Ammoxidation Reaction Research Articles

Ethane Ammoxidation over Sn/H-Zeolite Catalysts: Toward the Factors Contributing to the Yield of Acetonitrile.

Different Sn/H-zeolite (β, MOR, SSZ-13, FER, and Y zeolite) catalysts are prepared with the improved impregnation method. The effects of reaction temperature and the composition of the reaction gas (ammonia, oxygen, and ethane) on the catalytic reaction are investigated. Adjusting the fraction of ammonia and/or ethane in the reaction gas can effectively strengthen the ethane dehydrogenation (ED) route and ethylamine dehydrogenation (EA) route and inhibit the ethylene peroxidation (EO) route, whereas the adjustment of oxygen cannot effectively promote acetonitrile formation because it cannot avoid enhancing the EO route. By comparing the acetonitrile yields on different Sn/H-zeolite catalysts at 600 °C, it is revealed that the ammonia pool effect, the residual Brönsted acid in the zeolite, and the Sn-Lewis acid synergistically catalyze ethane ammoxidation. Moreover, a higher L/B ratio of the Sn/H zeolite is beneficial to the improvement of acetonitrile yield. With a certain application potential, the Sn/H-FER-zeolite catalyst shows an ethane conversion of 35.2% and an acetonitrile yield of 22.9% at 600 °C; although a similar catalytic performance was observed on the best Co-zeolite catalyst in literature, the Sn/H-FER-zeolite catalyst is more selective to ethene and CO than the Co catalyst. In addition, the selectivity to CO2 is less than 2% of that on the Sn-zeolite catalyst. This may be attributed to the special 2D topology and pore/channel system of the FER zeolite, which guarantee an ideal synergistic effect of the ammonia pool, the residual Brönsted acid in the zeolite, and the Sn-Lewis acid for the Sn/H-FER-catalyzed ethane ammoxidation reaction.

Excellent hydrocarbon tolerance of CeO2-WO3-SnO2 oxide catalyst for the NH3-SCR of NO

The tolerance of NH3-SCR catalysts towards hydrocarbon compounds (HCs) is very important for their practical application on diesel vehicles. In this study, the HC resistance of CeWSnOx, V2O5-WO3/TiO2 and Cu-SSZ-13 catalysts was systematically investigated using propene, toluene and n-pentane as model HCs. Experimental results suggested that the fresh and hydrothermally aged CeWSnOx showed much better HC tolerance than the Cu-SSZ-13 and V2O5-WO3/TiO2. This property mainly originated from the strong HC oxidation capacity of the CeWSnOx due to Sn introduction, which significantly inhibited side reactions, including the HC ammoxidation and the carbon deposition reactions. In contrast, an undesired HC ammoxidation reaction occurred at medium temperatures over the Cu-SSZ-13 and at medium-high temperatures over V2O5-WO3/TiO2, especially in the presence of propene, accompanied by the emission of toxic HCN gas. The high HC tolerance of CeWSnOx gives it promise for application on heavy-duty diesel after-treatment systems in the future, especially those with the SCR-on-DPF or cc-SCR configuration.

A Review of the Catalysts Used in Propane Ammoxidation Reaction to Produce Acrylonitrile

Abstract: Background: Various catalysts were studied to synthesize acrylonitrile via propane ammoxidation. The catalysts used for this process can be categorized as antimony-based catalysts, molybdenum-based catalysts, zeolites, nitride material catalysts, and other catalysts. The catalyst which was proved to be an efficient catalyst among all other catalysts is the mixed metal oxide catalyst MoVNbTe due to its high selectivity and yield.

Continuous-Flow Ammoxidation of 2-Methylpyrazine to 2-Cyanopyrazine with High Space-Time Yield in a Microreactor.

