Vanadium Phosphorus Oxide Catalysts Research Articles

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.

How to achieve a highly selective yet simply available vanadium phosphorus oxide-based catalyst for sustainable acrylic acid production via acetic acid-formaldehyde condensation.

A series of unsupported and supported vanadium phosphorus oxide catalysts were prepared by employing a new strategy, which significantly reduced the complexity of catalyst preparation. The greatly simplified catalyst fabrication benefits a greener and lower-cost process for practical applications. The currently fabricated systems showed ca. 90% target product(s) selectivity with a promising yield as well as catalyst durability.

Precisely phase-modulated VPO catalysts with enhanced inter-phase conjunction for acrylic acid production through the condensation of acetic acid and formaldehyde

A type of precisely phase-modulated vanadium phosphorus oxides (VPOs) was fabricated for the first time by quantitatively mixing the pure phase of γ-VOPO4, δ-VOPO4, and (VO)2P2O7 in certain ratios through a mechanical milling approach. The resulting materials were used as catalysts for very efficient condensation of acetic acid and formaldehyde to acrylic acid as well as methyl acrylate. The modulated dual phase VPO catalyst outperforms the single-phase counterpart, and by optimizing the reaction conditions especially the contact time, we can further considerably enhance the catalyst performance. Over an optimized catalyst of δ-VOPO4/γ-VOPO4 (w/w, 3/1), the (AA + MA) yield of 84.2% with the equivalent (AA + MA) formation rate of 1.71 mmol·g−1·h−1 or the (AA + MA) yield of 41.8% with the equivalent (AA + MA) formation rate of 4.25 mmol·g−1·h−1 is achievable at 360 °C on the formaldehyde input basis. This sort of catalyst is rather durable within a period of 110 h, and fully recovered by simple air-treatment at the reaction temperature. Due to the enhanced conjunction at the interface of two phases, the surface property of phase-modulated catalyst such as the P-O bond length and surface acidity is notably modified/enhanced, accounting for the promising catalytic performance.

Synthesis of Vanadium Phosphorus Oxide Catalysts Assisted by Deep-Eutectic Solvents for n-Butane Selective Oxidation

The effects of choline chloride/oxalic acid deep eutectic solvents (ChCl/OA DES) as a green and effective promoter assisting the synthesis of vanadium phosphorus oxide (VPO) catalysts for the selec...

Nb-Doped Vanadium Phosphorus Oxide Catalyst for the Aldol Condensation of Acetic Acid with Formaldehyde to Acrylic Acid

Nb-doped vanadium phosphorus oxide catalysts were prepared and characterized using a variety of methods, including XRD, FT-IR, XPS, TPD and BET. The catalysts were examined for their ability to promote the aldol condensation of acetic acid with formaldehyde to acrylic acid. Catalyst composition and the conditions used to prepare the catalysts were investigated for their effects on catalytic activity. The addition of Nb changes the properties and catalytic properties of the catalyst to some extent, especially the surface acidity of catalyst and the average valence of surface V atoms, which have the greatest influence on the catalyst. When Nb/V = 0.06, the catalyst surface has the greatest acidity, the valence of surface V atoms is the lowest, and the selectivity (83.4%) and yield of acrylic acid (18.1%) are maximized.

Highly Efficient Gas-Phase Oxidation of Renewable Furfural to Maleic Anhydride over Plate Vanadium Phosphorus Oxide Catalyst.

Maleic anhydride (MAnh) and its acids are critical intermediates in chemical industry. The synthesis of maleic anhydride from renewable furfural is one of the most sought after processes in the field of sustainable chemistry. In this study, a plate vanadium phosphorus oxide (VPO) catalyst synthesized by a hydrothermal method with glucose as a green reducing agent catalyzes furfural oxidation to MAnh in the gas phase. The plate catalyst-denoted as VPOHT -has a preferentially exposed (200) crystal plane and exhibited dramatically enhanced activity, selectivity and stability as compared to conventional VPO catalysts and other state-of-the-art catalytic systems. At 360 °C reaction temperature with air as an oxidant, about 90 % yield of MAnh was obtained at 10 vol % of furfural in the feed, a furfural concentration value that is much higher than those (<2 vol %) reported for other catalytic systems. The catalyst showed good long-term stability and there was no decrease in activity or selectivity for MAnh during the time-on-stream of 25 h. The high efficiency and catalyst stability indicate the great potential of this system for the synthesis of maleic anhydride from renewable furfural.

