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．     

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.     

Enhancement of catalytic activity by effect of graphite on Ru?Pt/C catalysts

Surface composition and catalytic activity of Ru–Pt/C catalysts were determined. A surface enrichment in Pt was found over the entire composition range. Catalytic activity showed a maximum value (140) on 66% Ru bimetallic catalyst. These results are correlated with the nature of the impregnating salts and with the conductive properties of graphite.

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Ru–Pt/C. Pt . (140) 66% Ru . .

     

Highly efficient VOx/SBA-15 mesoporous catalysts for oxidative dehydrogenation of propane

Highly dispersed vanadia species on SBA-15 mesoporous silica have been found to exhibit a highly efficient catalytic performance for the oxidative dehydrogenation (ODH) of propane to light olefins (propene + ethylene).     

Effect of aluminum modification on catalytic properties of PtSn-based catalysts supported on SBA-15 for propane dehydrogenation

The catalytic properties of PtSn-based catalysts supported on siliceous SBA-15 and Al-modified SBA-15, such as Al-incorporated SBA-15 (AlSBA-15) and alumina-modified SBA-15 (Al2O3/SBA-15), for propane dehydrogenation were investigated. Al2O3/SBA-15 was prepared either by an impregnation method using aluminum nitrate aqueous solution, or by the treatment of SBA-15 with a Al(OC3H7)3 solution in anhydrous toluene. N2-physisorption, FT-IR spectroscopy, solid-state 27Al MAS NMR spectroscopy, hydrogen chemisorption, XRF, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy and TPO were used to characterize these samples. Among these catalysts, the PtSn-based catalyst supported on Al2O3/SBA-15, which was grafted with Al(OC3H7)3, exhibited the best catalytic performance in terms of activity and stability The possible reason was due to the high Pt metal dispersion and/or the strong interactions among Pt, Sn, and the support.     

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al₂O₃ catalyst were studied. Performance test runs were carried out in a fixed-bed integral reactor. Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics, the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared. To avoid fluctuation of time-derivatives of conversion required for differential analysis, the conversion-time data were first fitted with appropriate functions. While the time-zero and rate constant of reaction were largely insensitive to the function employed, the rate constant of deactivation was much more sensitive to the function form. The advantage of the proposed differential method, however, is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible. It was also found that the reaction is not limited by external and internal mass transfer limitations, implying that the employed kinetics could be considered as intrinsic ones.     

Kinetic laws for dehydrogenation of cyclohexane over Pd/C catalysts

A kinetic equation for cyclohexane dehydrogenation at P_O=1.0 MPa has been obtained.

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1,0 .

     

In situ UV-vis-NIR diffuse reflectance and Raman spectroscopy and catalytic activity studies of propane oxidative dehydrogenation over supported CrO3/ZrO2 catalysts

The molecular structures, oxidation states, and reactivity of 3 and 6% CrO3/ZrO2 catalysts prepared by incipient wetness impregnation were examined under different conditions. The in situ Raman spectroscopic studies under dehydrated conditions reveal that the 3 and 6% CrO3/ZrO2 catalysts possess equal amounts of monochromate and polychromate species. Consequently, monolayer coverage on this ZrO2 support is about 3% CrO3. The 6% CrO3/ZrO2 possesses an additional Raman band due to Cr2O3 crystals corresponding to the remaining 3% CrO3. Furthermore, during reaction conditions the polychromate species is preferentially reduced, the monochromate species are slightly affected, and the Cr2O3 crystals are not affected. The in situ UV-vis-NIR diffuse reflectance spectroscopy results reveal that under steady-state reaction conditions the extent of reduction and edge energy position of surface Cr6+ cations increase with an increase in reduction environment for the 3 and 6% CrO3/ZrO2 samples. Propane oxidative dehydrogenation (ODH) studies reveal that the catalytic activity expressed in moles of propane converted per gram catalyst per second is similar for the two catalysts, which is consistent with equal amounts of molecularly dispersed chromia present. The turnover frequency for the 6% CrO3/ZrO2 catalyst is, however, smaller than that for the 3% CrO3/ZrO2 sample due to the presence of Cr2O3 crystals, which are relatively inactive for propane ODH. For this catalytic system and for the experimental conditions used, propene, CO, and CO2 are primary products. Furthermore, the 33-39% propene selectivity is not affected by the C3H8/O2 ratio for both catalysts. Structure-reactivity studies suggest that the molecularly dispersed species are present in equal amounts in the 3 and 6% CrO3/ZrO2 samples as Cr6+ monochromate and polychromate species are the most effective catalytic active sites taking part in the propane ODH reaction.     

