freshly reduced and under sulfur-free conditions (Table XVI) were in good agreement with values reported for supported metal catalysts (220). At 673 K, Ni and Ru exhibited only very slow losses in activity apparently due to slow carbon deposition, whereas Co and Fe underwent rapid, severe carbon deactivation after maintaining their fresh catalyst activity for a few hours. After rapid deactivation the final steady-state activity, which was about 100-fold lower than the activity of the fresh catalyst, was approached slowly this activity region was referred to as the lower pseudosteady state. Likewise, the fresh catalyst behavior was referred to as the upper pseudo-... 

AES studies of in situ sulfur-poisoned Ni and Ru showed the complete absence of carbon on the surface or in the near-surface region for Co, on the other hand, a fraction of a monolayer of carbon was present but there was no bulk carburization. For Co which was carbon deactivated prior to sulfur poisoning, surface carbon and bulk carburization were both observed (205). 

That the activation energies and rate concentration dependences for methanation over sulfur-poisoned Ni and Ru are the same as those observed under sulfur-free conditions (99-100,140,147,209) provides further evidence that sulfur poisoning of Ni and Ru involves geometric blockage of active metal sites. However, the observations that (i) the activation energies for methanation over sulfur-poisoned and carbon-deactivated Co are both 50 kJ/mol lower than that for fresh Co and (ii) the rate dependence on CO partial pressure is positive order for both carbon-deactivated Co and sulfur-poisoned Co, suggest that the deactivations of Co by sulfur and carbon are similar and may involve electronic as well as geometric effects. 

Bueno-Lopez and Garcia-Garcia (2005) IR Potassium-carbon Deactivation by SO2/ phase formation between potassium and sulfur + + NO reduction by carbon... 

The operating conditions have been chosen so as to minimize secondary reactions as well as carbon deactivation total pressure, P = 6.0 bar temperature, T = 473-533 K catalyst weight, Wc = 0.0319-0.4541 g feed-stream, Fmcp = 0.25 mol h H2/MCP = 40/1 N2/MCP = 80/1. The activity measurements were achieved in a fixed bed differential reactor (conversion below 10-15 %), designed to minimize the time necessary to reach the steady state [18,19]. 

Based on the mechanism of carbon formation presented in Fig. 1, carbon filaments do not deactivate the catalyst as encapsulating carbon does. The encapsulating carbon deactivates the catalysts by decreasing the total number of active sites. This is described by a site conservation equation (Eq. (1)) in the present work ... 

Fixed-bed hydropyrolysis tests at 15 MPa were conducted using either ca. 0.5 or 1 g of sample for the low and high carbon deactivated catalysts selected for detailed investigation. For some tests, the deactivated catalysts (extrudates) were ground and diluted in sand. The procedure used has been described elsewhere a relatively slow heating rate of 5 C min... 

Fig. 2. Carbon contents for the low and high carbon deactivated HDS catalysts - as received, after chloroform extraction and after hydropyrolysis...

While monometallic ruthenium/carbon deactivated progressively during 300 h on stream when the reaction was performed in 2-sec-butyl-phenol solvent at 180 °C and 3.5 MPa in a flow fixed-bed reactor, bimetallic ruthenium-tin/carbon catalysts exhibited a stable activity. The optimised ruthenium/tin atomic ratio of unity led to ruthenium and RuaSng alloy species. Neither tin nor ruthenium leaching occurred. In addition, the hydrogenation of the C=0 bond of levulinic acid was 100% selective. 

---