Modification of VPO catalysts for oxidative dehydrogenation of ethane

Based on the previously discussed hypothesis concerning the mechanism of conversion of paraffins, we have modified the structure of VPO catalysts by developing the (220) plane of VOHPO₄·0.5H₂O and introducing a bismuth additive. We have shown that this leads to an increase in the P/V ratio on the surface, an increase in the number of Lewis centers and the strength of such centers, and a change in the ratio of Lewis centers to Brönsted centers. The change in the surface characteristics of the samples, in accordance with the hypotheses, improves their properties in oxidative dehydrogenation of ethane, increasing the catalytic activity and the yield of the target product ethylene.     

Catalytic activity in the oxidative dehydrogenation of ethane over Ni and/or Co molybdate catalysts: Synthesis and characterization

Ni and/or Co molybdate based catalysts were synthetized by co-precipitation for the oxidative dehydrogenation of ethane reaction. The catalysts were characterized by several techniques such TGA-DTA, HT-XRD, XRD, LRS, N₂ adsorption, XPS and TPR. The results showed that the addition of Ni or Co to MMoO₄matrices (M=Ni or Co) led to a high dispersion of additives into the molybdenum matrix without the formation of a significant amount of other bulk metal oxides. Compared to the pure MMoO₄, the modified molybdenum (Ni_0.5Co_0.5MoO₄) presents a higher thermal stability (up to 1000 °C). It has a lower BET surface area and higher reduction temperature compared to those of the NiMoO₄ sample. In the ODH of ethane, Ni_0.5Co_0.5MoO₄ shows a lower catalytic activity compared to that of MMoO₄ samples; however, the ethylene selectivity is enhanced (exceeding 90%). As a result, these series of catalysts show improved efficiency for ethylene production in the ethane ODH reaction.     

The selective oxidative dehydrogenation of ethane over hydrothermally synthesised MoVTeNb catalysts

Mo-V-Te-Nb metal oxide catalysts prepared by hydrothermal synthesis and heat-treated in N2 at high temperatures (600-700 degrees C) show high activity and selectivity for the oxidative dehydrogenation of ethane to ethene. Yields of ethene of 75% have been obtained at 400 degrees C on the best catalysts.     

助剂P对Ni-Al-O催化剂乙烷氧化脱氢性能的影响

通过一锅水热法制备了一系列磷改性Ni-Al-O催化剂(Px-Ni-Al-O)，以O₂为氧化剂，评价了系列催化剂的乙烷氧化脱氢制乙烯性能。结果表明，助剂P的掺入不仅可以减小NiO晶粒的尺寸，还影响了Ni和Al之间的相互作用。在350~475℃的温度范围内，P改性Ni-Al-O催化剂上乙烯选择性均高于未改性的催化剂，且适量P的引入还可以提高乙烷转化率。当反应温度为475℃时，P_0.15-Ni-Al-O催化剂上乙烯选择性和收率分别为61.4%和31.9%。此外，P改性后的催化剂表现出较强的抗积碳性能，连续反应22 h不失活。     

助剂P对Ni-Al-O催化剂乙烷氧化脱氢性能的影响

通过一锅水热法制备了一系列磷改性Ni-Al-O催化剂(P_x-Ni-Al-O),以O₂为氧化剂,评价了系列催化剂的乙烷氧化脱氢制乙烯性能。结果表明,助剂P的掺入不仅可以减小NiO晶粒的尺寸,还影响了Ni和Al之间的相互作用。在350～475℃的温度范围内,P改性Ni-Al-O催化剂上乙烯选择性均高于未改性的催化剂,且适量P的引入还可以提高乙烷转化率。当反应温度为475℃时,P_0.15-Ni-Al-O催化剂上乙烯选择性和收率分别为61.4%和31.9%。此外,P改性后的催化剂表现出较强的抗积碳性能,连续反应22 h不失活。     

Thiophene hydrodesulfurization on P?Mo, Si?Mo and Ti?Mo catalysts

Studies of the catalysts obtained by supporting P–Mo, Si–Mo and Ti–Mo heteropolyacids on anatase in thiophene hydrodesulfurization have revealed that the presence of HPA in the initial catalysts promotes the formation of the molybdenum state ensuring high reaction rates. A possibility for HPA synthesis when supporting paramolybdate on TiO₂, accounts for the great effect of the support on the properties of the catalyst.

---

, -, -, - , . , , . .

