Catalytic Oxidation of CO and Benzene over Metal Nanoparticles Loaded on Hierarchical MFI Zeolite

Abstract

In order to obtain highly active catalytic materials for oxidation of carbon monoxide and volatile organic compounds (VOCs), monometallic platinum, copper, and palladium catalysts were prepared by using of two types of ZSM-5 zeolite as supports—parent ZSM-5 and the same one treated by HF and NH4F buffer solution. The catalyst samples, obtained by loading of platinum, palladium, and copper on ZSM-5 zeolite treated using HF and NH4F buffer solution, were more active in the reaction of CO and benzene oxidation compared with catalyst samples containing untreated zeolite. The presence of secondary mesoporosity played a positive role in increasing the catalytic activity due to improved reactant diffusion. The only exception was the copper catalysts in the reaction of CO oxidation, in which case the catalyst, based on untreated ZSM-5 zeolite, was more active. In this specific case, the key role is played by the oxidative state of copper species loaded on the ZSM-5 zeolites.

Catalytic Oxidation of VOC over Cobalt-Loaded Hierarchical MFI Zeolite

“…A similar result has been observed in platinum, copper and palladium catalysts supported on hierarchical MFI zeolite in the oxidation reactions of CO and benzene [17]. A more noticeable effect of acid treatment on the activity of the complete n-hexane oxidation is most likely related to the fact that the n-hexane molecule (d nHex = 10.3 Å) [45] is larger than that of propane and the presence of secondary mesoporosity had a higher effect on n-hexane oxidation.…”

“…Our expectation was that obtaining a second level of porosity would increase the catalytic activity as a result of the improved access of reactants to the active sites. A similar effect was observed in hierarchical MFI zeolites modified with Pt and Cu in CO and benzene complete oxidation [17], as well as hierarchical mordenite in the reaction of m-xylene transformation [18]. No diffraction lines for Co3O4 or cobalt silicates are observed in the case of the cobalt supported by the treated ZSM-5 samples.…”

“…As was discussed in our previous investigation concerning the parent ZSM-5 zeolites [16], type IV isotherms with a hysteresis loop from P/P 0 = 0.45 to P/P 0 = 1, which were caused by the coherence of both micropores and mesopores (Figure 2), were obtained. The higher nitrogen uptake was observed in the isotherms of the samples after acid attack (Figure 2) at partial pressure close to 1 as a result of the secondary porosity and reduced crystallite size [17]. This is more pronounced in the sample with Si/Al = 50. a V t -total pore volume; b V micro -microporous volume evaluated using the Vt method; c V sec -secondary meso-and macropores formed through chemical treatment (V sec = V t − V mi ), d according to XRF (X-ray fluorescence) analysis.…”

“…After acidic treatment the particle size decreases (Figure 7b). It was established that the zeolite dissolution through HF initially affects the structural defects and/or the adhesion positions of the individual crystallites and then continues deep inside the crystals [17]. As can be seen from the SEM micrograph that the Si/Al = 50 sample has the smallest aggregates among all studied samples.…”