Styrene Oxidation to Valuable Compounds over Nanosized FeCo-Based Catalysts: Effect of the Third Metal Addition

Abstract

Nanosized FeCo-based solids were prepared via distinct preparation procedures. The catalytic performances of the solids for styrene oxidation in the presence of hydrogen peroxide were evaluated. The addition of promoters in FeCo such as Sn, Mo, or Cu was also investigated. The catalysts were characterized with XRD, Raman spectroscopy, TEM, chemical analyses, EPR and SEM-EDS. Of these solids obtained via four different methods, the catalyst prepared via the NC and CM procedures enabled a partial incorporation of the Sn into the FeCo matrix forming a very active phase, namely the Heusler alloy. This was ascribed to the high initial dispersion of Sn as a promoter into the FeCo matrix, which led to available FeCoSn (FCS) particles well dispersed and stable on the catalyst surface. In the case of incorporating Mo or Cu to the nanosized FeCo catalyst, a poor stability towards leaching was observed when operating under the same reaction conditions. Cu was much less active than both Sn and Mo, mainly leading to acetophenone, ethylbenzene, 2-phenyl ethanol, 2-phenyl acetic acid, and 2-phenyl acetaldehyde products. The best catalytic results under the optimized reaction conditions, especially at 50 • C and styrene/H 2 O 2 molar ratio of 1 were achieved with nanosized FCS. This solid had a conversion of ca. 70% and selectivity for aldehydes of ca. 27%, and the selectivity for the condensation products was 29%.

CeFe-Based Bead Nanocomposites as Catalysts for Oxidation of Ethylbenzene Reaction

“…These modes may be overlapped with that at 690 cm -1 from Fe 3+ in distorted tetrahedral symmetry as well as Fe 3+ /Fe 2+ in octahedral symmetry from γ-Fe 2 O 3 [25]. At a high frequency region (Figure 3c), the modes attributable to the vibrations of α-Fe 2 O 3 at 1100 and 1300 cm -1 and the γ-Fe 2 O 3 at about 1370 cm -1 are not visible due to CeO 2 covering the previously mentioned iron phases, as observed elsewhere [17]. These results indicate that the semi-crystalline materials have the CeFe as a matrix besides the third oxide existing as NiO, Co 3 O 4 , or MnO x appears isolated, respectively, in CFN, CFC, and CFM solids.…”

“…As found elsewhere, it can also be related to Fe 2+ and Fe 3+ dimers or their clusters in interstitial defects of the structure, which suggests the presence of the α-Fe 2 O 3 and γ-Fe 2 O 3 . This is in line with the findings [17,27]. This confirms the XRD and Raman results that detected these phases in CFC and CFN.…”

“…To our knowledge, a reason for the catalytic activity of the solids can be anticipated by noticing that the binary CeFe catalyst offers the acid-base and redox species to accentuate this effect [25]. This supports the idea that the reactivity of the binary nanocasted oxides under study is thanks to the transition metals Fe 3+ /Fe 2+ and Ce 4+ /Ce 3+ pairs having predominant Lewis acid sites, which is demonstrated by using transition metals and which act as catalysts for oxidation reactions [17,39,40]. The ethylbenzene oxidation reaction over the monoxides may follow similar approaches for mechanistic considerations as those of gold nanoparticles-catalyzed epoxidation of stilbene by involving a formation of a reactive oxygen species through the metal nanoparticles surface, which induces the decomposition of the peroxyl radical intermediate [41,42].…”

“…The nature of the third metal added to Fe 2+ /Fe 3+ and Ce 3+ /Ce 4+ active sites could improve significantly the catalytic property of solids, which is found elsewhere [17]. In particular, Co existing as Co 2+ species has been recently reported to be effective for styrene oxidation due to the intra-lattice cobalt ions being stable, which avoids the Co 2+ oxidation to Co 3 O 4 and Co 2 O 3 phases [24,43].…”

“…Following previously reported porous CeFe catalysts, the surface Fe 3+ /Fe 2+ and Ce 4+ /Ce 3+ accessible active sites provide a redox cycle during the oxidation reaction. Consequently, the efficient catalysts to hydrocarbon oxidation reactions are obtained [17]. Keeping this idea in mind, the present work aims to develop Fe-based catalysts by the nanocasting technique for ethylbenzene (EB), styrene (St), and benzyl alcohol (BA) oxidations.…”