Vanadium Phosphorus Oxide Catalysts Research Articles

An efficient vanadium phosphorus oxide catalyst prepared by tuning vanadium precursor for selective oxidation of n-butane to maleic anhydride

Maleic anhydride (MA), as an industrially important chemical, is currently produced through selective oxidation of n-butane (SOB) over vanadium-phosphorus-oxygen (VPO) catalyst, but sufferring from low selectivity by overoxidation. Therefore, preparing selective VPO catalysts is urgent, but remains a challenge. Herein, we prepared an efficient VPO catalyst (VPO-Vsg) by using the pre-synthesized V2O5 (V2O5-sg) via a sol–gel process as V source. It shows about 90 % n-butane conversion with more than 70 % MA selectivity under 2000 h−1 and 400 °C conditions. It shows much superior MA yield (more than 60 %) to the VPO catalyst prepared by using commercially available V2O5 (V2O5-ca) as V source, ascribed to the optimal V oxidation state and lattice oxygen content, and the decreasing V5+ contributes its higher selectivity. This study not only generates an excellent VPO catalyst for MA production, but also provides a facile and effective approach for designing efficient catalysts for hydrocarbon selective oxidation.

Impact of Ultrasound Treatment Duration on Dihydrate Precursor Implying the Sesquihydrate Route

AbstractThe present invention relates to a technique for synthesizing vanadium phosphorus oxide (VPO) catalyst employing an ultrasonic treatment approach while assessing phase composition and hydrocarbon oxidation activity to a conventionally synthesized catalyst. The ultrasonic treatment approach has been shown to produce a catalyst with improved surface constitution and accelerated hydrocarbon conversion in 3 h, as opposed to the typically heating process, which takes 24 h. Product selectivity is influenced by the nature of the catalyst, with an integration consisting of (VO)2P2O7 (V4+) and VOPO4 (V5+) being optimal for high rate of conversion. A 39 % conversion rate and 89 % maleic anhydride selectivity were achieved under optimum reaction conditions.

Effect of Ⅲ B metals (Sc, Y, La and Ce) on active components regulation of VPO catalyst in n-butane selective oxidation

Vanadium phosphorus oxide (VPO) catalyst has been modified by the Ⅲ B elements (Sc, Y, La, Ce) have been prepared. Those catalysts were tested in n-butane selective oxidation, and it was shown that Y-VPO catalyst has the highest maleic anhydride (MA) yield among the studied catalysts. The VPO catalyst was characterized by a series of techniques. As evidenced by property characterization in conjunction with catalytic performance, we found that the presence of rare earth metals alters the phase composition of VPO catalyst. And then, the acidity of VPO catalyst was adjusted. Finally, the change of acidity could impact the n-butane activation process, which affected the n-butane conversion. Moreover, the rare earth metals also modulated the ratio of lattice oxygen and surface oxygen and then the MA selectivity.

New insight into vanadium phosphorus oxides (VPO/TiO2) catalysts for NOx removal with NH3-SCR at low temperature: Relationship between non-VOx phases and SO2&H2O resistance

Enhancing SO2&H2O resistance has important environmental implications for the NH3-selective catalytic reduction (NH3-SCR) catalysts in NOx removal. Herein, vanadium phosphorus oxides (VPO) were synthesized as active phases for NH3-SCR catalysts. Non-VOx phases containing (VO)2P2O7 and δ-VOPO4 were generated by adjusting the P/V molar ratio and the atmosphere properties of the activation and calcination. The NOx conversion of the VPO-1.5/TiO2 sample did not decrease (about 90%) after 6 h exposure to 180 °C, 500 ppm SO2 and 6% H2O. The abundant acid content (especially increased content of the weak Brønsted acids) corresponding to the non-VOx phases significantly inhibited stable SO2 adsorption on the catalyst surface. In-situ DRIFTS results showed that SO2 + O2 pre-adsorption on the catalyst surface had no significant influence on the adsorbed NH3 species. Density functional theory calculation also proves that SO2 has low competitive adsorption activity with NH3 and NO in the non-VOx phases. Under more severe conditions, the non-VOx phases still minimized the influence of SO2&H2O poisoning on surface acidity by inhibiting the accumulation of ammonium bisulfate. This work proposes a mechanism for enhancing SO2&H2O resistance with non-VOx phases, which is essential for extending the application of VPO/TiO2 catalysts from alkane selective oxidation to NH3-SCR.

