Temperature-programmed Reoxidation Research Articles

Unveiling the morphology dependence of ceria nanocrystals for boosting low−temperature cyclohexane oxidative dehydrogenation

Tailoring the oxygen vacancy concentration by controlling the morphology of CeO2 has been proved to be a feasible strategy to construct excellent catalysts for oxidative dehydrogenation (ODH) reactions. Here, the morphology dependence of ceria nanocrystals for low−temperature cyclohexane ODH was investigated. The results reflected the variation of oxygen vacancy concentration of ceria with morphologies, resulting in different reactivity. Temperature−programmed re-oxidation (TPRO) and temperature−programmed reduction (TPR) tests demonstrated that prepared catalysts possessed the opposite replenishment and consumption capacity of active oxygen species. In addition to superficially correlating the facet effect of ceria with the formation of oxygen vacancies, as reported in most literatures, the facet dependence on the selectivity of the target product also has come to light by density functional theory (DFT). Furthermore, the temperature programmed isotope exchange (TPIE) and kinetic experiments revealed the Langmuir−Hinshelwood (LH) mechanism rather than the recognized Mars−van Krevelen (MvK) mechanism. That is, the lower reaction temperature makes the main active agent electrophilic oxygen species, and the competitive adsorption of cyclohexane and oxygen on the intrinsic oxygen vacancies causes the dependence of reaction rate on oxygen concentration. The findings provide fresh insights into the optimization of the CeO2−based catalysts in cyclohexane oxidative dehydrogenation.

CO2 Reduction on the Pre-reduced Mixed Ionic-Electronic Conducting Perovskites La0.6 Sr-0.4 FeO3-δ and SrTi0.7 Fe0.3 O3-δ.

The activity of the pre-reduced perovskites La0.6 Sr0.4 FeO3-δ (LSF64) and SrTi0.7 Fe0.3 O3-δ (STF73) for the CO2 reduction to CO was investigated with special focus on the reactivity of oxide-dissolved hydrogen. This is of particular interest in hydrogen solid-oxide electrolysis cell (H-SOEC) technology, where proton-conducting ceramics are used and the reaction 2e- +2H+ +CO2 →CO+H2 O is of central importance. To clarify if hydrogen dissolved in LSF64 and STF73 partakes in the CO2 reduction, temperature-programmed reduction (TPR) in H2 , followed by temperature-programmed reoxidation (TPO) in CO2 and, moreover, temperature-programmed desorption (TPD) of ad- and absorbed species were utilized. The experiments reveal that 50 mol % of the CO2 is converted by hydrogen dissolved in STF73 and reacts quantitatively. On the other hand, LSF64 converts less than 20 mol % of CO2 via dissolved hydrogen and a residual of bulk OH is still detectable after CO2 -TPO.

The role of active phase in Ce modified BiMo catalysts for oxidative dehydrogenation of 1-butene

BiMoCex catalysts (x=0–0.4) were prepared by co-precipitation method and tested in the oxidative dehydrogenation (ODH) of 1-butenes to 1,3-butadiene. The results indicate that the cerium content has significant effects on the performance of catalyst. BiMoCe0.2 exhibits the superior activity and stability during the 100h test. X-ray photoelectron spectroscopy (XPS), temperature-programmed re-oxidation (TPRO), 1-Butene temperature-programmed desorption (TPD) and pulse O2 adsorption characterization reveal that the oxygen mobility and the adsorption ability of 1-butene of catalysts are two crucial factors determining catalytic performance in ODH reaction. The active phases on BiMoCex play different roles in the reaction.

Influence of the catalyst composition in the oxidative dehydrogenation of 1-butene over BiVxMo1−x oxide catalysts

BiVxMo1−x oxide catalysts with varying compositions were investigated in the oxidative dehydrogenation (ODH) of 1-butene to 1,3-butadiene (BD). Notably, incorporation of vanadium in the Bi-Mo oxide significantly enhanced the catalytic performance in the ODH of 1-butene. Among the tested catalysts, the BiV0.6Mo0.4 oxide catalyst exhibited superior oxygen mobility in temperature-programmed re-oxidation experiments, revealed the facile desorption of adsorbed BD species in the temperature-programmed desorption of 1-butene, and displayed the highest performance (72.2% conversion of 1-butene and 64.0% yield in BD) in the ODH of 1-butene. Moreover, the performance of the tested catalysts decreased in the following order BiV0.6Mo0.4>BiV0.4Mo0.6>BiV0.8Mo0.2>BiV0.2Mo0.8>BiMo>BiV. In addition, the BiV0.6Mo0.4 oxide catalyst displayed stable performance over 85h and its excellent catalytic ability makes it economically viable.

