Selective Oxidation Of Propane Research Articles

Chromium-incorporated TUD-1 as a new visible light-sensitive photo-catalyst for selective oxidation of propane

Chromium was incorporated in the framework of TUD-1 mesoporous silica by a one-pot synthesis procedure, using triethanolamine as a bi-functional template. The Cr-TUD-1 catalyst was characterized by means of X-ray diffraction, high-resolution transmission electron microscopy, UV–vis and Raman spectroscopy, as well as elemental analysis and N 2 sorption measurements. The results indicate that chromium is incorporated as tetrahedrally co-ordinated Cr 6+ in the framework of TUD-1. When tested as a catalyst for the photo-oxidation of propane, Cr-TUD-1 showed high activity and high selectivity towards acetone under visible light irradiation ( λ = 435 nm).

Selective oxidation of short-chain alkanes over hydrothermally prepared MoVTeNbO catalysts

MoVTe-Nb oxide catalysts have been prepared by a hydrothermal method and tested in the selective oxidation of propane to acrylic acid and in the oxidative dehydrogenation of ethane to ethylene. The influence of the concentration of oxalate anions in the hydrothermal gel has been studied for two series of catalysts, Nb-free and Nb-containing, respectively. Results show that the development of an active and selective active orthorhombic phase (Te2M20O57, M = Mo, V, Nb) requires an oxalate/Mo molar ratio of 0.4–0.6 in the synthesis gel in both types of samples. The presence of Nb favours a higher catalytic activity in both ethane and propane oxidation, and a better production of acrylic acid.

The deoxygenation of benzoic acid as a probe reaction to determine the impact of superficial oxygen vacancies (isolated or twin) on the oxidation performances of Mo-based oxide catalysts

The deoxygenation of benzoic acid (DBA) is a probe reaction of the organisation of oxygen vacancies at the surface of molybdenum based oxide catalysts. In the present work, the DBA was used in coupling with the selective oxidation of propylene so that it could offer an insight into the nature of oxygen vacancies involved in the later reaction. By correlating the superficial oxidation state of the catalytic elements measured by X-ray photoelectron spectroscopy with the information provided by the DBA probe reaction, it was possible to progress in the description of the atomic scale architecture of the oxidation sites at work. Sites bringing boosted performances in the oxidation of propylene are those which are slightly reduced thanks to the presence of single (isolated) oxygen vacancies. Conversely, twin oxygen vacancies do not participate in the oxidation reaction.

Effect of preparation condition on the performance of silica-supported MoVTeO catalysts for selective oxidation of propane to acrolein

The effects of chemical composition and preparation conditions, especially calcination atmosphere on the catalytic performances of silica-supported MoVTeO catalysts for the selective oxidation of propane to acrolein have been studied. Among the catalysts studied, the MoV 0.2Te 0.1/SiO 2 catalyst calcined in inert atmosphere showed the best performance in terms of propane conversion and selectivity to acrolein. The results of XRD, XPS and Raman revealed that the calcination atmosphere affected greatly the catalysts in many ways including structure, chemical composition and Mo oxidation state, which are related to their catalytic performances.

The influence of the calcination conditions on the catalytic activity of Bi 2MoO 6 in the selective oxidation of propylene to acrolein

The activity of Bi 2MoO 6 catalysts with small amounts of excess bismuth in the selective oxidation of propylene is strongly dependent on the calcination conditions. These catalysts show reasonable activities and high selectivities after calcination for a short period of time or after calcination at a moderate temperature. However, these catalysts become low active and low selective after calcination for a long period of time or after high temperature calcination. This difference is ascribed to relative low Bi/Mo-ratios at (parts of) the surface after calcination for a short period of time. The active surface becomes enriched with bismuth during prolonged calcination or reaction, resulting in a deactivation of the catalyst. The deactivated catalysts can be reactivated by reduction, this supports that the deactivation is due to a surface enrichment with bismuth. The dependence of the catalytic activity on the calcination conditions is likely one of the reasons behind the conflicting results on the activity of Bi 2MoO 6 found in the literature.

Study of Ga modified Cs 2.5H 1.5PV 1Mo 11O 40 heteropolyoxometallates for propane selective oxidation

The selective oxidation of propane by oxygen has been investigated on a series of gallium modified Cs 2.5H 1.5PV 1Mo 11O 40 samples, with Ga content varying from 0 to 0.32 per Keggin unit (KU). The physicochemical properties of the samples have been studied by using a variety of techniques, namely ICP, FTIR, XRD, 31P-NMR, BET and TG-DTG-DSC. The effect of several parameters, such as pre-treatment temperature, reaction temperature, residence time (W/F) on the conversion and product distribution has been examined. The presence of gallium has been observed to increase surface area by a factor of more than two and to improve the selectivity to oxygenates (acrylic and acetic acids, acrolein). It has been found that there is an optimum value of Ga content of 0.16 per KU in the Keggin structure and of pre heating temperature of 300 °C for maximizing propane conversion and acrylic acid selectivity. The latter aspect is related to the presence of both Brønsted acid and redox sites.

