Deactivation mechanism of activated carbon supported copper oxide SCR catalysts in C₂H₄ reductant

Abstract

Current state‐of‐the‐art NH3‐SCR technology based on vanadium catalysts suffers problems associated with NH3 slip and poisoning of the catalyst and blockage of heat recovery steam generators (HRSG). If environmentally‐friendly catalysts capable of efficient operation at lower temperatures could be developed that used a reductant other than NH3, the issues with current state‐of‐the‐art SCR could be significantly lessened. Hence, in this study, activated carbon (AC) supported copper oxide‐based catalysts for SCR while using C2H4 as a reductant was discussed. Reaction testing of catalysts demonstrated high initial NO conversion with steeply declining activity over 2 h of testing when C2H4 was used as the reductant; in comparison, with the same catalyst and NH3 as the reductant, stable, long‐term NO conversion was achieved, but at a lower rate than the initial reactivity with C2H4. As a consequence, catalyst characterization studies were performed to assess deactivation mechanisms when C2H4 was the reductant. These studies included x‐ray diffraction, BET surface area and porosity, temperature programmed reduction, scanning electron microscopy, Raman spectroscopy and x‐ray photoelectron spectroscopy of both fresh and deactivated catalysts. The analytical results showed the surface area and porosity of the catalyst remained unchanged and the initially highly‐dispersed Cu species became agglomerated and more crystalline during reaction testing. Furthermore, carbon black was also detected on the catalyst surface after testing, presumably formed during the decomposition of C2H4. Both agglomeration of the active Cu species and blockage by carbon deposits would decrease the availability of active sites and lead to decreased catalytic activity.

Low Temperature deNOx Catalytic Activity with C2H4 as a Reductant Using Mixed Metal Fe-Mn Oxides Supported on Activated Carbon

“…Maintenance of the porous structure may have been beneficial for dispersing the active species or maintaining an effective pathway for access of reactants and products to and from the active sites; however, the surface areas and porosities of the mono-metal 3Mn/NAC also did not significantly change before and after reaction testing although its NO conversion activity rapidly declined after 15-20 min of testing. Hence, catalyst surface areas and porosities did not control NO conversion for these catalysts, in agreement with previous studies showing the surface area of supported MnOx catalysts was not a main cause of catalytic activity change during HC-SCR reactions [40]. The difference between NOx and NO of all tested catalysts was very small and was near 0% during the first 20 min of testing, and remained at less than 1-5 ppm during the entire tests.…”

“…This redistribution would decrease the availability of active catalytic sites and could cause decreased NO conversion at the longer reaction times near 2 h. Raman spectra from 1.5Fe3Mn/NAC were also acquired before and after reaction testing, as shown in Figure 10. The spectrum of the fresh catalyst contained bands at 1360 cm −1 (labeled D), 1610 cm −1 (G) and triplet structured bands near 3000 cm −1 (2D); these are attributed to the activated carbon support [40] and are present with similar intensities in the reaction tested catalyst. A peak at 650 cm −1 in the as-prepared catalyst is attributed to Fe-O-Mn bond vibrations [45]; this band also was observed in the reaction tested catalyst but is narrower and higher in intensity.…”

Investigation of deactivation effect of Au addition to Ce/TiO2 catalyst for selective catalytic reduction using real diesel engine exhaust samples at low temperature conditions

“…Among these, HC-SCR and OHC-SCR techniques have been considered as the most promising for NO x reduction due to their low cost, and being environmentally safe. 12,13 Different types of catalysts have been developed for the SCR system. Vanadium-tungsten-titanium catalysts are effective catalysts for NO x removal.…”

Experimental methods in chemical engineering: Raman spectroscopy

“…Eng. published 11 articles: six are directly related to catalysis, [27][28][29][30][31] three are in the area of combustion, [32] one combined Raman and EDS to identify a low melting lithium phosphate phase in lithium iron phosphate ingots, [33] and another applied confocal Raman to measure solute concentrations in a hanging droplet (mass transfer). [34] Raman spectrographs now record the whole spectral range (Raman shifts from 100 cm −1 to 4000 cm −1 ) at subsecond resolution and are applied to pulse experiments with isotopes, to measure reaction kinetics and spectroscopic characteristics.…”

“…Eng . published 11 articles: six are directly related to catalysis, [ 27–31 ] three are in the area of combustion, [ 32 ] one combined Raman and EDS to identify a low melting lithium phosphate phase in lithium iron phosphate ingots, [ 33 ] and another applied confocal Raman to measure solute concentrations in a hanging droplet (mass transfer). [ 34 ]…”