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Nitrogen oxides (NO_x), as one of the main atmospheric pollutants, seriously affect environmental safety and human health. Selective catalytic reduction (NH_3-SCR) is the most effective treatment method for NO_x removal at present, especially low-temperature SCR denitrification technology, which has very important application prospects and research significance. The research showed that VPO/TiO_2 catalyst had excellent low-temperature SCR denitrification activity. The adsorption of NH_3 and NO on V_2O_5 and (VO)_2P_2O_7 surface was simulated by DFT, and the reaction mechanism of VPO catalyst was studied at the micro level. The results showed that NH_3 exhibited stable chemisorption of Brønsted acid and Lewis acid on the surface of V_4P_4O_22H_14 cluster, and the adsorption effect on Brønsted acid sites was more stable. NH_3 adsorption effect on the surface of catalyst was excellent because of the hybridization of 2p orbital of N, 2p of O and 3d electron orbital of V. NO also showed chemisorption on the surface of V_4P_4O_22H_14 cluster. Due to the small amount of electron transfer, which was significantly lower than the adsorption energy of NH_3, NO could not strongly compete with NH_3 molecule. In addition, NO showed stable chemisorption on Brønsted acid and Lewis acid on the surface of V_6O_20H_10 cluster. The adsorption on Brønsted acid sites was more stable. The E-R mechanism and L-H mechanism of VPO/TiO_2 catalyst reaction mechanism were explained.

In this paper, a heteropolyacid catalyst VPO-Cr-PEG/TiO2 was developed and the low temperature de-NOx performance of catalyst was studied. The experimental results showed that the de-NOx efficiency reached over 98% at the low temperature of 150–350 °C. The catalyst exhibited excellent sulfur and water resistance in the presence of 1000 ppm SO2 and 8 vol% H2O. In the presence of polyethylene glycol (PEG), the crystal surface energy of the catalyst decreased, and (VO)2P2O7 was the main active crystal phase of the catalyst. The selective catalytic reduction of NOx by NH3 over VP(1/5)O-Cr-PEG/TiO2 catalyst simultaneously followed the Langmuir-Hinshelwood and Eley-Rideal mechanisms.

A catalyst 0.1VP(0.2)O-Cr(0.01)-PEG(1 × 10−4)/Ti for low-temperature SCR de-NOx was developed and the effects of SO2 and water vapor on its catalytic activity were investigated. Cr doping increases the molar ratio of V5+ to V4+ on the VPO catalyst, which promote oxidation of NO to NO2 and catalytic activity of the VPO catalyst. An appropriate amount of redox-coupled V5+/V4+ also promotes catalytic activity of the VPO catalyst. The denitration efficiency over 0.1VP(0.2)O-Cr(0.01)-PEG(1 × 10−4)/Ti was above 98% at 150–350°C. Cr doping also promotes the generation of Lewis acid around V5+ center and Brønsted acid (P-OH) on the VPO catalysts. The strong surface acidity of 0.1VP(0.2)O-Cr(0.01)-PEG(1 × 10−4)/Ti could restrain the adsorption of and oxidation of SO2. Characterization (FT-IR, TG) results indicate that nearly no sulfate was deposited on the surface of 0.1VP(0.2)O-Cr(0.01)-PEG(1 × 10−4)/Ti after activity test. The competitive adsorption of water molecules and nitric oxide on the catalyst surface decreases the catalytic activity of the VPO catalyst. The addition of Cr and PEG could increase the surface area and the exposure of active site of VPO catalyst, which also increase the unoccupied active sites of VPO catalysts in the presence of water vapor. The catalyst 0.1VP(0.2)O-Cr(0.01)-PEG(1 × 10−4)/Ti for low-temperature SCR de-NOx shows high catalytic activity and exhibits high resistance to SO2 and water vapor.