Analysis of structural transformations during the synthesis of a MoVTeNb mixed oxide catalyst

This work presents a detailed investigation of the preparation routine for the multi-metal oxide Mo 1V 0.30Te 0.23Nb 0.125O x used as catalyst for the selective oxidation of propane to acrylic acid. In situ Raman spectroscopy on the initial aqueous polyoxometalate solution prepared from ammonium heptamolybdate, ammonium metavanadate and hexaoxotelluric acid reveals the coexistence of Anderson-type anions [TeM 6O 24] n− , M = Mo, V; n ≥ 6 and protonated decavanadate species [H x V 10O 28] (6− x)− . Raman analysis showed that the monomeric motif of the Anderson-type tellurate is preserved after addition of the Nb precursor and the subsequent spray-drying process. Calcination of the X-ray amorphous spray-dried material in air at 548 K seems to be the essential step, leading to a re-arrangement of the tellurate building blocks, generating nanocrystalline precursors of the phases finally established during treatment in helium at 873 K.

Kinetic modeling to estimate fundamental yield bounds for selective propylene oxidation over bifunctional catalysts

The selective oxidation of propylene via heterogeneous catalysts is one of the most successful commercial processes to produce acrylic acid (CH 2CHCOOH). For this catalytic oxidation process where multiple products are possible, it is desirable to understand how a catalyst can control the reactivity of the system toward desired products. In this work, an elementary-step kinetic mechanism for the catalytic oxidation of propylene was constructed based on information in the literature and analogous surface and gas-phase reactions. This model was used in several distinct ways: to fit experimental data, to see if there are fundamental limits on the achievable yield, and to explore how the catalyst parameters would have to change to allow better yields. Such information can provide guidance to experimentalists designing new real-world catalysts with improved yields and selectivities, a process which is often expensive and time-consuming. From our modeling results, some byproducts are inevitable, but it appears that there is no fundamental reason that high (∼99%) yields of acrylic acid could not be obtained with the right catalyst, in either the one-step or the two-step process through acrolein. Some properties of any high-yield catalyst for acrylic acid production are outlined.

Effect of Brønsted acidity in propane oxidation over Cs 2.5H 1.5PV 1Mo 11− xW xO 40 polyoxometallate compounds

Cs 2.5H 1.5PV 1Mo 11− x W x O 40 Keggin-type polyoxometallate (POM) compounds have been synthesised and studied for selective propane oxidation in the 300–400 °C temperature range. Prior to reaction the samples were pre-treated at either 300 °C or 400 °C in order to change the concentration in Brønsted acid sites by decreasing the amount of constitutional water. Acid strength was enhanced by substituting increasing amounts of W 6+ in the Keggin anion for Mo 6+, between 0 and 6 per Keggin Unit (KU) as shown by NH 3-TPD of the H + form and IR of the lattice vibrational modes (M O and M O M with M = Mo 6+ or W 6+). As a matter of fact vibrational mode frequencies and thus the corresponding bond energies were observed to increase with W 6+ substitution. This results in more covalent M O bonds and thus to freer protons. Chemical analysis, IR and DTA/TG data allowed us to determine the extent of W 6+ substitution for Mo 6+, the amount of constitutional water and any structural change in the samples. It was observed that under catalytic conditions, (C 3/O 2/He = 2/1/2, flow rate 15 cm 3 min −1, 12 h on stream, reaction temperature in the 300–400 °C range) the catalyst structure was maintained, with only a very small part of the substituted elements (V 5+, W 6+ and Mo 6+ atoms) being extracted from the Keggin anion. Catalytic data have shown that introduction of W 6+ to replace Mo 6+ led to lower propane activation, which may be due to a decrease of lattice oxygen anion mobility, related to the stronger M O bond (see supra and as shown by the higher reaction temperature necessary for the same conversion level). Compared to pre-treatment temperature at 300 °C, pre-treatment at 400 °C was observed to result in a higher extent of constitutional water removal i.e. a loss of Brønsted acid sites by a factor of 2–4.5 when W 6+ amount varies from 0 to 6 per KU without destroying the primary Keggin structure, and to favour the formation of propene at the expense of acetic and acrylic acids and CO x . This also shows that substituting W 6+ for Mo 6+, which enhances Brønsted acid strength is detrimental to propene formation and leads to higher selectivity to acetic acid and CO x , i.e. the propane oxidation pathway via the isopropanol route and acetone rather at the expense of the usual main pathway forming acrylic acid via propylene.

