Weijie Ji

Novel modifications in preparing vanadium phosphorus oxides and their applications for partial oxidation of n-butane

Abstract One novel modification in preparing high surface area VPO catalyst was established by applying polyethylene glycols (PEGs) as the unique additives. The PEG-derived samples possessed considerably high surface areas of 41–54xa0m 2 /g, with the average particle size of 100–200xa0nm and well crystallized (VO) 2 P 2 O 7 phase, showing notably improved performances for the partial oxidation of n -butane to maleic anhydride (MA) even at lower reaction temperature. The principle function of PEG in preparation chemistry and the possible origins of the enhanced performance were preliminarily discussed. Another modification in preparing high surface area VPO catalyst adopted in this study was the combination of synthesizing high surface area VPO precursor by well-controlled addition of phosphoric acid, thermal pre-treating the precursor at certain temperature and ball milling in cyclohexane. The so-obtained catalysts also showed pronounced catalytic performance. The applied milling process not only effectively increased the surface areas of the milled samples and consequently the available number of active sites, but also somehow changed other sample characteristics such as the local environment and the redox behavior; which may also be responsible for the overall performance enhancement.

Effects of ball milling on the doped vanadium phosphorus oxide catalysts

Abstract Vanadium phosphorus oxide (VPO) catalyst precursors were prepared in organic phase by using isobutanol as the reducing agent. They were doped by combined components—Zn+Zr+Mo, Zr+Zn and Zr+Mo—through impregnation. In order to increase the catalyst surface areas, the catalyst precursors were ball milled in different solvents for a certain period of time. X-ray diffraction (XRD), X-ray fluorescence spectrometer (XFS), DTA/TGA, X-ray photoelectron spectrometer (XPS) and BET were used to examine the bulk and surface properties of the final catalysts and their precursors. Catalytic performances were measured in the selective oxidation of n -butane into maleic anhydride (MA). The results revealed that ball milling could improve the performances of these VPO catalysts, without destroying the active physico-chemical structure and without exerting great influence on the surface characteristics of the catalysts. Interaction between the combined moderators was also preliminarily discussed. The Mo component was found to have some kind of stabilizing effect on the catalyst surface of this system.

A Study on VPO Specimen Supported on Aluminum-Containing MCM-41 for Partial Oxidation of n-Butane to MA

Dispersed vanadium–phosphorus oxide species supported on Al-MCM-41 with different vanadium loadings have been synthesized for the first time for partial oxidation of butane to MA. It was found that the VPO species was dispersed over the Al-MCM-41 support material, both in the internal channel and on the external surface. With increasing vanadium loading, n-butane conversion increased but MA selectivity decreased considerably under the same reaction conditions. At lower conversions (<30%), rather high MA selectivity (ca. 70%) can be achieved on the low loading sample. Compared with the amorphous structure of large pore SiO2 support, the unique structure of the MCM-41 and the incorporated Al3+ in the framework do have an impact on the reaction behavior of the supported VPO specimen. The chemical nature of the supported VPO species and the interaction between the applied VPO species and the support was found to vary notably with the content of vanadium in the sample and likewise affected the related physico-chemical characteristics and their reaction behaviors.

Influence of the way of preparing vanadium phosphorus oxide (VPO) precursor and introducing multi-additives on the reaction performance

The VPO system synthesized in aqueous medium and doped with Mo, Zr and Znshowed high maleic anhydride (MA) selectivity at fair butane conversion. Thecatalytic performance was found to depend not only on the sort of additive but alsoon the preparation history of the VPO base and the manner of introducing theadditive.

Layered Double Hydroxide Derived Mg 2 Al-LDO Supported and K-Modified Ru Catalyst for Hydrogen Production via Ammonia Decomposition

Mg–Al mixed oxide is derived via the precursor of Mg2Al-layered double hydroxide (Mg2Al-LDH), and employed to load Ru and KNO3 to develop the K–Ru/Mg2Al-LDO catalyst for hydrogen production through ammonia decomposition. Single MgO and Al2O3 were used to prepare reference catalysts K–Ru/MgO and K–Ru/Al2O3 for comparison. A mechanically mixed K–Ru/MgO and K–Ru/Al2O3 sample was also made to explore the interaction of oxide constituents. K–Ru/Mg2Al-LDO generally outperforms K–Ru/MgO and K–Ru/Al2O3 as well as the Ru-based catalysts supported on other transition metal oxides. The comparison study demonstrated significant impact of structural homogeneity and strong interaction of the oxide constituents on activity. The unique structural feature of Mg2Al-LDO gives rise to the enhanced surface basicity, low-temperature feasible N2 desorption, and remarkable hydrogen spillover effect. All these aspects are favorable on K–Ru/Mg2Al-LDO for electronic modification of Ru sites, rate-determining steps in both low and high reaction temperature, and quick recycle of active sites, accounting for its superior activity plus good durability.Graphical Abstract