Partial oxidation of propane to acrylic acid at a Mo–V–Te–Nb-oxide catalyst

doi:10.1016/j.apcata.2004.02.019

Applied Catalysis A: General

Volume 266, Issue 2, 20 July 2004, Pages 211-221

https://doi.org/10.1016/j.apcata.2004.02.019 Get rights and content

Abstract

The partial oxidation of propane has been investigated at a multicomponent oxidic catalyst in the temperature range $360<T (° C)<420$ . The kinetic measurements were carried out in an integrally operated fixed bed reactor with distributed local sampling. The oxygen–propane ratio in the feed has been varied in the range 1.5<x_O₂/x_propane<4 and the water content was increased up to 50 vol.%. The results can be described quantitatively by a network of parallel and consecutive first order reactions.

Introduction

Up to now acrylic acid is commercially produced in a two-step process starting from propene. Overall selectivities to acrylic acid based on propene of 85–90% are obtained at conversions above 95% [1]. Using typical oxidic catalysts we determined yields above 85% in the oxidation of propene to acrolein [2] and up to 95% in the sequential oxidation of acrolein to acrylic acid [3].

An alternative route could be the partial oxidation of propane as feed. The economic importance of this possibility and the successful manufacture of maleic anhydride by selective oxidation of n-butane has stimulated various research. However, for a long period all efforts remained futile and the yields reported in the literature, except in a patent from Mitsubishi [24], were desperately low [4], [5]. In the last years the use of multi-component oxidic catalysts based on molybdenum, vanadium, niobium and tellurium seems to lead to a major breakthrough and promising developments. The actual state of the art of the selective oxidation of propane to acrylic acid has been reviewed by Lin [6]. Most of the applications of the catalytic system cited above are mentioned in the patent literature. Some of the results are listed in Table 7 of [6].

So far the open literature is mainly restricted to the study of catalyst preparation, its structure and the comparison with other catalytically active systems [6], [7], [8], [9]. By contrast, the matter of this work was a kinetic study. On the basis of the catalytic measurements a simple reaction network was developed and supported by using the intermediate propene as reactant too. Further, the influence of the temperature, the water content in the feed and of the ratio of propane to oxygen on the partial oxidation of propane was investigated.

With this network and the related rate expressions a quantitative description of the reacting system was possible. As we merely observe the evolution of the gas phase, the investigation is not aimed at the elucidation of mechanistic details but at the derivation of a sufficiently precise representation of the sequence in order to give guide lines for improved engineering measures and future catalyst developments.

Following a note published recently [10] the present article will give a more detailed insight in the results and the approach chosen.

Section snippets

Catalyst and kinetic measurements

The oxidic catalyst has the bulk composition MoV_0.33Te_0.22Nb_0.11O_x and was synthesised according to the patent literature [11]. Its preparation has been described in more detail before [10]. It is of the egg-shell type and contains 10 or 20 wt.% active compound on spherical steatite, named S10 and S20 in the following. The mean diameter is equal to 3 mm. The use of both catalysts has given results indicating the absence of inner mass transfer resistances.

The experiments were run in an integrally

Reaction network and rate expressions

The measurements have been made using different egg-shell catalysts, catalyst fillings and dilutions. No significant influence could be observed.

Typical results obtained in the partial oxidation of propane are shown in Fig. 2, Fig. 3. Interesting products of the reaction are propene and acrylic acid, only traces of acrolein have been observed. The species “by-products” consists of CO_x and acetic acid, no acetone could be detected by online gas chromatography. Fig. 2 illustrates the decrease of

Conclusions

The present investigation of the Mo–V–Te–Nb mixed oxide has shown that its catalytical performance can rival not only with the results reported in the open literature but also with regard to the claims in different patents.

The attempt to model the kinetics by a reaction network is quite successful. Based on the criteria of simplicity and the minimum of adjustable parameters a system of first order rate expressions with respect to organic compounds allows the description of the reacting system.

