Propane Ammoxidation Research Articles

Reduction characteristics of Fe‐Bi‐P mixed oxide catalysts and their ammoxidation activities of propylene

AbstractThe characteristics of Fe‐Bi‐P mixed oxide catalysts of different compositions for reduction by propylene or ammonia and the ammoxidation activities of propylene were studied using a McBain type thermobalance and the pulse reaction technique respectively. By comparing the dependency of the reduction characteristics and catalytic activity with oxide composition and also the reduction rates and reoxidation rates of the reduced catalyst it was concluded that the ammoxidation of propylene on Fe‐Bi‐P mixed oxide catalyst proceeds through alternate repetition of reduction by propylene and reoxidation by oxygen, and that abstraction of allylic hydrogen from adsorbed C3H6 is the rate determining step.

Ammoxidation of propylene by pulse reaction technique

AbstractThe ammoxidation of propylene on Fe‐Bi‐P mixed oxide catalyst was studied at 500 °C by the pulse reaction technique, to examine the effects of P(P = 0–4) and P (P/P = 0–3) on the catalyst activity. Since the ammoxidation of propylene proceeds through consumption of oxygen from the catalyst even in the absence of oxygen, the reduction of catalyst progresses with the number of O2‐free pulse, losing its activity. In the presence of oxygen, however, the conversion of propylene and the selectivities of acrylonitrile, acetonitrile, CO2, and CO vary with the pulse number, but settle to some steady values corresponding to P/P. It is also found that the conversion and the selectivities depend on the oxidation state of the catalyst, the latter also depending on P/P in the reactants, and that the catalyst working in the flow system may be being reduced to some extent.

The ammoxidation of propylene and isobutene over a tin-vanadium-phosphorus oxide catalyst

Studies have been made of the ammoxidation of propylene and isobutene over a tin oxide-vanadia-phosphorus oxide catalyst. Values of the kinetic parameters based on initial rates are reported for the ammoxidation of the olefins to unsaturated nitriles and to other products. The results are consistent with a mechanism in which the abstraction of an allylic hydrogen from the adsorbed olefins by adsorbed peroxy species is rate determining. The reaction is suggested to occur at Sn 4+ surface sites from which electron transfer to neighboring vanadium ions is possible.

ChemInform Abstract: ON THE MECHANISM OF AMMOXIDATION OF PROPENE OVER CERIUM‐DOPED BISMUTH MOLYBDATE CATALYSTS

The origin of the products of the ammoxidation of propene over cerium-doped silica supported bismuth molybdates was derived from the effects of temperature (380°-480°C) on overall conversion and selectivity in fixed-bed operations. At low (< 80 %) conversion levels, the ammoxidation reaction leads to acrylonitrile at Mo(VI) active sites and to by-products (HCN, acetonitrile, CO and CO2) at Mo(V) sites; at the highest conversions, by-products derive from consecutive oxidation of acrylonitrile.

On the mechanism of ammoxidation of propene over cerium‐doped bismuth molybdate catalysts

AbstractThe origin of the products of the ammoxidation of propene over cerium‐doped silica supported bismuth molybdates was derived from the effects of temperature (380°‐480°C) on overall conversion and selectivity in fixed‐bed operations. At low (&lt; 80 %) conversion levels, the ammoxidation reaction leads to acrylonitrile at Mo(VI) active sites and to by‐products (HCN, acetonitrile, CO and CO2) at Mo(V) sites; at the highest conversions, by‐products derive from consecutive oxidation of acrylonitrile.

The adsorption of butene, butadiene, and ammonia on UO3$z.sbnd;Sb2O3 catalysts

The adsorption equilibria of butene-1, butadiene, and ammonia were studied on antimony-uranium oxide catalysts. On UO 3 and U 3 O 3 , which are nonselective oxidation catalysts, there is strong and irreversible adsorption of butene-1. However, butene-1 was found to be adsorbed rapidly but weakly and reversibly on USb 3 O 10 which proved to be active and selective for the oxidation of olefines. Similar types of adsorption sites for butene-1, butadiene and ammonia on Bi 2 MoO 6 were observed on USb 3 O 10 . From these results a surface reaction site model is proposed which refers to special mobile bulk oxygens in rows on USb 3 O 10 and is very similar to that given earlier for Bi 2 MoO 6 . On the basis of this model the mechanism of the ammoxidation of propene to acrylonitrile was discussed.

