How oxide carriers affect the reactivity of V2O5 catalysts in the oxidative dehydrogenation of propane

The catalytic pattern of several oxide carriers (MgO, Al₂O₃, ZrO₂, TiO₂, SiO₂, HY zeolite) and supported V₂O₅ (4.7–5.3 wt%) catalysts in the oxidative dehydrogenation of propane to propylene (PODH) has been comparatively investigated. The fundamental role of the oxide support on both reducibility and reactivity of vanadia catalysts has been assessed. A direct relationship between the specific surface activity of oxide carriers and that of vanadia catalysts is discussed. The inverse relationship between the specific activity and the onset temperature of reduction marks the prevailing redox behaviour of V₂O₅ catalysts in the PODH reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

铂系丙烷脱氢催化剂助剂研究进展

铂基催化剂用于丙烷催化脱氢的主要缺点是稳定性差、选择性低,通过添加助剂可以大大改善该催化剂的脱氢性能.针对催化剂助剂,综述了铂基丙烷脱氢催化剂的研究现状,分别介绍了碱金属、碱土金属、稀土金属和过渡金属作为助剂对铂基催化剂的影响,探讨了所添加助剂的作用机制,并对铂基催化剂研究前景进行了展望.     

Effect of vanadia loading in propane oxidative dehydrogenation on V2O5/SiO2 catalysts

The influence of V₂O₅ loading on the catalytic behaviour of V₂O₅/SiO2₂ catalysts in the oxidative dehydrogenation of propane to propylene (POD) has been investigated. The different activity-selectivity pattern of low (5 wt%) and highly (>10 wt%) loaded V₂O₅/SiO₂ catalysts is explained in terms of different surface vanadia species.     

The selective oxidative dehydrogenation of propane on vanadium aluminophosphate catalysts

VAPO-5 and V/ ALPO-5 catalysts have been tested for the oxidative dehydrogenation of propane. Depending on the vanadium contents and the preparation procedure, different vanadium species and different catalytic behavior are observed. The catalyst containing V⁵⁺ species with a tetrahedral coordination presents the higher yield of propene in the oxidative dehydrogenation of propane. The same yields of CO₂ are observed on all vanadium aluminophosphate catalysts, while the higher the yield of propene the lower the yield of CO is.     

氧化铝煅烧温度对丙烷脱氢催化剂性能的影响

针对丙烷脱氢催化剂用氧化铝作为载体时存在的孔结构与表面酸性调节的问题,开发了以海藻酸盐为黏合剂,采用挤出滚圆方法,制备了大孔球形氧化铝颗粒,并以此作为载体负载Pt、Sn活性组分制备了丙烷脱氢催化剂,研究了氧化铝载体煅烧温度对催化剂晶型、孔道结构、表面酸性、H2还原性能与丙烷脱氢性能的影响.实验结果表明:随氧化铝载体煅烧...     

Dehydrogenation of Propane in the Presence and Absence of CO2 Over β-Ga2O3 Supported Chromium Oxide Catalysts

The dehydrogenation of propane to propene in the presence and absence of CO₂ over β-Ga₂O₃ supported chromium oxide catalysts has been studied. The effect of chromium content and feed composition on the dehydrogenation of propane has been investigated. It has been found that deposition of chromium oxide enhances the dehydrogenation activity and resistance to coke deposition. Moreover, it has been shown that CO₂ promotes the dehydrogenation of propane above 848 K. At that temperature in the presence of CO₂ both the yield of propene and conversion of propane were higher than in the inert gas atmosphere.     

逆水煤气变换耦合乙烷脱氢反应中载体对氧化铬催化剂性能的影响

研究了在逆水煤气变换耦合乙烷脱氢反应中担载型氧化铬催化剂的活性,考察了多种载体对于催化剂反应性能的影响。结果表明,不同的载体所担载的氧化铬催化剂具有不同的催化性能。其中二氧化硅担载的氧化铬催化剂具有较高的乙烷转化率和乙烯选择性,在700℃时分别达到30.7%和96.5%。CO₂的作用是通过与H₂反应促进乙烷脱氢、并减少催化剂表面积炭。运用XRD、TPR、 XPS、UV-DRS和微量吸附量热技术对催化剂体相与表面结构、表面酸性和铬物种价态等进行了表征,结果显示催化剂表面酸中心适当的强度、数量和分布有利于乙烷的活化和催化转化,Cr³⁺和Cr⁶⁺物种是反应的活性中心。     

