Investigating the Influence of Fe Speciation on N2O Decomposition Over Fe–ZSM-5 Catalysts

Abstract

The influence of Fe speciation on the decomposition rates of N2O over Fe–ZSM-5 catalysts prepared by Chemical Vapour Impregnation were investigated. Various weight loadings of Fe–ZSM-5 catalysts were prepared from the parent zeolite H-ZSM-5 with a Si:Al ratio of 23 or 30. The effect of Si:Al ratio and Fe weight loading was initially investigated before focussing on a single weight loading and the effects of acid washing on catalyst activity and iron speciation. UV/Vis spectroscopy, surface area analysis, XPS and ICP-OES of the acid washed catalysts indicated a reduction of ca. 60% of Fe loading when compared to the parent catalyst with a 0.4 wt% Fe loading. The TOF of N2O decomposition at 600 °C improved to 3.99 × 103 s−1 over the acid washed catalyst which had a weight loading of 0.16%, in contrast, the parent catalyst had a TOF of 1.60 × 103 s−1. Propane was added to the gas stream to act as a reductant and remove any inhibiting oxygen species that remain on the surface of the catalyst. Comparison of catalysts with relatively high and low Fe loadings achieved comparable levels of N2O decomposition when propane is present. When only N2O is present, low metal loading Fe–ZSM-5 catalysts are not capable of achieving high conversions due to the low proximity of active framework Fe3+ ions and extra-framework ɑ-Fe species, which limits oxygen desorption. Acid washing extracts Fe from these active sites and deposits it on the surface of the catalyst as FexOy, leading to a drop in activity. The Fe species present in the catalyst were identified using UV/Vis spectroscopy and speculate on the active species. We consider high loadings of Fe do not lead to an active catalyst when propane is present due to the formation of FexOy nanoparticles and clusters during catalyst preparation. These are inactive species which lead to a decrease in overall efficiency of the Fe ions and consequentially a lower TOF.

Perspective for Emission and Control of Nitrous Gas in Biological Wastewater Treatment

“…The results indicated that the adsorbed N2O can be easily decomposed to N2 without activation energy. Fe-ZSM-5 catalysts were used to remove N2O from gas by Richards et al (2018). Comparison of catalysts with relatively high and low Fe loadings achieved comparable levels of N2O decomposition when propane is present.…”

Influence of co-fed gases (O2, CO2, CH4, and H2O) on the N2O decomposition over (Co, Fe)-ZSM-5 and (Co, Fe)-BETA catalysts

“…O y clusters on the exchanged sites affects the catalytic performance [13,22]. Furthermore, it is also notable that Cosites were more active than Fe-sites due to lower activation energy barrier for the direct decomposition of N 2 O [19,24].…”

“…3d), the two bands observed at 200-260 nm and at 260-360 nm corresponding to the typical ligand to metal charge transfer (LMCT) bands of isolated Fe 3+ species in the cationic sites [19,34] and isolated or oligomeric extraframework Fe species in zeolite channels [22], respectively. The bands at 360-460 nm (iron oxide clusters) and > 450 nm (large surface oxide species) can be associated to Fe 2 O 3 particles on zeolite surface [22]. Note that the spectrum of the Fe-ZSM-5 catalyst was characterized by a low intensity absorption edge at 550 nm reflecting low concentration of Fe oxide nanoparticles, which was not detected by XRD (< 4 nm), however observed by TPR.…”

“…On the other hand, Fe-zeolite catalysts have been outstanding due to their high activity and resistance in co-fed of CH 4 , CO, O 2 and SO 2 [20,21]. Fe-ZSM-5 has been most studied experimentally and theoretically for the decomposition of N 2 O [22,23]. It is believed that isolated Fe 3+ and oligonuclear Fe x…”

Hydrothermal microwave‐assisted synthesis of LaFeO3 catalyst for N2O decomposition

“…All the noble metal based systems are supported catalysts, and the nature of the interactions of a noble metal with the support plays also a crucial role in their activity. [27][28][29] The main disadvantage of noble-metal catalysts is the high cost, so chemists are mostly looking for suitable catalytic materials from the second groupnon-noble-metal oxide catalytic systems 22 which include a wide range of oxide types such as bulk oxides, [30][31][32] spinels, 33,34 perovskites, hexaferrites, hydrotalcites [35][36][37][38][39][40][41] etc. The use of a support allows one to increase the specific activity of metal particles due to the enhanced dispersity, which is convincingly illustrated by examples of Fe 2 O 3 and Co 3 O 4 supported on ZrO 2 catalysts.…”