Olefin oxidation and ammoxidation studies over molybdate, tungstate, and vanadate catalysts having point defects

Point defects in the form of cation vacancies (φ) have been introduced into molybdates, tungstates, and vanadates with the scheelite-type crystal structure according to A1 − xφxMO4. Such defect phases have been examined as catalysts for many different reactions, but the primary emphasis has been on olefin oxidation and ammoxidation. The catalytic activity in the system Pb1 − 3xBi2xφxMoO4 has been studied for the ammoxidation of propylene to acrylonitrile. When x = 0, i.e., PbMoO4, there is essentially no activity. However, good catalytic activity is observed for x = 0.005, and the activity thereafter increases with increasing x. Conversions of propylene to acrylonitrile as high as 76% were obtained, and this is significantly higher than obtained for bismuth molybdates. The results were similar in other systems containing bismuth. Some other such systems studied were Pb1 − 3xBi2xφxWO4, Cd1 − 3xBi2xφxMoO4, Bi1 − xφxV1 − 3xMo3xO4, and systems of the type A5 − 3x1+Bi5 + xφ2xMoO4 where A1+ is Li, Na, or Ag. Defect scheelites of the type A1 − xφxMO4 were also studied without bismuth present. In these cases, there was generally a significant increase in activity as defects were introduced, but the activity and selectivity were not as high as in the bismuth containing defect scheelites. Systems with large concentrations of bismuth, but with no intentional defects, also showed very low activity.

An interpretation of the action of bismuth molybdates in ammoxidation of propylene

The experimental data of Aykan [ J. Catal. 12, 281 (1968)] which reveal a maximum in acrylonitrile yield in ammoxidation of propylene from a m Bi 2O 3 · n MoO 3 catalyst at an m, n value of 1, 2 are reinterpreted in terms of oxidation of Bi 3+ with a consequent increase in the concentration of Mo 5+. The relationship between the m n ratio and Mo 5+ concentration behaves in a manner exactly parallel to the experiental data of Aykan.

Adsorption equilibria of acrolein and ammonia on the bismuth molybdate koechlinite catalyst

Abstract The adsorption equilibria of acrolein and ammonia were studied on oxidized and partially reduced Bi2MoO6. Acrolein was found to be adsorbed according to two modes, one being a strong but slow adsorption of the dual-site type equal in amount to the number of A-sites. A similar adsorption exists on pure Bi2O3 which appears to support an earlier supposition that it is connected with Bi ions. The other one is a fast but weak adsorption, equal in volume to the number of B-sites, and again dual-site in character. For ammonia adsorption there is a strong adsorption (slow and dual-site type) that is double that of the number of A-sites and a weak adsorption (fast and single-site type) to the extent of 3 2 the B-sites. On the pre-reduced catalyst, the strong adsorption is eliminated and replaced by an equal amount of weak adsorption. Moreover, a new type of adsorption is observed (moderately strong and single-site type) equal to the number of A-sites. It is closely similar to the adsorption of water on the reduced catalyst. It was further observed that above 400 °C ammonia is oxidized according to a first order reaction, its rate being independent of the presence or absence of oxygen (activation energy is 37 kcal/mol−1). For this reaction we propose a model between two surface fragments of ammonia. The mechanism of the ammoxidation of propene to acrylonitrile is discussed on the basis of this model.

