Effect of the extent of reduction of V2O5 on the adsorption of propylene and the oxidative dehydrogenation of propane to give propylene on V2O5 and V2O5/TiO2-SiO2

An increase in the propylene output in the oxidative dehydration of propane on V₂O₅/TiO₂-SiO₂ was observed after prior reduction of V₂O₅ in the reaction mixture to V₂O₄, which reduces the destructive chemisorption of propylene. A low titanium dioxide content in TiO₂-SiO₂ hinders the deep reduction of V₂O₅ to V₂O₃, which reduces the conversion of propane. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 373–378, November–December, 2007.     

Influence of redox properties on the activity of iron oxide catalysts in dehydrogenation of propane with CO2

Different Fe-containing catalysts (pure Fe₂O₃, Fe₂O₃ supported on active carbon or g-Al₂O₃, and hydrotalcite derived Mg-Fe oxides) were examined in the dehydrogenation of propane performed in an Ar or CO₂ atmosphere at 873 K. A promoting effect of carbon dioxide was found for the Fe₂O₃ and Fe₂O₃/AC samples. The catalytic results are discussed in terms of redox properties of the catalysts determined by temperature-programmed reduction (TPR). This revised version was published online in August 2006 with corrections to the Cover Date.     

TG study on real role of active carbon support in propane dehydrogenation with CO2

Active carbon was used as a support for chromium(III) oxide phase. The synthesized materials appeared to be very active catalysts of the propane dehydrogenation in the presence of CO₂. An influence of the Cr content on the catalytic activity and selectivity was observed. The best results were achieved over the sample containing about 5 wt.% of Cr. A negative effect of activity decay with time-on-stream was found. The reasons of the observed deactivation were explained using the thermal analysis method. A behavior of the fresh and used samples was tested in a temperature range of 25–1000 °C in different atmospheres (inert gas, air or CO₂). It was found that the catalytic runs resulted in a partial decomposition of surface O-containing groups, which together with CrO_x species play a role of active centers. Moreover, a formation of inactive carbonaceous deposit on the catalyst surface was observed.     

Intrinsic kinetics of oxidative dehydrogenation of propane in the presence of CO2 over Cr/MSU-1 catalyst

The intrinsic kinetics of oxidative dehydrogenation of propane with CO2 has been investigated over Cr/MSU-1 catalyst in a fixed bed reactor. Without limitations of both internal and external diffusion, intrinsic kinetic data were obtained under the following conditions: 490-530 °C, space velocity of 3600?6000 mL·h-1·g-1 and 3/1 molar ratio for CO2/C3H8 under normal pressure. Based on Langmuir-Hinshelwood mechanism, the kinetic models were established, and they were validated by statistical analysis. The parameters were estimated using Simplex Method combined with Universal Global Optimization Algorithm. The model, taking the surface reaction process as the rate-determining step, is the best one in agreement with the experimental data.     

Catalytic dehydrogenation of isobutane in the presence of carbon dioxide

Summary The dehydrogenation of isobutane to isobutene in the presence and absence of carbon dioxide is discussed on the basis of catalytic studies. The V-Mg-O catalysts have been prepared using different preparation procedures. The structure and texture of the V-Mg-O catalysts were characterized by several techniques including X-ray diffraction (XRD), BET surface area measurements and infrared spectroscopy (IR). The results show that carbon dioxide enhances isobutane conversion in the reaction carried out over the V-Mg-O catalyst prepared by citrate method.     

Dehydrogenation of propane in the presence of CO2 on Cr(3%)/SiO2 catalyst under supercritical conditions

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Oxidative dehydrogenation of propane over Mo/g-Al2O3. effect of precursor

Alumina supported molybdenum oxide was prepared using ammonium heptamolybdate and molybdenum acetate as different precursors. The catalysts were characterized by BET, AAS, SEM-EDAX, XRD, TPR and surface acidity measurements. The characterization results and the catalytic behavior in oxydehydrogenation of propane were similar irrespective of precursor. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photocatalytic Synthesis of Hydrocarbon Oxygenates from C2H6 and CO2 over Pd-MoO3/SiO2 Catalyst

Pd-MoO3/SiO2 catalyst has been prepared using the method of incipient wetness impregnation. The photo absorbing behaviors and chemisorbing properties of the catalyst have been characterized by UV-vis spectra and TPD-MS experiments. The results indicated that metal Pd loaded on MoOe/SiO2 has a significant effect on the photo absorbing performance of MoO3/SiO2, and an obvious blue shift of the absorption edge is produced. Under UV irradiation, the chemisorption state of CO2 undergoes decomposing process to form CO at 481 K, and a two-site adsorption state of ethane can be formed at around 496 K. Photo-oxidation of ethane using carbon dioxide can mainly produce propanal, ethanol and acetaldehyde in the temperature range of 353-423 K. The presence of metal Pd improves the catalytic activity remarkably.     