SBA-16负载金属氧化物催化剂合成、表征及催化CO氧化反应活性

将V2O5, CeO2和CuO分散到提取自稻米壳的SBA-16上,考察了其催化CO氧化反应活性,并采用X射线衍射、扫描电镜、透射电镜、程序升温还原和紫外漫反射光谱对所制催化剂进行了表征。结果表明,掺杂CuO的介孔氧化硅是一种有前景的催化剂,其CO转化率可达98%以上。     

活性炭负载Pt-Ni双金属催化剂上十氢化萘脱氢

采用等体积浸渍法制备了活性炭负载的具有脱氢活性的Pt-Ni双金属催化剂及相应的Pt单金属催化剂,并用X射线衍射、N2吸附-脱附和NH3-程序升温脱附对其进行了表征.在290°C下,研究了间歇反应条件下催化剂以过热液膜状态催化十氢化萘脱氢活性,考察了温度、浸渍顺序和Pt/Ni摩尔比对十氢化萘脱氢活性和萘产率的影响.结果表明,与单金属催化剂相比,Pt-Ni双金属催化剂上产氢效率显著提高.当Pt/Ni摩尔比为1:1,Pt首先浸渍时,得到的催化剂上脱氢转化率和萘产率最高.将实验结果与密度泛函理论计算的氢原子在不同催化表面的结合能关联证实,具有更强原子氢结合能的双金属表面具有更高的脱氢活性.     

CO2氧化丙烷脱氢制丙烯V-Cr/SBA-15催化剂的研究

以介孔分子筛SBA-15为载体,V和Cr为活性组分,采用浸渍法制备了不同V和Cr质量分数的V-Cr/SBA-15催化剂,研究了其对二氧化碳氧化丙烷制丙烯反应的催化性能,采用XRD、BET、TPR等分析测试技术对催化剂的结构进行了表征。结果表明,催化剂中V组分的质量分数较大时以V2O5物相存在,Cr组分以Cr2O3物相存在,它们对SBA-15分子筛的介孔特征影响不大;V、Cr单组分和双组分催化剂都具有较好的CO2氧化丙烷脱氢制丙烯的催化性能,V和Cr质量分数相同的双组分催化剂比单组分催化剂具有更高的催化活性;在V-Cr/SBA-15催化剂中,V和Cr之间存在一定的相互作用,进而改变了催化剂的氧化还原性能,提高了催化剂的催化性能。     

Oxidative dehydrogenation of ethane over movmnw oxide catalysts

Catalysts based on mixed oxide of MoVMn are active at relatively low temperature for oxidative dehydrogenation of ethane. Incorporation of tungsten into MoVMn oxides enhances the catalytic activity. Enhancement of the activity is explained in the light of acid-base interaction accompanied with a redox mechanism of surface reoxidation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Lewis-type catalytic activity of direct incorporated Zr- and Sn-SBA-16 catalysts

Metal incorporation into nanoporous materials could give Lewis acid sites through the framework substitution of silica matrix, which are supposed to be in tetrahedral substitution of silica. In this work, Zr- and Sn-incorporated SBA-16 were directly synthesized by the microwave synthesis method. These microwave synthesized Zr- and Sn-incorporated mesoporous silica materials were applied in activation of ketones by Lewis acid sites to catalyze Meerwein-Ponndorf-Verly reduction of cyclohexanone and Baeyer-Villiger oxidation of adamantanone, respectively. Optimum incorporated Zr- and Sn-species gave almost 100% selectivity with high activity onto corresponding alcohol and lactone, respectively.     

