Formation Of Acrylic Acid Research Articles

Structure and properties of a Mo oxide catalyst supported on hollow carbon nanofibers in selective propene oxidation

In situ X-ray absorption spectroscopy (XAS) under reaction conditions of selective propene oxidation was employed to elucidate the local structure of as-prepared and activated molybdenum oxide supported on hollow vapor-grown carbon nanofibers (VGCNF). The local structure of as-prepared Mo x O y -VGCNF was very similar to that of hexagonal MoO 3. During heat treatment in propene- and oxygen-containing atmosphere, as-prepared Mo x O y -VGCNF transforms into activated Mo x O y -VGCNF above 623 K. The local structure around the Mo centers in activated Mo x O y -VGCNF is similar to that of α-MoO 3. Temperature- and time-dependent XAS measurements showed a rapid transformation from hex-MoO 3 to α-MoO 3 supported on VGCNF under reaction conditions. Subsequently, the resulting activated Mo x O y -VGCNF catalyst exhibited a slowly increasing average oxidation state. The latter coincided with the formation of acrylic acid, which is hardly detectable during catalysis on regular, binary α-MoO 3. Moreover, activated Mo x O y -VGCNF is much more active in the selective oxidation of propene compared to α-MoO 3. The correlation between catalytic selectivity and average oxidation state as a result of suitable reduction–oxidation kinetics corroborates the importance of structural complexity rather than chemical complexity.

Electrical conductivity of a MoVTeNbO catalyst in propene oxidation measured in operando conditions

A complex ac electrical conductivity study was performed on a Te 0.33 MO 3.33 ( M = Mo + V + Nb) pure phase (M2-type phase) in operando conditions, using the differential step technique (DST). The aim is to obtain new information about the influence of the oxidation and moisture on the catalytic behaviour of this phase in propene oxidation to acrylic acid. Three successive series of experiments were performed on the same batch of sample: (i) cycles of heating (up to 300, 350 and 400 °C, respectively)–cooling (to room temperature) in inert and in the catalytic test mixture, without intermediate oxidation; (ii) the same, but intercalating heating–cooling oxidation cycles (up to 300, 350 and 400 °C, respectively) before the corresponding catalytic test runs; and (iii) catalytic testing runs performed by heating up to 400 °C in the presence of pre-absorbed or co-adsorbed humidity. Based on the electrical conductivity results, it appears that 350 °C is a critical temperature in terms of surface reduction/re-oxidation: below this temperature no major surface changes of the relative oxidation level occur on flushing in dry helium or in the catalytic test mixture, while above it, an important reduction occurs in the same atmospheres. Re-oxidation in oxygen is not efficient if performed below 350 °C, but if done above (up to 400 °C) the surface recovers almost the initial behaviour. These results suggest the reversibility of the oxidation state of the catalyst surface, which is important in the practical use of this material. The activity and selectivity of acrylic acid formation are discussed in relation with the relative levels of oxidation/reduction of the surface.

Enhancement of acrylic acid yields in propane and propylene oxidation by selective P Doping of MoV(Nb)TeO-based M1 and M2 catalysts

Selective doping of (M1) Mo7.8V1.2NbTe0.94O28.9 and (M2) Mo4.67V1.33Te1.82O19.82 phases with P significantly enhance acrylic acid yields (2-15%) in propane/propylene oxidation. Amorphous overlayers (Te-molybdate) seriously inhibit acrylic acid formation. Detailed mechanisms are presented.

The influence of additives and their concentration on the selectivity of catalysts based on heteropoly compounds in the reaction of propane oxidation

The catalytic properties and X-ray phase structure of molybdophosphoric heteropoly acid modified with Sb, W, and Nb ions have been studied in the reaction of propane oxidation. The additive of Nb ions increases the total activity of catalyst and its selectivity to acrolein and acrylic acid and decreases the selectivity to propylene. The concentration of Nb ions in samples is varied from 0.025 to 1 mol %. The concentration of Nb ions at a level of 0.025–0.1 mol % has the most profound effect on the reaction selectivity and the yield of mild oxidation products. The reaction selectivity depends on both the concentration of added niobium and the reaction conditions. The growth in the reaction temperature increases the conversion and selectivity to acrolein and reduces the selectivity to acrylic acid and propylene. The use of reaction mixture with higher propane concentrations decreases sharply the selectivity to acrolein. The obtained data can be explained by the possibility of the rearrangement of Nb ions between the cationic and anionic sublattices of heteropoly acids and by the change in the ratio between the acrolein and acrylic acid formation rates. The development and application of heteropoly compounds modified with niobium permits to increase the yield of target products in the partial propane oxidation.

