Abstract
The poisoning effect of single elements on commercial V2O5-WO3/TiO2 catalysts has been studied in the past decades. In this study, the combined effects of two multi-element systems (phosphorus-potassium and phosphorus-lead) on V2O5-WO3/TiO2 catalysts were studied by diverse characterizations. The results show that potassium and lead can result in the deactivation of catalysts to different degrees by reacting with active acid sites and reducing the amount of V5+. However, phosphorus displays slight negative influence on the NOx conversion of the catalyst due to the comprehensive effect of reducing V5+ amount and generating new acid sites. The samples poisoned by phosphorus–potassium and phosphorus–lead have higher NOx conversion than that by potassium or lead, because doped potassium or lead atoms may react with new acid sites generated by phosphate, which liberates more V–OH on the surface of catalysts and reduces the poisoning effects of potassium or lead on vanadium species and active oxygen species.
Highlights
The selective catalytic reduction (SCR) of nitrogen oxides (NOx ) with ammonia is one of the most effective technologies to reduce NOx emission generated by combustion process [1,2,3], such as coal-fired power plants and municipal solid waste incinerators [4]
The NOx conversion rates of D-P-K and D-P-Pb pretreated with (NH4 )2 HPO4 are higher than that of D-K and D-Pb, respectively. It implies that the treatment with (NH4 )2 HPO4 counteracts the poisoning effects of K and Pb on the catalyst to some degree
The band located at 1659, 1426 and 1409 cm−1 were proved to be NH3 adsorbed on the Brønsted acid sites [23,27,28]. It implies that the treatment with (NH4 )2 HPO4 generates new Brønsted and Lewis acid sites and improves the acidity of V2 O5 -WO3 /TiO2 catalyst [29,30,31]
Summary
The selective catalytic reduction (SCR) of nitrogen oxides (NOx ) with ammonia is one of the most effective technologies to reduce NOx emission generated by combustion process [1,2,3], such as coal-fired power plants and municipal solid waste incinerators [4]. V2 O5 is considered as the active phase and WO3 is considered as a promoter that inhibits the transformation of anatase to rutile, favors the spreading of the vanadia on the catalyst surface, and increases the acidity of the catalyst [5,6]. Though V2 O5 -WO3 /TiO2 catalysts show excellent activity in NH3 -SCR process, many compounds including alkali/alkali earth metal elements, Pb, Zn, P and As are found in exhaust flue gas streams, which can lead to the deactivation of SCR catalysts in their lifetime. The combined effects of different elements in the flue gas aroused the attention of scholars. Yu et al [14,15] suggested that SO2 in the flue gas promoted the activity of K- and Pb-poisoned catalysts. Kong et al [16] discovered that new acid sites generated on the SCR catalyst by loading HgCl2. Our recent work indicated SO2 and HCl can Catalysts 2020, 10, 345; doi:10.3390/catal10030345 www.mdpi.com/journal/catalysts
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