title: The role of isolated Cu2+ location in structural stability of Cu-modified SAPO-34 in NH3-SCR of NO.
abstract: In this study, three different methods (ion exchange, wet mixing and impregnation) were employed to prepare Cu-modified SAPO-34 molecular sieves. All these freshly prepared catalysts showed excellent activities towards the selective catalytic reduction (SCR) of NO with NH3 (NH3-SCR) no matter which preparation method was used. However, hydrothermal ageing significantly reduced the catalytic activities of those catalysts prepared by the wet-mixing and impregnation methods, respectively. The results of X-ray powder diffraction, H2-TPR and electron paramagnetic resonance measurements for these catalysts suggested that the decrease in catalytic activity may be attributed to the migration of Cu2+ ion to the centre of the hexagonal prism (site III), the formation of CuxOy and the collapse of the molecular framework during hydrothermal ageing. The degrees of structural collapse of each Cu-modified molecular sieve were different, probably due to Cu2+ species in different sites (in the ellipsoidal cavity (site I) for ion-exchange sample, near the eight-ring window (site IV) for the wet-mixing and impregnation samples). Cu2+ located at site I was more stable than that located at site IV.
authors.affiliation: a Dalian National Laboratory for Clean Energy , Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023 , People's Republic of China.
authors.forename: Chundi
authors.initials: C
authors.lastname: Yan
authors.forename: Hao
authors.initials: H
authors.lastname: Cheng
authors.forename: Zhongshan
authors.initials: Z
authors.lastname: Yuan
authors.forename: Shudong
authors.initials: S
authors.lastname: Wang
mesh_terms: D000393:Air Pollutants / Q000737:chemistry / Q000302:isolation & purification*; D000641:Ammonia / Q000737:chemistry*; D002384:Catalysis; D003300:Copper / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods; D008422:Materials Testing; D009569:Nitric Oxide / Q000737:chemistry / Q000302:isolation & purification*; D001335:Vehicle Emissions / Q000032:analysis*; D017641:Zeolites / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D001335:Vehicle Emissions; D017641:Zeolites; D009569:Nitric Oxide; D000641:Ammonia; D003300:Copper
keywords: CuxOy; NH3-SCR; SAPO-34; isolated Cu2+; structural stability