Identification of synergistic Cu/V redox pair in VCu:AlPO-5; a comparison with VCu:ZSM-5

Abstract

Vanadium(V) and copper(II) were co-deposited into AlPO-5 and H-ZSM-5 three-dimensional microporous carriers to yield VCu:AlPO-5 and VCu:ZSM-5. The materials, along with copper analogues were tested for the selective oxidation of propene, and the catalysts perform in the following order: VCu:AlPO-5 > Cu:AlPO-5 > VCu:ZSM-5 > Cu:ZSM-5. Acrolein was selectively formed over VCu:AlPO-5 and Cu:AlPO-5 over a very wide range from 300 to 450 °C, whereas VCu:ZSM-5 displays a limited temperature window for acrolein formation (300-350 °C). Hence, the choice of carrier and presence of vanadium as a co-cation greatly affects the acrolein selectivity and activity window. The vanadium and copper reduction events were monitored by in situ X-ray Absorption Spectroscopy (XAS) during C3H6-TPR (1.11%) to 450 °C. The Cu(II)/(I) redox pair initiates reduction of V(V) → V(IV) in VCu:AlPO-5 and VCu:ZSM-5 at 375 °C. Metallic copper is the major valence fraction above 400 °C in both samples while vanadium is present as V(IV)/V(III) species. In the monometallic copper analogues Cu(I) is the major valence fraction above 350 °C, hence synergistic effects between the Cu/V pair causes hyper-reduction of copper. EXAFS shows that copper and vanadium are in close proximity in VCu:AlPO-5 only, being linked by bridging oxygens (Cu-O-V) believed to interact with propene. By contrast, propene adsorbs on Brønsted sites in VCu:ZSM-5 inhibiting acrolein formation at elevated temperatures, as confirmed by DRIFTS. We believe the reactive Cu/V pair in neutral AlPO-5 generates extralattice oxygens favouring acrolein formation over a wide temperature range.

High-Performance Metal Oxide-Modified V/TiO2 Catalysts for Selective Oxidation of 2-Methylnaphthalene to 2-Naphthaldehyde: An Experimental and Theoretical Study

“…It is conductive to the formation of oxygen vacancies as well as the reduction of the terminal VO and bridging V–O–V bond strength, which is a key parameter in the surface dehydrogenation and product desorption steps. Bøyesen et al have confirmed the existence of V–O–Cu at VCu:AlPO-5 by X-ray absorption near-edge structure (XANES) . Thus, we suggest that the formation of V–O–Cu from the synergy between VO x and Cu leads to the red shift and weaken VO and V–O–V bonds.…”

Simultaneous Desulfurization and Denitrification Using La–Ce–V–Cu–ZSM-5 Catalysts in an Electrostatic Precipitator

“…Microwave and additives are used to help H 2 O 2 solution perform desulfurization and denitrification simultaneously. − Some researchers in other countries use sodium hypochlorite and potassium permanganate to form a new type of absorbent that has a high absorption efficiency for SO 2 and NO. The oxidation reaction experiments are performed by loading V and Cu, between which a certain synergy exists. , For the collaborative desulfurization and denitrification of the dust collector, some researchers established a 1D fluid model of simultaneous desulfurization and denitrification through a negative DC corona discharge, which is similar to an electrostatic precipitator (ESP). The nonthermal plasma produced by corona discharge has a significant effect on the removal of SO 2 and NO in flue gas …”

“…The oxidation reaction experiments are performed by loading V and Cu, between which a certain synergy exists. 25,26 For the collaborative desulfurization and denitrification of the dust collector, some researchers established a 1D fluid model of simultaneous desulfurization and denitrification through a negative DC corona discharge, which is similar to an electrostatic precipitator (ESP). The nonthermal plasma produced by corona discharge has a significant effect on the removal of SO 2 and NO in flue gas.…”