Sb Oxide Catalysts Research Articles

Optimal biodiesel-additive synthesis under infrared excitation using pork bone supported-Sb catalyst: Engine performance and emission analyses

Glycerol (G) acetic acid (AA) esterification was conducted in an infrared irradiation (IRI) aided batch reactor for maximization of diacetin and triacetin yield (DT) using pork bone derived hydroxyapatite supported antimony (Sb) oxide catalyst. The catalyst possessed appreciable 40m2/g specific surface area; 4.5nm modal pore diameter and 0.0485cc/g pore volume with prominent Sb2O5 crystalline phase. Under derived optimal condition, 40% Sb precursor loading, 100°C reaction temperature and 6:1 AA:G mole ratio resulted maximum DT yield (88±1%). Notably, to achieve maximum DT yield (88±1%), conventionally heated batch reactor consumed 6 times more energy (reaction time 6h at 300J/s energy input rate) in comparison with IRI reactor (reaction time 2h at 150J/s energy input rate), indicating remarkable energy-efficiency of IRI. Additionally, synthesized product as additive to palm biodiesel evinced emission reduction by 50% and 20% for CO and HC respectively with 2 degrees depression in pour point.

ChemInform Abstract: Structural and Kinetic Studies in Propene Oxidation Over Sb Oxide Dispersed on TiO2.

Antimony oxide dispersed on Ti02 was characterized using FTIR, Raman, and Auger spectroscopies as well as XRD. They indicate that the electronic environment about Sb is perturbed at low concentration suggesting that the structure of Sb oxide on TiOr is somewhat distorted as compared to Sb60t3. The oxidation of labeled propene such as CHr==CH--CD,, ‘%ZHFCH-CH~, and cisCHD==CD-CH, was examined on Sb,O,, and Sb-Ti oxide catalysts. The results indicate that the first hydrogen abstraction is rate determining and that there is little or no isotope effect in the second hydrogen abstraction over Sb and Sb-Ti oxide catalysts. The oxidation kinetics was discussed on the basis of a modified redox mechanism. The reduction step was promoted by a factor of ca. 50 over Sb oxide dispersed on TiOr as compared to that on unsupported Sb60,,. Rate promotion was mainly attributed to the increase in the amount of active sites for the reduction step.

Effect of Fe doped over V–Sb oxide catalyst in toluene selective oxidation

Mixed oxides Fe x V 1− x SbO 4 with x = 0–1.0 were prepared by slurry method and characterized by X-ray diffraction (XRD), Mössbauer spectroscopy, and temperature-programmed reduction (TPR). The samples with x = 0, 0.4 and 1.0 were evaluated as catalyst in vapor phase toluene partial oxidation reaction. It was found by XRD that Fe, as doping, was introduced in the rutile structure of VSbO 4. The BET surface area of partially substituted solid with x = 0.4 was higher than those obtained for VSbO 4 and FeSbO 4 samples. It was shown that V is responsible of the hydrocarbon molecule activation. The catalyst with Fe x = 0.4 presented lower specific rate reaction and lower selectivity to total oxidation products than undoped solid (VSbO 4), which it would be related to a partial replace of V by Fe in the V–O–V chains. In conclusion, the solid activity and selectivity to total oxidation decrease due to a higher isolation of V sites, when V 3+ is substituted by Fe 3+ in the rutile structure.

Dehydrogenation of ethylbenzene with carbon dioxide over MgO-modified Al 2O 3-supported V–Sb oxide catalysts

Alumina-supported V 0.43Sb 0.57 oxide (VSb/Al) and MgO-modified alumina-supported V 0.43Sb 0.57 oxide catalysts (VSb/Mg n Al with Mg/Al atomic ratio, n = 0.1, 0.3 or 0.5) have been tested for the dehydrogenation of ethylbenzene with carbon dioxide as an oxidant. Their catalytic behaviors were interpreted by results of several catalyst characterization methods. The decrease in the surface acidity of the VSb/Mg n Al catalysts due to modification of alumina with MgO favors the prolonged time-on-stream activities. However, the addition of relatively large amounts of MgO ( n = 0.3 or 0.5) causes substantial decrease in their surface areas, reducibility of active vanadium oxide component and, consequently, ethylbenzene conversion. These negative factors did not become apparent for the most efficient VSb/Mg 0.1Al system demonstrating high and stable catalytic activity.