α II -V 1- x M x OPO 4 (M = W,Mo). • Solution combustion synthesis (SCS) leads to a variety of phase pure catalysts. • Doping with Mo and W tunes the oxidation state of V in VOPO 4 between 4+ and 5+. • α II -(V 1- x W x)OPO 4 reaches selectivities of maleic anhydride of more than 30%. • α II type solid solutions are a flexible platform for further research. The vanadyl pyrophosphate (VPP) based catalyst is unique in converting n -butane selectively (60–70%) into maleic anhydride (MAN), whereas a MAN selectivity of 20% may be regarded as high for structurally different catalyst systems. We present novel vanadium phosphorus oxides and mixed metal phosphate solid solutions tested for n -butane oxidation to MAN with a selectivity of >30%. The majority of the catalysts were prepared by solution combustion synthesis. (V 1- x W x)OPO 4 with α II structure was found to be more active and selective in the oxidation of n -butane compared to β -VOPO 4. By adjusting the tungsten content the oxidation state of vanadium in (V 1- x W x)OPO 4 can be tuned between 4.74 and 4.99, which is regarded as a key factor for MAN production. All catalysts were structurally stable, but the specific surface area increased during the reaction, as detected by X-ray diffraction and N 2 physisorption, respectively. (V 1- x Mo x)OPO 4 was also stable, but the MAN selectivity was lower compared to β -VOPO 4. Low conversions result from the low surface area of the screening samples, however, could be overcome by advanced synthesis protocols. [ABSTRACT FROM AUTHOR]

Abstract The vapor pressure osmometry (VPO) of metal dialkyldithiophospate (MDDPs) association in simple hydrocarbon solvents [1] has been analyzed using the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) [2]. From this analysis, we obtain a fluid-state free energy theory of MDDPs, including zinc dialkyldithiophosphates (ZnDDPs), an important class of multifunctional lubricant additives present in most automotive and commercial vehicle formulations marketed worldwide [3]. As expected, the PC-SAFT parameters of the MDDP compounds are found to vary smoothly with molecular size, metal atom type (Zn, Cd, Hg, Pb), and alkyl chain structure. Analysis of benzene/MDDP VPO isotherms with PC-SAFT suggests that selected MDDP compounds cross-associate with benzene. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Catalytic single-lifetime reduction could be due to coke deposits and imbalanced in I V 4+/I V 5+ ratio. • Change of physical and chemical property caused by coking is the reason of the bad regenerated performance of VPO catalyst. • The I V 4+/I V 5+ ratio could return to normal value after reactivation. • The correlations of carbon deposit and time were fitted by empirical Voorhies equations. Abstract Improvement in activity for the Zr doped VPO catalyst appears to be a general observation in aldol condensation of methyl acetate and formaldehyde to methyl acrylate. The deactivation behavior significantly differs between VPO and VPO-Zr catalysts. In this work, the deactivation/reactivation behavior and carbon formation in aldol condensation on VPO and VPO-Zr catalysts were investigated. After partial deactivation of the conversion of methyl acetate and formaldehyde to methyl acrylate with a fixed-bed reactor, the deactivated catalysts were fractionated from the reactor. The samples were then analyzed by spectroscopic techniques, gas adsorption measurements and thermogravimetry. The VPO-Zr catalyst showed differences in deactivation/reactivation behavior from the VPO catalyst under same reaction conditions. This finding could be partially ascribed to different coke locations in the deactivated catalysts with varied porosity. The I V 4+/I V 5+ ratio of V atom remarkably differed among fresh, used, and refreshed catalysts, which could be a key factor affecting catalyst deactivation. The relations of carbon formation and reaction time were fitted by empirical Voorhies equation over VPO and VPO-Zr catalysts. 1 [ABSTRACT FROM AUTHOR]