Effects of zirconium content on the catalytic performance of BiMoZrx in the oxidative dehydrogenation of 1‐butene to 1,3‐butadiene

AbstractBACKGROUNDOxidative dehydrogenation (ODH) of 1‐butene has been considered as a potential process for manufacturing 1,3‐butadiene (BD). The introduction of metal oxides to pure bismuth molybdate, a promising catalyst for the ODH reaction, can be expected to improve the catalysts performance. In this work, multicomponent bismuth molybdate oxide (BiMoZrx) catalysts for ODH of 1‐butene were prepared by a co‐precipitation method with variation of zirconium content (x = 0–0.5), and the influence of zirconium on catalytic performance was investigated.RESULTSThe zirconium content has a significant effect on the structure and performance of the catalyst. The conversion of 1‐butene and the BD yield over BiMoZrx catalysts display volcano curves with respect to zirconium content. Among the catalysts tested, BiMoZr0.4 exhibits superior activity.CONCLUSION1‐butene temperature‐programmed re‐oxidation (TPRO) and X‐ray photoelectron spectroscopy (XPS) characterizations demonstrate that zirconium content is related to the oxygen mobility of BiMoZrx catalysts, and oxygen mobility is a crucial factor determining catalytic performance in the ODH reaction. © 2014 Society of Chemical Industry

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.

Characterization and kinetic study of BiMoLax oxide catalysts for oxidative dehydrogenation of 1-butene to 1,3-butadiene

BiMoLax oxide catalysts with a variation of lanthanum component were prepared by a co-precipitation method, and applied to the oxidative dehydrogenation (ODH) of 1-butene to 1,3-butadiene (BD). The results reveal that the lanthanum content has significant effects on the catalyst performance. BiMoLa0.2 exhibits the superior activity and stability during the 100h test. H2 temperature-programmed reduction (H2-TPR), 1-Butene temperature-programmed re-oxidation (TPRO) and temperature-programmed desorption (TPD) characterization show that the oxygen mobility and the adsorption ability of 1-butene of catalysts are two crucial factors determining catalytic performance in ODH reaction. The kinetics analysis finds that the ODH reaction over BiMoLa0.2 can occur more easily.

Oxidative dehydrogenation of 1-butene to 1,3-butadiene over BiFe0.65NixMo oxide catalysts: Effect of nickel content

Abstract BiFe 0.65 Ni x Mo oxide catalysts (x = 0–0.2) were prepared and applied for the oxidative dehydrogenation of butenes to 1,3-butadiene. Temperature programmed reoxidation (TPRO) measurements revealed that the catalytic activity was closely related to the oxygen mobility. The surface modification by small amounts of nickel addition is favorable in this reaction. Among the catalysts studied here, BiFe 0.65 Ni 0.05 Mo oxide catalyst showed the highest conversion and BD yield (X = 86% and Y BD = 72%) due to the high oxygen mobility. The BiFe 0.65 Ni 0.05 Mo oxide catalyst is very stable and no deactivation during the 100 h reaction was shown.

Effect of Calcination Temperature on the Catalytic Performance of γ-Bi2MoO6 in the Oxidative Dehydrogenation of n-Butene to 1,3-Butadiene

γ-Bi2MoO6 catalysts prepared by a co-precipitation method were calcined at various temperatures (425–675 °C), and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene in a continuous flow fixed-bed reactor. Conversion of n-butene and yield for 1,3-butadiene were high at low calcination temperature (425–475 °C), but were decreased with increasing calcination temperature (525–675 °C). Temperature-programmed reoxidation (TPRO) measurements revealed that the catalytic performance of γ-Bi2MoO6 was well correlated with the oxygen mobility of the catalyst. Yield for 1,3-butadiene was increased with increasing oxygen mobility of γ-Bi2MoO6 catalyst. Among the catalysts tested, γ-Bi2MoO6 catalyst calcined at 475 °C showed the best catalytic performance due to its facile oxygen mobility.