Plasma catalytic reaction of natural gas to C2 product over Pd-NiO/Al2O3 and Pt-Sn/Al2O3 catalysts

The decomposition of natural gas over Pd-NiO/Al₂O₃ and Pt-Sn/Al₂O₃ is carried out in a microwave catalytic reaction at room temperature. The decomposition of methane is caused by collision by excitation of unstable electronic state. Measuring the flow rate and plasma power can provide kinetic data and indicate the mechanism. The conversion of C₂ products increases from 47 to 63.7% in the microwave plasma catalytic reaction with electric field. Comparing the activities of catalysts, Pd-NiO/Al₂O₃ bimetallic catalyst is more active than Pt-Sn/Al₂O₃ catalyst because of modification of the surface of catalysts by carbon formation. The kinetic modeling of plasma of methane conversion seems related to the power of the electric discharge. It was also revealed that proper coking or polymeric carbon formation improves the catalytic activity; therefore, the conversion of methane may increase over Pd-Ni/Al₂O₃ catalyst in the plasma system.     

PtZn-Sn/SBA-15合成、表征及对丙烷催化脱氢性能

以SBA-15为载体,利用浸渍法制备了单、双和三金属Pt催化剂,并对催化剂进行了N2物理吸附(BET)、程序升温还原(H2-TPR)、H2-化学吸附、透射电子显微镜(TEM)和O2-脉冲等技术表征,研究了它们对丙烷催化脱氢(CDH)制丙烯反应的催化性能。研究结果表明,Pt在三金属催化剂中的分散性能最好,并且部分负载组分可以进入SBA-15的孔道,Pt的分散度达到29%,Pt粒子尺寸为3 nm左右。三金属催化剂表现出优越的脱氢性能,这主要归结于载体的弱酸性、活性组分和助剂、载体之间的相互作用及Zn对Pt的电子调控作用。这些因素使催化剂的积炭量较低,因而具有较高的脱氢稳定性和极高的选择性。     

Ni-WO3/SBA-15催化剂上纤维素的水解加氢

采用等体积浸渍法制备了Ni-WO₃/SBA-15催化剂,将其应用于纤维素的水相氢解.考察了温度对纤维素水解和其形貌的影响及Ni、WO₃含量等对纤维素转化行为的影响.XRD表征结果表明,随着温度的升高纤维素颗粒粒径逐渐变小并趋于均一,结晶状态逐渐由晶型变为无定型态.H₂-TPR结果表明,Ni和WO₃间存在较强的相互作用,这种相互作用提高了W物种对C-C键的解离性能,同时,提高了Ni物种的加氢活性,促进了纤维素向乙二醇的转化.在3%Ni-15%WO₃/SBA-15催化剂上,反应条件为230 ℃、6.0 MPa、6.0 h时,纤维素完全转化,乙二醇的产率达到70.7%.     

Cu-ETS-10催化NH3选择性还原NOx性能

采用离子交换法制备了Cu-ETS-10钛硅分子筛催化剂,该催化剂对于NH₃选择性催化还原（SCR）NO_x反应具有较高的催化活性、N₂选择性和抗SO₂性能.结果表明,Cu-ETS-10钛硅分子筛具有丰富的微孔结构和较高的比表面积（288-380m²/g）;原子发射光谱、程序升温还原技术和原位红外漫反射等表征结果表明,Cu在Cu-ETS-10钛硅分子筛中具有多种存在形态,其中Cu²⁺物种为Cu-ETS-10的活性中心,其含量随Cu含量的增加而先增后降,与催化活性的变化趋势一致.     

