Dehydrogenation Of N-butane Research Articles

Oxidative dehydrogenation of n-butane to butadiene over Bi–Ni–O/γ-alumina catalyst

Oxidative dehydrogenation of n-butane to 1,3-butadiene over Bi–Ni oxide/γ-Al2O3 catalyst was studied with fixed bed/flow-type reactor at 400–500°C. The γ-Al2O3 support itself showed activity for oxidative dehydrogenation from n-butane to n-butenes as well as partial oxidation to CO. The role of Ni oxide on γ-Al2O3 was confirmed that sole Ni oxide loading until 30wt% Ni on γ-Al2O3 resulted higher activity and selectivity to butadiene by diminishing partial oxidation related to γ-Al2O3 and enhancing conversion to butadiene. The concerted effect of Bi and Ni in Bi–Ni oxide/γ-Al2O3 catalyst was confirmed with two methods: (1) partial or full substitution of Bi for 1/3, 2/3 and 3/3 Ni of 30wt% Ni on γ-Al2O3, and (2) various amounts of Bi addition to 20wt% Ni on γ-Al2O3. As for (1) Bi substitution, 10wt% Bi-20wt% Ni showed higher activity and selectivity than the others. As for (2) Bi addition, it until Bi/Ni=0.82 (60wt% Bi-20wt% Ni) lead to suppressed CO/H2 production and improved conversion to butadiene. 30wt% Bi-20wt% Ni oxide/γ-Al2O3 catalyst showing the highest butadiene selectivity of about 47% at 450°C was used to confirm the relation between the state of oxygen and the reaction pathways by changing reaction condition factors, oxygen-to-butane ratio and temperature. It was revealed by catalyst characterization that the catalyst of Bi modified and Ni oxide highly loaded on γ-Al2O3 has high activity and selectivity for oxidative dehydrogenation of n-butane to butadiene due to either an improved Ni dispersion and redox property or a couple of weak acidity and moderate basicity.

Synthesis of a Structured Material Based on Compact Spheres Coated with Zn or Mg Spinel

In this work, a synthesis method of coating with thin layers of MgAl2O4 or ZnAl2O4 over α-Al2O3 spheres were developed. The method consisted in the deposition of a primer of bohemite on the spheres, followed by the impregnation with a solution of Mg or Zn nitrates, and further thermal treatments in order to obtain MAl2O4 (M: Mg or Zn). This method was modified to improve the thickness and purity of the layer material. With this method, layers of uniform and adequate thickness and good adhesion were achieved. Pt catalysts prepared with these materials as supports displayed good catalytic performances in the n-butane dehydrogenation reaction, especially those obtained with purified supports.

Kinetic Modelling of n-butane Dehydrogenation Over CrOxVOx/MCM-41 Catalyst in a Fixed Bed Reactor

The kinetics of n-butane dehydrogenation over CrOxVOx/MCM-41 catalyst was studied. The models were developed based on the catalyst tests carried out in a packed bed reactor at reaction temperatures varied from 525 to 575 °C under atmospheric pressure. The dehydrogenation of n-butane mainly gives butene isomers (over 90%), 1,3-butadiene and cracked products consisting of methane, ethane, ethene and propene. Based on the experimental observations, power law type models were formulated and parameters were estimated by fitting the experimental data implemented in MATLAB. The activation energy for the formation of butenes (96.2 kJ mol−1) was found to be considerably less than the activation energy for the formation of the undesirable cracked products (130.4 kJ mol−1).

Mg3(VO4)2-MgO-ZrO2 nano-catalysts for oxidative dehydrogenation of n-butane.