Effect of ultrasonic irradiation on the production of a dihydrate precursor for selective n-butane oxidation

The invention pertains to a method for synthesising vanadium phosphorus oxide (VPO) catalyst using an ultrasonic irradiation approach and comparing phase composition and hydrocarbon oxidation activity to a traditionally synthesised catalyst. The ultrasonic irradiation method has been identified to create a catalyst with superior surface constitution and enhanced hydrocarbon conversionin a much shorter time of 3 h than the traditional heating method, which takes 24 h. The nature of catalyst influences product selectivity, with an integration comprising (VO)2P2O7 (V4+) and VOPO4 (V5+) being optimum for high rate of conversion. Under ideal reaction conditions, 89% selectivity to maleic anhydride and a 39% conversion rate were obtained.

Synthesis of an efficient VPO catalyst for the selective oxidation of n-butane to the MA product: Mechanism of crystal transformation

Serial VPO catalysts with different crystal structures were prepared by adjusting the ratios of air and N2 in the calcination process. The precursors and vanadium phosphorus oxide (VPO) catalysts were characterized by various measurements. As the air and N2 ratios were lower than 1:1, the ordered VOHPO4·0.5H2O phase was mainly formed in the precursors during calcination. However, as the ratio of air to N2 reached 3:1, amorphous VOPO4 phases were formed over the surface of the precursor during calcination, which prevented the formation of ordered V5+ species over the surface of the VPO catalyst after activation. Meanwhile, a high proportion of VOHPO4·0.5H2O in the precursor could facilitate more formation of the ordered α1-VOPO4 phase over the surface of the VPO catalyst. Interestingly, the crystal structure over the surface of active VPO catalysts was totally different from the core of VPO catalysts. There were more P species and V species with 5+ existing over the surface of the VPO catalysts. The evaluation results of n-butane oxidation showed that when the ratio of air to N2 was 1:3, the corresponding VPO-1A catalyst presented the highest conversion of n-butane and yield of the MA product (57.6 m% at 412 °C). The reason should be related to the fact that the VPO-1A catalyst possessed the highest acidity and proportions of surface V5+ species and Sur-O species. As the ratio of air to N2 reached 3:1, the VPO-3A catalyst showed the poorest performance in the oxidation of n-butane, which could be due to the formation of inactive and amorphous VOPO4 phases over the surface of the VPO catalyst. Finally, kinetic and thermodynamic models were established and calculated to investigate the characteristics of n-butane oxidation reactions for various VPO catalysts.

Oxidative Dehydrogenation of Ethane on Oxide-Supported Vanadium Phosphorus Oxide Catalysts

Oxidative Dehydrogenation of Ethane on Oxide-Supported Vanadium Phosphorus Oxide Catalysts

The critical role of steam during activation process on the catalytic performance of VPO for n-butane selective oxidation to maleic anhydride

Vanadium phosphorus oxide (VPO) catalyst activation method is essential for the catalytic oxidation form n-butane to maleic anhydride. Here, we evaluate the effect of steam content on VPO catalyst during the activation process and validate the adjustment of the steam content could modulate the VPO activity. The DRIFTS results reveal that the steam content governs the formation of P-OH and V-OH species on the surface of VPO catalyst, whereas these sites would not enhance the catalytic activity directly. In contrast, the L acid site V5+-O-PO, forming a mutual transformation relationship with the P-OH species under steam/O2 conditions, is the main active site that dominates the conversion of n-butane, and a moderate amount of steam plays a role in stabilizing the V5+-O-PO site.

Copper-based deep eutectic solvents (Cu-DES) assisted the VPO catalyst as a structural and electronic promoter for n-butane selective oxidation

Currently, deep eutectic solvents (DESs), as an exclusive class of ionic liquid analogs, are extensively employed in various fields. Herein, vanadium phosphorus oxide (VPO) catalysts assisted by copper-based deep eutectic solvent (Cu-DES) as an electronic promoter and structure directing agent were ingeniously synthesized and exploited in the selective oxidation of n-butane to maleic anhydride (MA). The DES is efficient, cost effective and highly green compared to conventionally use metal inorganic modifiers. Cu-DES was prepared from a eutectic mixture of an organic salt (ChCl) and a metal salt hydrate/metal salt of cupric (Cu(NO3)2.3H2O, CuCl2) and cuprous (CuCl) salt with a molar ratio of 1:1–1:3, which notably improved the catalytic performance compared to that of an unpromoted VPO catalyst. The MA selectivity and n-butane conversion of Cu–DES–VPO increased significantly, while the COx (CO and CO2) selectivity decreased. FTIR, DSC, XRD, SEM, EDS, TEM, Raman, TGA, XPS, and NH3-TPD characterization techniques were utilized to fully analyze the DES, precursor and catalyst to explore MA selectivity. This work shifts the significant increase of 13% n-butane conversion, 11% MA selectivity and 16% MA mass yield, which greatly influences low carbon alkane utilization. Importantly, the CO: CO2 ratio is reduced from 2.02 to 1.62, which is more beneficial for chemical plants as well as green environments.