An Overview on the Dehydrogenation of Alkylbenzenes with Carbon Dioxide over Supported Vanadium–Antimony Oxide Catalysts

Utilization of carbon dioxide as a soft oxidant for the catalytic dehydrogenation of ethylbenzene (CO2-EBDH) has been recently attempted to explore a new technology for producing styrene selectively. This article summarizes the results of our recent attempts to develop effective catalyst systems for the CO2-EBDH on the basis of alumina-supported vanadium oxide catalysts. Its initial activity and on-stream stability were essentially improved by the introduction of antimony oxide as a promoter into the alumina-supported catalyst. Insertion of zirconium oxide into alumina support substantially increased the catalytic activity. Modification of alumina with magnesium oxide yielded an increase of catalyst stability of alumina-supported V–Sb oxide due to the coking suppression. Carbon dioxide has been confirmed to play a beneficial role of selective oxidant in improving the catalytic performance through the oxidative pathway, avoiding excessive reduction and maintaining desirable oxidation state of vanadium ion (V5+). The positive effect of carbon dioxide in dehydrogenation reactions of several alkylbenzenes such as 4-diethylbenzene, 4-ethyltoluene, and iso- and n-propylbenzenes was also observed. Along with the easier redox cycle between fully oxidized and partially reduced vanadium species, the optimal surface acidity of the catalyst is also responsible for achieving high activity and catalyst stability. It is highlighted that supra-equilibrium EBDH conversions were obtained over alumina-supported V–Sb oxide catalyst in CO2-EBDH as compared with those in steam-EBDH in the absence of carbon dioxide.

Dehydrogenation of Ethylbenzene with Carbon Dioxide as Oxidant over Mg-modified Alumina-supported V–Sb Oxide Catalysts

Abstract Modification of alumina support with an appropriate amount of magnesia (Mg/Al = 0.1) leads to the stable activity of the supported vanadium–antimony oxide catalyst for the dehydrogenation of ethylbenzene into styrene in the presence of carbon dioxide as oxidant. Correlation between catalytic performance and surface acidity has been found.

Niobia-supported Sb–V–O catalysts for propane ammoxidation: effect of catalyst composition on the selectivity to acrylonitrile

The effect of the Sb/V atomic ratio and of the total Sb + V coverage for the ammoxidation of propane to acrylonitrile on niobia-supported V–Sb oxide catalysts is reported. In all cases, acrylonitrile is produced along with propylene and CO2. Depending on the Sb + V coverage two different activity behaviours are reported: below the Sb + V dispersion limit on niobia, the system is predominantly selective to acrylonitrile, this fact has been attributed to exposed Nb centres and to V–Nb–O mixed oxide phases promoted by Sb. At Sb + V loading above monolayer coverage, the system is also selective to acrylonitrile but product distribution is clearly different and characteristic of SbVO4 phases, affording selectivities to propylene similar to those to acrylonitrile.

Effect of Sb/V Ratio and of Sb + V Coverage on the Molecular Structure and Activity of Alumina-Supported Sb–V–O Catalysts for the Ammoxidation of Propane to Acrylonitrile

The effect of the total coverage of Sb + V oxides and the effect of the Sb/V atomic ratio on the ammoxidation of propane to acrylonitrile on alumina-supported V and Sb oxide catalysts is reported. The fresh and used catalysts are characterized by XRD and in situ Raman spectroscopy. Comparison with binary V–Al–O and Sb–Al–O catalysts shows that the presence of both Sb and V oxides strongly enhances the rate of propane ammoxidation to acrylonitrile on alumina-supported Sb–V oxide catalysts. The stability and structural changes during on-stream operation prior to reach steady-state operation originates from a close interaction between Sb and V oxides. The Sb–V interaction depends on total Sb + V coverage on alumina. Below the dispersion limit, SbVO4 phases are not stable under reaction and break into the individual oxides. At Sb + V loading beyond dispersion limit, SbVO4 phases are stable under reaction conditions while Sb and V oxides that did not combine during calcination of the precursor recombine into SbVO4 phases. This solid-state reaction accounts for a higher propane conversion and selectivity to acrylonitrile. Comparison of the performance and molecular structures of fresh and used catalysts further suggests that Sb–V–O phases are necessary for this reaction. The specific formation of acrylonitrile per vanadium site reaches a maximum at an atomic Sb/V ratio of 2. It is likely that a moderate excess of antimony may be necessary for an efficient ammoxidation of propane to acrylonitrile.