     

Niobium phosphates as new highly selective catalysts for the oxidative dehydrogenation of ethane

Several niobium phosphate phases have been prepared, fully characterized and tested as catalysts for the selective oxidation of ethane to ethylene. Three distinct niobium phosphate catalysts were prepared, and each was comprised predominantly of a different bulk phase, namely Nb(2)P(4)O(15), NbOPO(4) and Nb(1.91)P(2.82)O(12). All of the niobium phosphate catalysts showed high selectivity towards ethylene, but the best catalyst was Nb(1.91)P(2.82)O(12), which was produced from the reduction of niobium oxide phosphate (NbOPO(4)) by hydrogen. It was particularly selective for ethylene, giving ca. 95% selectivity at 5% conversion, decreasing to ca. 90% at 15% conversion, and only produced low levels of carbon oxides. It was also determined that the only primary product from ethane oxidation over this catalyst was ethylene. Catalyst activity also increased with time-on-line, and this behaviour was ascribed to an increase of the concentration of the Nb(1.91)P(2.82)O(12) phase, as partially transformed NbOPO(4), formed during preparation, was converted to Nb(1.91)P(2.82)O(12) during use. Catalysts with predominant phases of Nb(2)P(4)O(15) and NbOPO(4) also showed appreciable activity and selectivities to ethylene with values around 75% and 85% respectively at 5% ethane conversion. The presence of phosphorous is required to achieve high ethylene selectivity, as orthorhombic and monoclinic Nb(2)O(5) catalysts showed similar activity, but displayed selectivities to ethylene that were <20% under the same reaction conditions. To the best of our knowledge, this is the first time that niobium phosphates have been shown to be highly selective catalysts for the oxidation of ethane to ethylene, and demonstrates that they are worthy candidates for further study.     

Oxidative dehydrogenation of ethane and propane on CuTh oxide catalysts

CuThO oxides prepared with different atomic ratios Cu/Th have been tested in the oxidative dehydrogenation of ethane and propane. These catalysts are active and selective in the formation of ethene and propene, but the activity and selectivity change with the nature of the alkane.     

铯添加对VOx/SBA-15催化剂丙烷氧化脱氢性能影响

我们考察了碱金属铯的添加对具有单一活性中心（分立的VOx四面体）的VOx／SBA-15催化剂上丙烷氧化脱氢反应性能的影响,发现铯的加入可以显著改善丙烯的选择性．在相同的丙烷转化率时,丙烯选择性提高了约10％．对催化剂的X射线衍射,拉曼光谱,程序升温还原,吡啶吸附IR光谱和程序升温脱附表征结果表明,少量碱金属的加入,并未改变活性中心的结构及其可还原性能,但明显降低了催化剂表面酸量,尤其是B酸量,从而有利于产物丙烯的脱附,抑制了深度氧化产物COx的产生,提高了丙烯的选择性．     

乙烷氧化脱氢用Ni/Al2O3催化剂中活性镍物种前驱体（英文）

Ni/Al2O3 catalysts for oxidative dehydrogenation(ODH) of ethane were prepared by impregnation of Al2O3 with nickel acetate or nickel nitrate,and by mechanical mixing of NiO and Al2O3.The Ni-based catalysts were characterized by N2 adsorption-desorption,X-ray diffraction,diffuse reflectance UV-visible diffuse reflectance spectroscopy,and temperature-programmed reduction of hydrogen.The results showed that formation of crystalline NiO particles with a size of < 8 nm and/or non-stoichiometric NiO species in the Ni/Al2O3 catalysts led to more active species in ODH of ethane under the investigated reaction conditions.In contrast,tetrahedral Ni species present in the catalysts led to higher selectivity for ethene.Formation of large crystalline NiO particles(22-32 nm) over Ni/Al2O3 catalysts decreased the selectivity for ethene.     

Promoted catalytic performances of highly dispersed V-doped SBA-16 catalysts for oxidative dehydrogenation of ethane to ethylene

V-doped SBA-16 catalysts（V-SBA-16） with 3D nanocage mesopores have been successfully synthesized by a modified one-pot method under weak acid condition.The obtained materials were characterized by means of small angle XRD,N₂ adsorption–desorption,TEM,UV–Vis and UV-Raman spectroscopy.These characterization results indicated that well-order mesoporous structures were maintained even at higher vanadium loadings and high concentration of VOx species were incorporated into the framework of SBA-16 support.The catalytic performances of V-SBA-16,V/SBA-16 and V/Si O₂ catalysts were comparatively investigated for the oxidative dehydrogenation of ethane to ethylene.The highest selectivity to ethylene of 63.3% and ethylene yield of 25.6% were obtained over 1.0V-SBA-16 catalyst.The superior catalytic performance of V-SBA-16 catalysts could be attributed to the presence of isolated framework VO x species,the unique structure of SBA-16 support and weak acidity.Moreover,V/Si O₂ catalyst exhibited relatively poor catalytic activity duo to the formation of V₂O₅ nanoparticles on the surface of Si O₂ support and the low dispersion of VO x species.These results indicated that the catalytic performances of the studied catalysts were strongly dependent on the vanadium loading,the nature and neighboring environment of VO x species and the structure of support.     

