Temperature swing adsorption of NOx over Keggin type heteropolyacids

Abstract

Temperature swing NO x adsorption-desorption cycles with gas mixtures consisting of 1000 ppm NO x , 5% O 2 , 3% H 2 O and N 2 were carried out on heteropolyacid adsorbents in the temperature range 80-170 C. Keggin type heteropolyacids having tungsten, molybdenum or their combination in octahedral coordination in combination with P, Si, Ge or B atoms in tetrahedral coordination were investigated. The heteropolyacids were used as pure compounds or supported on zeolite Y or the metal-organic framework Cu 3 (BTC) 2 (BTC represents 1,3,5-benzenetricarboxylic acid). The property of reversible adsorption of equimolar mixtures of NO and NO 2 was observed with Keggin type heteropolyacids based on W and combinations of W and Mo. Regeneration of the saturated adsorbent was achieved by cooling in a water vapor containing gas stream. The investigated heteropolyacids showed different water adsorption behavior. The capability of NO x adsorption was found to be related with crystal hydrate formation. Crystal water was much stronger retained in W-based compared to Mo-based Keggin compounds. Co-adsorption of NO and NO 2 molecules occurred only on Keggin compounds containing crystal water. The formation of H 2 NO 2 + compound out of NO, NO 2 and H 2 O in the interstitial spaces between Keggin units is proposed. The H-form and Co, Cu, Fe, Ni and Mn salts of Wells-Dawson type heteropolyacids were found to be readily dehydrated upon heating and did not show reversible NO x adsorption. Supported W-based Keggin heteropolyacid showed lower NO x adsorption capacity compared to the unsupported heteropolyacid.

The Keggin Structure: An Important Factor in Governing NH3–SCR Activity Over the V2O5–MoO3/TiO2 Catalyst

“…Of the many structural types of HPAs, the majority used in catalytic applications are Keggin HPAs, such as H 3 12 O 40 because of their stronger acidity, higher thermal stability, and easier availability [11,12]. It has been reported that Keggin HPAs have excellent NO adsorption behavior and that rapid heating can cause absorbed NO to be decomposed into N 2 [13][14][15]. Other research has shown that Pt loaded on Keggin HPAs can enhance the activity of NO reduction [16].…”

Carbon capture turned upside down: high-temperature adsorption & low-temperature desorption (HALD)

“…34,35 At high temperature, NO x molecules are chemisorbed in the crystal structure of the acid, substituting the H 2 O molecules that were present in the crystal structure before. The NO x moieties are released only at low temperature and in the presence of H 2 O.…”

Template Design and Economical Strategy for the Synthesis of SSZ‐13 (CHA‐Type) Zeolite as an Excellent Catalyst for the Selective Catalytic Reduction of NOx by Ammonia

“…[1][2][3] In addition, zeolites are also applied in the control of harmful exhaust gases (such as NO x )t hat come from automobile engines and power plants, which can causes eriouse nvironmental issues,s uch as acid rain, the greenhouse effect,a nd photochemicals mog. [4,5] Previously,w ep resented ac atalystc ombination of MnCeTia nd VWTia ctive materials that had aw ide de-NO x temperature window (150-400 8C, > 85 %). [6] However, as ar esult of the presence of poisonous V 2 O 5 and secondary pollutionb yV 2 O 5 sublimation and fall off, the USA and Japan have already forbidden the use of V-containing catalysts in diesel-engine exhausts.…”