A set of vanadium phosphorous oxide (VPO) catalysts, mainly consisting of (VO) 2 P 2 O 7 , VO(PO 3 ) 2 or VOPO 4 ·2H 2 O bulk crystalline phases, has been investigated for the oxidative dehydrogenation (ODH) of ethane to ethylene, a key potential reaction for a sustainable industrial and socioeconomic development. The catalytic performance on these VPO catalysts has been explained on the basis of the main crystalline phases and the corresponding surface features found by XPS and LEISS at 400 °C, i.e. within the temperature range used for ODH reaction. The catalysts based on (VO) 2 P 2 O 7 phase presented the highest catalytic activity and productivity to ethylene. Nevertheless, the catalysts consisting of VO(PO 3 ) 2 structure showed higher selectivity to ethylene, reaching 90% selectivity at ca. 10% ethane conversion. To the best of our knowledge, this is the highest selectivity reported on a vanadium phosphorous oxide at similar conversions for the ethane ODH. In general, catalysts consisting of crystalline phases with vanadium present as V 4+ , i.e. (VO) 2 P 2 O 7 and VO(PO 3 ) 2, were found to be significantly more selective to ethylene than those containing V 5+ phases. The surface analysis by XPS showed an inverse correlation between the mean oxidation state of vanadium near surface and the selectivity to ethylene. The lower averaged oxidation states of vanadium appear to be favoured by the presence of V 3+ species near the surface, which was only found in the catalysts containing V 4+ phases. Among those catalysts the one based on VO(PO 3 ) 2 phase shows the highest selectivity, which could be related to the most isolated scenario of V species (the lowest V content relative to P) found at the outermost surface by low energy ion scattering spectroscopy (LEISS), a “true” surface technique only sensitive to the outermost atomic layer. [ABSTRACT FROM AUTHOR]

The synthesis of two novel catalytic materials based on vanadium mixed oxides has been described in present study. The first material was a Vanadium-Phosphorous mixed oxide (VPO) carbon-supported material with fibrous morphology and a very high surface area, and stable under oxidizing conditions up to 350 °C. The other material is a bulk mixed VPO oxide with fibrous structure obtained after optimizing the calcination of the supported carbon fiber catalyst, which presents a very high surface area. Both materials seem to be very attractive as catalysts in a wide range of partial oxidation processes in both liquid and gas phase based on the structural and chemical characterization data. [ABSTRACT FROM AUTHOR]

The effect of calcination temperature on the catalytic activity of VPO catalyst for one step synthesis acrylic acid with acetic acid and formalin was systematically studied using a fixed-bed tubular micro-reactor. The influence of calcination temperature on physicochemical properties especially crystal phase structure of VPO catalysts was obtained. The catalysts were analyzed and characterized with in situ high temperature XRD (HT-XRD), BET, TEM, TG/DTA, XPS, as well as NH 3 , CO 2 -TPD, and pyridine-FTIR methods. Larger special surface area and higher V 4+ concentration favored higher conversion and selectivity. The optimum special surface area and I V 4+ / I V 5+ ratio was obtained with controlling calcination temperature. The catalyst deactivation was also explored. [ABSTRACT FROM AUTHOR]

El estudio de las resinas y los asfaltenos, las fracciones más pesadas del petróleo, se ha convertido en un área de interés, debido a la abundancia de crudos pesados en Colombia y en América Latina. En este trabajo se estudió la composición quómica de las fracciones pesadas del crudo Castilla, se evaluaron algunos de sus parámetros moleculares y se evidenció la interacción entre la resina extraóda del crudo con los asfaltenos del crudo original. Para este propósito, se realizó, la precipitación, a nivel de planta piloto, del agregado resina-asfalteno (R-A), por adición y mezcla a condiciones controladas, de un solvente parafónico, proveniente de la refineróa de Apiay, denominado Apiasol. Mediante extracción Soxhlet con el mismo solvente, se separó la resina I del agregado R-A. La resina II, definida como la fracción soluble que hace parte de los maltenos, se separó del crudo desasfaltado, por cromatografóa de columna abierta, utilizando alúmina como soporte según el método Saturado, Aromáticos, Resinas (SAR). Las fracciones de resinas y los asfaltenos obtenidos, se caracterizaron por: Resonancia Nuclear Magnética (RNM), FT-IR, Difracción de Rayos X (DRX), análisis elemental (C, H, N, S), contenido de metales (Ni y V), distribución del peso molecular por Cromatrografóa de Permeación por Gel (GPC), y peso molecular promedio por Osmometróa de Presión Vapor (VPO). Los resultados obtenidos, evidencian que la resina I que forma parte del agregado es de menor peso molecular promedio que la resina II presente en la fracción de maltenos. Adicionalmente, se encuentran algunos cambios en el análisis elemental entre las resinas. Por otro lado y teniendo en cuenta las teoróas existentes respecto a las interacciones moleculares entre estas fracciones, se encontró que las resinas I separadas del agregado R-A, al adicionarse al crudo estabilizan sus asfaltenos. Esta evaluación se realizó, analizando el punto de floculación del crudo y sus mezclas con 1,9% y 3,8% de resina I, cuando son tituladas con un agente precipitante, en una celda NIR que trabaja a alta presión y temperatura.