Synthesis of vanadium phosphorus oxide catalysts promoted by iron-based ionic liquids and their catalytic performance in selective oxidation ofn-butane

Catalytic performance of undoped and Fe-doped VPO catalysts.

Selective oxidation of toluene to benzaldehyde by H2O2 with mesoporous silica KIT-6 supported VOHPO4 0.5H2O catalyst

Highly ordered and rosebud like KIT-6 silica materials containing different amounts of vanadium phosphate have been synthesized using nonionic surfactant P123 as a structure-directing agent. The unique properties of KIT-6 such as three-dimensional cubic Ia3d symmetry, high surface area, large pore volume and large pore size enabled good dispersion of vanadium phosphorus oxide (VPO) species in crystalline form. The structure and morphology of the samples were systematically characterized by XRD, N2 physisorption, SEM/EDX, elemental mapping, TEM, ICP-AES, UV–vis and FT-IR spectroscopy techniques. Various VPO loadings showed a clear influence on catalytic activity and selectivity. Within the studied range, the optimum conditions to improve toluene conversion and selectivity towards benzaldehyde over vanadium phosphorus oxide catalyst was performed in the presence of 17wt% catalyst VPO-loading at 75°C with 1:1.4 (toluene:H2O2) molar ratio, in acetonitrile as the solvent. Under these reaction conditions, 17.76% toluene conversion and 69.24% selectivity for benzaldehyde were observed after 10h of reaction time. Finally, the recyclability of the catalysts was studied through five consecutive catalytic runs.

Modeling the dynamic behavior of industrial fixed bed reactors for the manufacture of maleic anhydride

The industrially important selective oxidation of n-butane over vanadium phosphorus oxide catalysts in fixed bed reactors is affected by phosphorus induced dynamic changes of the catalyst activity. An economic process management therefore requires an adequate control of the operating conditions including the precise addition of a phosphorus containing compound in the ppm range. In a previous work (Lesser et al., 2016) we experimentally investigated these phenomena and related our findings to the diverse literature discussions abound reaction mechanism and active sites. Based on our conclusions, the present work provides a detailed model for the phosphorus dynamics which is connected to a two-dimensional heterogeneous reactor model. The model is able to describe the reactor behavior properly over 500h time on stream including many variations of the operating conditions. The dynamically changing activity profiles reflect the evolution of temperature profiles and product compositions with only minor deviations.

Catalysts, Process Optimization, and Kinetics for the Production of Methyl Acrylate over Vanadium Phosphorus Oxide Catalysts

Vanadium phosphorus oxide (VPO) catalysts were developed for the aldol condensation of methyl acetate (MeOAC) with formaldehyde (HCHO) to methyl acrylate (MA). The influence of P/V ratio on catalytic activity and selectivity was revealed and optimized with a fixed bed reactor. The controllable preparation of VPO catalyst was reached, and the influence of carrier gas on the resistance of carbon deposition was also systematically investigated. Response surface methodology (RSM) with three independent variables of molar ratio of MeOAC to HCHO, space velocity, and reaction temperature was employed to optimize MA yield with VPO catalysts. The high value of “R-squared” presented a reasonable correlation of regression model to the experimental data. Lastly, the kinetics of aldol condensation to produce MA over VPO catalyst was studied.

Effects of Support for Vanadium Phosphorus Oxide Catalysts on Vapor-Phase Aldol Condensation of Methyl Acetate with Formaldehyde

Vapor-phase aldol condensation of methyl acetate with formaldehyde over vanadium phosphorus oxide (VPO) deposited on SiO2, TiO2, ZrO2, Nb2O5, Sb2O3, γ-Al2O3, and n-γ-Al2O3 (γ-Al2O3 treated with H3PO4) for methyl acrylate production was developed. The VPO/n-γ-Al2O3 was found to have the best performance based on the evaluated experiments in a fixed-bed reactor. The physicochemical properties of the catalysts were investigated by different characterization methods such as the Brunauer–Emmett–Teller method, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, H2 temperature programmed reduction, Fourier transfrom infrared spectroscopy, and NH3- and CO2-temperature programmed desorption. The influence of P–OH intensity and acid strength on activity was obtained through systematic studies over the formation process of VPO phases and the acidity distribution. Preparation and reaction parameters were investigated and optimized.