Influence of gel composition in the synthesis of MoVTeNb catalysts over their catalytic performance in partial propane and propylene oxidation

MoVTeNb mixed oxides catalysts have been prepared by a slurry method with different molar compositions (Mo/Te ratio from 2 to 6 and Nb/(V + Nb) ratio from 0 to 0.7) in the synthesis gel leading to different crystalline phases distribution and catalytic behaviour in the partial oxidation of both propane and propylene to acrylic acid. Chemical analysis indicates that the composition of samples before and after the heat-treatment changes, especially the Te-content, since a significant amount of Te is lost during the heat-treatment step when the amount of oxalate (from niobium oxalate) increases in the synthesis gel. Thus, the nature of the crystalline phases and the catalytic performance of heat-treated materials will be related to the final chemical composition. On the other hand, only the catalysts presenting Te 2M 20O 57 (M = Mo, V, Nb) crystalline structure, the so-called M1 phase, were active and selective in the partial oxidation of propane to acrylic acid. Moreover, all catalysts were active and relatively selective to the formation of O-containing products, i.e. acrolein and/or acrylic acid, during the partial propylene oxidation although the more active ones were those presenting M1 phase.

Bi 4Cu 0.2V 1.8O 11−δ based electrolyte membrane reactor for selective oxidation of propane to acrylic acid

An electrochemical membrane reactor using Bi 4Cu 0.2V 1.8O 11−δ as a solid electrolyte membrane was employed to investigate the selective oxidation of propane to acrylic acid over a MoV 0.3Te 0.17Nb 0.12O catalyst. By applying an external current to the membrane reactor, the ionic oxygen was pumped to the surface of the MoV 0.3Te 0.17Nb 0.12O catalyst, which exhibited higher conversion of propane and selectivity to acrylic acid than that in the fixed-bed reactor. The results indicate that the enhancement of catalytic performance in the membrane reactor is mainly due to the presence of the lattice oxygen, which has been proved to be necessary for the formation of acrylic acid. Thus, the Au/Bi 4Cu 0.2V 1.8O 11−δ/Au/MoVTeNbO membrane reactor achieved a higher conversion of propane (42%) and selectivity to acrylic acid (79.6%) at 380 °C with a 0.6 A current.

Selected ion flow tube studies to investigate the formation of acrylic and propionic acid protonated clusters in low power, low pressure RF plasmas

A selected ion flow tube is used to investigate ion-molecule reactions in acrylic acid plasma; (nM + H)(+) ions form through transfer of H(+) from H(3)O(+) and further clustering of acrylic acid molecules.

Influence of the Reducing Atmosphere on the Structure and Activity of Mo-V-Te-Nb-O Catalysts for Propane Selective Oxidation

The effects of the addition of the reductant (ammonium chloride) on Mo-V-Te-Nb-O mixed oxide catalysts for propane selective oxidation to acrylic acid were systematically investigated. The presence of the reductant during catalyst preparation had a significant impact on the mobility of lattice oxygen mainly responsible for the catalytic activity of the Mo-V-Te-Nb-O catalysts. Furthermore, the addition of the reductant resulted in clear changes in catalyst morphology and phase composition, which are important factors in the formation of acrylic acid. A high content of the orthorhombic M1 phase led to a high selectivity to acrylic acid at low temperatures ( 653 K).

How important is the (001) plane of M1 for selective oxidation of propane to acrylic acid?