Rare earth metal based DES assisted the VPO synthesis for n-butane selective oxidation toward maleic anhydride

Deep eutectic solvents (DESs) are now considered a new class of ionic liquid analogs that have been generously used in various fields. Herein, vanadium phosphorus oxide (VPO) catalysts are synthesized in combination with a deep eutectic solvent containing rare earth metal (rE-DES), and their catalytic performance in n-butane selective oxidation to produce maleic anhydride (MA) is evaluated. The rE-DES is produced from the interaction of choline chloride (ChCl) and rare earth metal salts (Cerium, Europium, Lanthanum, and Samarium metal salt) (ChCl:rE = 1:0.5–1:3) under mild conditions. It was found that DESs served as structural modifiers and electronic promoters during VPO synthesis. It regulated the chemical state of the catalyst surface, such as the vanadium valence state, acid-base properties, and ratios of V4+/V5+, Lat–O/Sur–O and P/V. Various characterization techniques, such as FT-IR, DSC, XRD, SEM, EDS, TEM, Raman, TGA, NH3-TPD, and XPS, were used to examine its physical and chemical characteristics. These characteristics were correlated with the catalytic performance. The VPO catalyst modified by rE-DES showed a significant enhancement of n-butane conversion and MA selectivity while suppressing the selectivity of CO and CO2 as well as the CO/CO2 ratio compared to the unpromoted VPO catalyst. Especially for Ce-DES-VPO, it increased the n-butane conversion and MA mass yield up to approximately 11% and 10%, respectively. In addition, we evaluated the catalytic performance under different activation atmospheres.

Synthesis of Tunable-Acidity Vanadium Phosphorus Oxide Catalysts Modified by Layered Double Oxide for the Selective Oxidation of n-Butane

Synthesis of Tunable-Acidity Vanadium Phosphorus Oxide Catalysts Modified by Layered Double Oxide for the Selective Oxidation of <i>n</i>-Butane

A vanadium phosphorus oxide catalyst synthesized in rotating packed bed for high‐efficiency selective oxidation of n‐butane

AbstractOxidation of n‐butane to produce maleic anhydride (MA) by the vanadium phosphorus oxide (VPO) catalyst is important for the fine chemical industry. However, the improvement in MA yield exceeding 60% is still a big challenge. In this article, a VPO catalyst with increased MA yield originated from the tailored structure of VPO precursor prepared in a rotating packed bed (RPB) reactor with excellent micro‐mixing efficiency. The activated VPO‐RPB catalyst displayed the coexistence of X1‐VOPO4 and αI‐VOPO4 phases and enhanced reducibility of V4+ state. Remarkably, the MA yield in n‐butane oxidation catalyzed by VPO‐RPB reached up to 66%, showing an increment by 14% compared with VPO‐STR prepared in a stirring tank reactor (STR). The VPO‐RPB showed the repeatable catalytic performance and achieved a promising scale‐up production. This work provides the experimental evidence of a dual‐phase (X1‐VOPO4 and αI‐VOPO4) mechanism for n‐butane oxidation, and reveals the structure–activity dependence of VPO catalyst.

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

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.

Sparse ab initio x-ray transmission spectrotomography for nanoscopic compositional analysis of functional materials.

The performance of functional materials is either driven or limited by nanoscopic heterogeneities distributed throughout the material's volume. To better our understanding of these materials, we need characterization tools that allow us to determine the nature and distribution of these heterogeneities in their native geometry in 3D. Here, we introduce a method based on x-ray near-edge spectroscopy, ptychographic x-ray computed nanotomography, and sparsity techniques. The method allows the acquisition of quantitative multimodal tomograms of representative sample volumes at sub-30 nm half-period spatial resolution within practical acquisition times, which enables local structure refinements in complex geometries. To demonstrate the method's capabilities, we investigated the transformation of vanadium phosphorus oxide catalysts with industrial use. We observe changes from the micrometer to the atomic level and the formation of a location-specific defect so far only theorized. These results led to a reevaluation of these catalysts used in the production of plastics.

Cover Picture: Phosphoric Acid: A Key Role in Control of Structure and Properties of Vanadium Phosphorus Oxide Catalysts During Synthesis (04/2021)

Cover Picture: Phosphoric Acid: A Key Role in Control of Structure and Properties of Vanadium Phosphorus Oxide Catalysts During Synthesis (04/2021)

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

AbstractThe catalytic performance of vanadium phosphorus oxide (VPO) catalysts is closely related to the synthetic conditions of precursors. Herein, the role of phosphoric acid during VPO precursors synthesis process was thoroughly studied by investigating the morphology, crystal phase composition, and surface chemical property of VPO catalysts and their precursors. The H3PO4 concentration, the temperature of reaction system at the time of H3PO4 adding, and H3PO4 adding speed were optimized to prepared efficient VPO catalysts which applied in selective oxidation of n‐butane to produce maleic anhydride (MA). The obtained VPO catalyst by adding 85 % H3PO4 at or above 110 °C with the speed of approximate 1.1 mL/min could exhibit promising catalytic performances, which are 93.8 % of n‐butane conversion and 62.4 % of MA yield at 420 °C. Thus, this study emphasized the role of H3PO4 adding during VPO synthesis process, which is favorable to understand and fabricate the compositional, structural, and morphological properties of VPO catalysts.