A microreactor (MR) with a vaporization microchamber and a sinusoidal wave microchannel was fabricated to synthesize 2-cyanopyrazine (CP) directly with an aqueous 2-methylpyrazine (MP) solution. A continuous-flow process with high space-time yield was achieved under the premise of strong exothermality of this ammoxidation reaction. The vanadium metal oxide catalysts with four different supports (α-Al2O3, γ-Al2O3, ZSM-5(50), ZSM-5(80)) were evaluated by simply stacking in the wave microchannel from 350 to 540 °C. The process parameters (temperature, reactant ratio, and size of catalysts) were optimized with the selected CrVPO/γ-Al2O3 catalyst, and an optimal ammoxidation process with MP conversion (XMP) of 71.5% and CP selectivity (SCP) of 93.7% was obtained by a volume space velocity (GHSV) of 13 081 h–1 at 480 °C. Correspondingly, the space-time yield of CP (STYCP) was 1724–77 082 gCPkgcat–1h–1, which was the highest value ever reported for this reaction. Meanwhile, the ammoxidation reaction showed a great continuous-synthesis stability of 50-h running in the microreactor with the CP yield (YCP) remaining 56%–68%.

Highly dispersed Co species in N-doped carbon enhanced the aldehydes ammoxidation reaction activity

Developing environmentally friendly catalysts with high activity for the ammoxidation of aromatic aldehydes to aromatic nitriles is greatly important for this industrial transformation. Herein, natural vitamin B12 was used as a carbon source for the preparation of a cobalt- and nitrogen-doped catalyst precursor, which was pyrolyzed at different temperatures to obtain cobalt- and nitrogen-doped carbon (Co@NC-T) (T denotes pyrolysis temperature) catalysts. The Co@NC-800 exhibited excellent activity and selectivity in the ammoxidation of aromatic aldehydes with ammonium carbonate to aromatic nitriles compared to the Co@NC-700, Co@NC-600 and Co@NC-500 catalysts. The high catalytic performance of Co@NC-800 could be due to the presence of the low-density electron cloud of the highly dispersed Co species, which could interact with the benzene ring of benzaldehyde bearing p-π conjugate, thereby promoting the adsorption and activation of benzaldehyde. Consequently, the activated benzaldehyde reacted with amino groups that were decomposed from ammonium carbonate and subsequently underwent a dehydration process to form nitriles.

Kinetic Study of Meta-Xylene Ammoxidation Reaction over a Commercial V–Cr Mixed Oxide Catalyst

The reaction behavior of meta-xylene ammoxidation on a commercial V–Cr mixed oxide catalyst (NC-IV) were studied in a fixed bed reactor, by kinetic modeling of experimental data of designed conditi...

Thermally stable imidazole/heteropoly acid composite as a heterogeneous catalyst for m-xylene ammoxidation

Ammoxidation of m-xylene is evaluated in the presence of a customized heteropoly acid catalyst as an imidazole/molybdovanadophosphoric acid (imidazole/PMoV). Imidazole is employed to maintain its heterogeneous phase during the ammoxidation reaction and to provide the thermal stability of PMoV with the expectation that imidazole can generate strong electronic interactions with terminal molybdenum-oxygen on PMoV. The characterizations of the prepared catalysts are performed using SEM–EDX, XRD, FT-IR, Raman, XPS, and TGA to prove the physical and chemical changes by incorporating imidazole to PMoV, respectively. Also, the thermal stability of the developed catalyst is confirmed by the means of heat treatment test at relatively high temperature. The composite catalyst, imidazole/PMoV, shows an excellent conversion rate of over 98% with high selectivity of isophthalonitrile in m-xylene ammoxidation. Moreover, while the imidazole-free PMoV catalyst is deactivated and washed out during the reaction, the catalyst durability of the imidazole/PMoV is preserved without significant activity loss after 5 reaction cycles at 380 °C.

Rapid scan FTIR reveals propane (am)oxidation mechanisms over vanadium based catalysts

Rapid scan FTIR coupled with Mass Spectrometry (MS) has been used to determine the role of spectroscopically observed species in the reaction media during propane dehydrogenation over a V/Al catalyst, and propane ammoxidation on a Sb-V-O sample. During the propane dehydrogenation reaction, it was shown that oxygenates are not formed during the first minutes and propylene is formed directly from propane via dehydrogenation on a V-O site. Oxygenates may form though secondary reactions due to further propylene oxidation. Propane dehydrogenation is the first step during the propane ammoxidation reaction. This is followed by the transformation of propylene into acrylonitrile, which is the rate limiting step. Rapid scan FTIR/MS is shown to be a useful technique for monitoring chemical reactions in order to identify or eliminate observed surface species as potential reaction intermediates. Understanding of the reaction mechanism is necessary in order to improve the chemical process design and the catalytic material.

