Mono-, Bi-, and Tri-Metallic DES Are Prepared from Nb, Zr, and Mo for n-Butane Selective Oxidation via VPO Catalyst

Abstract

In recent work, deep eutectic solvents (DESs) as ionic liquid analogues have been abundantly used in catalysis. Herein, vanadium phosphorus oxide (VPO) catalysts were synthesized from mono-, bi-, and tri- metallic DES of Nb, Zr, and Mo metal dopants as structure-directing agents and electronic promoters for n-butane selective oxidation towards maleic anhydride. Higher MA selectivity and larger n-butane conversion was successfully obtained using the newly developed catalysts, while oxidation by-product COx (CO, CO2) was minimized. Characterization techniques including FTIR, DSC, XRD, TEM, SEM, EDS, Raman spectroscopy, TGA, XPS, and NH3-TPD were employed to fully characterize the DESs, precursors and catalysts. This work led to an increase of 7.8% in MA mass yield with 16% more n-butane conversion as compared to an unpromoted VPO catalyst. Moreover, the utilization of a low-carbon alkane brought in a green impact on the chemical plant as well as the environment.

Regulation of Maleic Anhydride Selectivity for n-Butane Oxidation by Sb2O3-Modified Vanadium Phosphorus Oxide Catalysts

“…Recently, ionic liquids (ILS) and deep eutectic solvents (DESs) have been applied to modify the VPO catalysts and achieved outstanding n-butane conversion and MA selectivity. 4,5,14,19,20 Especially, DESs could act as a structural directing agent in the preparation of VPO catalysts, effectively promoting the crystal nucleation and growth processes of VHP. 5 For instance, the optimal VPO-ChCl-BDO catalyst significantly improved the MA selectivity and reduced the byproducts.…”

“…The active phase of the VPO catalyst is vanadyl pyrophosphate ((VO) 2 P 2 O 7 ) . Furthermore, the VPO catalysts contain active phases of V 4+ species ((VO) 2 P 2 O 7 ) and V 5+ species (α I -VOPO 4 , α II -VOPO 4 , β-VOPO 4 , γ-VOPO 4 , and VOPO 4 ·2H 2 O) . Usually, V 4+ phase is considered as the dominant active phase for n -butane oxidation, which is obtained from the topotactic solid-state transformation from the VHP.…”

“…4 Furthermore, the VPO catalysts contain active phases of V 4+ species ((VO) 2 P 2 O 7 ) and V 5+ species (α I -VOPO 4 , α II -VOPO 4 , β-VOPO 4 , γ-VOPO 4 , and VOPO 4 • 2H 2 O). 5 Usually, V 4+ phase is considered as the dominant active phase for n-butane oxidation, which is obtained from the topotactic solid-state transformation from the VHP. In addition, the V 5+ phase also plays an essential role in the selective oxidation of n-butane.…”

“…4,5,14,19,20 Especially, DESs could act as a structural directing agent in the preparation of VPO catalysts, effectively promoting the crystal nucleation and growth processes of VHP. 5 For instance, the optimal VPO-ChCl-BDO catalyst significantly improved the MA selectivity and reduced the byproducts. 19 Besides, Cu-ILs could simultaneously serve as structural directing agents and electron promoters, thus synergistically optimizing the V 4+ /V 5+ and lattice defects.…”

Advances in Deep Eutectic Solvents: New Green Solvents

“…DESs are also used to prepare catalysts for chemical reactions. Faizan et al [11] prepared DESs from ChCl as a HBA, and mono-, bi-and tri-metallic salts of niobium, molybdenum and zircon as HBDs. The DESs were used to prepare vanadium phosphorus oxide (VPO) catalysts for the selective oxidation of n-butane to maleic anhydride in a fixed-bed reactor.…”