Preparation of 2-Chlorobenzonitrile, and benzonitrile are reported here from the corresponding 2-Chlorobenzaldehyde and benzaldehyde by the reaction of ammonium hydroxide/VPO titania, VPO bulk (ammonium metavanadate) CuCr catalyst/air system in methanol. All these catalysts showed better conversions with reasonable selectivity to aromatic. The results prove that BET surface area results show VPO is present on the catalysts surface which has high surface area, attributed to increase in activity of the catalysts.

Abstract: In heterogeneous catalysis, catalyst precursor activation and subsequent initial operation (‘conditioning’) under reaction conditions are often highly dynamic steps which are important in delivering effective catalyst performance over time scales of years. In many cases however, the phenomena occurring in both steps are often poorly understood. A novel approach to assess the conditioning step, comprising advanced catalyst testing methods in micro-reactors, catalyst characterisation and detailed kinetic and activity modelling techniques is demonstrated for a model system: the selective oxidation of n-butane to maleic anhydride (MA) using a pre-activated vanadium phosphorus oxide (VPO) catalyst. A transient kinetic model for the conditioning step is presented which describes the decline of population of active sites for three reaction pathways on the catalyst surface over time. Two reaction pathways, n-butane --> MA and n-butane --> COx decay similarly with time whilst a third, MA --> COx declines very sharply. The approach used provides important mechanistic information on catalyst reaction kinetics whilst also providing understanding the impact of reaction conditions on the catalyst during conditioning. [Copyright &y& Elsevier]

The structural properties and oxidation state of vanadium in alumina-supported vanadium-phosphorous oxides at nearly monolayer coverage influence its catalytic performances. The population distribution VVO and VIVO species in the amorphous VPO phase strongly depends on the sample history. By using alumina-supported VPO instead of conventional bulk catalysts, we facilitate enhanced discrimination between active phase and bulk phase signals in the vanadium-phosphorous oxygen system. This brings light on the speciation of VPO catalysts in general. Our observations were achieved by using mainly in situ EPR operando Raman–GC spectroscopic techniques at relevant temperatures and gas conditions, showing that the (VivO)2P2O7 phase is formed during propane ammoxidation at 753K. Such transformation is less intense in inert atmosphere at 753K. Ammonia adsorption on the VPO catalyst surface leads to the formation of VO2+ sites, probably bearing Brønsted and/or Lewis acidity. Propane ammoxidation appears to promote the formation of mixed valence compounds. [ABSTRACT FROM AUTHOR]

Abstract: The formation of dispersed VPO phases on a lignocellulosic-based activated carbon results in a catalyst that is selective for the partial oxidation of propane, and stable under oxidizing conditions. The use of a stable activated carbon as a catalytic support for active VOx species during the partial oxidation of propane is described for the first time. [Copyright &y& Elsevier]