A series of X-Mg3(VO4)2-MgO-ZrO2 nano-catalysts with different vanadium content (X = 3.3, 5.3, 7.0, 10.2, and 13.4) were prepared by a single-step citric acid-derived sol-gel method for use in the oxidative dehydrogenation of n-butane to n-butene and 1,3-butadiene. The effect of vanadium content of X-Mg3(VO4)2-MgO-ZrO2 nano-catalysts on their physicochemical properties and catalytic activities in the oxidative dehydrogenation of n-butane was investigated. Successful formation of X-Mg3(VO4)2-MgO-ZrO2 nano-catalysts was confirmed by XRD, Raman spectroscopy, and ICP-AES analyses. The catalytic performance of X-Mg3(VO4)2-MgO-ZrO2 nano-catalysts strongly depended on vanadium content. All the X-Mg3(VO4)2-MgO-ZrO2 nano-catalysts showed a stable catalytic performance without catalyst deactivation during the reaction. Among the catalysts tested, 7.0-Mg3(VO4)2-MgO-ZrO2 nano-catalyst showed the best catalytic performance in terms of yield for total dehydrogenation products (TDP, n-butene and 1,3-butadiene). TPRO (temperature-programmed reoxidation) experiments were carried out to measure the oxygen capacity of the catalyst. Experimental results revealed that oxygen capacity of the catalyst was closely related to the catalytic performance. Yield for TDP increased with increasing oxygen capacity of the catalyst.

Bifunctional Catalytic System Effective for Oxidative Dehydrogenation of 1-Butene and n-Butane Using Pd-Based Intermetallic Compounds

The catalytic performance of Pd-based intermetallic compounds supported on silica (PdmMn/SiO2: M = Bi, Fe, Ge, In, Sn, Zn) was investigated in oxidative dehydrogenation of 1-butene and n-butane. A remarkable increase in selectivity (and also yield) of dehydrogenation products (1,3-butadiene and/or 1-butene) was obtained when PdIn, PdBi, or Pd3Fe replaced monometallic Pd. Temperature-programmed reduction and X-ray diffraction (XRD) studies on the catalysts with various treatments (i.e., the fresh, spent, and calcined) suggested that redox of the second metal was involved in the catalysis. XRD, X-ray photoelectron spectra, and transmission electron microscopy–energy dispersive X-ray spectroscopy analyses using the spent PdIn/SiO2 catalyst revealed the formation of a core–shell structure consisting of a PdIn1−δ core and Pd–In2O3 composite shell formed by oxidative decomposition of PdIn during the reaction. A mechanistic study suggested that the presence of In atoms, adjacent to Pd atoms, effectively inhibits...

Oxidative Dehydrogenation of n-Butane: Activity and Kinetics Over VO x /Al2O3 Catalysts

The catalytic activity of a VO x /Al2O3 catalyst for the oxidative dehydrogenation of n-butane is investigated. The effects of reaction temperature, oxygen to n-butane ratio and GHSV on the catalytic performance are examined and optimized. Interestingly, this simple catalyst gives good conversion and selectivity. Butane was 22–24 %, and the selectivity to C4 alkenes was 56 %, of which 20–22 % to 1,3-butadiene. Moreover, the catalyst is stable for at least 72 h on stream. Kinetic studies show that the activation barriers for the formation of (butene + butadiene), CO and CO2 amount to 70.2, 65 and 81.3 kJ/mol respectively.

