SO2 deactivation

The presence of SO2 deactivated the trap as shown in Figure 7. The trap was initially treated with 1000 vppm NOx in background gas (minus the SO2) for 15 minutes. The desorption profile generated by injection of 6500 vppm C, as propylene, is shown as the fresh catalyst. After aging in 150 vppm SO2 in air and 10% H2O at 500 C for 24 hours the trap effectively loses all of its NOx adsorption/desorption capacity. Even with a calcination at 800 C in sulfur free air only about 30% of the initial capacity could be recovered. The absence of regeneration is primarily due to retained SOx which occupies NOx adsorption sites although some thermal deactivation at 800 "C also occurs. 

In an extension of the work by Foley et Tsai et al.43 undertook the determination of the causes of SO2 deactivation of supported metal catalysts in the reduction of NO with NH3. They placed foils of Ni, Ru, Pd and Pt in the beds of catalyst particles of these metals supported on AI2O3, then, after reaction, they removed and examined the foils by Auger electron spectroscopy (AES). This determination of the surface composition and depth of penetration of the elements enhances the interpretation of the sulfur-poisoning mechanism. 

SO2 nearly completely deactivated the Cu-ZSM-5, resulted in an inhibition for Co-ZSM-5 and an enlargement of the N2O conversion over Fe-ZSM-5 (figure 9). Both the Fe and the Co systems returned to their original activity after removal of the SO2, this took several hours. 

SO2 also increases the N2O conversion in the case of Fe, probably according to eq. (11), although no product analysis is available. Co-ZSM-5 is inhibited by the SO2 or SO3, but not irreversibly. Copper is completely deactivated, as for other reactions over copper zeolites. 

The Bis A-PSF can be sulfonated on the Bis A residue, but the Bis S-PSF will not sulfonate due to the deactivating effect of -SO2- on electrophilic aromatic substitution. Therefore, such a block copolymer would allow the study of sequence length effects on membrane performance. 

In the presence of 80 ppm SO2, the deactivation of LaFco 8CU0 2O3 however became severe and the loss in catalytie aetivity was proportional to the poisoning time. Furthermore, the original activities of spent LaFeo.8Cuo.2O3 cannot be reeovered after switching the stream from 80 ppm SO2 containing feed to a 5 ppm SO2 one. 

To show the alumina effect quantitatively, a series of catalysts was made in which the amount of alumina in the matrix was varied from 25 to 100% by adding alumina sol to a 25% alumina, silica-alumina slurry. These catalysts were formulated with REY molecular sieve. The results for SO2 removal are shown in Figure 3 where SO2 removal (corrected for unit factor) increases with increasing alumina. Our conclusion that alumina was important for SO2 adsorption also confirmed the results of Blanton and Flanders at Chevron (22). The non-linearity of the relationship implies an antagonistic effect between silica and alumina. The silica-alumina antagonism will be discussed relative to deactivation subsequently. 

Fresh activity, however, only partially determines the efficacy of these catalysts. Among other important factors, as we have seen, are how easily the catalyst releases SO2 during the cracking cycle and how resistant it is to deactivation by steam. 

A major deactivating mechanism has been shown to be the sulfation of the active hydroxyl or oxide ion sites by chemical reaction with the chemisorbed SO2 (29, 30). 

Finally, there is evidence (48, 90, 91) that the presence of small amounts of noble metal on the surface of base metal catalysts can suppress catalyst deactivation by SO2 to some extent. 

These polar transformation products and sulfur oxides (SO2, SO3) arising in the ultimate stages of the transformation process are formed in trace amounts in the aged polymer matrix. Volatile products may be sources of undesirable organoleptic problems. This limits the use of organic thiocompounds in odor-sensitive applications. Organic S-proto-nic acids 85, 86 deactivate basic stabilizers (HAS). The peroxidolytic effect of 85, 86 is reduced in the presence of some antiacids or fillers, e.g., calcium carbonate. 

Reverse-flow operation for Sulfur Production over Bauxite Catalysts by the Claus Reaction has been considered in Refs 9 and 31. The rate of H2S oxidation by SO2 on bauxite catalysts is very high even at ambient gas inlet temperature, but sulfur condensing at low temperatures blocks the active catalyst surface, and the reaction stops because of catalyst deactivation. In a reverse-flow reactor the periodic evaporation of condensed sulfur from the outlet parts of the catalyst bed occurs. Although it is difficult to remove all the sulfur condensed within the catalyst pellets at the bed edges, after a certain time a balance between the amount of sulfur condensed and evaporated is attained. Using a reverse-flow reactor instead of the two-bed stationary Claus process provides an equal or better degree of... 

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

Thus, 222kcalmol must be transferred to HOH to produce atomic oxygen, which is a measure of the deactivation and stabilization of atomic oxygen in the formation of a water molecule. Another important and unique characteristic of water molecules is their tendency to cluster through intermolecular hydrogen bonds (more properly hydrogen-oxygen bonds) (equation 2). In contrast, for ambient conditions, BH3, CH4, NH3, and HF are monomeric gas molecules (as are CO, CO2, H2S, and SO2). 

Figure 6 demonstrates the same point by con aring the MgO based trap to the Barium Titanate lab prototype. Again loss of performance in the presence of sulfur is observed. For these experiments SO2 gas was used to effect the sulfation during the regeneration mode of cyclic deactivation. SO2 gas may also be bled into the system dxiring the Transfer Method experiment allowing sulfur to directly con ete with trap sites as in the above two studies. 

Thus, reaction (30) could specify either an excited singlet or triplet SO. The excited state may, of course, degrade by internal transfer to a vibrationally excited ground state which is later deactivated by collision, or it may be degraded directly by collisions. Fluorescence of SO2 has not been observed above 2100 A. The collisional deactivation steps known to exist in laboratory experiments are not listed here in order to minimize the writing of reaction steps. 

Three different Cr-Co spinels were prepared and tested as catalysts for the oxidation of methane in the presence of SO2, a typical catalyst poison. The spinels were prepared from nitrate precursors using a co-precipitation method, followed by calcining at three different temperatures, (400, 600 and 800 °C) for 5 hours. Characterisation results indicate that the catalyst calcined at 800 C presents a structure of pure spinel, whereas the presence of single oxides is observed in the catalyst calcined at 600 C, and the catalysts calcined at 400 C presents a very complex structure (probably a mixture of several single and binary oxides). Experiments show an important influence of calcining temperature on the catalyst performance. In absence of SO2, catalysts calcined at 400"C and 600 C performs similarly, whereas the activity of the catalysts calcined at 800 C is worse. When sulphur compounds were added to the feed, catalyst calcined at 600"C deactivated faster than the other two catalysts. 

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