Abstract
Vanadia supported on TiO2, ZrO2, and sulphated-ZrO2 have been prepared. These catalysts were characterized by elemental analysis, N2-BET, XRD, FTIR, and NH3-TPD methods. The stability of surface sulphated groups, studied by FTIR-spectroscopy, was found to depend dramatically on the temperature of the calcination of the samples. No considerable decomposition of surface sulphates was observed below 350°C. The influence of potassium oxide additives on the acidity and activity in NO SCR with ammonia was studied. It was found that the introduction of small amounts of potassium (K/V molar ratio<0.5) led to almost complete depression of the samples acidity and considerable weakening of the remaining acid sites for TiO2 and ZrO2 based systems. For the sulphated system, surface sulphur groups, due to their strong acidity, represent attractive sites for the localization of potassium oxide and the decrease in the total acidity is less pronounced in this case. The results of NO SCR with ammonia reveal a noticeable shift of the maximum catalytic activity towards higher temperatures in going from the conventional catalyst to vanadia supported on sulphated zirconia. The loading of the catalysts with potassium leads to considerable decrease of their catalytic activity, and to a shift of the maximum catalytic activity towards lower temperatures. Among all the catalysts, V2O5/sulphated-ZrO2 reveals the highest resistance towards alkali poisoning. The presence of SO2 in the reaction mixture was found to enhance stability and activity of the V2O5/sulphated-ZrO2 probably due to regeneration of surface sulphated groups at the reaction conditions. The potassium-doped V2O5/sulphated-ZrO2 catalyst reveal high activity and stability at 300°C, comparable with unpoisoned catalysts. At 400°C the presence of potassium compounds seems to enhance the deactivation of the catalyst under reaction conditions during 30h, possibly due to formation of potassium sulphate–pyrosulphate species reacting with vanadium oxide.
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