Physics of the multi-functionality of lanthanum ferrite ceramics

In the present work, we have illustrated the physics of the multifunctional characteristics of nano-crystalline LaFeO3 powder prepared using auto-combustion synthesis. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. The temperature dependence of dielectric constant of pure LaFeO3 exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. The dielectric relaxation of LaFeO3 correlates well with small polaron conduction. The occurrence of polarization hysteresis in LaFeO3 (with centro-symmetric Pnma space group) is thought to be spin current induced type. The canting of the Fe3+ spins induce weak ferromagnetism in nano-crystalline LaFeO3. Room temperature saturation magnetization of pure LaFeO3 is reported to be 3.0 emu/g. Due to the presence of both ferromagnetic as well as polarization ordering, LaFeO3 behaves like a single phase multiferroic ceramics. The magneto-electric coupling in this system has been demonstrated through the magneto-dielectric measurements which yield about 0.8% dielectric tuning (at 10 kHz) with the application of 2 T magnetic field. As a typical application of the synthesized nano-crystalline LaFeO3 powder, we have studied its butane sensing characteristics. The efficient butane sensing characteristics have been correlated to their catalytic activity towards oxidation of butane. Through X-ray photoelectron spectroscopy analyses, we detect the surface adsorbed oxygen species on LaFeO3 surface. Surface adsorbed oxygen species play major role in their low temperature butane sensing. Finally, we have hypothesized that the desorbed H2O and O2 (originate from surface adsorbed hydroxyl and oxygen) initiate the catalytic oxidative dehydrogenation of n-butane resulting in weakening of the electrostatics of the gas molecules.

Direct dehydrogenation of n-butane over Pt/Sn/M/γ-Al2O3 catalysts: Effect of third metal (M) addition

A series of Pt/Sn/M/γ-Al2O3 catalysts with different third metal (M=Zn, In, Y, Bi, and Ga) were prepared by a sequential impregnation method for use in the direct dehydrogenation of n-butane to n-butene and 1,3-butadiene. In the direct dehydrogenation of n-butane, Pt/Sn/Zn/γ-Al2O3 catalyst showed the best catalytic performance. Catalytic performance decreased in the order of Pt/Sn/Zn/γ-Al2O3>Pt/Sn/In/γ-Al2O3>Pt/Sn/γ-Al2O3>Pt/Sn/Y/γ-Al2O3>Pt/Sn/Bi/γ-Al2O3>Pt/Sn/Ga/γ-Al2O3. The catalytic performance increased with increasing metal–support interaction and Pt surface area of the catalyst.

CO2 promoted oxidative dehydrogenation of n-butane over VOx/MO2–ZrO2 (M = Ce or Ti) catalysts

The CO2 promoted oxidative dehydrogenation (ODH) of n-butane was investigated over mixed metal oxide supported vanadium catalysts. The investigated mixed metal oxide supports namely, CeO2–ZrO2 (CZ) and TiO2–ZrO2 (TZ) were synthesized by coprecipitation method, and the vanadium oxide was deposited on the supports by wet impregnation method. The synthesized samples were characterized by BET surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) techniques. The XRD analysis of CZ and CZ supported V2O5 samples revealed the formation of CexZr1−xO2 solid solution and a highly dispersed vanadium oxide over the CZ support, respectively. On the other hand, different mixed oxide phases (ZrV2O7 and TiZrO4) were observed in the case of TZ supported vanadia catalyst. The TPR reduction temperature of supported samples is lower than the bulk V2O5. XPS results revealed that vanadium and cerium are in V5+ and Ce4+/Ce3+ oxidation states, respectively. Among the investigated catalysts, the CZ supported vanadium oxide catalyst exhibited a high activity and good time-on-stream stability. The redox property of the catalyst significantly influenced the catalytic activity in the ODH of n-butane with CO2.

Effects of Si/Al Ratio on the Distribution of Framework Al and on the Rates of Alkane Monomolecular Cracking and Dehydrogenation in H-MFI

The aim of this study was to investigate the influence of Si/Al ratio on the locations of exchangeable cations in H-MFI and on the monomolecular cracking and dehydrogenation reactions of n-butane. On the basis of UV-visible spectroscopic analysis of Co(II) exchanged into MFI, it was inferred that the fraction of Co(II) (and, by extension, Brønsted protons) located at channel intersections relative to straight and sinusoidal channels increases with increasing Al content. Concurrently, turnover frequencies for all monomolecular reactions, and the selectivities to dehydrogenation versus cracking and to terminal cracking versus central cracking, generally increased. The changes in selectivity with Al content are consistent with the finding that the transition-state geometry for dehydrogenation is bulky and resembles a product state, and should therefore exhibit a stronger preference to occur at channel intersections relative to cracking. Increases in turnover frequencies are attributed partly to increases in intrinsic activation entropies that compensate for concurrent increases in intrinsic activation energies, most strongly for dehydrogenation and terminal cracking, resulting in increased selectivity to these reactions at higher Al content. This interpretation contrasts with the view that intrinsic activation barriers are constant. It is also observed that isobutene inhibits the rate of n-butane dehydrogenation. Theoretical calculations indicate that this effect originates from adsorption of isobutene at the channel intersections. Because cracking reaction rates are not affected by the presence of isobutene, this result suggests that the preference of dehydrogenation to occur at channel intersections is much stronger than the preference for cracking to occur at these locations.

