The H2O Effect on Cu Speciation in Cu-CHA-Catalysts for NH3-SCR Probed by NH3 Titration

Catalysts

Andrew P. E. York¹  Maria Pia Ruggeri¹  David Thompsett¹  Jillian Collier¹  Shaojun Liu²  Federica Gramigni²  Umberto Iacobone²  Roberta Villamaina²  Isabella Nova²  Enrico Tronconi² 

[1] Johnson Matthey Technology Centre, Blounts Court Road, Sonning Common, Reading RG4 9NH, UK;Laboratory of Catalysis and Catalytic Processes, Dipartimento di Energia, Politecnico di Milano, via La Masa 34, 20156 Milano, Italy;

关键词: Cu-CHA;    NH₃-SCR;    Si/Al ratio;    Cu loading;    H₂O effect;    Cu speciation;   

DOI  :  10.3390/catal11070759

来源: DOAJ

【 摘 要 】

The present work is focused on the effect of water on NH₃ adsorption over Cu-CHA SCR catalysts. For this purpose, samples characterized by different SAR (SiO₂/Al₂O₃) ratios and Cu loadings were studied under both dry and wet conditions. H₂O adversely affects NH₃ adsorption on Lewis acid sites (Cu ions) over all the tested catalysts, as indicated by the decreased NH₃ desorption at low temperature during TPD. Interestingly, the NH₃/Cu ratio, herein regarded as an index for the speciation of Cu cations, fell in the range of 3–4 (in the presence of gaseous NH₃) or 1–2 (no gaseous NH₃) in dry conditions, in line with the formation of different NH₃-solvated Cu species (e.g., [Cu^II(NH₃)₄]²⁺ and [Cu^II(OH)(NH₃)₃]⁺ with gaseous NH₃, [Z₂Cu^II(NH₃)₂]²⁺ and [ZCu^II(OH)(NH₃)]⁺ without gaseous NH₃). When H₂O was fed to the system, on the contrary, the NH₃/Cu ratio was always close to 3 (or 1), while the Brønsted acidity was slightly increased. These results are consistent both with competition between H₂O and NH₃ for adsorption on Lewis sites and with the hydrolysis of a fraction of Z₂Cu^II species into ZCu^IIOH.

【 授权许可】

Unknown