Vanadium Phosphorus Oxide Research Articles

Role of Cerium-Layered Double Hydroxide-Derived Oxide Dopants in Vanadium Phosphorus Oxide for Selective Oxidation of n-Butane

Role of Cerium-Layered Double Hydroxide-Derived Oxide Dopants in Vanadium Phosphorus Oxide for Selective Oxidation of <i>n</i>-Butane

Role of regulating synthetic solvents in enhancing the catalytic performance of VPO catalysts for n-butane oxidation to maleic anhydride

Vanadium phosphorus oxide (VPO) catalysts have been successfully applied in the selective oxidation of n-butane to maleic anhydride (MA). However, there is still much work to be done to enhance the n-butane conversion while maintaining a relatively high MA selectivity. Regulating the solvents in preparing VPO catalysts is an effective way to improve the catalytic performance. In this work, the correlation between the physicochemical properties of VPO catalysts and the composition of solvents was investigated by combining various characterization techniques to reveal the role of regulating synthetic solvents in enhancing the catalytic performance. Varying synthetic solvents could regulate both the synthetic mechanism and crystal growth of VOHPO4·0.5H2O. The VOHPO4·0.5H2O tended to form a nice plate-like structure in isobutanol but possessed large crystallite sizes and a low specific surface area. The introduction of n-butanol prevented the continuous growth of VOHPO4·0.5H2O, reducing the crystallite sizes and thus increasing the specific surface area. Introducing the n-butanol also optimized the catalyst surface chemical properties. The best catalyst synthesized in a solvent containing 80 % n-butanol and 20 % isobutanol enhanced the n-butane conversion from 71 % to 87 % while maintaining the MA selectivity (64 %) almost unchanged compared to the catalyst synthesized in a conventional solvent.

Selective oxidation of methanol to green oxygenates on vanadium-aluminum phosphate based catalysts

The methanol transformation reaction in the presence of oxygen was carried out in the temperature range of 210–310 ºC, over vanadium catalysts based on vanadium oxide (V2O5) and on vanadium-phosphorus oxide (VPO) calcined at 450 ºC in air. Specifically, the vanadium oxide systems with V2O5 loadings below, above or corresponding to the theoretical monolayer (1–34 wt% of V2O5) were obtained by the impregnation of a mesoporous amorphous aluminum phosphate, AlPO4, calcined at different temperatures (from 350 ºC to 650 ºC) with vanadyl oxalate. Additionally, mechanical mixtures of either VPO or V2O5 with AlPO4 were also employed. Under the experimental conditions employed, with a methanol enriched feed (O2/methanol molar ratio=0.6), formaldehyde and dimethoxymethane were the main products obtained with all the catalysts studied. Vanadyl phosphate (VPO) exhibited slightly lower activity than vanadium oxide, formaldehyde being the main product (SFA ≥ 95%). The conversion of both vanadium oxide and vanadyl phosphate appreciably increased when mixed with the AlPO4, also promoting the formation of dimethoxymethane. The interaction of the vanadium species with the aluminum phosphate surface took place preferentially through the surface Al-OH groups, the vanadium species with less development being the most active in the formation of formaldehyde and dimethoxymethane, per at-g of vanadium.

Role of the catalyst structure–activity relationship in enhancing the selective oxidation yield of n-butane to maleic anhydride

Vanadium phosphorus oxide (VPO) catalysts are synthesized for utilization of lighter alkanes such as n-butane to produce maleic anhydride (MA) by a selective oxidation process.

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

Comparative results of studying the oxidative dehydrogenation of ethane (ODE) on catalytic vanadium-phosphorus oxide systems deposited by the molecular layering method on the surface of oxide supports (Al2O3, SiO2) have been presented. It has been found that the highest activity in ODE and selectivity for ethylene are exhibited by vanadium-phosphorus-containing catalysts. The influence of the acidity of catalytic systems on the activity and selectivity of the process has been revealed. The selectivity of the ODE process for ethylene reaches 90%. An increase in the oxygen concentration in the initial mixture from 3.5 to 20% leads mainly to a decrease in the selectivity of the ODE process with respect to the ethylene yield.

High-efficiency and durable V-Ti-Nb ternary catalyst prepared by a wet-solid mechanochemical method for sustainably producing acrylic acid via acetic acid-formaldehyde condensation.

Based on the precise phase control V species adjustment of vanadium phosphorus oxides (VPOs), a series of metal oxides (Nb2O5, MoO3, WO3, and Bi2O3) were selected as modification agents to further enhance the catalytic activity and retain the excellent durability of VPO-TiO2-based catalysts for the new procedure of producing acrylic acid via acetic acid-formaldehyde condensation. At an elevated liquid hourly space velocity (LHSV), the (AA + MA) selectivity reached 92.3% with a (MA + AA) formation rate of 63.8 μmol-1 gcat -1 min-1 over the Nb-decorated catalyst (catalyst VTi-Nb), and it maintained good durability for up to 100 h. The detailed characterization results of XRD, Raman, XPS, NH3-TPD, CO2-TPD, and H2-TPR, demonstrated that the addition of Nb2O5 could observably enhance the catalytic efficiency of the VPO-TiO2 catalyst. It not only improved the catalyst durability by enhancing prereduction of the V5+ species, but also enhanced the active site density to improve the catalytic activity.

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

Synthesis and properties of VPO catalysts for oxidation of n-butane to maleic anhydride

Bulk and supported vanadium-phosphorus oxide VPO catalysts were synthesized by traditional and barothermal methods. It was shown that the use of aerosil as a support for the VPO phase, depending on the time of its introduction into the reaction mixture. It can lead to the formation of catalyst precursor of vanadyl hydrogen phosphate VOHPO4 0.5H2O, or a phase of vanadyl pyrophosphate (VO)2P2O7 as already the catalytically active phase for selective oxidation of n-butane to maleic anhydride. The use of a modified aerosil gel formed from pyrogenic aerosol, as a support for the VPO phase, leads to the formation of VOHPO4∙0.5H2O phase. It has been found that the nature of support affects the features of formation of VOHPO4∙0.5H2O phase, in particular, the ratio of crystallographic planes in resulting VPO phase. The use of aerosil as a support leads to a decrease in the relative content of the basal plane, while use of aerosil gel leads to an increase in the relative content of the basal plane in applied VPO phase. The catalytic properties of bulk and supported VPO samples were studied in the selective oxidation of n-butane to maleic anhydride in standard (1.7 vol.%) and enriched (3.4 vol.%) n-butane mixtures. It has been found that in an enriched n-butane mixture for bulk samples, the n-butane conversion and selectivity for maleic anhydride are sharply reduced. It has been found that supported VPO samples have a higher specific rate of n-butane oxidation and higher productivity compared to bulk samples. It was shown that use of barothermal synthesis and aerosol gel as a support made it possible to increase the selectivity of maleic anhydride, which is associated with an increase in the relative content of the basal plane of VPO phase. The achieved improved catalytic properties of VPO catalysts supported with aerosol gel make recycling technology promising. This can make the production of maleic anhydride more economical.

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.