Effect of potassium addition on bimetallic PtSn supported θ-Al2O3 catalyst for n-butane dehydrogenation to olefins

PtSn/θ–Al2O3 catalysts with different amount of potassium (0.4, 0.7, 0.95, 1.2 and 1.45wt.%) were prepared by an impregnation method, and their catalytic activity in n-butane dehydrogenation was investigated at 823K, an atmospheric pressure and a GHSV of 18,000mL(gcath)−1. The compositions listed in order of n-C4= yields at 823K were as follows: K0.95(PtSn)1.5>(PtSn)1.5>K0.4(PtSn)1.5>K0.7(PtSn)1.5>K1.2(PtSn)1.5>K1.45(PtSn)1.5>K0.9(Pt)1.5. The K0.9(Pt)1.5 and K0.95(Sn)1.5 catalyst severely deactivated in n-butane dehydrogenation. The (PtSn)1.5 (without K) catalyst showed the highest n-butane conversion, while K0.95(PtSn)1.5 did the highest n-C4= yield. The small amount of potassium on bimetallic PtSn/θ-Al2O3 catalyst improved n-C4= selectivity, but slightly decreased n-butane conversion, resulting in the increase of n-C4= yield. The effect of potassium was caused by blocking the acid sites of Pt catalyst. The TPR and HAADF STEM-EDS study suggested the reduction procedure of the Pt, Sn and K species. However, the higher loaded potassium (1.2 and 1.45wt.%) doped (PtSn)1.5 catalysts were rather highly deactivated because the sizes of Pt particles were increased by weakening the interaction between Pt and Sn. The n-C4= selectivity of the (PtSn)1.5 catalyst increased with respect to the reaction, while that of the potassium doped catalysts maintained the high n-C4= selectivity from the beginning of the reaction. Also, different alkali metals (Ca, Na and Li) were tested for the comparison with K. The potassium doped catalyst showed the highest n-C4= yield among the other alkali metals for n-butane dehydrogenation.

Oxidative Dehydrogenation of n-Butane Over Magnesium Vanadate Nano-Catalysts Supported on Magnesia–Zirconia: Effect of Vanadium Content

Magnesia-zirconia (MgO-ZrO2) support was prepared by a sol-gel method, and magnesium vanadate nano-catalysts supported on magnesia-zirconia (X-Mg3(VO4)2/MgO-ZrO2) were then prepared by a wet impregnation method with a variation of vanadium content (X = 6.6, 9.9, 12.8, 15.2, and 19.1 wt%). X-Mg3(VO4)2/MgO-ZrO2 nano-catalysts were applied to the oxidative dehydrogenation of n-butane to n-butene and 1,3-butadiene. The formation of X-Mg3(VO4)2/MgO-ZrO2 nano-catalysts was well confirmed by XRD, XPS, and ICP-AES analyses. 15.2-Mg3(VO4)2/MgO-ZrO2 and 19.1-Mg3(VO4)2/MgO-ZrO2 catalysts experienced a catalyst deactivation, while the other Mg3(VO4)2/MgO-ZrO2 catalysts showed a stable catalytic performance during the whole reaction time. The effect of oxygen property of X-Mg3(VO4)2/MgO-ZrO2 nano-catalysts on the catalytic performance in the oxidative dehydrogenation of n-butane was investigated. Experimental results revealed that oxygen capacity of the catalyst was closely related to the catalytic performance, while oxygen mobility of the catalyst played an important role in the catalyst stability. Among the catalysts tested, 12.8-Mg3(VO4)2/MgO-ZrO2 catalyst showed the best catalytic performance in terms of yield for TDP (total dehydrogenation products).

