Phosphorus-Based Ionic Liquid as Dual Function Promoter Oriented Synthesis of Efficient VPO Catalyst for Selective Oxidation of n-butane

Fei Dai,Ruirui Zhang,Ruixia Liu,Zihang Li,Ting Zhang,Muhammad Faizan,Suojiang Zhang,Yanan Shi

doi:10.1007/s10562-020-03293-x

Abstract

Vanadium phosphorus oxide (VPO) catalysts promoted by phosphorus-based ionic liquids (ILs) as structure directing agent and promoters have been innovatively synthesized and investigated for selective oxidation of n-butane to maleic anhydride (MA). The catalytic performances showed that the IL addition notably improved the n-butane conversion and MA selectivity, during which the optimized 3%IL-VPO catalyst exhibited the maximum MA yield of 59.2% that is much better than that of blank VPO with 49.4% MA yield under the same reaction conditions. XRD, FI-IR, Raman, SEM, TG, BET, XPS and H2-TPR techniques were utilized combinatorically to elaborate the synergistic effect of cations and anions of ILs. Results demonstrated that IL-cations oriented synthesis of VPO precursor showing a vertically intercrossed slice structure morphology having smaller lamellar thickness. Correspondingly, it notably enhanced the specific surface area of the VPO catalysts and exposed the more active surface of (VO)2P2O7 after activation. Meanwhile, IL-anions as promoters largely modulated the P/V ratio, valence state of V and oxygen species amounts on the surface of VPO catalyst, etc. All of these influence factors were subsequently discussed in detail and correlated to the catalytic performance of VPO catalysts.Graphic

Highlights

Maleic anhydride (MA) is a vital basic chemical material that is extensively applied in the production of unsaturated resins, coating, pesticides, medicines, etc
Metal-based ionic liquids (ILs) acting as additives and promoters were firstly proposed and applied in the synthesis of vanadium phosphorus oxide catalysts (VPO) catalyst for selective conversion of n-butane in our previous work [25, 26], the ILs including iron metal was observed to have largely increased the proportion of active phase (VO)2P2O7 and induced a great change in structure morphology of VPO owing to their synergistic action between the metal anions and structureguided cations in ILs, the obtained VPO catalyst exhibited excellent performance with high conversion of n-butane and selectivity of MA
It is founding that the VPO precursors with IL addition exhibit a smaller relative integral intensity of the (001) and (130) planes than the Blank-PVPO, especially for 1%IL-PVPO and 5%IL-PVPO, which is different with conventional method that the addition of metal dopant will remarkably increase the I (001)/(130) values [27]

Summary

Introduction

Maleic anhydride (MA) is a vital basic chemical material that is extensively applied in the production of unsaturated resins, coating, pesticides, medicines, etc. Extensive researches indicated that addition of metal dopants [7, 11,12,13,14,15,16,17,18,19], organic structural directing agent [20,21,22,23] and surfactant [24] during the preparation of VPO were usually employed as effective strategies to enhance its catalytic performance by modulating the crystal structure, morphology as well as chemical properties of the surface (such as P/V ratio, valence state of V, amounts of lattice oxygen, etc.). The aforementioned work provide a new strategy for the development of efficient VPO catalyst by utilizing ILs as structural directing agent or promoters in view of their unique physical properties, such as good thermal stability, negligible volatility, high polarity and excellent dissolving ability, etc

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