Heterogeneous selective ammoxidation over bismuth molybdate catalysts

The ammoxidation of propene and of acrolein has been studied over two catalysts, one (UBM4) with Bi:Mo = 0.73:1 similar to commercial bismuth molybdate catalysts and the other (GS1) consisting of the koechlinite phase Bi 2O 3 · MoO 3. The rates, reaction orders, Arrhenius parameters, and selectivities of the ammoxidations and of several selected reactions which appear in routes proposed by other workers were studied in a static vessel at 400 °C. The results show that oxides of nitrogen are not realistic intermediates in the ammoxidations, nor is the main route for ammoxidation of propene over UBM4 through gaseous acrolein, even though the dissociative adsorption of propene is probably the rate determining step. The ammoxidations over GS1 show resemblances to the reactions over UBM4 in rate laws, and in the rates per unit area of the catalysts at 400 °C. However, the selectivities are much higher, being about 95% for both over GS1 compared with 50% for propene and 70% for acrolein over UBM4. The rate of ammoxidation over GS1 is twice the rate of selective oxidation, suggesting that the adsorbing propene molecule reacts immediately with a surface species containing nitrogen, rather than reacting first with the oxide lattice to form allyl and hydroxyl radicals as it seems to do on UBM4.

Preparation and activity of bismuth tungstates in oxidation and ammoxidation of olefins

Investigations have been carried out on the catalytic behavior of Bi tungstates at the different ratios Bi W : 2 3 , 1 1 , 1.8 1 , 2 1 , 6 1 in the oxidation and ammoxidation of propylene and 1-butene. Bi 2WO 6 is the only active and selective compound. WO 3 is active but the main products of oxidation of both 1-butene and propylene are CO and CO 2. At low temperatures WO 3 shows a high isomerizing power towards 1-butene while Bi 2WO 6 is inactive. Ammonia present in the reagent mixture modifies the catalytic behavior of WO 3, keeping the distribution of products of ammoxidation of olefines nearer to the distribution given by Bi 2WO 6. The surface acidic sites and the formation of CO and CO 2 were attributed to the pressence of ▪ bonds of covalent type. These types of bonds are not present in Bi 2WO 6 which has a rather polar structure.

Mechanism of [3-13C]propene ammoxidation on bismuth molybdate catalyst

To study the mechanism of acrylonitrile formation, the ammoxidation of [3-13C]propene was studied in the presence of a bismuth molybdate catalyst on a silica support. The reaction was carried out at 723 K with a conversion of about 40 vol % of the propene to acrylonitrile and a small amount of acetonitrile. The 13C distribution among the reaction products was examined quantitatively with a high-resolution mass spectrometer. Half of the 13C in the acrylonitrile was found to be in the CN-group and the other half in the C2H3-group. This result points to a symmetrical intermediate, such as an allylic species, in the ammoxidation reaction. A similar intermediate was observed in the catalytic oxidation of propene to acrolein. The total 13C content in the acetonitrile amounted only half that of the acrylonitrile, which indicates carbon-carbon bond fissure of the allylic intermediate in the mechanism of acetonitrile formation. Ammoxidation of propene does not seem to involve acrolein as an intermediate. As a matter of fact, the addition of ammonia to a mixture of propene + oxygen + helium completely suppresses acrolein formation at 623 K.

Aspects of structure and activity in USboxide acrylonitrile catalysts

A uranium-antimony-oxide catalyst, known to be particularly efficient for the synthesis of acrylonitrile, has been studied in order to develop an understanding of structural features related to catalytic activity. The formation of an active and highly selective phase, USb3O10, of this catalyst and its equally active but less selective precursor, USbO5, were followed by X-ray and low frequency infrared measurements in controlled temperature experiments. Verification of the USb3O10 phase as the catalytically most important was made. Pulse microreactor studies show that there are at least two types of lattice oxygen operative in the reaction. The more labile but less abundant type is mainly involved in the formation of desired products (acrylonitrile and acrolein). Oxygen transfer through the lattice is an important aspect of the oxidation reaction.A mechanism for the oxidation and ammoxidation of propylene is proposed involving allylic intermediates. The active catalyst site is believed to involve pentavalent antimony, which is stabilized and regenerated through the action of uranium.