Vanadium Mesoporous Silica Catalyst Prepared by Direct Synthesis as High Performing Catalyst in Oxidative Dehydrogenation of n-Butane

The catalytic oxidative dehydrogenation (ODH) of light alkanes has great potential to be used for production of alkenes instead classically used dehydrogenation. We report successful direct synthesis of vanadium mesoporous silica material—nSi/nV = 10 which could be convenient catalyst for ODH of alkane. The extraordinary high productivity (1.92 kgprod kg cat −1 h−1) in n-butane ODH is 3–4 times higher in comparison to supported vanadium catalysts usually prepared by wet impregnation method. It ranks this catalyst among the best materials investigated so far in this reaction. Moreover, reported catalytic system exhibits catalytic activity stable for more than 8 h in the stream.

N-Butane dehydrogenation over Pt/Mg(In)(Al)O

The thermal dehydrogenation of butane to butene and hydrogen was investigated over Pt nanoparticles supported on calcined hydrotalcite containing indium, Mg(In)(Al)O. Prior work has shown that upon reduction in H2 at temperatures above 673K, bimetallic Pt-In particles of are formed, as evidenced by XANES and EXAFS. The performance of Pt/Mg(In)(Al)O for butane dehydrogenation was found to be highly dependent on the bulk In/Pt ratio. The optimal ratio was found to be between 0.33 and 0.88, yielding >95% selectivity to butenes. Hydrogen co-fed with butane was shown to suppress coke formation and catalyst deactivation, a ratio of H2/C4H10=2.5 providing the best catalytic performance. Regeneration of catalysts after removal of accumulated carbon and reduction in H2 restored the original catalyst activity and selectivity. Butane dehydrogenation above 803K resulted in higher formation of butadiene, a known precursor to coke. No evidence for butane cracking was found to occur on Pt/Mg(In)(Al)O due to moderately basic nature of the support. The present study shows that Pt/Mg(In)(Al)O exhibits superior performance for butane dehydrogenation compared to supported Pt catalysts promoted with Sn, Ge, Pb, and In prepared by successive incipient wetness impregnation of the Pt and promoter precursors.

Dehydrogenation of n-butane on the industrial microspherical chromia-alumina catalyst AOK-73-24 in a membrane reactor

The basic features of the catalytic membrane dehydrogenation of n-butane have been studied in a reactor with membrane modules based on Pd/Ag foil of 9.3 and 30 μm thickness and in the absence of the membrane (temperature, 500–550°C; feed space velocity, 150–1200 h−1). It has been shown that in the absence of the membrane, the dehydrogenation of n-butane occurs in the kinetic region. The membrane thickness has a significant effect on the performance of the catalytic membrane reaction, presumably, because of the difference in the rate of H2 withdrawal from the reaction mixture. In the reactor with the 9.3-μm thick Pd/Ag-foil, the reaction is controlled by the H2 formation rate. As the thickness of the palladium foil is increased to 30 μm, the reaction proceeds to the diffusion region, thereby resulting in both enhancement of selectivity for butenes and a reduction of the yield of hydrocarbon deposits.