The role of the (001) crystallographic plane of the M1 phase of MoVTeNb mixed-oxide catalysts in selective oxidation of propane to acrylic acid was addressed by investigating a phase-pure M1 material preferentially exposing this surface. A model catalyst was prepared by complete silylation of M1, followed by breakage of the SiO 2-covered needles. Using this approach, the reactivity of the M1 (001) surface was investigated by combining a microreactor study of propane oxidation with high-sensitivity low-energy ion scattering (HS-LEIS). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the shape and microstructure of the model system and verify the surface exposure of the model catalyst. The specific rate of formation of acrylic acid on the model catalyst was found to be similar to that on the phase-pure M1 reference material, indicating that the (001) plane of the M1 crystal structure did not have better catalytic properties compared with the lateral surface of M1 needles in propane oxidation.

Degradation of 1,4-Dioxane by Photo-Fenton Processes

1,4-Dioxane is an EPA priority pollutant found in contaminated groundwater and industrial effluents. The common treatment techniques are not effective for 1,4-dioxane degradation. Thus there is a need to find an efficient degradation method such as a photo-Fenton process and understand the degradation mechanism of 1,4-dioxane during such reactions. In this study, the effect of the reaction parameters such as initial concentration of 1,4-dioxane, H2O2 and FeSO4 dosages, and UV light intensity on 1,4-dioxane degradation has been examined. Under optimal conditions, over 95% of 1,4-dioxane is degraded by photo-Fenton (UV with H2O2 and FeSO4), while little 1,4-dioxane is degraded by FeSO4 alone. It was proposed that 1,4-dioxane was oxidized by OH radicals and sequentially led to formation of malonic acid, formic acid and acrylic acid. Based on the experimental results of 1,4-dioxane, the application of advanced oxidation processes (AOPs) appears to be a promising alternative for 1,4-dioxane removal in various environment systems.

Nanoscale Elastic and Tribological Properties of Poly(Acrylic Acid) Superabsorbent Gels

ABSTRACTUltrasonic Force Microscopy and Friction Force Microscopy have been applied to the characterization of the elastic and tribological responses of poly(acrylic acid) hydrogels at ambient conditions. The gels were prepared by free radical polymerization of acrylic acid monomers partially neutralized by sodium hydroxide, using N, N'-methylen-bis-acrylamide as a crosslinker. Nanoscale domains with different stiffness and friction are observed. Increasing the amount of crosslinker leads to the formation of smaller, more densely packed domains. The domains with higher stiffness also exhibit higher friction and lower topographic high. The results can be understood by assuming that (i) neutralization by sodium hydroxide leads to the formation of both acrylic acid and sodium acrylate polymeric strands (ii) the observed domains differ in their acrylic acid / sodium acrylate content. In the acrylic acid rich domains, hydrogen bonding among the polymeric strands explains a higher stiffness and lower topography. In the sodium acrylate rich domains, lubrication by water molecules linked by solvation to the sodium counterions accounts for a lower friction.

Characterization, chain mobility, and thermal properties of the hydrophilic poly(methyl methacrylate‐co‐acrylic acid) colloids

AbstractAn amphiphilic colloidal copolymer containing methyl methacrylate (MMA) and sodium acrylate at different compositions was prepared by a free‐emulsion polymerization method with potassium persulfate as an initiator, and it was then doped in HCl solution to obtain the acid form poly(methyl methacrylate‐co‐acrylic acid) (PMMAA) copolymer. The copolymers were characterized by means of gel permeation chromatography, 1H nuclear magnetic resonance spectrometer, 13C solid‐state nuclear magnetic resonance spectrometer, infrared spectra, and differential scanning calorimeter. The copolymers have only a single, and nearly constant, glass transition temperature of 124°C, at which there is no observable effect on the structure of the copolymer. The monomer reactivity ratios rNaAA and rMMA were rNaAA = 1.06, rMMA = 0.70 and rNaAA = 1.02, and rMMA = 0.63 estimated respectively by using the classical Fineman‐Ross and the Kelen‐Tüdös methods. The results revealed that the copolymer had a tendency towards the formation of small acrylic acid blocks that have very short segments of MMA. The proton spin‐lattice relaxation time in the rotating frame T indicated single composition‐dependent for all copolymers, which imply dynamic homogeneity and a good miscibility with chain dynamics on the upper spatial scale of 3 nm existed in the PMMAA copolymer. An increase of the thermal stability of the copolymers was shown from the apparent activation energy of the thermal degradation process for the copolymers relative to the homopolymers. POLYM. COMPOS., 29:37–44, 2008. © 2007 Society of Plastics Engineers

