Oxidative Dehydrogenation Of Isobutane Research Articles

Modifying SBA-15 with Binary Elements of Chromium and Molybdenum for Improved Catalytic Performance in the Oxidative Dehydrogenation of Isobutane to Isobutene

In the oxidative dehydrogenation of isobutane to isobutene, selectivity and stability were improved by introducing chromium and molybdenum into SBA-15. The direct synthesis method (DM) was used to introduce these binary elements into SBA-15. Use of the DM resulted in a higher specific surface area of the catalyst and a greater dispersion of chromium and molybdenum species compared with a corresponding binary catalyst prepared using the incipient wetness impregnation method (IM). Selectivity to isobutene was improved, along with a decrease in the selectivities to CO and CO2 with the introduction of greater amounts of molybdenum, which suggests that molybdenum must suppress the tendency of isobutene to over-oxidate to either CO or CO2. The molybdenum species must be in close proximity to the chromium species, which results in the formation of an active Cr-O-Mo site.

Effect of Introduction of Trace Amount of Chromium Species in Improving Catalytic Performance of MCM-48 in Oxidative Dehydrogenation of Isobutane

The catalytic performance of MCM-48 was greatly improved by the introduction of a small amount of chromium during the oxidative dehydrogenation of isobutane. Various characterization procedures such as XRD, N2 adsorption–desorption isotherms, TEM, NH3-TPD, XPS, and XAFS were used to identify the role that chromium played in the improvement, and XPS and XAFS results provided the most valuable information. Both measurements revealed that the chromium species existed as Cr6+ inside the framework of MCM-48 before oxidative dehydrogenation, but was reduced to Cr3+ during the reaction. The characteristic pore nature of MCM-48 also contributed to an enhancement of the selectivity to isobutene via the suppression of consecutive oxidation reactions.

Oxidative dehydrogenation of isobutane over vanadia catalysts supported by titania nanoshapes

Support plays a complex role in catalysis by supported metal oxides and the exact support effect still remains elusive. One of the approaches to gain fundamental insights into the support effect is to utilize model support systems. In this paper, we employed for the first time titania nanoshapes as the model supports and investigated how the variation of surface structure of the support (titania, TiO2) impacts the catalysis of supported oxide (vanadia, VOx). TiO2 truncated rhombi, spheres and rods were synthesized via hydrothermal method and characterized with XRD and TEM. These TiO2 nanoshapes represent different mixtures of surface facets including [101], [010] and [001] and were used to support vanadia. The structure of supported VOx species was characterized in detail with in situ Raman spectroscopy as a function of loading on the three TiO2 nanoshapes. Oxidative dehydrogenation (ODH) of isobutane to isobutene was used as a model reaction to test how the support shape influences the activity, selectivity and activation energy of the surface VOx species. It was shown that the shape of TiO2 support does not pose evident effect on either the structure of surface VOx species or the catalytic performance of surface VOx species in isobutane ODH reaction. This insignificant support shape effect was ascribed to the small difference in the surface oxygen vacancy formation energy among the different TiO2 surfaces and the multi-faceting nature of the TiO2 nanoshapes.

Effect of the template ion exchange behaviors of chromium into FSM-16 on the oxidative dehydrogenation of isobutane

The template ion exchange of chromium cations into FSM-16 (#16 Folded Sheets Mesoporous Materials) for 247 h resulted in a 2.89 wt% incorporation of those cations into the FSM-16, although only a 0.3 wt% incorporation had previously been reported. The XRD pattern of the resultant solid (Cr-FSM-16) showed that the hexagonal structure characteristic of FSM-16 remained after the 2.89 wt% incorporation of chromium cations. XPS could be used to detect the Cr3+ and Cr6+ species on the surface of Cr-FSM-16. A pre-edge peak that was due to a tetrahedrally coordinated Cr6+ species was confirmed in the XANES spectrum of the Cr-FSM-16, which showed that the coordination state around some Cr species was similar to that around the Si species in FSM-16. With the increase in the amount of chromium cations in FSM-16, its catalytic activity and stability during the oxidative dehydrogenation of isobutane were evidently improved.

Catalytic performance of a novel Cr/ZnAlLaO catalyst for oxidative dehydrogenation of isobutane

A novel Cr/ZnAlLaO catalyst for the isobutane oxidative dehydrogenation (ODH) reaction: from catalytic performance to surface structure analysis.

Oxidative dehydrogenation of isobutane on carbon xerogel catalysts

The oxidative dehydrogenation of isobutane was investigated with oxidised and nitrogen-doped carbon xerogel catalysts in a fixed-bed reactor at 375°C using a stoichiometric feed composition. The oxygen groups were selectively removed from the surface by thermal treatments performed on the oxidised samples, confirming the carbonyl-quinone groups as the active sites for the reaction, but also highlighting the negative role played by the carboxylic anhydride groups. Turn-over frequencies could be calculated from correlations between the catalytic activity and the concentration of carbonyl-quinone groups. On the other hand, the results obtained with the nitrogen-doped samples showed that the catalytic activity increased with the nitrogen content of the carbon xerogels.