Dehydrogenation of alkane to light olefin over PtSn/θ-Al2O3 catalyst: Effects of Sn loading

Pt0.5Snx.x/θ-Al2O3 catalysts with different amount of tin (0.5, 0.75, 1.0 and 1.5wt%) were prepared by a co-impregnation method. Propane dehydrogenation was performed at 873K and a GHSV of 53,000mL/(gcath). The Pt0.5/θ-Al2O3 catalyst showed severe deactivation in alkane dehydrogenation reaction. The Sn addition decreased the cracking products of C1–C2 and the Pt0.5Sn0.75 catalyst with the highest Pt dispersion showed the highest C3 yield and C3 selectivity. n-Butane dehydrogenation was performed at 823K and a GHSV of 18,000mL/(gcath). Similarly to propane dehydrogenation, the Sn addition to the Pt0.5/θ-Al2O3 catalyst decreased the cracking products of C1–C3. However, the Pt0.5Sn1.0 showed the highest n-C4 yield and the catalyst was steadily deactivated even at 823K differently from propane dehydrogenation at 873K.The small amount of Sn addition improved the C3 and n-C4 selectivity by blocking the cracking sites of Pt catalyst. The PtSn alloy formed after the reduction at 500°C. The PtSn formation can enhance the C3 and n-C4 selectivity. The Pt dispersion on the Pt0.5/θ-Al2O3 catalyst increased with the Sn addition up to 0.75 wt%. The highest Pt metal dispersion was observed on the Pt0.5Sn0.75 catalyst. The conclusion was given to the Sn effects on the increase of Pt dispersion to enhance the activity as well as on the electronic and geometric effect of PtSn alloy to increase the stability and olefin selectivity.

Catalytic properties of Pt-based intermetallic compounds in dehydrogenation of cyclohexane and n-butane

A series of Pt-based intermetallic compounds supported on silica (PtmMn/SiO2: M=Co, Ge, Sn, Tl and Zn) were prepared by conventional impregnation and chemical vapor deposition. Catalytic properties of the intermetallic compounds in dehydrogenation of cyclohexane and n-butane were investigated. Pt3Sn/SiO2 and PtGe/SiO2 showed higher yields of benzene and butenes than Pt/SiO2 and other intermetallic catalysts (Pt3Zn, Pt3Co, PtCo, Pt3Tl2 and PtSn). Especially in n-butane dehydrogenation, Pt3Sn/SiO2 exhibited much higher butenes yield than other intermetallic catalysts and Pt/SiO2. However, a similar Pt–Sn intermetallic catalyst, PtSn/SiO2, showed very poor yields in both reactions. Pt3Sn and PtSn, Pt3Sn was the most active species in the n-butane dehydrogenation among several Pt–Sn bimetal phases, Pt1−xSnx solid solution (0<x<0.3).

Behavior of PtPb/MgAl2O4 catalysts with different Pb contents and trimetallic PtPbIn catalysts in n-butane dehydrogenation

The behavior of PtPb/MgAl2O4 catalysts in butenes production through the n-butane dehydrogenation has shown that at low contents, the Pb acts as promoter, improving the conversion and selectivity, whereas at higher contents it has a poisoning effect on the catalytic activity. The PtPb(0.25wt%)/MgAl2O4 catalyst showed the maximum yield to butenes. The characterization results of PtPb catalysts displayed that at low Pb contents there are both dilution and electronic effects of Pb on the Pt sites. On the other hand, at high Pb contents, there is a strong blocking effect of the Pb on the active sites of Pt. In order to study the effect of the In addition in different sequences to PtPb(0.25wt%)/MgAl2O4 catalyst, two catalysts were prepared: PtPb(0.25%)In(0.28wt%)/MgAl2O4 and PtIn(0.28%)Pb(0.25wt%)/MgAl2O4. The first catalyst did not show significant advantages with respect to the catalytic behavior of the PtPb(0.25wt%)/MgAl2O4, but the second trimetallic catalyst displayed an increase of both the conversion and the selectivity. The characterization results indicated similar effects of blocking and dilution of promoters on the active sites of Pt for both trimetallic catalysts, but the best catalyst, PtIn(0.28%)Pb(0.25wt%)/MgAl2O4, showed the highest percentages of In° and Pb°, thus indicating stronger interaction between Pt, Pb and In.