Characterization of Mn-Doped Vanadium Phosphorus Oxide (VPO) Catalyst: Effect of Ball Milling

&lt;p&gt;The effect of ball milling on the structure and surface reactivity of the Mn-doped vanadium phosphorus oxide (V–P–O) catalyst is discussed. Mn-doped VOHPO&lt;sub&gt;4&lt;/sub&gt;·½H&lt;sub&gt;2&lt;/sub&gt;O precursor was prepared via organic method. The precursor was ball milled in isopropyl alcohol using agate balls for 60 min at 800 rpm. XRD, BET surface area measurements, SEM, O&lt;sub&gt;2&lt;/sub&gt;-TPD, H&lt;sub&gt;2&lt;/sub&gt;-TPR and TPD of NH&lt;sub&gt;3&lt;/sub&gt; were used to characterize properties of the final catalysts. The results revealed that mechanical treatment of Mn-doped V–P–O catalyst increased surface area as well as reduced particle size of the material. Furthermore, process also increased exposure of (001) crystallographic plane of VOHPO4·½H&lt;sub&gt;2&lt;/sub&gt;O precursor. The secondary structure of the milled material is also lost. The total amount of oxygen desorbed (from O&lt;sub&gt;2&lt;/sub&gt;-TPD) and removed (by H&lt;sub&gt;2&lt;/sub&gt;-TPR) from milled material is higher compared to the unmilled one. The surface acidity of the catalyst was also increased after milling process, as evidenced by lower desorption temperature and higher total amount of the ammonia desorbed.&lt;/p&gt;

Enhancing catalytic performance of phosphorus-modified ceria supported VPO catalysts for n-butane oxidation

Vanadium phosphorus oxide (VPO) catalysts supported on CeO2 and P-modified CeO2 (P-CeO2) have been firstly synthesized for selective oxidation of n-butane to maleic anhydride (MA). The catalysts supported on P-CeO2 showed higher catalytic performance, especially higher MA selectivity than catalysts on pure ceria, and their specific activities (normalized to per unit mass of VPO loading) were also superior to that of bulk VPO. TG, TEM, XRD, Raman, H2-TPR and XPS results revealed that the structure and property of VPO are largely affected by the support. The loaded VPO existed almost wholly as VOPO4 phases on pure ceria, while mainly in the form of (VO)2P2O7 with small amount of VOPO4 phases on phosphorus-modified ceria. Both VPO/P-CeO2 and bulk VPO catalysts have the similar VPO phase structure, but the former showed the enhanced reducibility of V4+ phase. These differences in structure and properties of the catalysts were discussed and related to their different catalytic performances.

Synthesis, characterization of VPO catalyst dispersed on mesoporous silica surface and catalytic activity for cyclohexane oxidation reaction

A precipitation-deposition method in an organic medium was used to prepare vanadium phosphorus oxide (VPO) catalysts supported on SBA-15 and TUD-1. Oxidation of cyclohexane has been examined over mesoporous silica supported VPO catalyst. The supported VPO catalyst has been characterized by XRD, N2 physisorption, SEM, HRTEM, H2-TPR and NH3-TPD techniques. The characteristic X-ray diffraction patterns of bulk VPO catalyst and VPO catalysts supported on mesoporous SBA-15 and TUD-1 showed that each of them are having well-crystallized vanadyl pyrophosphate [(VO)2P2O7] phase. The vanadium redox centers were easily accessible for supported VPO catalyst. The TUD-1 supported VPO catalyst had higher acidity as found in NH3-TPD studies. The conversion of cyclohexane increased in the case of VPO dispersed on TUD-1 mesoporous material. From SEM and HRTEM results it is found that the nature of the support and VPO loading had a profound influence on the crystallinity, morphology and chemical property of the dispersed VPO phase. The changes in all the property had a prominent role on its catalytic activity for the oxidation of the cyclohexane.

Transient behavior of vanadyl pyrophosphate catalysts during the partial oxidation of n‑butane in industrial-sized, fixed bed reactors

The industrially important application of vanadium phosphorus oxide catalysts is the partial oxidation of n -butane in multi-tubular fixed bed reactors. Despite many decades of investigation about the functionality of the catalyst, the reaction mechanism is still under debate. However, the loss of phosphorus from the catalyst as a technically important phenomenon was until now hardly considered in the scientific literature: this phosphorus loss during long term operation has a strong effect on the temperature distribution in the reactor, which in turn significantly affects the catalyst selectivity. Therefore, technical reactor operation usually requires the addition of ppm levels of an organic phosphorus compound together with water to the reactor feed. For a macro-scale investigation of the phosphorus dynamics, the present study reports elaborated experiments in an industrial scale fixed bed reactor. The experiments revealed significant changes in catalyst activity and reactor performance induced by only minor variations in the feed contents of phosphorus and water as function of butane feed and space velocity, as well as strong interactions between these two additional feed components. These observations are further related to the many literature reports about the active catalyst surface. Common aspects explaining the dynamic catalyst behavior were combined in a new scheme for the VPP/VPO surface chemistry.