Different Supports-Supported Cr-Based Catalysts for Oxidative Dehydrogenation of Isobutane with CO2

The effect of supports (MSU-1,), gamma-Al2O3, AC (activated carbon), and MgO) on the catalytic activity of Cr-based catalysts was investigated for the dehydrogenation of isobutane with CO2. The catalytic activity was in the order of CrO,IMSU-1 > CrOx/Al2O3 > CrOx/AC > CrOx/MgO. The catalysts were characterized by N-2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). The XRD results indicate that the active species of Cr are dispersed well on the supports. N-2 adsorption-desorption shows that the support MSU-1 has the largest surface area (804.2 m(2)/g), which results in excellent dispersion of Cr and highest activity. The XPS results reveal that Cr6+ is one of the active centers. The results of NH3-TPD indicate that catalyst activity is proportional to the amount of weak acid adsorption sites. As a result, the best support is the MSU-1 zeolite owing to its high specific area and a large amount of weak acid sites. The 59.2% conversion of isobutane and the 39.5% yield of isobutene are achieved on the CrOx/MSU-1 catalyst.

Effect of Various Supports on the Physico-chemical Properties of V-Sb Oxides in the Oxidative Dehydrogenation of Isobutane

V0.9Sb0.1Ox systems, bulk and deposited on different supports (five types of γ-aluminas, α-alumina, silica-alu- mina, silica gel, magnesium oxide), have been tested in the oxidative dehydrogenation (ODH) of iso-butane. This statement is derived from the data obtained by a set of characterisation techniques(specific surface area measurements, X-ray diffraction, X-ray photoelectron spectroscopy, laser Raman spectroscopy, in situ differential scanning calorimetry and in situ diffuse reflectance-absorption infrared Fourier transform spectroscopy).

Oxidative dehydrogenation of isobutane on phosphorous-modified graphitic mesoporous carbon

Graphitic mesoporous carbon was modified with phosphorous heteroatoms in order to tune the catalytic selectivity and to investigate the roles of different oxygen species for the oxidative dehydrogenation reaction of isobutane to isobutene. Small changes in the isobutane apparent activation energy are consistent with the notion that the phosphorous groups do not change the nature of the active sites but they interfere with the availability of the sites. Our results show that the improvement on selectivity is not proportional to the amount of phosphorous added. Small phosphorous content improved the selectivity by suppressing the combustion of isobutane. However, a higher amount of phosphorous groups lead to coverage of selective quinone sites and/or creation of active sites favorable to total oxidation.

A kinetic study of oxidative dehydrogenation of isobutane to isobutylene over chromium oxide supported on lanthanum carbonate

Kinetics of oxidative dehydrogenation of isobutane to isobutylene over chromium oxide supported on lanthanum carbonate was studied. The formation rate of isobutylene was found to be first order in isobutane and zero order in oxygen concentration and the rate limiting step was the regeneration of active sites by the gas phase oxygen. The formation of CO2 was due to the consecutive oxidation of isobutylene which occurred on the same active sites used for isobutylene formation, not by the parallel oxidation of isobutane.

Oxidative dehydrogenation of isobutane over supported V-Mo mixed oxides

Vanadium-molybdenum oxides supported on Al2O3, CeO2 and TiO2 were prepared by a ?wet? impregnation method, characterized using DRX, N2 adsorption, UV-Vis spectroscopy, electrical conductivity measurements and tested in the oxidative dehydrogenation of isobutane. The catalytic performance in the oxidative dehydrogenation of isobutane at 400-550?C depended on the nature of support and on the content of VMoO species on the support. The catalysts supported on alumina were more active and selective than those supported on ceria and titania.

Physicochemical study of catalysts for the oxidative dehydrogenation of isobutane: Cobalt, nickel, and manganese molybdates

Temperature-programmed desorption and IR spectroscopic studies of the physicochemical properties of cobalt, nickel, and manganese molybdates are reported. These properties are correlated with the catalytic properties of the molybdates in the oxidative dehydrogenation of isobutane with atmospheric oxygen. It is demonstrated by an analysis of the IR spectra of the molybdates that the isobutene yield grows as the proportion of tetrahedrally coordinated molybdenum in the catalyst structure increases in isobutane dehydrogenation. NiMoO4 has the highest surface concentration of strong acid sites, and it binds adsorbed isobutene more strongly than the other catalysts

Preparation, characterization, and catalytic activity of chromia supported on SBA-15 for the oxidative dehydrogenation of isobutane