Production of 1,3-Butadiene From C4 Raffinate-3 Through Oxidative Dehydrogenation of n-Butene Over Bismuth Molybdate Catalysts

Recent progress on the bismuth molybdate catalysts for oxidative dehydrogenation of n-butene to 1,3-butadiene was reported in this review. A number of bismuth molybdate catalysts, including pure bismuth molybdates (α-Bi2Mo3O12, β-Bi2Mo2O9, and γ-Bi2MoO6) and multicomponent bismuth molybdates, were prepared by a co-precipitation method for use in the production of 1,3-butadiene from C4 raffinate-3 through oxidative dehydrogenation of n-butene. It was observed that multicomponent bismuth molybdate catalyst was more efficient than pure bismuth molybdate catalyst in the oxidative dehydrogenation of n-butene. Various experimental measurements such as temperature-programmed reoxidation, X-ray photoelectron spectroscopy, and O2-temperature-programmed desorption analyses were carried out to elucidate the different catalytic activity of bismuth molybdate catalysts. It was revealed that a bismuth molybdate catalyst with a higher oxygen mobility showed a better catalytic performance in terms of conversion of n-butene and yield for 1,3-butadiene. We have successfully demonstrated from experimental findings that oxygen mobility of bismuth molybdate catalyst played a key role in determining the catalytic performance in the oxidative dehydrogenation of n-butene to 1,3-butadiene.

Effect of pH in the preparation of γ-Bi2MoO6 for oxidative dehydrogenation of n-butene to 1,3-butadiene: Correlation between catalytic performance and oxygen mobility of γ-Bi2MoO6

γ-Bi2MoO6 catalysts were prepared by a co-precipitation method with a variation of pH value (pH 1–7), and they were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene in a continuous flow fixed-bed reactor. Temperature-programmed reoxidation (TPRO) measurements were carried out to determine the oxygen mobility to make up lattice oxygen of γ-Bi2MoO6 consumed in the reaction. It was observed that the catalytic performance of γ-Bi2MoO6 was closely related to the oxygen mobility of γ-Bi2MoO6. The yield for 1,3-butadiene was monotonically increased with decreasing TPRO peak temperature and with increasing TPRO peak area. Among the catalysts tested, the γ-Bi2MoO6 catalyst prepared at pH 3 showed the best catalytic performance due to its facile oxygen mobility.

Preparation, characterization, and catalytic activity of bismuth molybdate catalysts for the oxidative dehydrogenation of n-butene into 1,3-butadiene

Three types of bismuth molybdate catalysts, α-Bi 2Mo 3O 12, β-Bi 2Mo 2O 9, and γ-Bi 2MoO 6, were prepared by a co-precipitation method for use in the oxidative dehydrogenation of n-butene. Unlike α-Bi 2Mo 3O 12 and γ-Bi 2MoO 6, it was found that β-Bi 2Mo 2O 9 was thermally unstable and decomposed into α-Bi 2Mo 3O 12 and γ-Bi 2MoO 6 at the reaction temperature of 420 °C. Therefore, β-Bi 2Mo 2O 9 could not serve as an efficient catalyst in the reaction. In the oxidative dehydrogenation of n-butene into 1,3-butadiene, γ-Bi 2MoO 6 showed a better catalytic performance than α-Bi 2Mo 3O 12. The different catalytic performance between α-Bi 2Mo 3O 12 and γ-Bi 2MoO 6 catalysts was elucidated by temperature-programmed reoxidation (TPRO) experiments. It was revealed that the enhanced catalytic performance of γ-Bi 2MoO 6 was attributed to the facile oxygen mobility of γ-Bi 2MoO 6.

Catalytic properties and characterization of Pd supported on hexaaluminate in high temperature combustion

The catalytic activities of palladium-supported Sr 0.8La 0.2MnAl 11O 19 (SLMA) and the effect of phase transformation of palladium on the catalytic activity after high temperature treatments were studied by XRD, TPD, temperature programmed reaction (TPRX) and temperature programmed reoxidation (TPRO). Also the interaction of palladium with Sr 0.8La 0.2MnAl 11O 19 at high temperature was studied by XPS. PdO formed on Sr 0.8La 0.2MnAl 11O 19 was dissociated to metallic Pd after calcination at 1000 °C. TPD and TPRX study revealed that the surface oxygen of PdO cluster was the major source of oxygen to react with CH 4 in the absence of O 2. TPRO after TPRX experiments showed the reoxidation of catalysts was dependent on the calcination temperature. High temperature treatments caused the interaction of palladium and Sr 0.8La 0.2MnAl 11O 19 support resulting in the change of the oxidation state of palladium.