Preparation and Characterization of SBA-15-Supported Vanadia Catalysts for Ammoxidation Reaction

Preparation and Characterization of SBA-15-Supported Vanadia Catalysts for Ammoxidation Reaction

Propane Versus Ethane Ammoxidation on Mixed Oxide Catalytic Systems: Influence of the Alkane Structure

Catalysts from three different catalytic systems, Ni–Nb–O, Mo–V–Nb–Te–O and Sb–V–O, have been prepared, characterized, and tested during both ethane and propane ammoxidation reactions, in order to obtain acetonitrile and acrylonitrile, respectively. The catalytic results show that Mo–V–Nb–Te–O and Sb–V–O catalyze propane ammoxidation but are inactive for ethane ammoxidation whereas Ni–Nb–O catalysts catalyze both, ethane and propane ammoxidation. The activity results, and the characterization of fresh and used catalysts along with some data from previous studies, indicate that the ammoxidation reaction mechanism that occurs in these catalytic systems is different. In the case of Mo–V–Nb–Te–O and Sb–V–O, two active sites appear to be involved. In the case of Ni–Nb–O catalysts, only one site seems to be involved, which underlines that the mechanism is different and take place via a different intermediate. These catalysts activate the methyl groups in ethane, on the contrary, neither ethane nor ethylene appear to adsorb on the Mo–V–Nb–Te–O and Sb–V–O active sites.

Probing the Structural Changes and Redox Behavior of Mixed Molybdate Catalysts under Ammoxidation Conditions: An Operando Raman Spectroscopy Study

AbstractMixed model molybdate catalysts that contain CoMoO4, Bi2Mo3O12, and Fe2Mo3O12 were investigated in the ammoxidation reaction of propene to acrylonitrile to study the redox behavior of the iron molybdate component. The flexible changes of the oxidation state of the Fe component during ammoxidation were followed by examining the intensity changes of the characteristic bands of Fe2Mo3O12 and FeMoO4 in the Raman spectra and could be correlated with the catalyst performance examined by simultaneous MS analysis. Depending on the catalyst composition and the oxygen content in the feed, Fe2Mo3O12 is reduced to a different extent, and consequently, FeMoO4 is formed, which is accompanied by a restructuring of the catalyst and the formation of nanostructured MoOx species. In accordance with previous investigations, operando Raman studies revealed that CoMoO4 and Bi2Mo3O12 influence the redox behavior of Fe2Mo3O12 in different ways.

Evaluation of M‐xylene ammoxidation at bench‐scale operation in the presence of V2O5/Γ‐Al2O3 catalyst

A bench‐scale ammoxidation reaction of m‐xylene was evaluated in the presence of V2O5/γ‐Al2O3 catalyst. The experiment was performed in a packed‐bed reactor with 25 mm i.d. using 200 g of catalyst. To alleviate sudden temperature hikes during ammoxidation, molten salt system was carefully built in the outer part of the reactor in a jacket‐type. Higher value of heat capacity of molten salt led to the stabilized reaction temperature within tolerable ranges without significant deactivation of catalytic activity. Isophthalonitrile (IPN) was a main product to compare reaction performance, while m‐tolunitrile, even hardly observed in a lab‐scale experiment, was a noticeable by‐product in this study. Reaction parameters include reaction temperature, oxygen to m‐xylene ratio, NH3 to m‐xylene ratio, and gas hourly space velocity. The selectivity of IPN over m‐tolunitrile was clearly improved when reaction temperature was raised from 320 to 380 °C. For a long‐term test, the reaction was evaluated in the period of one year. The catalyst was characterized before and after the long‐term experiment and its changes were analyzed by N2‐physisorption, SEM, XRD and XPS.