Key aspects of crystalline Mo-V-O-based catalysts active in the selective oxidation of propane

Mo-V-O-based complex metal oxide catalysts were synthesized hydrothermally for the first time, characterized structurally and tested in the selective oxidation of propane to acrylic acid, and the results obtained were compared on the basis of catalyst crystal structures in order to clarify key aspects of alkane selective oxidation over multifunctional metal oxide catalysts. The catalysts tested were black solids of rod-shaped crystals, which had a layer structure in the direction of fiber axis and various high dimensional arrangements of metal octahedra in the cross-section plane. A strong dependency on the octahedra arrangements and a facet dependency were observed, and the roles of metal elements in the course of selective oxidation of propane were clarified by comparing the catalytic performance of various Mo-V-O-based catalysts. We discuss the multi-functional character derived from high dimensional structures of the catalysts and mechanism of the selective oxidation of propane.

Effect of zeolite geometry for propane selective oxidation on cation electrostatic field of Ca 2+ exchanged zeolites

The effects of zeolite geometry on propane selective oxidation were studied by in situ infrared spectrometry on Ca 2+ exchanged Y, MOR and ZSM5 zeolites. Oxygen and propane adsorption at room temperature, revealed that the electrostatic field of Ca 2+ increased in the order CaY < CaMOR < CaZSM5. The electrostatic field of Ca 2+ cations in CaY and CaZSM5 was observed to correlate with propane selective oxidation activity and selectivity. At 353 K, low activity but high selectivity to acetone was observed for propane oxidation on CaY zeolite, while high activity and a 2:1 mixture of 2-propanol and acetone was observed on CaZSM5. CaMOR showed the lowest activity for oxygenates formation of propane oxidation, but deep oxidation to CO and CO 2 was found. The results convincingly show that the geometrical structure of a zeolite determines activity and selectivity of propane partial oxidation on Ca 2+ exchanged zeolites to a large extent.

Influence of the active phase structure Bi-Mo-Ti-O in the selective oxidation of propene

Bismuth molybdenum titanium oxides were prepared in a highly dispersed state by the sol–gel method and in a largely crystallized state by coprecipitation and impregnation. The catalysts contained 14 or 25 wt.% of bismuth molybdate. Their catalytic performance in propene oxidation to acrolein was studied. The increase in activity of Bi-Mo-Ti oxides in propene oxidation as compared to that of bulk bismuth molybdate can be tentatively related, in the case of the sol–gel samples, to the stabilization of small aggregates of Bi- and Mo-containing phases due to the beneficial presence of the titania matrix. The catalytic performance of the samples prepared by coprecipitation or impregnation is enhanced once a crystal size of bismuth molybdate close to 23 nm is reached, i.e., the crystal size should not be too small (samples prepared by the sol–gel method) nor too large (samples prepared by impregnation and coprecipitation), but an optimum size should exist to enhance the catalytic performance.

Importance of nanostructured vanadia for selective oxidation of propane to acrylic acid

Highly dispersed nanostructured vanadia supported on mesoporous silica SBA-15, prepared by controlled grafting/ion-exchange, has been found to exhibit high selectivities in propane partial oxidation to acrylic acid demonstrating its unique potential for mixed metal oxide catalyst development.

Utilization of Combinatorial Method and High Throughput Experimentation for Development of Heterogeneous Catalysts

The combinatorial method and high throughput experimentation have been applied to catalysis development in the last decade. Here we describe equipment for catalyst preparation, catalysis evaluation and product analysis with a gas sensor system. High throughput experimentation using these devices has allowed us to optimize catalyst composition with stochastic methods such as the genetic algorithm. The improvement of propane selective oxidation catalysis is described. High throughput experimentation allowed the construction of a database for elemental reactions. We have developed novel catalysts for ethanol steam-reforming catalysts and a dimethyl ether steam-reforming catalyst by combining good catalysts for each elemental reaction. Our new concept of "Materiomics" is introduced as a promising method for material science based on combinatorial technology.