Reaction mechanism of ammoxidation of toluene: IV. Oxidation state of vanadium oxide and its reactivity for toluene oxidation

In order to determine the mechanism of the ammoxidation of toluene, vanadium oxide supported on Al 2O 3 during the ammoxidation has been characterized by the titrimetric method, ESR, and the temperature-programmed reoxidation. Vanadium oxide was severely reduced during the reaction, and in the state almost equivalent to V 2O 4. The oxidation state was influenced profoundly by the atmospheric condition because of the thin layer of vanadium oxide on Al 2O 3. Furthermore, the adsorbed hydrocarbon material on the surface of vanadium oxide inhibited the reoxidation, stabilizing the severely reduced surface. Pulse experiments on the definite oxidation state of vanadium revealed that only benzaldehyde could be formed significantly on the V 2O 4 catalyst. Therefore, the first step of the ammoxidation of toluene could be deduced to be the formation of benzaldehyde on V 2O 4.

The oxidative dehydrodimerization of propylene over BiSn oxide catalysts: III. Reduction and temperature-programmed reoxidation of the catalyst

A bismuth-tin oxide catalyst, which is active for the oxidative dehydrodimerization of propylene, was studied with the objective of characterizing its redox properties. The redox properties were investigated by kinetic methods and temperature-programmed reoxidation. The initial rate of reduction of the catalyst exhibited a first-order dependence on propylene partial pressure and an activation energy of 22 kcal/mol. The results of the temperature-programmed reoxidation investigation suggested a low-temperature reoxidation region and a high-temperature reoxidation region. The activation energy for the low-temperature reoxidation was 23 kcal/mol; the activation energy for the high-temperature reoxidation was 45 kcal/mol. Additional information regarding the physicochemical changes which occur in the catalyst in the two temperature regions was obtained from an examination of the catalyst by Auger and ESCA. The results obtained from these investigations suggested that the tin cations are more resistent to reduction than the bismuth cations. In addition, the low-temperature reoxidation appears to be associated with the transformation of Sn 0 to Sn 4+ and Bi 0 to possibly an intermediate oxidation state. The high-temperature reoxidation appears to be associated with the full reoxidation of Bi to Bi 3+. The redox properties and the physicochemical changes also correlated with the mechanism suggested for the oxidative dehydrodimerization of propylene in the earlier studies.

The catalytic oxidation of propylene: VII. The use of temperature programmed reoxidation to characterize γ-bismuth molybdate

Temperature programmed reoxidation (TPR) was used to characterize the redox properties of γ-Bi 2MoO 6. Reoxidation of a prereduced catalyst by this technique yielded two well-defined temperature ranges for reoxidation. When the catalyst was prereduced by propylene, the maximum of a low-temperature peak occurred at 158 °C and the maximum of a high-temperature peak occurred at 340 °C. The physicochemical changes associated with these reoxidation temperatures were further investigated by X-ray diffraction, Auger spectroscopy, and kinetic measurements. The low-temperature reoxidation peak was found to be a result of the reoxidation of Mo 4+ to Mo 6+ and Bi 0 to Bi m+, where 0 < m < 3. The high-temperature reoxidation peak was found to be a result of the reoxidation of Bi m+ to Bi 3+. The high-temperature reoxidation may involve the direct oxidation of bismuth by gas phase oxidation or may involve shear structures. The high-temperature reoxidation process also appears to be related to the rate-limiting step for propylene oxidation to acrolein at temperatures below 400 °C.

Studies on the reduction-reoxidation of bismuth molybdate catalysts by temperature programmed reoxidation method

A new method of temperature programmed reoxidation (TPR) which gives a correlation of reoxidation rates with temperature in curved lines was devised and applied to slightly reduced MoO 3, Bi 2O 3 and bismuth molybdate catalysts. Those oxide catalysts are found to be characterized by peaks in TPR. That is, MoO 3 and Bi 2O 3 give TPR peaks at 410 and 180 °C, respectively. An increase in the extent of prereduction results in another peak with both oxides, indicating that reoxidation takes place in two steps. Bismuth molybdate catalysts of different compositions give different peaks which may be identified as composites of three TPR peaks. Every bismuth molybdate catalyst which gives the TPR peak at 320 °C is invariably active for selective oxidation of propylene to acrolein. The addition of phosphoric acid to bismuth molybdate catalysts increases the peak area at 320 °C and consistently enhances the formation of acrolein from propylene. The activation energies were determined for reduction of bismuth molybdate catalysts, reoxidation of slightly reduced catalysts and catalytic oxidation of propylene to acrolein. Those values are correlated to the TPR peak.