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The preparation of vanadium-phosphate catalysts by Atomic Layer Deposition (ALD) was studied for application to selective oxidation of n-butane to maleic anhydride (MA). Modification of bulk V2O5 by ALD with trimethylphosphate significantly increased the selectivity to MA but the catalyst performance was still much worse than that observed for bulk vanadium phosphate (VPO). Silica-supported VPO was then prepared by ALD of P and V and compared to a VPO/SiO2 catalyst prepared by impregnation. Raman spectra showed that the ALD-prepared materials were more homogeneous, and temperature-programmed desorption of 2-propanol demonstrated that the VPO phase covered the silica more uniformly when deposited by ALD. However, the bulk VPO catalyst remained the most selective for MA. Possible reasons for why the supported catalysts showed lower performance are discussed and suggestions made for improving these catalysts. [ABSTRACT FROM AUTHOR]

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.

Vanadium phosphorus oxide (VPO) was immobilized on SBA-15 via a facile impregnation process. The structure and VPO species on SBA-15 were characterized by XRD, TEM, BET, FTIR and XPS techniques. It was found the VPO/SBA-15 catalysts maintained the two-dimensional hexagonal structure of SBA-15, and the supported VPO species existed in a highly dispersed amorphous state. VPO/SBA-15 catalyst was tested for the ammoxidation of dichlorotoluenes (DCTs) to corresponding dichlorobenzonitriles (DCNs) in a lab-scale tube reactor. Compared with VPO/SiO2 (large-pore silica-supported VPO), VPO/SBA-15 exhibited appreciable enhancement in the catalytic performance due to the unique channel structure of SBA-15. The yield and selectivity toward 2,4-DCN increased by 7% and 6%, while toward the sterically hindered 2,6-DCN increased by 7% and 13%, respectively. [ABSTRACT FROM AUTHOR]

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]

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, N 2 physisorption, SEM, HRTEM, H 2 -TPR and NH 3 -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) 2 P 2 O 7 ] phase. The vanadium redox centers were easily accessible for supported VPO catalyst. The TUD-1 supported VPO catalyst had higher acidity as found in NH 3 -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. [ABSTRACT FROM AUTHOR]

The vanadium phosphorous oxide (VPO) catalysts, supported on Santa Barbara amorphous molecular sieve (SBA-15) with different vanadium loadings, were prepared by the precipitation method in an organic phase. Techniques such as X-ray diffraction, Bruner–Emmett–Teller method, scanning electron micrograph (SEM), and transmission electron micrograph (TEM) were used for characterization of the catalysts. The high surface area, large pore volume, and pore size of SBA-15 provide an excellent dispersion of (VO)2P2O7species on the support surface. Oxidation of various alcohols was studied in the liquid phase over the VPO/SBA-15 catalyst, usingtert-butylhydroperoxide as an oxidant. The activities of VPO/SBA-15 samples were considerably higher than that of the bulk VPO catalyst. At 90°C, the obtained activities were 0.567 andover the bulk VPO and 15 wt.% VPO/SBA-15 catalysts, respectively. The effects of substrates, oxidants, reaction time, oxidant/alcohol molar ratio, solvents, amount of catalyst, catalyst recycling, and leaching of VPO in the liquid phase were also investigated. [ABSTRACT FROM PUBLISHER]

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]