Characterization and evaluation of Mo [sbnd]V [sbnd]Te [sbnd]Nb mixed metal oxide catalysts fabricated via hydrothermal process with ultrasonic pretreatment for propane partial oxidation

Mo 1.00V x Te 0.20Nb 0.16O n ( x = 0.35 – 0.50 ) mixed-metal oxide catalysts were synthesized through ultrasonic and hydrothermal treatments. Both TeO 2 and H 6TeO 6 were used as tellurium sources. The enhanced dispersion of TeO 2 by ultrasonic treatment is crucial for obtaining an active and selective Mo V Te Nb O catalyst for acrylic acid (AA) formation from propane oxidation. The TeO 2-derived Mo 1.00V x Te 0.20Nb 0.16O n ( x = 0.35 – 0.41 ) are superior to their H 6TeO 6-derived counterparts; propane conversion and AA selectivity over the Mo 1.00V 0.41Te 0.20Nb 0.16O n is 55% and 60 mol% at 380 °C, respectively, giving an AA formation rate of 22.3 μmol g −1 min −1. Based on the physicochemical properties of the catalysts, we propose that the ultrasonic treatment can give rise to (i) enhanced presence of the orthorhombic Te 2 M 20 O 57 ( M = Mo , V, Nb) and hexagonal Te 0.33 MO 3.33 ( M = Mo , V, Nb) phases, (ii) surface enrichment of Te, (iii) enhanced reactivity of lattice oxygen, (iv) an increase in Mo O Te and V O Te entities, and (v) better isolation of active sites.

Selective oxidation of propane and ethane on diluted Mo–V–Nb–Te mixed-oxide catalysts

Te-free and Te-containing Mo–V–Nb mixed oxide catalysts were diluted with several metal oxides (SiO 2, γ-Al 2O 3, α-Al 2O 3, Nb 2O 5, or ZrO 2), characterized, and tested in the oxidation of ethane and propane. Bulk and diluted Mo–V–Nb–Te catalysts exhibited high selectivity to ethylene (up to 96%) at ethane conversions < 10 % , whereas the corresponding Te-free catalysts exhibited lower selectivity to ethylene. The selectivity to ethylene decreased with the ethane conversion, with this effect depending strongly on the diluter and the catalyst composition. For propane oxidation, the presence of diluter exerted a negative effect on catalytic performance (decreasing the formation of acrylic acid), and α-Al 2O 3 can be considered only a relatively efficient diluter. The higher or lower interaction between diluter and active-phase precursors, promoting or hindering an unfavorable formation of the active and selective crystalline phase [i.e., Te 2M 20O 57 (M = Mo, V, and Nb)], determines the catalytic performance of these materials.

Electrochemical Investigations of 3-(3-Thienyl) Acrylic Acid Protected Nanoclusters and Planar Gold Surfaces

Formation of self assembled monolayers on gold surface by thiols and disulphides is a well known phenomenon and extensive research work has been carried out in this area with envisaged applications in the area of sensors, molecular electronics, lithography, device fabrication using bottom-up approach, etc. Recently, it has been established that thiophene molecules can self assemble on gold surface due to Au-S interactions. 3-(3-thienyl) acrylic acid, a bifunctional ligand is used in this work to form self-assembled monolayers on planar gold surfaces (two dimensional assemblies) and to prepare monolayer protected gold nano clusters (three-dimensional assemblies). The electron transfer blocking properties of the two-dimensional monolayers were evaluated by using standard redox probes like ferrocyanide anions and Ruthenium hexamine cations. The functionalisation of the two-dimensional and three-dimensional assemblies has been carried out with ferrocene carboxylic acid and the functionalised monolayers were characterized by Cyclic voltammetry. The formation of thienyl acrylic acid protected nanoclusters has been verified by TEM and surface plasmon resonance absorption. It has been observed that when thiophene based ligands are used as stabilizers for the formation of metal nanoparticles, they tend to aggregate as a result of pi-pi interactions between adjacent thiophene ligands. In this case it is found that aggregation is prevented. The substituent at the thiophene ring hinders pi-pi interactions. The quantised nature of electrochemical charging of these nanoparticles has been demonstrated by differential pulse voltammetry (DPV), which exhibit peak like features (coulomb's staircase). This work also explores the possibility of using 3-(3-thienyl) acrylic acid as building blocks or spacers on planar and colloidal gold surfaces for potential applications in the field of sensors and devices.