Abstract: Cycling catalyst between a net oxidizing and reducing gaseous environment has been practiced commercially to produce maleic anhydride from n-butane over vanadium pyrophosphate. Typically, the oxidation period is less than 1min to minimize catalyst inventory. In this study, the effect of the oxidation period on maleic anhydride productivity was assessed in the range of 0.3–10min. Irrespective of the feed gas composition during the reduction period, the productivity increased linearly with the oxidation soak time in air. A full range of reducing conditions was examined from the pure redox mode (10% n-butane in argon) to highly oxidizing conditions typical of fixed bed operation (1.4% n-butane and 18.1% oxygen). On average, maleic anhydride yield increased by up to 50% when the oxidation time was extended from 0.3 to 10min. The maleic anhydride yield was lowest under redox mode and it was highest when the feed composition was close to equimolar in n-butane (∼6%) and oxygen. Our results show that industrial CFB reactor performance may be improved considerably by efficient regeneration of the catalyst and optimization of the reducing feed gas composition. [ABSTRACT FROM AUTHOR]

Abstract: The kind and percentage of point defects in commercial as well as laboratory prepared hemihydrate VPO precursors have been analysed using a combination of electron diffraction experiments and diffraction pattern simulation. Experimental patterns reveal the systematic existence of kinematically forbidden reflections that are attributed to vacant lattice sites in the VOHPO4·1/2H2O matrix. The vacancies are associated with vanadium ions and are distributed into the bulk and surface of hemihydrate in an ordered fashion. The amount of vacancies is in similar proportion between the two precursors studied. A considerable enhancement in the forbidden reflections intensity in doped hemihydrate samples has been experimentally observed, which is attributed to the partial substitution of dopant ions into V vacant sites. The beneficial effect of such a modified hemihydrate structure on the resulting VPO catalyst performance is demonstrated, since the facilitation of promoter incorporation in V-based vacant active sites brings upon an enhanced activity and selectivity for the catalyst. [Copyright &y& Elsevier]

Abstract: Cited advantages of circulating fluidized bed reactors (CFB) include higher selectivity and conversion together with the ability to optimize the process conditions of each vessel independently—temperature, gas partial pressure and residence time. DuPont commercialized a CFB process to produce maleic anhydride in which a vanadium pyrophosphate (VPO) was cycled between a fast bed riser and an air fed regenerator. Together with VPO, we examined two other redox catalyst systems—MoVSb (acrylic acid from propane) and FeMoO (methanol to formaldehyde). The lattice oxygen capacity of the FeMoO catalyst was about five times higher than either the VPO or MoVSb with little adsorbed carbon but a significant quantity of chemisorbed water. Above 350°C, carbon deposition was detected and increased with increasing temperature. Carbon deposition decreased with increasing temperature for the MoVSb system and its lattice oxygen capacity was slightly higher than for VPO. The carbon deposition pattern for VPO was the opposite of the MoVSb and increased with temperature. Based on a hydrogen and carbon mass balance during the catalyst re-oxidation treatment, the molecular composition of the adsorbed species were C4H6 and C3H3—like for the VPO and MoVSb, respectively. Based on the high lattice oxygen capacity, the formaldehyde reaction appears to be ideally suited for development in a CFB. Whereas the lattice oxygen contribution of the MoVSb is equivalent to VPO, less oxygen is required to produce acrylic acid (compared to maleic anhydride) so the incentive of developing a CFB process should be greater than for butane oxidation to maleic anhydride. [Copyright &y& Elsevier]

Abstract: A series of silver-doped vanadium phosphorus oxides (Ag-VPO) catalysts were prepared by in situ synthesis, the catalytic tests showed that silver component significantly increased the overall activity for the oxidation of styrene by tert-butyl hydroperoxide (TBHP). It is interesting that Ag-VPO catalysts show no epoxidation selectivity but good selectivity for benzaldehyde in this study. To investigate the origin of the silver effect, the solids were characterized using X-ray diffraction (XRD), Fourier transformed-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and other instruments, the (VO)2P2O7, β-VOPO4, Ag(V2P2O10) and Ag2(VO2)(PO4) phases were detected in all the Ag-VPO catalysts. This study also confirms that ratios of P/V play a crucial role in the activity and the selectivity of the catalyst, meanwhile, the other factors, such as solvent, oxidant concentration, reaction time, also have been investigated and reaction conditions are optimized. [Copyright &y& Elsevier]

