Operando diffuse reflectance infrared detection of cyanide intermediate species during the reaction of formaldehyde with ammonia over V2O5/WO3-TiO2

• Published in: Applied catalysis. B, Environmental Vol. 298; p. 120629
• Main Authors: Nuguid, Rob Jeremiah G., Elsener, Martin, Ferri, Davide, Kröcher, Oliver
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.12.2021; Elsevier BV
• Subjects: Ammonia; Catalysts; Chemical reduction; Cyanides; DRIFTS; Formaldehyde; HCN; Hydrogen cyanide; Infrared spectroscopy; Modulated excitation; Polyamide resins; Polyamides; Reflectance; SCR; Selective catalytic reduction; Species; Species diffusion; Titanium dioxide; Vanadium pentoxide; Vapor phases; HCN; Cyanides; Modulated excitation; SCR; DRIFTS; Formaldehyde
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2021.120629

[Display omitted] •Formaldehyde present in exhaust gas can react with NH3 to produce HCN.•This reaction was studied by operando DRIFTS on V2O5/WO3-TiO2 and TiO2 at 300 °C.•Formaldehyde and NH3 formed adsorbed cyanide species, and gas phase HCN was detected.•Formic acid reacted with NH3 but did not form adsorbed cyanide species or HCN.•HCN production does not involve adsorbed formate species at 300 °C. Hydrogen cyanide (HCN) is a highly poisonous gas that can form through the reaction between formaldehyde and ammonia (NH3) in the exhaust. While this detrimental side reaction has been the subject of recent catalytic studies under selective catalytic reduction conditions, the molecular mechanism leading to the release of HCN remains far from elucidated. Here, we report the detection of the cyanide intermediate species by operando diffuse reflectance infrared spectroscopy, thereby providing unambiguous evidence that the HCN-forming reaction occurs on the catalyst surface. Formaldehyde likely reacts from the gas phase with pre-adsorbed NH3 to form HCN. Although formate species were formed abundantly upon formaldehyde introduction, they were not responsible for the high level of HCN emissions observed. TiO2 alone is sufficient to catalyze the side reaction, but VOx and/or WOx sites increase HCN production by preventing the formation of inactive polyamide species. These mechanistic insights should serve as a basis for understanding the chemistry responsible for the side reaction so that mitigation measures can be put forward.