What is the enthalpy of formation of acrylic acid?

Acrylic acid is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious—even ignoring “ancient” determinations, there is a 12 kJ mol−1 range of values reported for the gas phase quantity, −320 to −332 kJ mol−1. Our quantum chemical calculations using current methodology suggest the value of −321 ± 3 kJ mol−1.

A key step in the formation of acrylic acid from CO2and ethylene: the transformation of a nickelalactone into a nickel-acrylate complex

The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.

Oxidative conversion of propane to acrylic acid and acetic acid over mixed oxide catalysts

The oxidative conversion of propane to acrylic acid and acetic acid over MoVSbRO (RLa, Ce, Nd and Sm) catalysts at different reaction conditions (viz. temperature, C3H8/O2 ratio, H2O/C3H8 ratio, space velocity, etc.) was investigated. The catalytic activity and selectivity of the MoVSb catalyst are strongly influenced by the addition of rare earth metals to the catalyst. The addition of water vapour to the feed of propane and oxygen enhances greatly the formation of oxygenated products, particularly acrylic acid and acetic acid. The ratio of selectivities of acrylic acid to acetic acid was found to depend on the rare earth metal used in the catalyst's preparation and the reaction conditions. High contact times, i.e. high degrees of propane conversion, are detrimental to the formation of acrylic acid but beneficial for acetic acid formation. Copyright © 2005 Society of Chemical Industry

A Study of the Surface Region of the Mo−V−Te−O Catalysts for Propane Oxidation to Acrylic Acid

The bulk mixed Mo-V-Te oxides possess high activity and selectivity in propane oxidation to acrylic acid and represent well-defined model catalysts for studies of the surface molecular structure-activity/selectivity relationships in this selective oxidation reaction. The elemental compositions, metal oxidation states, and catalytic functions of V, Mo, and Te in the surface region of the model Mo-V-Te-O system were examined employing low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). This study indicated that the surfaces of these catalysts are terminated with a monolayer, which possesses a different elemental composition from that of the bulk. The rates of propane consumption and formation of propylene and acrylic acid depended on the topmost surface V concentration, whereas no dependence of these reaction rates on either the surface Mo or Te concentrations was observed. These findings suggested that the bulk Mo-V-Te-O structure may function as a support for the unique active and selective surface monolayer in propane oxidation to acrylic acid. The results of this study have important practical consequences for the development of improved selective oxidation catalysts by introducing surface metal oxide components to form new surface active V-O-M sites for propane oxidation to acrylic acid.

The influence of Te-precursor in Mo-V-Te-O and Mo-V-Te-Nb-O catalysts on their catalytic behaviour in the selective propane oxidation

A comparative study on the catalytic behaviour of Mo-V-Te-Nb-O and Mo-V-Te-O catalysts prepared from Te 6+- or Te 4+-containing precursors, i.e. H 6TeO 6 and TeO 2, respectively, in the absence or in the presence of Nb oxalate and/or oxalic acid is presented. The characterization of catalysts by X-ray diffraction (XRD), diffuse reflectance and photoelectron spectra (XPS) before and after the calcination step suggests that the nature of metal precursors in the synthesis gel strongly modifies both the nature of crystalline phases and the oxidation state of reducible metals. The catalytic activity (and probably the incorporation of vanadium in the crystalline structures) is favoured by using a Te 6+-containing precursor and Nb oxalate or a Te 4+-containing precursor. However, Nb-containing catalysts present the better catalytic performance in the selective oxidation of propane to acrilic acid suggesting an important influence of the presence of Nb 5+ cations in the catalysts on the formation and/or stability of acrylic acid.