丙烷氧化脱氢制丙烯的钒基介孔催化材料研究进展

介绍了近年来丙烷氧化脱氢催化技术的最新研究进展,针对其中应用最广泛的钒基介孔催化剂,对其反应机理、载体性能和制备方法进行了综述,并比较了不同催化体系的丙烷氧化脱氢性能,提出了改善钒基介孔催化剂催化活性与选择性的途径。通过比较已经报道的同类研究结果,着重阐述了载体的孔结构对于氧化脱氢过程的影响,比表面积和孔径的优化对于提高催化剂的活性组分分散度以及活性位的数量效果明显。今后研究应着重提高催化剂孔道结构在高温下的稳定性以及使用寿命。     

A Fourier-transform infrared study of CO2 and CO2/H2 interactions with caesium-doped copper catalysts

FTIR spectra are reported of CO₂ and CO₂/H₂ on a silica-supported caesium-doped copper catalyst. Adsorption of CO₂ on a “caesium”/silica surface resulted in the formation of CO₂ ⁻ and complexed CO species. Exposure of CO₂ to a caesium-doped reduced copper catalyst produced not only these species but also two forms of adsorbed carboxylate giving bands at 1550, 1510, 1365 and 1345 cm⁻¹. Reaction of carboxylate species with hydrogen at 388 K gave formate species on copper and caesium oxide in addition to methoxy groups associated with caesium oxide. Methoxy species were not detected on undoped copper catalyst suggesting that caesium may be a promoter for the methanol synthesis reaction. Methanol decomposition on a caesium-doped copper catalyst produced a small number of formate species on copper and caesium oxide. Methoxy groups on caesium oxide decomposed to CO and H₂, and subsequent reaction between CO and adsorbed oxygen resulted in carboxylate formation. Methoxy species located at interfacial sites appeared to exhibit unusual adsorption properties.     

Structure and catalytic consequence of Mg‐modified VOx/Al2O3 catalysts for propane dehydrogenation

Supported VO_x catalysts are promising nonoxidative propane dehydrogenation (PDH) materials for their commercially attractive activity and propylene selectivity. However, they frequently suffer from rapid deactivation caused by coke deposition. This article describes the promoting role of magnesium on the stability of VO_x/Al₂O₃ catalysts for PDH. A series of VO_x/Al₂O₃ and Mg‐modified VO_x/Al₂O₃ catalysts were synthesized by an incipient wetness impregnation method. The catalysts were carefully characterized by Raman spectra, UV‐Vis spectra, STEM, TGA and in situ DRIFTS. We showed that the stability of a 12V/Al₂O₃ catalyst was significantly improved on addition of small amounts of MgO. Experimental evidences indicate that V₂O₅ nanoparticles emerge in the 12V/Al₂O₃ samples, and appropriate Mg addition helps dispersing the V₂O₅ nanoparticles into 2D VO_x species thus decreasing coke formation and improving stability in nonoxidative dehydrogenation of propane. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Catalytic dehydrogenation of propane over cluster-derived Ir–Sn/SiO2 catalysts

The dehydrogenation of propane was studied in gas-phase at 773 K over two series of silica-deposited Ir–Sn systems: the bimetallic catalysts obtained from Ir–Sn carbonyl clusters precursors and the ones prepared by deposition of a metallorganic Sn precursor onto preformed Ir nanoparticles. In the comparison, cluster-derived catalysts showed good propane conversion, optimal selectivity to propene and high stability under the severe reaction conditions.     

Effect of MgF2 and Al2O3 supports on the structure and catalytic activity of copper–manganese oxide catalysts

Structure and catalytic activity of double copper–manganese oxide catalysts supported on MgF₂ and Al₂O₃ have been studied. All samples were calcined at 400 °C and those supported on Al₂O₃ also at 550 and 950 °C. The properties of surface species have been characterized by low temperature adsorption of nitrogen, XRD and TPR-H₂. The catalytic activities have been tested in low-temperature CO oxidation and in NO reduction by propene. The supported oxides react with each other during calcination to form CuMn₂O₄ spinel. The spinel seems to be responsible for the catalytic activity of the double copper–manganese catalysts. The temperature of calcination changes the strength of interaction between the active phase and the supports influencing the catalytic activity.     