Co-Cu/SiO2催化剂的表征

用溶胶-凝胶法制备了Co-Cu/SiO2系列的担载型催化剂,采用SBET、TPR、XRD、O2滴定等技术对该催化剂进行了研究,并考察了催化剂在F-T合成反应中的催化性能.结果表明,样品的SBET较大,Co和Cu组分均很好分散;Cu2+的加入使得Co更易于被氢气还原,Co是经由Co3+→Co2+→Co0的还原过程,Cu的还原为Cu2+→Cu0;Cu2+的引入使得样品中钴的还原度增大,对F-T合成的催化性能有了一定的改善.     

Nitrogen‐doped mesoporous carbon materials for oxidative dehydrogenation of propane

The CN‐15‐x series materials with different doses of SBA‐15 template and the CN‐y‐2.0 series materials with different hard templates were prepared by the hard template method with hexamethylenetetramine as the carbon and nitrogen source. The obtained mesoporous carbon materials were characterized by X‐ray diffraction (XRD), N₂ adsorption–desorption, transmission electron microscopy (TEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The catalytic performance of propane oxidative dehydrogenation was determined. The characterization results indicate that the catalytic activity of CN‐15‐2.0 with a bipartite hexagonal ordered structure was higher than those of the other materials. The conversion of propane was 22.98%, and the selectivity toward propylene was 41.70%.     

等离子体技术对CO2甲烷化用Ni/SiO2催化剂的改性作用

采用浸渍法制备了Ni/SiO₂催化剂,应用等离子体技术对催化剂进行改性处理。以CO₂甲烷化为模型反应对催化剂进行活性评价,通过H₂程序升温还原(H₂-TPR)和CO₂程序升温脱附(CO₂-TPD)技术对催化剂进行表征。研究了等离子体技术强化处理对催化剂吸附性能和还原性能的影响。结果表明,与常规焙烧的催化剂相比,等离子体技术改性处理提高了催化剂活性组分的分散度,增加反应活性位并调变了活性位对吸附物种的吸附强度,改进了催化剂的还原性能,CO₂甲烷化反应活性和甲烷的时空产率显著提高。     

Design and synthesis of the honeycomb PtSnNa/ZSM-5 monolithic catalyst for propane dehydrogenation

A novel PtSnNa/ZSM-5 monolithic catalyst was designed and synthesized for the propane dehydrogenation reaction, which was a significant transformation in industry. Experimental results showed that although the propane conversion and the propylene selectivity gradually fell down along with the reaction time, the descent speed of the PtSnNa/ZSM-5 monolithic catalyst was slower than that of the granule catalyst and the propane conversion and propylene selectivity of the reaction with monolithic catalyst still remained at a high level after 12 hr. The monolithic catalyst had regular pore structure that facilitated the separation of the product from the catalyst and reduced the limitation on internal and external diffusion and mass transfer, and led to the high catalytic activity and stability. The catalyst could be easily fabricated and was of highly industrial application potential.     

Synergetic effect between NiO and Ni3V2O8 in propane oxidative dehydrogenation

The oxidative dehydrogenation (ODH) of propane was investigated on Ni-V-O catalysts in a wide range of vanadium contents (5-40%). The addition of a small amount of vanadium significantly increased the catalytic activity of NiO for oxidative dehydrogenation of propane to propene. The formation of propene has a good correlation with the coexistence of NiO and Ni₃V₂O₈. This result strongly suggests that a synergetic effect exists between them in Ni_XV_1-XO_Y (X = 0.95 to 0.6). The best results were obtained with a high Ni/V ratio (e.g. X = 0.95 to 0.85). The active sites and selective oxygen species are discussed. The influence of the catalyst preparation technique and the redox properties of the catalyst were also examined.     