Propylene Adsorption On a Nonstoichiometric VSbO4(110) Surface

Density functional theory calculations were performed to investigate propylene adsorption on the nonstoichiometric VSbO4(110) surface. V and Sb sites and two extreme ways of propylene approximation to the surface were considered. Among the six computed configurations, the most stable geometry corresponds to a parallel approach on the surface on a Sb site. This geometry makes possible a simultaneous adsorption of NH3 on a V site during the ammoxidation reaction to acrylonitrile. Sb(5s and 5p orbitals) interactions with C(2p) from double bond C═C were found, and no interactions with H atoms of CH3 and CH2 were produced.

Mechanism of the Products Formation in the Vapor Phase Ammoxidation Reaction of 4-Phenyl-o-Xylene

On the basis of kinetic data of 4-phenyl-o-xylene and 4-phenyl-o-tolunitrile ammoxidation, formation mechanism of the products was analyzed and generalized. It has been shown that dissociative adsorption of a substrate and mononitrile occurs on the centers with high heats of adsorption of oxygen and as a consequence, completely covered with it, competitive adsorption of NH3 and O2 occurs on the centers with low heats of adsorption of the latter; mononitrile and dinitrile are formed correspondingly from adsorbed fragments of both substrate and NH3, and tolunitrile and NH3; surface interaction of adsorbed fragments of substrate and O2 with low heat of adsorption gives imide and CO2; hydrolysis of dinitrile into imide occurs on centers completely covered with ammonia; imide decarboxylation occurs on the centers covered with it; oxidative destruction of tolunitrile occurs on centers covered with substrate and mononitrile.

Catalytic Consequences of a Revised Distribution of Key Elements at the Active Centers of the M1 Phase of the MoVNbTeOx System

In an earlier publication (Grasselli et al., Top Catal 54:595, 2011) [1] we analyzed the distribution of key catalytic elements at the active site of the M1 phase of the MoVNbTeOx catalyst system based on the definition of this center put forth in our original work (Grasselli et al., Top Catal 23:5, 2003) [2]. From that analysis we derived the probabilities of the metal element distributions at the active center and its immediate surroundings, and based on those results, proposed a model for propane ammoxidation on M1. Recently, the occupancies and concomitant charges of the various elements of the M1 phase have been revised (Li et al., Top Catal 54:614, 2011) [3]. Based on this revised structural model we have now recalculated the elemental probabilities at the active center and its immediate surroundings, and describe here the catalytic consequences in the ammoxidation mechanism of propane that these changes portend. Our revised model (REV) predicts more closely the actual experimental results of propane ammoxidation over MoVNbTeOx than does our first model (ORIG). The results obtained are: ORIG Model: 41 % AN (acrylonitrile) concerted, 82 % total possible AN; REV Model: 43 % AN concerted, 59 % total possible AN; experimental: 42 % AN concerted, 62 % total possible AN using both the M1 + M2 phases. Comparing the original (Grasselli et al., Top Catal 23:5, 2003) [2] and current (Li et al., Top Catal 54:614, 2011) [3] elemental distributions at the active centers of M1 and the ORIG and REV ammoxidation reaction pathways (from the derived models), it is readily apparent that higher concentrations of V5+ at the active centers lead to undesirable overoxidation of propane and thus lower AN selectivity. Therefore, decreasing the surface concentration of vanadium in M1 (to favor more site isolated V5+ sites) should be beneficial and lead to better AN selectivities and yields. Additionally, selective doping or selective isomorphous substitution of M1 (and/or M2) should also be useful approaches towards improved AN yields.

Comparison of Different Chemical Processes from a Life Cycle Perspective

Life Cycle Assessment methodology was applied to the industrial sector, with the aim to evaluate the environmental sustainability of different chemical processes. In particular, the ammoxidation reaction to produce acrylonitrile was chosen as a case study, comparing the environmental loads of the traditional process (SOHIO) with the alternative routes starting from propane on the base of the same amount of acrylonitrile produced (1 kg). Information reported on patents, and data collected on Ecoinvent 2.2 database were used to create each ammoxidation scenario in SimaPro 7.3.3 software. The system boundaries of the study include the main production stages on industrial scale: reaction flows, heat exchange, raw materials for catalyst manufacture, the main plant emissions and transportation phase. The comparison was carried out using ReCiPe 2008 method, expressing results in terms of midpoint impact categories, as: climate change (both damage on human health and on ecosystem), particulate matter formation, fossil fuel depletion and metal depletion. Results show how the alternative routes starting from propane seem to have higher potential impact than the traditional SOHIO process, due to the lower catalysts activity. Also, to quantify the environmental load of ammoxidation processes a comparison with other common chemical industrial productions was done. This simplified approach is able to show the environmental impacts of the ammoxidation scenarios in a broader industrial context.