Involvement of active sites of promoted vanadyl pyrophosphate in selective oxidation of propane

Involvement of active sites in the selective oxidation of propane was investigated using (VO) 2P 2O 7 catalysts promoted by Sb, Ti, Zr, Hf, Cu, and Ce. Based on X-ray diffraction patterns, infrared spectra, and Raman spectra, the formation of a (VO) 2P 2O 7 phase was confirmed for all of the promoted catalysts; no other phases were detected. After the addition of Sb, Ti, and Zr, the selectivity to acrylic acid increased, whereas Cu-, Ce-, and Hf-promoted catalysts showed lower selectivity than pure (VO) 2P 2O 7. The effect of promoters on the activity and selectivity for the propane oxidation was investigated on the basis of the nature of surface active sites. The surface V O species, evaluated by the nitric oxide–ammonia rectangular pulse technique, decreased with the addition of the promoters. A proportional correlation between the number of surface V O species and reaction rate of propane clarified that the surface V O species is the controlling factor for the catalytic activity of propane oxidation. In the case of Sb-, Ti-, and Zr-promoted catalysts, the selectivity to acrylic acid increased significantly. The selectivity was compared with the number and strength of Brønsted and Lewis acid sites estimated from dimethylpyridine temperature-programmed desorption. A good correlation was observed between the selectivity to acrylic acid and the surface concentration of Lewis acid sites. It was experimentally demonstrated that Lewis acid sites represent the key factor in selective oxidation.

Formation of M2+(O2)(C3H8) Species in Alkaline-Earth-Exchanged Y Zeolite during Propane Selective Oxidation

The adsorption of oxygen and d2-propane (CH3CD2CH3) on a series of alkaline-earth-exchanged Y zeolite at room temperature was studied with in situ infrared spectroscopy. Surprisingly at room temperature, oxygen adsorption led to the formation of supercage M2+(O2) species. Further, at low propane coverage, propane was found to adsorb linearly on Mg2+ cations, but a ring-adsorption structure was observed for propane adsorbing on Ca2+, Sr2+, and Ba2+ cations. It is demonstrated that O2 and propane can simultaneously attach to one active center (M2+) to form a M2+(O2)(C3H8) species, which is proposed to be the precursor in thermal propane selective oxidation. Selectivity to acetone in the propane oxidation reaction decreases with increasing temperature and cation size due to the formation of 2-propanol and carboxylate ions. An extended reaction scheme for the selective oxidation of propane over alkaline earth exchanged Y zeolites is proposed.

05/01461 Selective oxidation of propane and propene on MoVNbTeO catalysts. Effect of chemical composition in catalysts prepared by slurry: Solsona, B. et al. Catalysis Today, 2004, 91–92, (15), 247–250

05/01461 Selective oxidation of propane and propene on MoVNbTeO catalysts. Effect of chemical composition in catalysts prepared by slurry: Solsona, B. et al. Catalysis Today, 2004, 91–92, (15), 247–250

Highly efficient conversion of propane to maleic anhydride and acetic acid by partial oxidation

Propane-selective oxidation was investigated over VMoO alone or over VMoO catalysts promoted by metal ions. Through this reaction, propane was efficiently converted to maleic anhydride, and acetic acid over VMoO itself and over metal-ion-doped VMoO catalysts. Over 70%Mo20%V10%AgO catalyst, 37.4% of propane single pass conversion was obtained at 300 °C with maleic anhydride selectivity of 53.6% and acetic acid selectivity of 38.9%. The studies on propylene oxidation indicated that propylene might not be a reaction intermediate for maleic anhydride formation in propane oxidation. A typical carbon–carbon bond cracking and reformation reaction occurred in propane oxidation by using molecular oxygen as oxidant.

Effects of Brønsted acidity in the mechanism of selective oxidation of propane to acetone on CaY zeolite at room temperature

The importance of Brønsted acid sites for partial oxidation of propane to acetone in CaY was investigated by in situ FTIR spectroscopy. With an increasing number of protons in Ca-Y, Volcano plots were observed for (1) amount of adsorbed propane; (2) initial acetone formation rate; (3) total amount of acetone after 20 h of reaction; (4) acetone selectivity. The results clearly show that Brønsted acidity increases the isopropylhydroperoxide (IHP) formation rate, most likely via a catalytic H + transfer, and IHP decomposition into acetone and water. Moreover, with increasing IHP concentration 2-propanol was found in addition to acetone. Since an increasing number of Brønsted acid sites implies a decreasing number of Ca 2+ in the zeolite, an optimal H +/Ca 2+ ratio was observed for both activity and selectivity for acetone.

Synergy effects between bismuth molybdate catalyst phases (Bi/Mo from 0.57 to 2) for the selective oxidation of propylene to arcrolein

In this work, the synergy effect between different phases of bismuth molybdate catalysts was investigated systematically. The catalysts were prepared by spray drying and had a Bi/Mo atomic between 0.57 and 2. It is found that the synergy effect is only observed in mixtures containing γ-phase. A mixture with Bi/Mo ratio = 1.3 consisting of γ- and α-phase, exhibits the highest activity. Less homogeneous ‘artificial mixtures’ exhibit reduced synergy effects when compared to homogeneous ‘in situ mixtures’.