Comparing CuAPO-5 with Cu : ZSM-5 in the selective catalytic reduction of NOx: An in situ study
(2007) The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces — Vol. 111, n° 7, p. 3130-3138 (2007)
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- Abstract
- The CuAPO-5 and Cu:ZSM-5 systems are compared in the selective catalytic reduction (SCR) of NOx. Within the Cu:ZSM-5 system materials with high and low metal contents were prepared by hydrothermal and conventional ion exchange, respectively. X-ray absorption spectroscopy (XAS) was used to follow changes in the valence state and the local environment of copper as the different materials reacted with the individual components of this particular deNOx process. This was effected by measuring the XAS spectra after each consecutive stage of the treatment with propene and NOx. In the CuAPO-5 system the reduction of copper(II) by propene to copper(I) is only partial and metallic copper or copper oxides are formed during the NOx and propene treatments. This can explain the relatively low activity (16-18%) of both the low and high copper content CuAPO-5 samples toward NOx reduction. By contrast, in the Cu:ZSM-5 system, copper(II) is reduced to copper(I) by propene and subsequently reoxidised by NOx. Copper is only partially reoxidised in Cu: ZSM-5 prepared by hydrothermal ion exchange (45% deNO(x) conversion), but the amount of copper exchanged by this method (133%) is significantly higher than in the conventional ion exchanged preparations (35%). The final propene treatment establishes that the Cu(I)/Cu(II) redox pair is formed in both Cu:ZSM-5 samples when reducing NOx. Previous studies suggest that dimeric copper species, in addition to isolated copper ions, are responsible for the activity of high copper content Cu:ZSM-5. We find no evidence of copper clustering in this system with the protocol used here.
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Mathisen, K., Nicholson, D. G., Beale, A. M., Sanchez-Sanchez, M., Sankar, G., Bras, W., & Nikitenko, S. (2007). Comparing CuAPO-5 with Cu : ZSM-5 in the selective catalytic reduction of NOx: An in situ study. The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces, 111(7), 3130-3138. https://doi.org/10.1021/jp066099z (Original work published 2007)