Abstract Mesoporous SBA-15 and 1–12 wt% CrO x /SBA-15 have been prepared by triblock copolymer P123-templated hydrothermal synthesis and incipient wetness impregnation method, respectively. The materials were characterized by means of a number of analytical techniques and their catalytic activities were evaluated for the oxidative dehydrogenation (ODH) of isobutane. It is found that with rise of chromia loading, the morphology of SBA-15 changed from long interconnected chains to short banana-like rods, and finally changed to spheres with wormholes. The results of Raman and X-ray photoelectron spectroscopic investigations reveal that the surface Cr species are mainly Cr 6+ in mono- and polychromate, with a minor amount of Cr 3+ due to α-Cr 2 O 3 formation. The H 2 temperature-programmed reduction study demonstrates that the catalysts at chromia loading of 6–10 wt% are more reducible. The 10 wt% CrO x /SBA-15 catalyst exhibits the best activity, showing 79% C 4 -olefin selectivity and 11% C 4 -olefin yield at 540 °C. One monolayer CrO x coverage on SBA-15 occurs at Cr surface density = 1.05–1.43 Cr-atom/nm 2 . We conclude that factors such as (i) presence of active Cr 6+ in mono- and polychromate, (ii) strong redox ability of Cr species, and (iii) good dispersion of CrO x on banana-like rods of well-ordered mesoporous SBA-15 are responsible for the good performance of the SBA-15-supported chromia in isobutane ODH.

Selective Oxidation and Oxidative Dehydrogenation of Isobutane over Hydrothermally Synthesized Mo–V–O Mixed Oxide Catalysts

A series of Mo–V–O catalysts were prepared by calcining the orthorhombic (M1) Mo–V–O phase containing precursors under different conditions (T = 500 or 600 °C in atmosphere of N2 or air) and tested for the oxidation of isobutane and isobutene. Characterization results (BET, XRD, XPS, FTIR, and TPR) showed that their structure and properties depend on the composition of the calcined samples and the calcined conditions. Catalytic tests showed that relatively high isobutane conversion and desired product selectivity can be achieved over MoV0.3-500-N and MoV0.3-600-A catalysts. It is also found that both orthorhombic M1 phase and (V0.07M0.93)5O14 phase are active and selective for the selective oxidation of isobutane to methacrolein, whereas higher selectivity toward methacrolein (40.4%) can be achieved over the former phase at a moderate isobutane conversion (6.4%). Moreover, (Mo0.3V0.7)2O5 phase may be propitious to complete oxidation for the selective oxidation of isobutane. On the other hand, the presence of V affects the activity and selectivity, and a low surface V4+ concentration prefers selective oxidation products. In addition, specific surface areas of the catalysts appear to be little important in determining the catalytic activation.

Kinetics and mechanism of the oxidative dehydrogenation of isobutane on cobalt, nickel, and manganese molybdates

The kinetics of oxidative dehydrogenation of isobutane in the presence of atmospheric oxygen on manganese molybdate has been studied. The experiments have been carried out in a circulation flow reactor at 470–530°C. The form of kinetic equations and the mechanism of the formation of isobutene, carbon oxides, and cracking products on manganese molybdate are similar to those found previously for the same reaction on cobalt and nickel molybdates. The highest yields of isobutene and propene (isobutane cracking products) are achieved on Co0.95MoO4. The mechanism of the process has been investigated by the unsteady-state response method. Manganese molybdate contains the largest amount of reactive oxygen, whereas nickel molybdate contains the smallest amount of reactive oxygen. The earlier conclusion that molybdate lattice oxygen and chemisorbed oxygen play the main role in the formation of iso-C4H8 and in deep oxidation processes, respectively, is confirmed.

DC magnetron sputter deposited vanadia catalysts for oxidation processes

Abstract New model catalysts were prepared by applying DC magnetron sputter deposition of vanadia onto ZrO 2 /SiO 2 and TiO 2 /ZrO 2 /SiO 2 supports and were characterized by X-ray diffraction (XRD), X-ray energy dispersive spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma emission spectroscopy (ICP) and catalytic activity towards propane and isobutane oxidative dehydrogenation. Titania interlayer enhances oxidative dehydrogenation activity and decreases the total oxidation side reactions. A Mars–van Krevelen mechanism is operative.

Oxidative dehydrogenation of isobutane over activated carbon catalysts

In past work, we reported on the textural and chemical modifications induced by treating an activated carbon under nitrous oxide, oxygen and hydrogen. In this work, we are reporting on the testing of surface modified activated carbons in the oxidative dehydrogenation of isobutane (ODHI). The results show that the different treatments lead to a given catalytic performance associated with the degree of oxidation. At 648 K, isobutene yields are higher in the initial stages for the activated carbons with the highest amounts of carbonyl/quinone groups on the surface, which are considered the active sites for this reaction, and the isobutene yields are lower for the catalysts with lower concentrations of these groups. As the reaction proceeds, the reactant mixture (isobutene–oxygen and argon as carrier gas) is able to introduce active sites onto the carbon surface to the point where they are stabilized for the case of treatment in H 2 and without pretreatment. For the other treatments, N 2O and oxygen, the active sites are rearranged and stabilized after a while. It is observed that there is a tendency towards a similar CO/CO 2 relationship as measured by TPD, corresponding to a yield of about 7% after 5 h of reaction.