丙烷脱氢制丙烯用单原子催化剂研究进展

丙烯是一种重要的有机化工原料和石油化工原料中间体,近年来在国内外市场的需求量持续增长。丙烷直接脱氢制丙烯技术具有收率高、技术成熟、经济环保等优点,备受研究者们的广泛关注。文中综述了丙烷直接脱氢制丙烯用单原子催化剂的研究进展,介绍了单原子催化剂的丙烷脱氢反应机理,探讨了单原子催化剂的失活行为,总结了活性组分、助剂及载体对单原子催化剂催化丙烷脱氢性能的影响,并分析讨论了单原子催化剂在当前研究中存在的问题。最后针对单原子催化剂虽具有优异的丙烯选择性和稳定性,但存在丙烷脱氢活性依旧不足的问题,提出了调控单原子催化剂电子结构促进丙烷脱氢活性的设计思路,为未来丙烷脱氢制丙烯高效单原子催化剂的设计提供了指导方向。     

Effect of promoters on catalytic performance of Cr/SiO2 catalysts in oxidative dehydrogenation of ethane with carbon dioxide

Several acidic and basic oxide promoted Cr/SiO₂ catalysts were prepared and investigated in oxidative dehydrogenation of ethane in the presence of carbon dioxide. The effects of SO₄ ^2–, WO₃ and alkali metal oxides (Li₂O, Na₂O, and K₂O) on the catalytic activity were studied. It is found that sulfation of silica produces a positive effect on ethane conversion and ethylene yield while tungstation and addition of strong basic promoters (alkali metal oxides) suppress the catalytic activity. Characterization indicates that the varying activity of the promoted catalysts can be attributed to the difference in acid/base property and redox potential.     

Sn掺杂量对Pt/Sn-MFI催化剂的丙烷脱氢性能影响

随着对丙烯需求的日渐增加,由丙烷催化脱氢制丙烯来实现对丙烯的增产,已成为增产丙烯的重要手段之一。利用水热法制备一系列不同Sn掺杂量的Sn-MFI载体,采用等体积浸渍法制备相同Pt负载量的Pt/Sn-MFI催化剂,通过XRD、N2吸附-脱附、FT-IR和H2-TPR等表征考察不同Sn掺杂量的催化剂对丙烷催化脱氢性能的影响。结果表明,Pt/Sn1. 3%-MFI催化剂具有最高的催化丙烷脱氢活性和稳定性,丙烷初始转化率为43. 3%,丙烯选择性为98. 9%。反应360 min后,丙烷转化率为25. 1%,选择性保持不变。     

不同载体对Pt-Sn催化剂丙烷催化脱氢性能影响

分别以Hβ分子筛和γ-Al₂O₃为载体,采用浸渍法制备不同Sn含量的负载型Pt-Sn双组分丙烷催化脱氢催化剂。在固定床微反装置上对制备的催化剂进行活性评价,并采用NH₃-TPD方法测定催化剂表面酸量和酸强度分布。结果表明,负载型Pt-Sn/Hβ和Pt-Sn/γ-Al₂O₃催化剂对丙烷催化脱氢反应性能与Sn含量密切相关,弱酸中心的存在对丙烷催化脱氢反应有利,对于特定的Pt-Sn体系,γ-Al₂O₃为载体的催化剂性能优于Hβ分子筛为载体的催化剂,当负载Sn质量分数为0.9时,Pt-Sn/γ-Al₂O₃催化剂性能最好。     

Surface phase transformation of ZrO2 in VOx/ZrO2 catalysts for boosting propane nonoxidative dehydrogenation

