Ferrierite and Its Delaminated Forms Modified with Copper as Effective Catalysts for NH3-SCO Process

Abstract

Ferrierites and their delaminated forms (ITQ-6), containing aluminum or titanium in the zeolite framework, were synthetized and modified with copper by an ion-exchange method. The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD, UV-Vis DRS), textural parameters (N2-sorption), surface acidity (NH3-TPD), form and reducibility of deposited copper species (UV-Vis DRS and H2-TPR). Ferrierites and delaminated ITQ-6 zeolites modified with copper were studied as catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO). It was shown that aggregated copper oxide species, which were preferentially formed on Ti-zeolites, were catalytically active in direct low-temperature ammonia oxidation to NO, while copper introduced into Al-zeolites was present mainly in the form of monomeric copper cations catalytically active in selective reduction of NO by ammonia to dinitrogen. It was postulated that ammonia oxidation in the presence of the studied catalysts proceeds according to the internal-selective catalytic reduction mechanism (i-SCR) and therefore the suitable ratio between aggregated copper oxide species and monomeric copper cations is necessary to obtain active and selective catalysts for the NH3-SCO process. Cu/Al-ITQ-6 presented the best catalytic properties possibly due to the most optimal ratio of these copper species.

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“…It was shown that the presence of aluminum or titanium in the zeolite framework influenced the form and aggregation of deposited copper species. In the case of Ti-zeolites, a significant contribution of aggregated copper species was identified, in contrast to Al-zeolites with higher contribution of the highly dispersed forms of copper [9]. This is not surprising, considering the dominant role of the ion exchange mechanism of copper deposition in Al-zeolites, as well as the much more complex mechanisms involved for Ti-zeolites.…”

“…Therefore, aggregation of such copper species under calcination conditions is much easier for Ti-zeolites than Al-zeolites. The study byŚwięs et al [9] showed the better activity of the copper-modified layered titanium-silicon zeolites at lower temperatures compared to catalysts based on Alzeolites (Figure 7). This effect was more evident for the Cu-Ti-FER and Cu-Al-FER catalysts than for their delaminated analogous counterparts (Figure 7).…”

“…The ion exchange and acidic properties of aluminum-silicon zeolites are dependent on the Si/Al ratio, while interlayer spaces in such materials can be opened via their intercalation or delamination. Zeolitic materials modified by these methods are characterized by their bimodal micro-and mesoporous structure, and have been reported to be very promising in various catalytic applications [5,6,9,43,44], including the selective catalytic reduction of NO x with ammonia [7,61,[74][75][76][77].…”

“…In the next stage, titanium-silicon ferrierites (Ti-FER) and their delaminated forms (Ti-ITQ-6) modified with copper by ion exchange were tested as potential catalysts of the NH 3 -SCO process [9]. These catalysts, which were based on titanium-silicon zeolites, were compared with the analogous zeolitic aluminum-silicon-based catalysts.…”

“…The efficiency of this process, called selective catalytic oxidation of ammonia (NH 3 -SCO or AMOx), should be strictly controlled using suitable catalysts [8]. Modified layered clays and layered zeolites were reported to be very promising catalysts of NH 3 -SCR and NH 3 -SCO [7,9,10]. This is not surprising, considering the presence of acid sites in both cationic clay minerals and layered zeolites, which are necessary for ammonia chemisorption and catalytic activation for NH 3 -SCR and NH 3 -SCO processes [8].…”