Selective and stable bimetallic PtSn/θ-Al2O3 catalyst for dehydrogenation of n-butane to n-butenes

PtSn/θ-Al2O3 with various Pt and Sn compositions was prepared by a co-impregnation method using θ-Al2O3 support for n-butane dehydrogenation reaction. The monometallic Pt1.5/θ-Al2O3 catalyst showed severe deactivation in n-butane dehydrogenation. The bimetallic PtSn/θ-Al2O3 catalyst improved the n-C42− yield and the stability. The compositions listed in order of n-C42− yield at 823K are as follows: (PtSn)1.5>(PtSn)1.0>(PtSn)2.0>(PtSn)0.5>Pt1.5>Sn1.5. The n-C42− yields increased with the specific metal surface area. The Sn loading was varied on the Pt1.5 loaded catalyst. Then, the compositions listed in order of n-C42− yield at 823K were as follows: (PtSn)1.5>Pt1.5Sn1.0>Pt1.5Sn2.0>Pt1.5Sn0.5>Pt1.5. The n-C42− yield was maximized at a Pt/Sn weight ratio of 1.0. The n-C42− selectivity of the Pt1.5 catalyst was substantially improved by the Sn addition. TEM and XRD studies indicated PtSn alloy formation on the bimetallic PtSn catalysts during the reduction. The PtSn alloy can increase the n-C42− selectivity by blocking the cracking and hydrogenolysis sites of the Pt catalyst. TPR and HAADF STEM-EDS studies suggest the reduction procedure of the Pt and Sn species. The scattered Pt oxides in the vicinity of the well-dispersed Sn oxides were co-reduced, and then the reduced Sn metals migrated to the PtSn particles, resulting in a PtSn alloy. The specific metal surface area of the Pt1.5 sample was much lower than that of the (PtSn)1.5 sample. Therefore, it can be suggested that Pt metal sintering can be retarded by PtSn alloy formation during the reduction, resulting in high specific metal surface area. These observations demonstrate that the addition of Sn can enhance the activity and n-C42− selectivity.

Oxidative dehydrogenation of n-butane over bimetallic mesoporous and microporous zeolites with CO2 as mild oxidant

Oxidative dehydrogenation of n-butane was tested using carbon dioxide as a mild oxidant over bimetallic Cr–V supported catalysts (MCM-41, ZSM-5, MCM-22 and mesoZSM-5). The textural properties of the catalysts were measured by means of XRD, N2 adsorption, SEM-EDX, Raman, H2-TPR, pyridine FT-IR, NH3 and CO2-TPD techniques. The metal content of Cr and V was maintained around 1.2 and 2.8 wt% for the catalytic test in packed bed reactor at different temperatures (525–600 °C) for 180 min. 1.2Cr2.8 V/MCM-41 and 1.2Cr2.8 V/ZSM-5 exhibited maximum conversion of 14 and 13.1 %, respectively at 10 min and 600 °C. Significantly, high butenes selectivity was observed over MCM-41 (86.27 %) than ZSM-5 support (58.1 %). The mesoporosity in ZSM-5 had a negative impact on conversion level (7.1 %) but improved the butenes selectivity slightly. 1.2Cr2.8 V/M-22 showed the highest cracking ability leading to overall reduced butenes selectivity (57.9 %). The study shows that over all catalysts, n-butane conversion is independent of CO2 conversion. 1.2Cr2.8 V/M-22 showed highest CO2 conversion in the range 2.35–2.2 % between 525 and 550 °C. The apparent activation energies of dehydrogenation and cracking reaction over the four catalysts were evaluated. The ratio of conversion to coke weight per cent over the four catalysts are observed in the following order: 1.2Cr2.8 V/M-41 > 1.2Cr2.8 V/Z-5 > 1.2Cr2.8 V/mesoZ-5 > 1.2Cr2.8 V/M-22.