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Propane ammoxidation on Bi promoted MoVTeNbO<inf>x</inf> oxide catalysts: Effect of reaction mixture composition
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MoVTeNbO catalysts were characterized with XRD, XPS, and FTIR techniques and tested in the ammoxidation of propane. Bismuth-modified MoVTeNbO catalysts showed a higher acrylonitrile yield than the base four-component system. The effect of the reaction mixture composition (C₃H₈, NH₃ and O₂) on selectivity towards different products was studied at propane conversion above 80%. The favorable effect of bismuth promoter on the selectivity towards acrylonitrile was explained by suppression of acrylonitrile transformation connected with decreasing acidity of the catalyst.
The reaction network in propane oxidation over phase-pure MoVTeNb M1 oxide catalysts
2014, Journal of Catalysis
Citation Excerpt :
The most important observations are listed below: The presence of steam is beneficial for acrylic acid synthesis, which is in agreement with previous literature reports [3,11,38–40]. Propane conversion increases with increasing oxygen:propane ratio, but the selectivity is hardly influenced by the oxygen partial pressure.
MoVTeNb oxide catalysts exclusively composed of the M1 phase (ICSD No. 55097) have been studied in the direct oxidation of propane to acrylic acid applying a broad range of reaction conditions with respect to temperature (623–633–643–653–663 K), O₂ concentration in the feed (4.5–6.0–9.0–12.0%), steam concentration in the feed (0–10–20–40%), and contact time (0.06–0.12–0.18–0.24–0.36–0.48–0.72–1.44 s g_cat Nml⁻¹). The molar fraction of propane was kept at 3.0%. Model experiments were performed to study the reactivity of possible intermediates propene, acrolein, and CO. The impact of auxiliary steam on the chemical nature of the catalyst surface was analyzed by in situ photoelectron spectroscopy, while in situ X-ray diffraction has been carried out to explore the structural stability of the M1 phase under stoichiometric, oxidizing, and reducing reaction conditions. Phase purity apparently accomplishes absolute stability in terms of the crystalline bulk structure and the catalytic performance over month even under extreme reaction conditions. In contrast, the catalyst surface changes dynamically and reversibly when the feed composition is varied, but only in the outermost surface layer in a depth of around one nanometer. The addition of steam causes enrichment in V and Te on the surface at the expense of Mo. Surface vanadium becomes more oxidized in presence of steam. These changes correlate with the abundance of acrylic acid detected in the in situ photoelectron spectroscopy experiment. Analysis of the three-dimensional experimental parameter field measured in fixed bed reactors revealed that the complexity of the reaction network in propane oxidation over MoVTeNb oxide is reduced compared to less-defined catalysts due to phase purity and homogeneity. The oxidative dehydrogenation of propane to propene followed by allylic oxidation of propene comprises the main route to acrylic acid. The oxygen partial pressure was identified as an important process parameter that controls the activity in propane oxidation over phase-pure M1 without negative implications on the selectivity. High O₂ concentration in the feed keeps the catalyst in a high oxidation state, which provides an increased number of active sites for propane activation. Auxiliary steam increases activity and selectivity of M1 by changing the chemical nature of the active sites and by facilitating acrylic acid desorption.
Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid
2012, Journal of Catalysis
The surface of a highly crystalline MoVTeNb oxide catalyst for selective oxidation of propane to acrylic acid composed of the M1 phase has been studied by infrared spectroscopy, microcalorimetry, and in situ photoelectron spectroscopy. The acid–base properties of the catalyst have been probed by NH₃ adsorption showing mainly Brønsted acidity that is weak with respect to concentration and strength of sites. Adsorption of propane on the activated catalyst reveals the presence of a high number of energetically homogeneous propane adsorption sites, which is evidenced by constant differential heat of propane adsorption q_diff,initial = 57 kJ mol⁻¹ until the monolayer coverage is reached that corresponds to a surface density of approximately 3 propane molecules per nm² at 313 K. The decrease of the heat to q_diff,initial = 40 kJ mol⁻¹ after catalysis implies that the surface is restructured under reaction conditions. The changes have been analyzed with high-pressure in situ XPS while the catalyst was working applying reaction temperatures between 323 and 693 K, different feed compositions containing 0 mol.