Unveiling the catalytic active sites of iron-vanadium catalysts for the selective oxidation of methanol to formaldehyde

doi:10.1016/S1872-2067(24)60279-2

Abstract

Abstract:

Iron-Vanadium (FeV) catalyst showed a unique catalytic activity for the selective oxidation of methanol to formaldehyde; however, due to its complex compositions, the identification of catalytic active sites still remains challenging, inhibiting the rational design of excellent FeV-based catalysts. Here, in this work, a series of FeV catalysts with various compositions, including FeVO₄, isolated VO_x, low-polymerized V_nO_x, and crystalline V₂O₅ were prepared by controlling the preparation conditions, and were applied to methanol oxidation to formaldehyde reaction. A FeV_1.1 catalyst, which consisted of FeVO₄ and low-polymerized V_nO_x species showed an excellent catalytic performance with a methanol conversion of 92.3% and a formaldehyde selectivity of 90.6%, which was comparable to that of conventional iron-molybdate catalyst. The results of CH₃OH-IR, O₂ pulse and control experiments revealed a crucial synergistic effect between FeVO₄ and low-polymerized V_nO_x. It enhanced the oxygen supply capacity and suitable binding and adsorption strengths for formaldehyde intermediates, contributing to the high catalytic activity and formaldehyde selectivity. This study not only advances the understanding of FeV structure but also offers valuable guidelines for selective methanol oxidation to formaldehyde.

Key words: Iron-vanadium, Selective oxidation, Methanol, Formaldehyde, Synergistic effect

Yujie Zhan, Chengqin Zhong, Mingli Bi, Yafei Liang, Yuji Qi, Jiaqi Chen, Jiaxu Liu, Xindang Zhang, Shuai Zhang, Yehong Wang, Feng Wang. Unveiling the catalytic active sites of iron-vanadium catalysts for the selective oxidation of methanol to formaldehyde[J]. Chinese Journal of Catalysis, 2025, 72: 334-343.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(24)60279-2

https://www.cjcatal.com/EN/Y2025/V72/I5/334

Figures/Tables 8

Fig. 1. V/Fe molar ratios and preparation yield (a), XRD patterns (b), Raman spectra (c), and UV-vis spectra (d) of FeV catalysts prepared at different pH values. a Obtained from XRF results.

Fig. 2. V/Fe molar ratios and preparation yield (a), XRD patterns (b), UV-vis spectra (c), Raman spectra (d), and enlarged Raman spectra (e) in the range of 980-1040 cm-1 of FeV catalysts prepared under different feed V/Fe molar ratios from 1.2 to 1.8. a Molar ratio of NH4VO3 to Fe(NO3)3·9H2O during catalyst preparation. b Obtained from XRF results.

Table 1 Typical catalysts composition and supposed structure.

Entry	Catalyst	Fe	V
1	FeV_0.5	Fe₂O₃	FeVO₄
2	FeV_1.0	—	FeVO₄
3	FeV_1.05	—	FeVO₄ + VO_x
4	FeV_1.1	—	FeVO₄ + V_nO_x
5	FeV_1.4	—	FeVO₄ + V₂O₅

Fig. 3. Catalytic performances of typical FeV catalysts: Methanol conversion and formaldehyde selectivity. Reaction conditions: catalyst (0.9 mL, 40-60 mesh), 230 °C, 0.1 MPa, CH3OH/O2/N2 as feedstock, GHSV = 9000 h-1.

Table 2 Catalytic performances of typical FeV catalysts in methanol oxidation at similar MeOH consumption rates.

Catalyst	T (°C)	Surface area ^a	MeOH rate ^b	Selectivity (%)
Catalyst	T (°C)	Surface area ^a	MeOH rate ^b	HCHO	HCOOH	CO_x	CH₂(OCH₃)₂	Others
FeV_1.05	220	17.10	1.06	90.52	3.38	1.19	1.28	3.63
FeV_1.1	210	11.11	1.05	93.31	1.39	0.39	2.76	2.15
FeV_1.4	230	12.86	1.04	94.61	1.04	0.49	1.21	2.24

Fig. 4. Catalytic performances of FeV1.1 catalyst at different reaction temperatures (a) and different GHSV (b). Reaction conditions: catalyst (0.9 mL, 40-60 mesh), 0.1 MPa, CH3OH/O2/N2 as feedstock.

Fig. 5. CH3OH-IR spectra of FeV1.1 (a), FeV1.4 (b), and FeV1.05 (c) catalysts, and normalized intensity of ν(C=O) (d). Normalization procedure: Subtract the peak value of ν(C=O) at each target temperature from the peak value at room temperature (where methanol does not dissociate to form an aldehyde group), and divide all differences by the maximum difference obtained.

Fig. 6. O2 pulse experiments on FeV1.1 (a), FeV1.4 (b), and FeV1.05 (c) catalysts at 230 °C. (d) H2-TPR profiles of three catalysts. All catalysts were pretreated with methanol before O2 pulse experiments.

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