SO2 poisoning

Figure 19. XRD patterns of corresponding LaFeo 8Cuo.203 mixed oxides, (a) fresh LaFeo.gCuo 2O3 (b) LaFco gCuo 2O3 after 80 ppm SO2 poisoning at 500 °C for 3 h (c) LaFco 8CU0 2O3 after 80 ppm SO2 poisoning at 500 °C for 36 h (d) LaFco 8Cuo 2O3 after 5% FI2 reduction up to 900 °C (e) sample (d) after oxidation by 5% O2 at 900 °C [86]...

Resistance of LaCoi FexOs To SO2 Poisoning During Methane Oxidation... 

Zhang, RD Alamdari, H Kaliaguine, S. SO2 poisoning of LaFeo sCuo 2O3 perovskite prepared by reactive grinding during NO reduction by CsH , Appl Catal A General, 2008, Volume 340, 140-151. 

The effect of SO2 poisoning was investigated both for the decomposition of NO and for its reduction over Cu/ZSM-5 (349). It was found that the catalytic activity for NO decomposition completely disappeared after addition of SO2. In contrast, the catalytic activity for NO reduction by propylene in the presence of O2 was only slightly lowered by the presence of SO2. This result suggests that selective reduction of NO by hydrocarbons has potential for practical applications. The O2 concentration is important for maintaining a high activity level, in particular in the presence of sulfur. O2 addition initially increases the N2 yield, but at higher O2 concentration the yield decreases. 

Here, we only show two pulses of O2 (m/c=32) and CO (m/e=28) from a long string of essentially idenlical, alternating pulses. A complete discussion of this data is given in the original reference however, simple observation indicates that much more CO2 (m/e=44) is formed upon the introduction of CO at -1500 sec on the SO2-poisoned catalyst compared to the unpoisoned catalyst. In this example, approximately 1000 mol/g of oxygen could be removed from the poisoned catalyst compared to only 700 fimol/g on the unpoisoned catalyst. This increased, reversible oxygen uptake on the S02-poisoned catalyst is due to oxidation and reduction of... 

The effect of having SO2 present in the reaction mixture is dramatic under reducing conditions [18]. Small amounts of SO2 poison the steam-reforming and WGS reactions [17,25). For CO oxidation, the enhancement normally found by... 

The current generation of catalysts would be sufficient to meet some of the most stringent requirements if sulfur were not present in essentially all hydrocarbon fuels. The combustion of sulfur-containing fuels produces SO2 in the engine exhaust. In high concentrations and for reducing environments, SO2 poisons sites on the precious-metal catalysts by forming adsorbed sulfur atoms, which in turn block a portion of the active metal sites and reduce the activity of adjacent metal sites [5]. 

The effect of SO2 on catalyst activity has been much less pronounced for CH4 oxidation than for CO, therefore, only results for CO are presented here. Table 2 gives data of SO2 tolerance of catalyst A for CO oxidation with a reactant of 2 vol% of CO in air, at 56000/h. In this Table, "poisoned means the activity dropped to less than 5% of the original value, "reversible" means the activity did not recover after shutting off SO2 for 30 minutes at otherwise the same condition, resumed some of its activity at 250°C, recovered completely at 280°C, and remained so when the temperature was lowered to 200°C again. At 200°C SO2 poisoning was very quick and the fatal dose was 0.02 ml/m2 or 0.14 monolayer on the basis of 30 A2 for the area occupied by one SO2 molecule from Yao. (ref. 3)), but it took 40 minutes at 300°C, and 5.2 monolayers. 

From subsequent tests, Tsai et al. 3 report the effects of oxygen in the feed gas on the SO2 -poisoning of the same catalysts studied with the same procedures. Here, with 0.5 mole % oxygen in the gas stream, in the absence of SO2, the activity of Pt, Ru, and Ni for NO reduction was increased by the presence of oxygen whereas that of Pd was reduced. AES confirmed that the Pd had been converted to the oxide. Most important, Tsai et al. found that the addition of 0.5% O2 to the gas stream largely restored the activity of all these catalysts severely poisoned by SO2. This is explained by the incorporation of high concentrations of oxygen into the subsurface layers of the metal foils (revealed by AES), which apparently counteracts the sulfur incorporation that still existed. They found no evidence of sulfate formation, only metal oxides and sulfides. 

Hepburn and Stenger investigated the effects of SO2 poisoning in the reduction of NO with H2 on Al203-supported Rh, Pd, and Pt only at temperatures less than 200 °C. Their feed gas contained no O2 or H2O, but only NO with a high excess of H2, wdth He as the carrier and either pulses or continuous injection of 1.5% SO2 in He. They observed both reversible and irreversible SO2 poisoning at these conditions. Small pulses of SO2 poisoned Pt irreversibly, but such pulsed... 

From the preliminary results of the bench scale pilot plant of the U.S. Environmental Protection Agency, Tseng et al. reported that a commercial SCR catalyst, extruded V20sA i02 based with some W, gave reduced NO conversion when 95 ppm SO2 was introduced into their flue gas stream from natural gas combustion. They also stated that this catalyst was less active at 440 °C than at 353 °C when 95 ppm SO2 was present in the flue gas. No further comments regarding this SO2 poisoning were offered. 

J. S. Hepburn and H. G. Stenger, "NO Reduction by Al203-Supported Rhodium. Palladium, Platinum. 2. Effects of SO2 Poisoning", Energy Fuels, 1988,2, 289-292. 

The most popular poisons to the cathode are NO and SO2 emitted out from the ICE vehicles and some chemical plants. They can poison the cathode at ca. 1 ppb level. The voltage loss caused by NO poisoning is fully recoverable, but that caused by SO2 poisoning is not due to the formation of a S layer according to Reactions 4.14 and 4.15 ... 

---