The role of water in promoting the oxidative dehydrogenation of ethane

The addition of water vapor has a strong positive effect on the rate of ethane oxidation at 575°C. This effect is attributed to the role of H₂O as a third body in the decomposition of H₂O₂ to OH radicals. Carbon tetrafluoride likewise enhances the rate of ethane conversion, although not to the extent realized with H₂O. A kinetic model, based on known elementary reactions, adequately accounts for the conversions and selectivities observed as a function of H₂O pressure, temperature, contact time, and O₂ pressure. © 1994 John Wiley & Sons, Inc.     

NbMCM-41 mesoporous molecular sieves in oxidative dehydrogenation of ethane and propane

It has been evidenced that the dissolution of niobium in silica mesoporous matrix significantly increases the catalytic effectiveness in the oxidative dehydrogenation of alkanes as compared with unsupported Nb₂O₅. This revised version was published online in June 2006 with corrections to the Cover Date.     

Advantages of ethane oxidative dehydrogenation on the MoVNbTeOx catalyst under elevated pressure

1. Download : Download high-res image (97KB)
2. Download : Download full-size image

     

Electric heating of the Mo–V–Fe–Nb–Ox catalyst bed in oxidative dehydrogenation of ethane

1. Download : Download high-res image (113KB)
2. Download : Download full-size image

     

On the possibility of formation of Ti?Mo heteropolyacids on Ti?Mo catalysts

According to IR spectroscopic studies, a Ti–Mo heteropolyacid is formed on the surface of Ti–Mo catalysts prepared from ammonium paramolybdate and TiO₂.

---

- , Ti–Mo TiO₂ Ti–Mo .

     

乙烷在氧化镍上催化氧化脱氢的反应机理研究

应用O~2-TPD,脉冲实验,原位Weiss磁测量以及TAP(temporalanalysisofproducts)技术对NiO上的乙烷氧化脱氢制乙烯催化作用机理进行了研究。结果表明,NiO中的非化学计量氧表现出与气相氧交换的可逆性,其中在较低温度下脱附的α氧(很可能是O~2^-,O~2^2^-)仅存在于催化剂表面,与气相氧交换迅速,而较高温下脱附的β氧(很可能是O^-)不仅存在于催化剂表面,还存在于催化剂体相。β氧较α氧表现出更高的乙烯选择性。在反应条件下,Ni均应处于高氧化态(Ni^(^2^+^δ^)^+,0≤δ≤1),一旦催化剂中有微量Ni^0生成,乙烷便发生裂解反应,乙烯选择性立即降为零。乙烷在NiO上的氧化脱氢(ODHE)的可能反应机理为:首先乙烷与NiO中的非化学计量氧O~n(~s~)作用脱除一个α-H生成乙基自由基,然后进一步脱除一个β-H生成乙烯,乙烯生成的整个过程是在催化剂表面上进行的;副产物CO~2是由表面乙烯进一步氧化(很可能是与O~2^-,O~2^2^-作用)生成的。失去O~n~(~s~)的NiO在反应体系(一定的氧分压)中,重新生成含非化学计量氧的NiO。     

Catalytic performance of silica-supported chromium oxide catalysts in ethane dehydrogenation with carbon dioxide

The oxidative dehydrogenation of ethane into ethylene by CO₂ over a series of silica-supported chromium oxide catalysts was investigated. The results showed that the catalysts were effective for the reaction and CO₂ in the feed promoted the catalytic activity. The 5%Cr/SiO₂ catalyst exhibited the excellent performance with 30.7% ethane conversion and 96.5% ethylene selectivity at 700^oC. ESR and UV-DRS were used to probe the active sites and the species with high valent states (Cr⁵⁺ and/or Cr⁶⁺) were found to be important for the reaction.     

Molecular structure and reactivity of titania-supported transition metal oxide catalysts synthesized by equilibrium deposition filtration for the oxidative dehydrogenation of ethane

The molecular structure and catalytic performance of (MoO_x)_n/TiO₂, (WO_x)_n/TiO₂ and (VO_x)_n/TiO₂ catalysts (synthesized by the equilibrium–deposition–filtration/EDF method) for oxidative dehydrogenation (ODH) of ethane were studied by in situ Raman spectroscopy at 430 °C and catalytic measurements in the temperature range of 420–480 °C. The extent of association within the deposited oxometallic phase followed the sequence (VO_x)_n/TiO₂ >> (MoO_x)_n/TiO₂ > (WO_x)_n/TiO₂; a concurrent trend in reduction susceptibility was evidenced by exploiting the relative normalized Raman band intensities while monitoring the response of the vibrational properties of the catalytic samples under reactive (C₂H₆/O₂/He) and reducing (C₂H₆/He) conditions by in situ Raman spectroscopy. The catalyst reactivity tracks the corresponding trend in reduction susceptibility as evidenced by the in situ Raman spectra. Selective reaction pathways are favored at high coverage whilst combustion routes are activated at low coverages due to the involvement of carrier lattice oxygen sites. The observed apparent reaction rates and activation energies are discussed in relation to various structural and reactivity aspects.