The Influence of Phosphorous Precursor on the Structure and Ammoxidation Activity of Molybdenum Phosphate Catalysts

Two series of molybdenum phosphate catalysts were synthesized by reacting ammonium heptamolybdate with (1) diammonium hydrogen phosphate and (2) ammonium dihydrogen phosphate. The structural and textural properties of the catalysts, formed during the calcination between 400 and 550 °C, were determined by physico-chemical methods and their catalytic activity evaluated in the ammoxidation of 2-methylpyrazine (MP). The catalysts formed using diammonium hydrogen phosphate displayed higher activity and selectivity during the ammoxidation reaction as compared to those prepared using ammonium dihydrogen phosphate. Formation of a regenerable Mo(OH)3PO4 appears to be responsible for the higher performance of the catalyst.

Catalytic activity and characterization of V2O5/γ-Al2O3 for ammoxidation of m-xylene system

An ammoxidation of m-xylene was evaluated in a fixed-bed reactor using V2O5 on various oxides. Catalysts were prepared by wet impregnation method. At first, the loading of V2O5 was varied from 5 wt% to 20 wt% on γ-Al2O3 support to estimate the most effective amount of V2O5. Second, the effect of catalyst supports was examined at 10 wt% loading of V2O5. V2O5/TiO2 and V2O5/SiO2 catalysts were employed to compare the ammoxidation reaction with V2O5/γ-Al2O3. Most catalytic activity was observed when γ-Al2O3 was used as a support. Careful characterization was followed by physicochemical techniques, such as BET measurement, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). The results provided the clue that monolayer V2O5 was favorably dispersed on the surface of γ-Al2O3 up to 10 wt%, which led to the highest yield of isophthalonitrile (IPN).

Titanium Containing Solid Core Mesoporous Silica Shell: A Novel Efficient Catalyst for Ammoxidation Reactions

Novel titanium containing solid core mesoporous shell silica has been synthesized by using octadecyltrichloro silane and triethylamine. The synthesized material was characterized by various physicochemical techniques. The mesoporous character of the material has been revealed from PXRD studies. The presence of octadecyltrichloro silane and triethylamine in the sample has been confirmed from EDAX studies. TG/DTA analysis reveals the thermal characteristics of the synthesized material. The presence of titanium in the frame work and its coordination state has been studies by UV-vis DR studies and XPS analysis. Chemical environment of Si in the framework of the material has been studied by 29 SiMASNMR studies. The surface area of the material is found to be around 550 m 2 g �1 and pore radius is of nano range from BET analysis. The spherical morphology and particle size of the core as well as shell has been found to be 300 nm and 50 nm respectively from TEM analysis. The catalytic application of this material towards the synthesis of caprolactam from cyclohexanone in presence of hydrogen peroxide through ammoxidation reaction has been investigated. The optimum conditions for the reaction have been established. The plausible mechanism for the formation of core silica and conversion of cyclohexanone has been proposed.

Niobia-Supported Nanoscaled Bulk-NiO Catalysts for the Ammoxidation of Ethane into Acetonitrile

Two series of supported nanoscaled NiO catalysts have been prepared using Nb2O5 supports with different surface areas. NiO nanoparticles interacting with Ni–O–Nb mixed phases are active and selective for ethane ammoxidation; both are required in order to have an active and selective catalyst. In this paper we report the dispersion of NiO nanoparticles on two Nb2O5 supports in order to generate an active phase for ethane ammoxidation. The use of a support stabilizes NiO nanoparticles, which otherwise would sinter. This work shows how the activity can be modulated by the size of the NiO nanoparticles and by the NiO/Ni–Nb–O ratio, which depends on the nickel coverage and support surface area. The catalysts obtained are very promising for ethane ammoxidation reaction.