Ammoxidation of Propylene on Catalysts of Fe-Bi-P Mixed Oxide Systemt

Ammoxidation of propylene on Fe2O3-Bi205 (44.5: 44.5: 11.0, mol%) catalysts was studied in a fixed-bed reactor, under the following conditions: reaction temperature, 410∼490°C; W/F, 0.3∼1.8 sec; particle size of catalyst, 40∼400 mesh and feed compositions; a AcN, 11.1: CO, 36.6: CO, , 16.0 kcal/mol), were obtained.From the effects of the feed composition on propylene conversion and products selectivities, it was concluded that two types of adsorption centers for propylene (I, II) exist on these catalysts and that the rates of propylene conversion on the type I and II site were proportional to (PO6/PC3H6)0 and (PO2/PC3H6)0, respectively. As the results, the following reaction scheme was suggested.The reaction seemes to proceed by either of the two reaction paths, depending on the oxidation state of the catalyst.

White's method of thermodynamic calculations applied to ammoxidation of propylene

AbstractA method of steepest descent first applied by White et al. to the calculation of complex chemical equilibrium was used in this article to compute the equilibrium composition of a mixture resulting in the ammoxidation of propylene. As many as twenty species are likely to be present, some in insignificant quantities. A FORTRAN II Program was written for an IBM 1620 computer and calculations were made varying the feed composition, temperature and pressure. The results were discussed and qualitatively compared with those of the plant practice reported in the literature. The agreement is reasonably good when the oxygenated compounds are excluded from consideration.

Kinetics of the ammoxidation of propylene over a bismuth‐molybdate catalyst

AbstractIntegral conversion data for the ammoxidation of propylene were obtained using a flow reactor and 10.0 gms. of a bismuth‐molybdate catalyst. Analysis by gas chromatography for carbon‐containing compounds in the product gases showed the presence of unreacted propylene, acrolein, acrylonitrile, carbon dioxide and small amounts of acetonitrile.The data obtained at 390°C were correlated on the basis of a simplified scheme of first‐order reactions with acrolein as an intermediate. The results from experiments at higher temperatures and with reduced amounts of oxygen in the feed indicated that both the activity and selectivity of the catalyst were affected by the oxygen content of the catalyst.

Reduction of Bi 2O 3MoO 3 catalyst during the ammoxidation of propylene in the absence of gaseous oxygen

The reduction of a P 2O 5Bi 2O 3z.sbnd;MoO 3 SiO 2 catalyst (a catalyst for the acrylonitrile process), consisting of Bi 2O 3z.sbnd;MoO 3 + BiPO 4 + amorphous SiO 2, during the ammoxidation of propylene to acrylonitrile in the absence of gaseous oxygen was studied quantitatively by X-ray diffraction techniques and by catalytic activity measurements. Amorphous SiO 2 and BiPO 4 are not affected in synthesis. The overall reduction of catalytically active Bi 2O 3 · 3MoO 3 to metallic Bi and MoO 2 proceeds according to the following two consecutive reactions, where Bi2O 2 · MoO 3 (koechlinite) is an intermediate: Bi 2 O 3·3 Mo O → ( C 3 H 6, NH 3) Bi 2 O 3· Mo O 3+2 Mo O 2+ O 2 Bi 2 O 3·3 Mo O → ( C 3 H 6, NH 3)2 Bi+ Mo O 2+2 O 2 The catalytic activity decreases rapidly with the increasing reduction of the catalyst. The phase changes of the catalyst and the product formation in synthesis correspond quantitatively to the depletion of lattice oxygen from the catalyst. In the absence of gaseous oxygen, the optimum activity for acrylonitrile of silica supported Bi 2O 3z.sbnd;MoO 3 catalysts is at a Bi:Mo atomic ratio of about 1. For the catalytic ammoxidation of propylene to acrylonitrile on Bi 2O 3z.sbnd;MoO 3 based catalysts, a steady state mechanism involving simultaneous reduction and reoxidation of the catalyst surface with gaseous oxygen is suggested.

The ammoxidation of propene over complex oxide catalysts

The ammoxidation of propene over complex oxide catalysts