Mechanochemystry as advanced methodology in green chemistry for applied catalysis

In this survey we have assessed how mechanochemistry techniques comply with the aims of Green Chemistry to minimise the use of environmentally damaging reactants and unwanted by-products. In the publications the preparation of vanadium-phosphorus oxides as industrial catalysts for maleic anhydride production from n-butane and perspective catalysts of phthalic anhydride manufacture by direct n-pentane oxidation were analyzed. It is shown that mechanochemical activation and synthesis reduces the amount of harmful waste used in the production of the catalyst and increases its effectiveness. Improvement of a catalyst’s properties, help limit production of harmful emissions such as carbon oxides and hydrocarbons. It was established that mechanochemical treatment can by successfully used in the process of industrial vanadium-phosphorus oxide catalysts modification or in the process of introduction in its composition of additives which lead to increase of activity and selectivity of hydrocarbons oxidation. The possibility of the mechanochemistry use in the vanadium-titanium oxide catalysts preparation which are the base catalysts in industrial phthalic anhydride production from o-xylene was determined. It was established that mechanochemical treatment of the vanadium and titanium oxides mixture permits to delete the nitrogen oxides emission in atmosphere and prepared catalysts demonstrate the same phthalic anhydride yield but at low reraction temperature. Catalysts, manufactured by mechanochemical treatment (on the base of molybdenum oxide), provide new techniques for producing compounds as exemplified by the direct oxidation of benzene to form phenol which can replace industrial two-step process from cumene or proposed process of benzene oxidation by N2O. Mechanochemistry treatment could produce catalysts which eliminated the need to use highly toxic nitrogen oxides as reducing agents. The article describes activating Cu-Ce-O catalysts which reduce the temperature of the process for removing carbon monoxide from exhaust gases and as a method for purifying hydrogen u sed in fuel cells. Finally, there is a description of mechanochemically treated catalysts, containing metals and supported on stainless steel supports which are used to remove aromatic hydrocarbons from water sewers.

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

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

Hydroxyl‐Rich Deep Eutectic Solvents Assistant Synthesis of VPO and Its Application in Selective Oxidation of n‐Butane

AbstractDeep eutectic solvents (DESs) consisting of choline chloride (ChCl) and polyols (Ethylene glycol (EG), 1,4‐Butanediol (BDO), Glycerol (GL), and Xylitol (XYL)) as a green and effective promoter assisting the synthesis of vanadium phosphorus oxide (VPO) were innovatively proposed and investigated in detail for the selective oxidation of n‐butane to maleic anhydride (MA). The catalytic results showed that the performance of VPO catalysts was improved significantly with the addition of polyols DESs. A combination of techniques including SEM, TEM, XRD, FT‐IR, Raman, XPS, and TG‐DTA were employed to investigate the effect of DES on the structure of VPO. We correlated the structure of the catalysts with catalytic performance and found that the n‐butane conversion was positively correlated with the intensity ratio of I (020)/I (204) for catalysts, and the MA selectivity of VPO catalysts was negatively correlated with the vanadium average oxidation state on the catalyst surface.

Synthesis of Porous and Highly Crystallinity Vanadium Phosphorus Oxide Catalysts by Multifunctional Biomass-Based Deep Eutectic Solvents.

Deep eutectic solvents (DESs) as a novel class of ionic liquid analogues has been widely used in various fields. Herein, a multifunctional biomass-based DES composed of choline chloride (ChCl) and glucose (GLU) was synthesized and used for the modification of vanadium phosphorus oxide (VPO) catalyst, which is the sole catalyst for the selective oxidation of n-butane to maleic anhydride (MA) in industry. The DES is more green, cost-effective and efficient compared with traditional modifier (metal inorganics and organic polymers). A combination of structure and catalytic performance was investigated in detail to deeply understand its functions. Initially, this DES plays the role of structure directing agent at the stage of precursor synthesis, which can induce the formation of active plane and obtain highly crystalline precursors. Accordingly, the active phase with highly crystalline was obtained after the activation of precursors. Additionally, the DES was decomposed during the precursors activation, resulting in the formation of porous structure around 20 nm on the active plane. Besides this, the surface chemical state including the valence state and acid-base property was changed significantly due to the function of DES. All of these lead to about an 11% increase of MA mass yield, which has great significance to the high value utilization of low carbon alkanes.