Sustainable solution to the recycling of spent SCR catalyst and its prospective gas sensor application

Nitrogen oxides (NO_X) are often produced in industrial combustion processes and are among the most harmful air contaminants. Selective catalytic reduction (SCR) is currently the most effective technology for reducing effluents. Due to increasingly strict environmental regulations, the demand for SCR catalysts has increased, and inevitably, the need to dispose of the spent catalysts has increased and produced an environmental burden. The necessity for disposal while finding secondary sources for the vanadium, tungsten and titanium present in the catalyst makes recycling of spent SCR catalysts a pressing issue. During this investigation, two tertiary amines were compared to determine their effectiveness in extracting vanadium and tungsten from a spent SCR catalyst. The enrichment process was optimized, and the loaded organic solution (9-fold increased concentration) was further stripped to prepare a mixed metal oxide (MMO) based active sensing material for use in H₂S gas detection. The H₂S gas sensing characteristics of the MMO material were studied systematically. The MMO sensor showed an excellent sensing response to H₂S gas with a high sensitivity of 12.73 % for 100 ppm and quick response/recovery times (t_r = 101 s/t_f = 133 s) at a low operating temperature of 130 °C. In addition, the sensor exhibited enhanced selectivity, long-term stability, and a detection limit of ∼47 ppb to H₂S gas. The experimental findings of this work suggest that the recycled materials from spent SCR catalysts could have sustainable potential in reproducing the active sensing catalyst materials for the practical applications in the field of environmental protection.