Abstract: Vanadium phosphate catalysts were synthesized via VOPO4·2H2O and were calcined in two different hydrocarbon reaction environments, i.e. n-butane/air and propane/air. Both catalysts are denoted VPDB and VPDP, respectively. Both catalysts exhibited a good crystalline with characteristic peaks of pyrophosphate phase. However, the peaks for VPDP are shown to be more prominent than those of VPDB. BET surface area showed that VPDB gave higher surface area (23m2 g−1) compared to VPDP (18m2 g−1). The average V valence state for VPDP is 4.08 and the higher V valence state for VPDB is 4.26 due to higher amount of VV for VPDB. Furthermore 14.2% of VIII was found for VPDP but none for VPDB. SEM micrographs clearly revealed that the morphologies of both catalysts composed of plate-like crystallite that was arranged into the characteristic of rosette cluster. However, the catalyst calcined in n-butane/air environment (VPDB) resulted in an increment of the amount of plate-like crystal formed in the rosette rosebud agglomerates. TPR in H2 profiles of both catalysts gave two reduction peaks corresponding to two kinetically different oxygen species which were associated with VV and VIV phases, respectively. VPDB removed larger amount of active oxygen species linked to VIV phase which eventually caused a higher conversion rate in the selective oxidation of n-butane and propane to maleic anhydride and acrylic acid, respectively. [Copyright &y& Elsevier]

Abstract: The present work addresses the issue of the promoter effect produced by group VIB elements added to the basic VPO formulation using different methods and loads in order to obtain information linking the catalytic behavior of the solids with their physicochemical properties. The unpromoted VPO precursor (VOHPO4·1/2H2O) was prepared from V2O5 reduced with an alcoholic mixture and 100% H3PO4. Cr, Mo or W were either impregnated on the VPO precursor or co-precipitated during the precursor synthesis. The precursors containing varying loads of the promoter were activated following a standard procedure in the same flow micro-reactor where the catalytic performance was evaluated. The precursors and the catalysts were characterized by X-ray diffraction (XRD) and laser Raman spectroscopy (LRS). Acetonitrile was used as a probe molecule to test the strength of the Lewis acid sites monitored by FTIR. The amount of chemisorbed acetonitrile was measured in a standard high vacuum system. The addition of the promoters invariably increased the catalytic activity but in every case there was an optimum load to achieve the best selectivity. The origin of this maximum could be ascribed to the right balance between the presence of very strong Lewis acid sites and the development of V5+ isolated sites in the matrix of the vanadyl pyrophosphate, by far the major crystalline phase present in the catalyst. The three group VIB promoters affect the balance between acid and redox properties but increase the overall activity in all cases. [Copyright &y& Elsevier]

Time resolved in situ X-ray diffraction was used to study the formation of vanadyl hydrogen phosphate hemihydrate (VOHPO4·0.5H2O) in organic media. This technique has identified a new phase at early synthesis times (less than 300 s) at a d-spacing of 7.5 and 3.1 Å. The feature at 7.5 Å shifted to 6.7 Å during the first 20 min of synthesis and this phase collapsed as VOHPO4·0.5H2O formed. Thin symmetrical platelets of 10 μm×10 μm dimensions were observed when samples were recovered after short synthesis times. Energy dispersive X-ray analysis indicated that these platelets contained vanadium and phosphorus. The platelets appeared to delaminate possibly associated with the strain generated when the d-spacing shifted from 7.5 to 6.7 Å, from which growth of the VOHPO4·0.5H2O into the familiar rosette morphology occurs. [Copyright &y& Elsevier]