The nanocatalysts of VO_x deposited on ZrO₂ supports with single monoclinic (ZrO₂-M), tetragonal (ZrO₂-T), and binary monoclinic-tetragonal (ZrO₂-MT) phase were synthesized. VO_x/ZrO₂-MT catalysts exhibit better performance during propane nonoxidative dehydrogenation than VO_x/ZrO₂-M and VO_x/ZrO₂-T catalysts. Among VO_x/ZrO₂-MT catalysts, the conversion and deactivation rate constant of VO_x/ZrO₂-M₃₁T₆₉ catalyst is 35.2% and 0.22 h⁻¹, respectively. The promoting role of ZrO₂-MT is revealed by experiments and theoretical calculations. The MT-mixed phase structure in VO_x/ZrO₂-MT catalyst improves the structural properties and dispersion of VO_x. The tetragonal-monoclinic transformation on the ZrO₂-MT surface facilitates VO_x reduction and produces additional V³⁺ active sites. The highly dispersed V³⁺ sites on the ZrO₂-MT surface accelerate C H bond breaking and boost the desorption of propylene, which is the key reason for enhancing activity and stability during the reaction, respectively. Insight into the role of surface phase transformation of ZrO₂-MT is expected to obtain high-efficient catalysts further.     

Effect of chromium promoter on copper catalysts in ethanol dehydrogenation

A series of chromium-promoted copper catalysts with various Cr to Cu molar ratios were prepared with the co-precipitation method. The promotional effects of chromium on copper catalysts were examined by X-ray powder diffraction (XRD), nitrous oxide decomposition, and the dehydrogenation reaction of ethanol. The dehydrogenation reaction was carried out in a continuous-flow microreactor between 523 and 583 K under atmospheric pressure. The results indicated that the promotional effect was dependent on the Cr/Cu molar ratio, and the predominant decay of catalysts in this study was caused by sintering. The catalyst with the Cr/Cu molar ratio of 4/40 has the highest activity and stability. The surrounded well-dispersed chromia strongly influenced the catalytic properties of copper metal. It also showed that the over-promotation of a catalyst has a disastrous effect on the total make of product. The ethanol dehydrogenation reaction follows a first-order reaction, and the kinetics for deactivation can be described by a second-order expression.     

CO2氧化乙苯脱氢制苯乙烯钒基氧化物催化剂研究进展

与现有乙苯直接脱氢工艺技术相比,CO₂氧化乙苯脱氢工艺具有缓解直接脱氢热力学平衡限制、苯乙烯选择性高、能耗低和二氧化碳资源化利用等显著优势,有望成为一条从乙苯生产苯乙烯的绿色工艺路线。为此,在总结乙苯直接脱氢反应体系和现有工业技术特点、面临的问题和发展方向的基础上,本文较为全面地分析了CO₂氧化乙苯脱氢的特点和反应机理,探讨了现有催化剂体系普遍快速失活的关键原因,表明高性能催化剂研究依然是推进CO₂氧化乙苯脱氢工业化应用的关键。鉴于钒基氧化物催化剂表现出较高的活性,成为近年来CO₂氧化乙苯脱氢相关研究关注的重点。为此,从钒物种含量及其聚集态结构、催化剂的氧化还原和酸碱性、催化剂表面积炭及其作用等角度,综合分析了活性中心结构、反应机理等方面的相关研究进展,认为孤立态V⁵⁺及其含量可能是决定钒基氧化物催化剂活性的关键,其稳定性主要取决于催化剂的氧化还原特性,而积炭对催化剂活性和稳定性的影响则与其组成和石墨化程度密切相关。基于上述认识,认为强化CO₂的高效活化、抑制V⁵⁺的深度还原等是今后钒基氧化物催化剂研究的重点发展方向,而利用移动固定床或提升管反应器等进行工艺优化,对推进CO₂氧化乙苯脱氢工业化应用具有重要的研究价值。     

On the NiMoO4 oxidative dehydrogenation of propane to propene: some physical correlations with the catalytic activity

The - and -phases of NiMoO₄ have been investigated with different techniques (X-ray diffraction, electrical conductivity, IR spectroscopy) in order to tentatively rationalise the different catalytic activities observed in the oxidative dehydrogenation of propane to propene. XRD analyses have shown that at 595 ° C, the -phase is already present but a temperature of 700 ° C is required to obtain a full conversion into a pure -phase. Electrical conductivity showed the presence of anionic vacancies. It is proposed that propene is formed by the reaction of propane with surface O^2- anions. The -phase is almost twice more selective in propene formation than the -phase for comparable conversion at identical temperatures. This could derive from different oxygen environments on the active catalytic site.