Synthesis of Vanadium Phosphorus Oxide Catalysts Assisted by Deep-Eutectic Solvents for n-Butane Selective Oxidation

Abstract

The effects of choline chloride/oxalic acid deep eutectic solvents (ChCl/OA DES) as a green and effective promoter assisting the synthesis of vanadium phosphorus oxide (VPO) catalysts for the selective oxidation of n-butane to maleic anhydride were investigated in detail. A combination of characterizations with the performance was considered to understand the essential effects of DES. DES play the role of a crystal induced agent and structural modifier, facilitating the formation of a single-crystal structure on the surface of precursor; correspondingly, topological transformation to the single-crystal active phase under the activation conditions accompany the decomposition of DES. It is suggested that ChCl/OA DES can interact with V2O5 and form a new vanadium complex, which affects the reaction between V2O5 and H3PO4. Meanwhile, the ChCl/OA DES could regulate the surface chemical state and redox characteristic, resulting in the enhancement on the catalytic performance of VPO.

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

“…Therein, the increase in relative intensity of I (020) /I (204) is directly correlated with the improvement of catalytic performance. As mentioned previously, the (001) plane of VOHPO 4 •0.5H 2 O in precursor can be converted topologically into the (020) plane of (VO) 2 P 2 O 7 [35] , yet it also noteworthy that the 3%IL-VPO catalyst with lower I (001)/(130) value in its precursor gave the higher I (020) /I (204) than the pure VPO catalyst. Obviously, the addition of appropriate IL content could induce the growth of active plane of (VO) 2 P 2 O 7 under activation conditions.…”

“…The blank VPO precursor was prepared in this work via organic route in the following way [35]: the V 2 O 5 (20 g) was reacted with benzyl alcohol (40 mL) in the solvent of isobutanol (160 mL) by refluxing at 383 K for 4 h, the H 3 PO 4 (15.6 mL, P/V ratio = 1.04) was then added and further refluxed for 10 h at 383 K under the mechanical stirring device (SCILOGEX, OS20-Pro) with 350 rpm/min. Noting that the reflux without water removal was performed by strictly controlling the reflux velocity of fluid via stopwatch counting, which conformed that all the tests were carried out in the identical conditions.…”

“…The gas mixture of 1.5% n-butane in air was flowed into reactor and the flow volume with GHSV of 2000 h −1 was controlled by a mass flow controller. After reaction, the exhaust was analyzed via an on-line gas chromatography (Shimadzu GC-2010 plus), the detailed analysis procedure has been described in our previous work [35]. The catalytic performance was calculated by the n-butane conversion, the MA selectivity and yield, which were listed as follows:…”

“…It can be clearly observed that the intensity of both peaks height enhanced initially and then weakened with the increasing of amounts of IL, indicating that the addition of IL induce the formation of (VO) 2 P 2 O 7 , this phenomenon is in accordance with the XRD results. Besides, the weak vibration bands appearing at 1016 and 1083 cm −1 can be linked to a small amount of γ-VOPO4, which was not detected in XRD analysis due to the low content or high dispersion of this V 5+ phase [35]. The existence of this phase usually has a significant impact on the catalytic activity and MA selectivity even though it has always been a controversial issue for decades [41,42].…”

Phosphoric Acid: A Key Role in Control of Structure and Properties of Vanadium Phosphorus Oxide Catalysts During Synthesis

“…In addition, organic promoters such as polyethylene glycol (PEG), [5b,c] poly(acrylic acid‐co‐maleic acid) (PAAMA), [5d] and poly(styrene‐alt‐maleic acid) (PSMA) [5e] were used as structure‐directing agents to enhance the crystallinity of VPO. Recently, our group found ionic liquid [4h,6] and deep eutectic solvents (DES) [7] could not only influence the surface chemical state and redox characteristic of catalyst but also benefit for forming single‐crystal structure on precursor surface. Both metal and organic promoters cannot influence the phase composition and structure of the catalyst significantly, key point still exist in the preparation of VPO precursor which determined the form of the active phase (amorphous versus crystallized) and the nature of the active components [8] .…”