Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

Kirsten Leistner,Ashok Kumar,Kurnia Wijayanti,Louise Olsson,Krishna Kamasamudram,Florian Brüsewitz

doi:10.3390/en10040489

Abstract

We developed a procedure for aqueous ion exchange to obtain different Cu loadings of Cu/SAPO-34 (between 0 and 2.6 wt %.) The catalysts were washcoated on monoliths and characterised with respect to their activity and selectivity under standard selective catalytic reduction (SCR), fast SCR, NH3 oxidation and NO oxidation reactions. They were further characterised using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), H2-temperature programmed reduction (H2-TPR), ultraviolet (UV)-vis spectroscopy and NH3 adsorption. As expected, activity of all reactions increased with copper loading, due to increased number of active sites. However, the N2O formation during standard and fast SCR yielded interesting mechanistic information. We observed that N2O formation at low temperature increased with copper loading for the standard SCR reaction, while it decreased for fast SCR. The low-temperature N2O formation during fast SCR thus occurs predominantly over Brønsted sites. Species responsible for N2O formation during standard SCR, on the other hand, are formed on the copper sites. We further found that the fast SCR reaction occurs to a significant extent even over the H/SAPO-34 form. The Brønsted sites in SAPO-34 are thus active for the fast SCR reaction.

Highlights

Continuous improvement of NOx removal technologies is made possible by the development of increasingly efficient catalysts
We have shown in an earlier study that, in fast selective catalytic reduction (SCR)
On the basis of the single peak in H2-temperature reduction (H2 -TPR) and in analogy with a previous finding for Cu/SSZ-13 [19], we suggest that the ion exchange positions occupied by copper ions in all our samples are those located in the 6-membered rings of the SAPO-34 chabazite structure

Summary

Introduction

Continuous improvement of NOx removal technologies is made possible by the development of increasingly efficient catalysts. Ammonia-selective catalytic reduction (SCR) was initially widely catalysed by noble metals [1,2,3]. Vanadia-based catalysts became common and later on, metal-exchanged zeolites [1,4,5,6]. Small-pore materials such as the zeolite Cu/SSZ-13 and the silicoaluminophosphate Cu/SAPO-34, have become popular subjects of research [7,8,9]. One aspect of Cu/SAPO-34 is the difficulty in producing it using conventional aqueous ion exchange [3,10]. A number of studies have been published on Cu/SAPO-34 synthesised via one-pot synthesis or solid state ion exchange and on commercially-produced catalysts [11,12]. Very few details are available as to the procedure of aqueous ion exchange for Cu/SAPO-34

Methods

Results

Discussion

Conclusion