Oxidative dehydrogenation of isobutane to isobutene III: Reaction mechanism over CePO 4 catalyst

Among rare earth phosphates, only CePO 4 and LaPO 4 exhibit very high activity for oxidative dehydrogenation (ODH) of isobutane. This phenomenon was studied in comparison with the corresponding oxides. Isobutene was formed over NdPO 4, which was used as a representative of inactive phosphate catalysts, by simple dehydrogenation with 30–32% selectivity, C 3H 6 and CO 2 were formed with a selectivity of 25–33% and 20–30%, respectively. Isobutene was obtained at a higher selectivity of 79–86% over CePO 4 and LaPO 4. No H 2 formation suggests that the essential reaction was the ODH of isobutane. In the oxidation over metal oxides, isobutene selectivity was relatively high: 60–70% over CeO 2; however, the essential reaction was considered to be a simple dehydrogenation. Isobutene was formed at 40–47% selectivity, but simple dehydrogenation of isobutane would proceed over Nd 2O 3 and La 2O 3. La 2O 3, Nd 2O 3, and NdPO 4 have only weak acidic sites. CeO 2 has weak acidic sites and those with intermediate strength; LaPO 4 and CePO 4 have relatively strong acidic sites in addition to the weak acidic sites and those of intermediate strength. Oxidative dehydrogenation activity was correlated with strong acidic sites. ODH of isobutane occurred in the reaction between lattice oxygen of CePO 4 and isobutane. Introduction of NH 3 into the reaction system reduced both ODH of isobutane and CO 2 formation; and stopping the NH 3 supply led to a resumption of the activity, which suggests the participation of acidic sites. CePO 4 catalyst contained 2% excess Ce to P; in the prepared CePO 4 sample, Ce 4+ was detected by XPS. We conclude that acidic sites and redox between Ce 4+ and Ce 3+ play important roles in the ODH of isobutane.

Oxidative dehydrogenation of isobutane on chromium oxide-based catalyst

Isobutane oxidative dehydrogenation offers a prospect of cheaper and environment friendly route to isobutene. The reaction has been studied at 250 °C, 1 atm and feed flow rate of 75 cm 3/min over supported chromium oxide-based catalysts. Effects of various supports (Al 2O 3, MgO, TiO 2 and SiO 2), catalyst precursors (K 2Cr 2O 7, CaCr 2O 7·H 2O, CrO 3, CrK(SO 4) 2·12H 2O and Cr(NO 3) 3·9H 2O) and binary mixed metal oxide catalysts of the form Cr-M-oxide/γ-Al 2O 3 (where M is V, Ni, Co, Mo, W, Ho, La, Li or Bi) were investigated. The supported catalysts are ranked (based on isobutene yields at 250 °C) as; Cr-Mg-O (3.4%) = Cr-Si-O (3.4%) < Cr-Ti-O (4.5%) < Cr-Al-O (6.0%). The performances of the catalysts showed strong dependence on the precursor used. The 10 wt.% Cr-Al-O prepared using K 2Cr 2O 7 and CrK(SO 4) 2·2H 2O exhibited the lowest isobutene yields of 0.14 and 0.3%, respectively. Partial substitution of chromium ions with nickel or tungsten exhibited minor increase in selectivity to isobutene of about 6% at comparable isobutane conversions. Substitution with other metals show similar or inferior performance compared with the base catalyst. Thus, showing that chromium oxide-based catalysts are active for the reaction and their performance could be improved by appropriate choice of active component precursor, support and additives.

Oxidative dehydrogenation of isobutane over titanium pyrophosphate catalyst

The catalytic properties of titanium pyrophosphate in the oxidative dehydrogenation of isobutane to isobutylene were investigated in the 400 ? 550 ?C temperature range. Asignificant change of the product distribution and of the apparent activation energy of the reaction was observed at about 490 ?C. This phenomenon, already observed in the oxidative dehydrogenation of n-butane, has been interpreted by the existence of two reaction mechanisms depending upon the reaction temperature. Comparison with the n-butane reaction allowed different activation pathways for the activation of alkanes to be proposed. The catalytic properties of TiP2O7 in the oxidative dehydrogenation of isobutane was also compared to those obtained previously with several other pyrophosphates and TiP2O7 was found to be less active and selective for this reaction.