碳催化剂用于异丁烷直接脱氢制异丁烯

异丁烯用途广泛,被认为是除乙烯和丙烯外最重要的基础化工原料.异丁烯的来源主要是石油裂化过程中产生的碳四馏分,但随着对其需求量的逐年增加,分离法已逐渐无法满足,因此异丁烷直接脱氢工艺逐渐受到工业界和学术界的重视.铬系和铂系催化剂是两类传统工业催化体系,但铬对环境污染严重,铂作为贵金属成本较高,而且现有工艺大多存在催化剂稳定性较差需要反复再生的问题.近年来碳材料用于烷烃氧化脱氢反应的研究较多,并表现出较高的活性和稳定性,甚至有研究组提出金属催化剂在反应中快速生成的活性积碳(active coke)可能是真正的催化活性中心.但氧化脱氢反应不同于直接脱氢,需在反应中加入氧气,这在实际生产中会带来一系列问题：考虑到烷烃的爆炸极限,实际应用时反应气必须稀释,这不利于产物的收集;而且氧气会导致反应物过度氧化产生CO和CO2等副产物,也限制了氧化脱氢工艺在工业上的应用和发展.
　　我们研究组将椰壳碳、煤质碳和碳纳米管等碳材料作为催化剂用于催化异丁烷直接脱氢反应,发现碳催化剂表现出较高的催化活性：在625 oC,椰壳碳上异丁烷转化率和异丁烯选择性分别为70%和78%,连续反应3d后仍能维持34%的转化率,且选择性基本不变.与铬基催化剂相比,碳催化剂在稳定性方面表现出更大优势.我们进一步采用N2吸脱附、X射线光电子能谱(XPS)、傅里叶变换红外光谱(FTIR)和场发射扫描电子显微镜(FE-SEM)等手段对反应前后的碳催化剂进行了详细表征. N2吸脱附结果表明,椰壳碳比表面积高达1190.2 m2/g,这可能是其具有较高催化活性的原因;而结合催化剂活性数据,对比反应前后椰壳碳催化剂比表面积和异丁烷转化率可知,两者呈现近乎线性的相关性,进一步证实比表面积大小对碳催化剂催化活性有重要影响. XPS谱图证明椰壳碳在反应前表面除了有少量硅(0.73%)外,不存在金属氧化物等杂质,证实碳材料无需负载氧化物等即可表现出较高的催化活性;反应后沉积的积碳附着在催化剂表面,使硅含量降低至0.47%;催化剂中氧含量也由4.43%降低至3.78%,同时有碳酸盐生成. FTIR谱图进一步证实反应前的椰壳碳表面有丰富的有机官能团,但反应开始后有机官能团很快消失,而催化剂仍保持较高的催化活性,因此有机官能团并非碳催化剂催化活性高的必要因素,这与文献中已报道的结果不同. FE-SEM照片中观察到反应后椰壳碳催化剂表面形成积碳,随着反应时间延长积碳明显增多,这与XPS结果一致.
　　碳材料具有来源广泛、绿色环保等显著优势,可作为一种新的催化体系应用于异丁烷直接脱氢反应,无需负载其他物质或添加氧化性气体即可表现出良好的催化活性和稳定性,其比表面积对催化活性有重要影响,反应中产生的积碳导致催化剂比表面积下降进而降低其催化活性,而有机官能团的存在对催化活性影响不大.     

Cyclohexane dehydrogenation over Pt-Dy/Al2O3 catalysts

The conversion of cyclohexane dehydrogenation over Pt–Dy/Al₂O₃ has been studied with a pulsed microcatalytic reactor. Two interesting experiments utilizing CS₂ and thiophene poisoning Pt/Al₂O₃ and Pt–Dy/Al₂O₃ for cyclohexane dehydrogenation are shown and the reaction mechanism is described. The kinetic parameters of cyclohexane dehydrogenation have been calculated. Correlation of the catalytic behavior with the properties of active sites is also discussed.     

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.