Statistical Optimization of Liquid Phase Oxidation of Benzyl Alcohol over Efficient Cobalt Promoted Vanadyl Pyrophosphate Catalysts by Box-Behnken Design

Vanadium phosphorus oxides (VPO) has been applied as a heterogeneous catalyst in gas phase oxidation reactions and its application is very limited in liquid phase. In this study a series of cobalt-doped vanadium phosphorus oxides (VPO-Co) catalysts with different loading of Co (0.01-1.0 mol ratio of Co/V) were prepared. Oxidation of benzyl alcohol was studied in the liquid phase over VPO and VPO-Co catalysts, using tert-butylhydroperoxide (TBHP) as an oxidant. These samples were characterized by XRD, SEM and Fourier transform infrared (FT-IR) techniques. The optimal design of experiments using Box-Behnken method was employed to evaluate the effects of individual process variables (+1, 0, ­1, levels) such as, reaction temperature (30, 60 and 90 °C), reaction time (30, 255 and 480 min) and molar ratio of Co/V (0, 0.5 and 1) and their optimum values were found to be 89.86 °C, 477.8 min and 0.64 molar ratio Co/V, respectively, to achieve a conversion of 65.44%.

Characterization and activity of N doped TiO2 supported VPO catalysts for NO oxidation

Nitrogen (N) doped TiO2 supported vanadium phosphorus oxide (VPO) catalysts were prepared and tested for catalytic oxidation of NO. The experimental results showed that 0.1V(5)PO/TiN(1) was the optimal catalyst for NO oxidation and the NO conversion could reach 61% at temperature of 350°C. The physico–chemical properties of 0.1V(5)PO/TiN(1) catalyst were characterized by Brunauer–Emmett–Teller measurements (BET), Photoluminescence (PL), X–ray photoelectron spectroscopy (XPS), Infrared spectroscopy measurements of NH3 adsorbed on catalysts (NH3–IR), and Infrared Fourier transform spectroscopy (FTIR). The PL and XPS spectra revealed that the oxygen storage capacity and catalytic activity of VPO/Ti catalyst can be improved by nitrogen doping. The H2–TPR profile also indicated that V(5)PO/TiN(1) catalyst had a superior redox property. Activity test results and FTIR spectra showed that 0.1V(5)PO/TiN(1) catalysts had a superior resistivity to SO2 and the NO oxidation rate is above 50% at temperature of 350°C when SO2 concentration is 200ppm to 800ppm.

Liquid-phase efficient oxidation of cyclohexane over cobalt promoted VPO catalyst using tert-butylhydroperoxide

A series of cobalt-doped vanadium phosphorus oxides (VPO-Co) catalysts, as well as unpromoted sample (VPO) was prepared using classical organic method via VOHPO4·0.5H2O precursor followed by calcinations in 1.5% butane/air environment at 400 °C for 24 h. Techniques such as XRD, BET surface area, chemical titration, SEM, TPR and FT-IR were used for characterization of the catalysts. The results showed that promoted VPO catalyst were contained crystalline form of V4+ (vanadyl pyrophosphate, (VO)2P2O7), CoPO4 phase and a small amount of V5+ (β-VOPO4 phase). However, Co promoted VPO contained poorer crystallinity compared to the unpromoted catalysts. Co was found to increase the average oxidation number of vanadium from 4.28 to 4.43 due to increase of V5+ oxidation state from 28 to 43%.Oxidation of cyclohexane, for the first time, was studied in the liquid phase over VPO and VPO-Co catalysts, using tert-butylhydroperoxide (TBHP) as an oxidant. The catalytic tests showed that cobalt doping significantly increased the overall activity for the oxidation of cyclohexane. At 90 °C, the obtained activities were 0.076 and 0.491 gpro/gVPO/h over the VPO and VPO-Co (molar ratio Co/V = 0.1) catalysts, respectively. The effects of Co loading, TBHP/cyclohexane molar ratio, amount of the catalyst, solvents and catalyst recycling were investigated. The kinetic of cyclohexane oxidation was investigated at different temperatures using VPO-Co(0.1) and excess TBHP. The order of reaction with respect to cyclohexane was determined to be pseudo-first order. The value of the apparent activation energy was also determined.