Cation Vacant Fe3−x−y V x □ y O4 Spinel-Type Catalysts for the Oxidation of Methanol to Formaldehyde

Abstract

The potential of Fe-V-oxide catalysts for use in methanol oxidation is explored. Our results show that although FeVO 4 is active and selective for formaldehyde (FA) formation, it is not completely stable towards volatilization under reaction conditions. Attempts to stabilize Fe-V-oxide were made using titania, alumina and silica supports. However, we observe that although some stabilization is achieved using titania and alumina, the supported catalysts are sensitive to volatilization considering the relatively low content of active oxide. Compared with supported V-oxide, the results show that iron causes stabilization of vanadium decreasing its volatility. Considering the observation that the neat FeVO 4 restructures to form a spinel-type phase under influence of the catalysis, we prepared a series of cation vacant spinel-type Fe 3-x-y V x h y O 4 catalysts with various V/Fe ratio and consequent number of cation vacancies h. Opposed to the activity, which is rather constant irrespectively of the vanadium content, the selectivity to FA passes through a maximum of about 90% for Fe/V = 14. A spinel-type phase with the composition Fe 2.62 V 0.19 h 0.20 O 4 was prepared and subsequently preoxidized to different degree. It is observed that the spinel-type structure is stable and that the oxidation of vanadium and iron is balanced by an increasing number of cation vacancies. Moreover, irrespectively of the original degree of preoxidation, it is found that in methanol oxidation a steady state is reached where all samples are equally active and selective and have the same composition both in the bulk and at the surface. The results clearly demonstrate that the spinel-type catalysts are phase-stable, nonvolatile and flexible in that the cations can change oxidation state retaining the same basic structure type and Fe/V ratio.

Alkali Earth Metal Molybdates as Catalysts for the Selective Oxidation of Methanol to Formaldehyde—Selectivity, Activity, and Stability

“…Thus, it is of major interest to either increase the stability of the iron molybdate or find alternative catalysts with similar activity and selectivity, but better stability and less volatile components. In the literature, much investigation has gone into various vanadium-based systems such as vanadium phosphates (90%-96% selectivity) [17,18], iron vanadates (90% selectivity) [3,[19][20][21][22][23][24][25][26], supported V 2 O 5 [27][28][29][30][31][32], and other vanadium-based catalysts [33,34]. The vanadium-based catalysts mostly show good activity, lower selectivity than iron molybdate, and the vanadium is also subject to volatilization [22,35].…”

“…In the literature, much investigation has gone into various vanadium-based systems such as vanadium phosphates (90%-96% selectivity) [17,18], iron vanadates (90% selectivity) [3,[19][20][21][22][23][24][25][26], supported V 2 O 5 [27][28][29][30][31][32], and other vanadium-based catalysts [33,34]. The vanadium-based catalysts mostly show good activity, lower selectivity than iron molybdate, and the vanadium is also subject to volatilization [22,35]. On the other hand only few publications looking into alternative molybdate catalysts are found in the literature [3,[36][37][38], and have mostly been done by Popov et al [36][37][38] during the 1970s and 1980s and, more recently, by the Andersson group at Lund University (Sweden) [3,20].…”

A Review and Experimental Revisit of Alternative Catalysts for Selective Oxidation of Methanol to Formaldehyde

“…The Fe 3-x-y V x y O 4 catalyst was further investigated by Massa et al [214] and compared to "theoretical" Fe-V-oxide layers (one theoretical layer was in this case defined as 12 µmol cations/m 2 surface area of the support) on TiO 2 , α-Al 2 O 3 , and SiO 2 supports at the same conditions but with 80% conversion. None of the investigated supported samples had better selectivity than FeVO 4 ranging from 80-88%; however, the surface area specific activity was higher for the TiO 2 supported Fe-V-oxide and much lower for the SiO 2 supported catalysts (Figure 38).…”

“…None of the investigated supported samples had better selectivity than FeVO 4 ranging from 80-88%; however, the surface area specific activity was higher for the TiO 2 supported Fe-V-oxide and much lower for the SiO 2 supported catalysts (Figure 38). It was possible to stabilize FeVO 4 by pre-oxidizing the samples into a spinel-like structure with the same selectivity [214]. A spinel-type catalyst of Fe, V, and Mo was investigated by Massa et al [215] at 300 • C by using a mixture of 10 vol.% MeOH and 10 vol.% O 2 in N 2 .…”

Magnetic properties of a new vanadate Cu13Fe4V10O44

“…It is known that components of this system as well as phases forming in its side systems, are active in catalytic oxidation reactions of: benzene to phenol [3], methanol to formaldehyde [4], isobutane to isobutene [5], or toluene to benzaldehyde [6]. Therefore, the compound Cu 13 Fe 4 V 10 O 44 , forming with an involvement of all components of the CuO-V 2 O 5 -Fe 2 O 3 system, can be considered as the phase with potential catalytic properties.…”