h-BN掺杂Na2WO4-Mn/SiO2催化剂用于乙烷氧化脱氢制乙烯

采用混浆法制备了一系列六方氮化硼掺杂的Na2WO4/Mn/BxSiy催化剂,并应用于乙烷氧化脱氢制乙烯（ODHE）。考察了Na2WO4/Mn/BxSiy催化剂的ODHE反应性能,并详细探讨了反应温度、稀释气比例等条件对催化剂反应活性的影响。结果表明,h-BN的掺杂发现显著提高了Na2WO4/Mn/BxSiy催化剂C2H4选择性。Na2WO4/Mn/B5.0Si95催化剂在700℃时,表现出相对较高的活性并且CO2生成量极低（>70% 乙烯选择性,46.5%的乙烯收率,1.80%的CO2选择性）。通过X-射线粉末衍射（XRD）、扫描电镜（SEM）、H2程序升温还原（H2-TPR）、O2程序升温脱附（O2-TPD）和C2H6程序升温脱附（C2H6-TPD）等手段对催化剂进行了表征。研究发现,h-BN的加入对改变催化剂表面元素的化学状态,形成了更多具有低温活性的物相,对抑制深度氧化起到重要作用。同时,h-BN的掺杂也调变了催化剂的导热能力,避免床层热点的形成,提高了C2H4的选择性。     

丙烷脱氢PtSn/Al_2O_3催化剂积炭行为研究

通过HRTEM、XRD、FT-IR、Raman、~(13)C NM R、NH_3-TPD、DTG及元素分析等表征手段,研究了丙烷脱氢PtSn催化剂积炭性质及其对催化剂结构的影响,分析了催化剂的积炭失活过程。结果表明,积炭覆盖活性位并堵塞催化剂孔道是催化剂失活主要因素;与新鲜催化剂相比,催化剂积炭完全失活后,Pt颗粒粒径并没有明显变化;完全失活时,XRD谱图出现了无定形石墨炭的衍射峰;随着积炭量的增加,焦的石墨化程度越高,芳构化程度加深,难以消除的炭增多,再生难度加大。提出丙烷在Pt活性位深度脱氢形成积炭并向载体转移的历程,认为更为稳定的C_(24)H_(12)是积炭前驱体。     

Chemical fixation of carbon dioxide to propylene carbonate over TBD/SiO2 and DBU/SiO2 catalysts

A simple and effective synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives from aldehydes, 1,3-dicarbonyl compounds and urea using copper(II) trifluoroacetate as catalyst under solvent-free conditions is described. Compared with the classical Biginelli reaction condition, this new method has the advantage of good to excellent yields and short reaction time.     

Oxidative dehydrogenation of propane on TiO2-supported chromium and zinc oxides

Oxidative dehydrogenation of propane has been studied on chromium, zinc and zinc-chromium mixed oxides supported on anatase titania. The order of activity and selectivity to propene was CrTi>ZnCrTi>ZnTi. The activity and selectivity to propene did not change markedly with increase in the reaction temperature.     

Theoretical research on Pd cluster catalysts for the direct dehydrogenation of propane to propylene

In this article, the feasibility of catalytic dehydrogenation of propane by Pd clusters (Pd₇, Pd₆C, Pd₆Si, Pd₆Ge, and Pd₆Sn) was investigated by using density functional theory (DFT). It was found that Pd₆Sn has the strongest electron mobility and the ability to activate C H bonds, and the highest adsorption barrier (−75.16 kcal/mol) with propylene. The first pathway of the Pd₆Sn-catalyzed primary reaction has the lowest decisive step barrier (16.65 kcal/mol), and the second pathway of the secondary reaction has the highest decisive step barrier (62.25 kcal/mol). It was demonstrated that both the catalyst's electron-leaping ability and the ability to activate C H bonds were the key factors affecting the activity, and the adsorption strength of the catalyst to the product was the main factor affecting the selectivity. It was shown that Pd cluster-catalyzed PDH is theoretically feasible and Pd₆Sn is likely to be a potential cluster catalyst for propane dehydrogenation.     

Simultaneous propane dehydrogenation andco2hydrogenation overCrOx/SiO2catalyst

Summary Single reverse water-gas shift (RWGS) and dehydrogenation of propane with CO₂(DH-CO₂) reactions in the presence and absence of the CrO_x/SiO₂ catalyst have been studied between 673 and 873 K. It was found that the CrO_x/SiO₂ catalyst is active both in the dehydrogenation of propane and in the RWGS reactions. The obtained results suggest that the dehydrogenation of propane to propene in the presence of CO₂on CrO_x/SiO₂can be facilitated by the RWGS reaction.</o:p>     

Dehydrogenation of propane in the presence of carbon dioxide over oxide-based catalysts

In the present study, we show the advantages of CO₂ use for the dehydrogenation of propane to propene on the basis of thermodynamic considerations and some experimental results. Several metal oxides Ga₂O₃, Cr₂O₃, Fe₂O₃ unsupported and supported on g- Al₂O₃ and SiO₂ were tested. Ga₂O₃ catalyst was found to be an effective agent for dehydrogenation of propane to propene. The yield of propene at 873 K was 30.1 %. This revised version was published online in June 2006 with corrections to the Cover Date.