Oxidation and ammoxidation of propane over Mo–V–Sb mixed oxide catalysts

Catalytic oxidation and ammoxidation of propane to acrolein and acrylonitrile, respectively, were carried out over Mo–V–Sb mixed oxide catalysts. V–Sb mixed oxide showed the activity for the oxidative dehydrogenation of propane to propene, and the selectivity to propene remarkably increased with increasing the concentration of cation vacancy in VSbO 4 phase. It is likely that the oxidative dehydrogenation of propane on the VSbO 4 phase is initiated via H-abstraction by acid–base concerted mechanism. The selectivity to acrolein and acrylonitrile increased by the addition of molybdenum species to V–Sb mixed oxide catalyst. Among a series of Mo–V–Sb oxide catalysts, Mo 1V 1Sb 10O x exhibited the highest selectivity to acrolein and acrylonitrile at 430 and 480°C, respectively. The highly dispersed molybdenum suboxide was formed together with the both phases of VSbO 4 and α-Sb 2O 4 in the Mo 1V 1Sb 10O x . The high catalytic activity of Mo 1V 1Sb 10O x can be explained by the bifunctional mechanism of the highly dispersed molybdenum suboxide and the VSbO 4 phases as follows: the oxidative dehydrogenation of propane proceeds on the VSbO 4 phase followed by the oxidation of propene into acrolein or the ammoxidation into acrylonitrile on the molybdenum suboxide phase. When large size of MoO 3 crystallites were formed, cracking reaction, i.e., C–C bond cleavage, occurred leading to non-selective total oxidation, resulting in decreasing the selectivities to acrolein and acrylonitrile.

Thermochemistry and Reactivity of Lattice Oxygen in V–Sb Oxide Catalysts for the Oxidative Dehydrogenation of Light Paraffins

Differential scanning calorimetry is used to study in situthe properties of strongly bound (lattice) oxygen in vanadium-containing supported catalysts for the oxidative dehydrogenation of paraffins C2–C4. Evidence is found that the process occurs via a stepwise redox mechanism with the participation of lattice oxygen from the catalyst. When the supported component is modified by an antimony additive, the amount of reactive oxygen increases and redox processes accelerate. Simultaneously, the rate of coke formation decreases. Additional modification by Bi and Ba leads to a further increase in the amount of reactive oxygen. In all cases, oxygen bound to vanadium atoms is responsible for the redox properties of the systems. The observed effects are analyzed from the standpoint of the ratio between different forms of active oxygen.

Selective oxidation of light alkanes over hydrothermally synthesized Mo-V-M-O (M=Al, Ga, Bi, Sb, and Te) oxide catalysts

Selective oxidations of ethane to ethene and acetic acid and of propane to acrylic acid were carried out over hydrothermally synthesized Mo-V-M-O (M=Al, Ga, Bi, Sb, and Te) complex metal oxide catalysts. All the synthesized solids were rod-shaped crystallites and gave a common XRD peak corresponding to 4.0 Å d-spacing. From the different XRD patterns at low angle region below 10° and from the different shape of the cross-section of the rod crystal obtained by SEM, the solids were classified into two groups: Mo-V-M-O (M=Al, possibly Ga and Bi) and Mo-V-M-O (M=Sb, and Te). The former catalyst was moderately active for the ethane oxidation to ethene and to acetic acid. On the other hand the latter was found to be extremely active for the oxidative dehydrogenation. The Mo-V-M-O (M=Sb, and Te) catalysts were also active for the propane oxidation to acrylic acid. It was found that the grinding of the catalysts after heat-treatment at 600°C in N 2 increased the conversions of propane and enhanced the selectivity to acrylic acid. Structural arrangement of the catalytic functional components on the surface of the cross-section of the rod-shaped catalysts seems to be important for the oxidation activity and selectivity.

Oxidation of isobutane over Mo–V–Sb mixed oxide catalyst

The catalytic performances of Mo–V–Sb mixed oxide catalysts have been studied in the selective oxidation of isobutane into methacrolein. V–Sb mixed oxide showed the activity for oxidative dehydrogenation of isobutane to isobutene. The selectivity to methacrolein increased by the addition of molybdenum species to the V–Sb mixed oxide catalyst. In a series of Mo–V–Sb oxide catalysts, Mo1V1Sb10Ox exhibited the highest selectivity to methacrolein at 440°C. The structure analyses by XRD, laser Raman spectroscopy and XPS showed the coexistence of highly dispersed molybdenum suboxide, VSbO4 and α-Sb2O4 phases in the Mo1V1Sb10Ox. The high catalytic activity of Mo1V1Sb10Ox can be explained by the bifunctional mechanism of highly dispersed molybdenum suboxide and VSbO4 phases. It is likely that the oxidative dehydrogenation of isobutane proceeds on the VSbO4 phase followed by the oxidation of isobutene into methacrolein on the molybdenum suboxide phase.