% and 40 mol.% steam and prolonged reaction times. The catalytic performance during the XPS experiments measured by mass spectrometry is in good agreement with studies in fixed-bed reactors at atmospheric pressure demonstrating that the XPS results taken under operation show the relevant active surface state. The experiments confirm that the surface composition of the M1 phase differs significantly from the bulk implying that the catalytically active sites are no part of the M1 crystal structure and occur on all terminating planes. Acrylic acid formation correlates with surface depletion in Mo⁶⁺ and enrichment in V⁵⁺ sites. In the presence of steam in the feed, the active ensemble for acrylic acid formation appears to consist of V⁵⁺ oxo-species in close vicinity to Te⁴⁺ sites in a Te/V ratio of 1.4. The active sites are formed under propane oxidation conditions and are embedded in a thin layer enriched in V, Te, and Nb on the surface of the structural stable self-supporting M1 phase.
Crystalline structure of mixed metal oxide catalysts for propane selective oxidation to acrylic acid
2011, Transactions of Nonferrous Metals Society of China (English Edition)
The effects of the preparation procedure on the formation of crystal phases and catalytic performance of the MoVTeNbO mixed metal oxide catalysts in selective oxidation of propane to acrylic acid were investigated. The results show that the preferred drying method is the rotavapor method, which favors the formation of an effective crystal phase and suppresses the formation of impurity phases. The preferred calcination atmosphere is an Ar atmosphere. The MoVTeNb mixed metal oxide catalysts can be obtained by solution method after heat-treatment at 600°C in an Ar atmosphere, via a rotavapor with a warm water bath at 60°C, and a pH value of 4.0. The catalyst with a MoVTeNb molar ratio of 1.0:0.3:0.23:0.12 is the most effective and extremely active.
Phase formation and selective oxidation of propane over MoVTeNbO <inf>x</inf> catalysts with varying compositions
2011, Applied Catalysis A: General
The selective oxidation of propane to acrylic acid on MoVTeNbO_x catalysts with varying concentrations of vanadium, tellurium and niobium was investigated. Catalysts containing M1 phase were obtained over the compositional range of MoV_0.14–0.22Te_0.1–0.2Nb_0.1–0.2O_x. Vanadium containing sites in the M1 phase are drastically more active for propane activation than in other materials studied. The catalytic activity is directly correlated to its fraction in the overall material and in particular the M1 phase. High concentrations of tellurium induce the formation of the M2 phase decreasing so the overall activity of the catalysts. The intrinsic activity of the M1 phase is, however, independent of the tellurium concentration. Although the presence of the M1 phase is not a stringent requirement for the oxidative dehydrogenation of propane to propene, it is required to oxidize the intermediately formed propene with high selectivity to acrylic acid. The active sites for propane activation and propene oxidation are structurally coupled, because the ratio between the rates of the two reactions was always 1:25. Oxygen defect sites in mixed oxides seem to enhance interaction with acrylic acid and lead to decarboxylation and total oxidation.
Effect of preparation conditions on selective oxidation of propane to acrylic acid
2009, Transactions of Nonferrous Metals Society of China (English Edition)
The effects of chemical composition and preparation conditions, especially calcination atmosphere and water content on the catalytic performances of MoVTeNbO mixed oxide catalyst system for the selective oxidation of propane to acrylic acid were investigated. Among the catalysts studied, Mo_1.0V_0.3Te_0.23Nb_0.12O_x catalyst calcined in inert atmosphere at 600 °C shows the best performance in terms of propane conversion and selectivity to acrylic acid. The results reveal that proper chemical composition, calcination atmosphere and water content affect greatly the catalysts in many ways including structure, chemical composition, which are related to their catalytic performances; and 51.0% propane conversion and 30.5% one-pass yield to acrylic acid can be achieved at the same time.

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Partial oxidation of propane to acrylic acid at a Mo–V–Te–Nb-oxide catalyst

Abstract

Introduction

Section snippets

Catalyst and kinetic measurements

Reaction network and rate expressions

Conclusions

Stud. Surf. Sci. Catal.

J. Catal.

Catal. Today

Catal. Today

Appl. Catal. A: General

J. Catal.

J. Catal.

Appl. Catal.

vt Verfahrenstechnik

J. Catal.

Chem. Eng. Technol.

Catal. Lett.