A novel reactor configuration is proposed to study the kinetics of heterogeneous catalytic reactions. It is based on the bubbling fluidization regime; gas velocities are sufficiently low to minimize bypassing but high enough to ensure solids backmixing and a uniform temperature gradient. The reactor is equipped with a gas manifold designed to operate the reactor either under steady-state feed conditions or with cyclical feeds. By cycling VPO catalyst between a reducing environment with butane and an oxidizing environment, we quantify the lattice oxygen contribution to the reaction. Furthermore, we show that carbon can build up on the VPO surface and this phenomenon increases with an increase in the severity of the reducing environment. We propose a simple kinetic model involving three sites—V5+, V4+ and VC4. The model adequately characterizes the transient partial oxidation of butane but further research is required to create a generalized model that fits all reaction environments. [Copyright &y& Elsevier]

This study presents information about crystal imperfections in the main phase of industrial vanadium phosphorous oxide catalysts that are used to catalyze the oxidation of n-butane to maleic anhydride, being an important intermediate in the chemical industry. The mechanism of this reaction is still debated, and the catalytically active and selective surface centers have not yet been identified. The results presented are based on X-ray diffraction data obtained by both laboratory-scale and synchrotron powder diffraction experiments, as well as laboratory-scale single-crystal diffraction experiments. It has been proven that pronounced Bragg reflection broadening effects found in laboratory-scale powder diffraction patterns of industrial VPO catalysts are real and not due to an insufficient 2-θ resolution of the apparatus. In the framework of this work, a powder diffraction full profile fitting strategy was developed using the TOPAS software, which was applied to analyze the X-ray diffraction data of four differently activated industrial catalyst samples, originating from one batch after they had been catalytically tested. It was found that the reflection broadening is mainly caused by an anisotropic crystal size, which results in platelet-shaped crystallites of vanadyl pyrophosphate. A further contribution to the reflex broadening, especially for (111), was found to be a result of stacking faults perpendicular to the a direction in the crystal structure of vanadyl pyrophosphate. These results were used to elaborate on possible correlations between structural proxies and catalytic performance. A direct correlation between the extension of coherently scattering domains in the z direction and the catalyst's selectivity could be proven, whereas the activity turned out to be dependent on the crystallite shape. Regarding the phase contents, it could be shown that sample catalysts containing a higher amount of β-VO(PO3)2 showed increased catalytic activity. [ABSTRACT FROM AUTHOR]

Prepared unique mesh-hole structure of VPO catalyst by POM-ILs anions-cations synergetic Interaction for promoting C H bond activation. • Design a single-component additive POM-ILs with dual-function to enhance the activity of VPO catalyst. • The synergistic interaction of anions and cations of POM-ILs was illuminated. • POM-ILs@VPO shows unique mesh-hole structure and forms more oxygen vacancies and crystal defects. • POM-ILs@VPO exhibits high activation ability of C–H bond. • Finely divide the poly-acids (α , β , γ -acid) sites to describe the acidic properties. Vanadyl pyrophosphate (VPO) catalyst exhibits a unique ability to activate C H bond and selectively oxidize n- butane to maleic anhydride (MA). Here, a novel "function-oriented design" strategy was proposed to design and develop single-component additive polyoxometalate-ionic liquids (POM-ILs) with dual-function to enhance the activity of VPO catalyst. And the synergistic interaction of anions and cations of POM-ILs was illuminated combined with characterizations. The IL-cations guide the growth of the catalyst precursor to ordered nanolamellar structure rather than three-dimensional disordered rose-like. Correspondingly, it makes the catalyst exhibit a unique mesh-hole structure and benefit exposure of the active surface (200) of (VO) 2 P 2 O 7. The POM-anions decompose into the defective O P Mo compound and cause more oxygen vacancies and crystal defects formed on the surface of VPO after activation. Besides, we established a specific method to divide the poly-acids (α , β , γ -acid) sites to describe the acidic properties on the surface of VPO by NH 3 -TPD in qualitatively and quantitatively and related with catalytic performance. [ABSTRACT FROM AUTHOR]