The structure of catalytically active vanadium sites in V–Sb oxides: an EPR study of asynthesized and tungsten promoted working catalysts

EPR investigation of complex V–Sb oxide catalysts used for the ammoxidation of propane to acrylonitrile (VSb y O x ( y=1, 2, 5), VSb 5WO x and 30 wt. % VSb 5WO x/Al 2O 3) indicated the presence of small amounts of isolated VO 2+ ions evidenced by characteristic hfs signals superimposed on broad singlets of interacting V 4+ centres. Almost equal g- and A-tensor parameters of the VO 2+ ions in the VSb y O x samples suggest their location in similar hosts, presumably in a XRD-amorphous V 5+O x -phase. Changes caused by tungsten doping indicate that W ions are incorporated in close neighbourhood to the vanadium ions. In samples with high antimony content additional V 4+–V 4+ pairs were detected. In situ measurements under reaction conditions (793 K, C 3H 8/N 2/O 2/NH 3) with a self-constructed in situ-EPR flow reactor revealed that not isolated VO 2+ centres but interacting V 4+ ions participate in the activation of propane while no changes of the vanadium signals occurred on addition of NH 3.

On the role of Sb excess in Fe–Sb oxides based catalysts

Fe–Sb oxide catalysts with different amounts of Ti were prepared by co‐precipitation technique. The stability of the systems is described in terms of the phases formed as a function of the calcination temperature, the Ti content and the use in the reactor.

Effect of ammonia chemisorption on the surface reactivity of V-Sb-oxide catalysts for propane ammoxidation

The influence of ammonia on the reactivity of a V—Sb-oxide catalyst in propane ammoxidation to acrylonitrile (ACN) was studied by infrared spectroscopy and flow reactor tests. Ammonia coordinates as such or as ammonium ions on the catalyst surface in relative amounts which depend on both the temperature at the time of contact and the hydroxylation state of the catalyst. The two chemisorbed species influence both the surface reactivity and the pathways of the reaction in propane ammoxidation. NH 3 chemisorbed on Lewis acid sites inhibits the activation of propane differently from that chemisorbed on Brønsted sites. The formation of the latter species, however, inhibits the reactivity of the Brønsted sites in catalyzing various side reactions which decrease the selectivity to ACN. The results of the infrared study are in good agreement with the change in surface reactivity observed in flow reactor tests as a function of the concentration of ammonia in the feed. Both the nature and the amount of the chemisorbed ammonia species thus determine the intrinsic surface reactivity and selectivity of V—Sb-oxide catalysts in the synthesis of acrylonitrile.

Surface chemistry of V–Sb–oxide in relation to the mechanism of acrylonitrile synthesis from propane Part 3.—Influence of ammonia on the competitive pathways of reaction

The effect of ammonia chemisorption on the surface reactivity of V–Sb–oxide catalysts with Sb/V=1.0 and the role of ammonia adspecies on the pathways of propane conversion to acrylonitrile are discussed in this third part of a series of three articles on the surface chemistry and reactivity of V–Sb–oxides for the synthesis of acrylonitrile from propane. Ammonia chemisorbed on Lewis-acid sites inhibits the activation of propane differently from that chemisorbed on Bronsted-acid sites, and the two ammonia adspecies play different roles in the further mechanism of transformation of the chemisorbed intermediates to acrylonitrile. Ammonium ions react with acrylate species to give acrylonitrile via acrylamine intermediates, whereas activated ammonia species formed by heterolytic splitting of coordinated NH 3 react with an allyl alcoholate intermediate to give an acrylimine adspecies further transformed to acrylonitrile. The second route is faster than the first. The conversion of Bronsted sites to ammonium ions by reaction with ammonia inhibits their negative action in catalysing side-reactions which decrease the selectivity to acrylonitrile. In particular, Bronsted-acid sites catalyse (i) a carbon chain degradation pathway leading to C 1 and C 2 species and (ii) the hydrolysis of an amide species, formed by reaction of ammonium ions with acrylate adspecies, with formation of free, weakly chemisorbed acrylic acid, the latter is probably an intermediate to the formation of carbon oxides. The overall reaction network in propane ammoxidation is also discussed with particular attention directed to the presence of multiple pathways of reaction from propane to acrylonitrile characterized by different rates and intrinsic selectivities.

Structure, activity and selectivity relationships in propane ammoxidation to acrylonitrile on V–Sb oxides Part 3Modifications during the catalytic reaction and effect of feed composition

The change in surface reactivity up until steady-state behavior is reached in propane ammoxidation of a series of V–Sb-oxide catalysts with Sb:V ratios in the range 1–10 and prepared either by calcination or heat treatment in vacuum at 600°C is reported and analyzed in terms of the change in the structural features of the catalyst determined as a function of the time on stream by IR spectroscopy, X-ray diffraction and chemical analysis data. The results indicate that during the catalytic reaction, V 5+ oxide when present, quickly reduces forming a V 4+ O 2 /VSbO 4 solid solution with an increase in the selectivity to propene, but not to acrylonitrile. An increase in the selectivity and productivity to acrylonitrile occurs when an Sb-rich approximate VSbO 4 phase forms (‘VSbO 4 ’). This phase, however, is partially metastable, decomposing to ‘VSbO 4 ’+Sb 2 O 4 when Sb 5+ ions are reduced and not rapidly reoxidized. V 5+ ions on the surface of the rutile phase stabilize the Sb-rich ‘VSbO 4 ’ phase, and catalyze the reoxidation of Sb 3+ . This side oxidation of ammonia to nitrogen competes for the reduction of these V 5+ ions and influences the above redox and solid-state reactions. Therefore, a considerable dependence of the surface reactivity on the feed was observed. The optimal catalytic behavior determined for the series of catalysts studied was found to depend on the feed composition indicating that in the analysis of the structure, activity and selectivity relationships in propane ammoxidation the concentration of reactants in the feed plays a specific important role.

An XPS, TEM, and TPD Study of the Oxidation and Ammoxidation of Propene Using Mixed Fe–Sb Oxide Catalysts

Two mixed Fe–Sb oxide catalysts were investigated for the selective oxidation of propene to acrolein and the ammoxidation of propene in the presence of ammonia to acrylonitrile. The techniques used were chiefly X-ray photoelectron spectroscopy (XPS), temperature deprogrammed desorption (TPD), X-ray diffraction, and transmission electron microscopy. After propene dosing TPD experiments were carried out in the absence of gas phase oxygen utilising lattice oxygen for oxidation. The samples contained a 1 : 1 and 2 : 1 atomic ratio of Sb : Fe (referred to as SbFe and Sb2Fe, respectively). XPS data indicate that the surface has an antimony oxide enriched selvedge which favours the selective ammoxidation of propene. The Sb enriched surface of SbFe was found to be highly reducible in low pressures of ammonia, yielding a metallic antimony overlayer. Subsequent thermal desorption of this metal coating revealed a surface with an increased iron (III) oxide content which was not so easily reduced and found to be of a lower selectivity to partial ammoxidation products. The Sb2Fe sample was more stable towards reduction.

Ammoxidation of α-methylstyrene to atroponitrile over U-Sb-oxide catalysts

Atroponitrile (α-phenylacrylonitrile) can be synthesized by the direct catalytic ammoxidation of α-methylstyrene. Conversions to atroponitrile of 57% per pass with a selectivity of 85% are attained using a Nb-promoted USb 4.6O 13.2 catalyst. Several other USboxide catalysts give similar results. A detailed study of reaction variables shows that an optimal yield of atroponitrile is formed under conditions of short contact times (0.5 sec), low surface area (7 m 2/g), low feed: air + diluent ratio ( 1 120 ), and N 2 dilution. The structure of the major product of α-methylstyrene ammoxidation has been unambiguously determined as α-phenylacrylonitrile by ir, NMR, and low-voltage mass spectrometry. Atroponitrile dimerizes to 1,4-dicyano-1-phenyl-1,2,3,4-tetrahydronaphthalene (DPT) in benzene solution with second-order kinetics and an E a of 14.8 kcal/mole, typical of other Diels-Alder reactions. The dimer exists in both crystalline and amorphous forms. The rate of cinnamonitrile formation from ammoxidation of allylbenzene is 2.9 times faster than from β-methylstyrene, suggesting that the ammoxidation of aromatic olefins proceeds through a common allylic intermediate.

Kinetics of propylene oxidation to acrolein on an Fe−Sb oxide catalyst

The kinetics of propylene oxidation to acrolein and CO2 on a Fe−Sb oxide catalyst have been studied in an integral reactor. A satisfactory rate equation has been derived with the assumption of a linear dependence of the activation energy and heats of adsorption of oxygen and water on the degree of reduction of the catalyst.