Oxidative Dehydrogenation of Ethane Over Novel Li/Dy/Mg Mixed Oxides: Structure–Activity Study

Oxidative dehydrogenation of ethane to ethylene was studied using variously prepared Li/Dy/Mg/Cl mixed metal oxides as catalysts. The catalytic performance was found to be strongly dependant on the method of preparation and the LiCl content of the solids. Ethylene yields of up to 77% were obtained with catalysts prepared by precipitation of the catalyst precursors with an equimolar mixture of NH₄Cl and HCl, and subsequent calcination in synthetic air (i.e., absence of CO₂). Both highest ethylene yields and best long-term stability were achieved with catalysts having the highest chloride loading.Based on kinetic data and high-temperature XRD measurements (under controlled atmosphere), a new reaction mechanism is proposed wherein the active sites of the catalytic system are postulated to reside in molten LiCl, supported on Dy₂O₃/MgO. Oxygen is solved dissociatively in the LiCl melt forming the catalytically active hypochlorite OCl^-. With increasing temperature, OCl^- decomposes to O + Cl^- or O^- + Cl. The two radical species are highly oxidative and can readily activate an alkane by homolytic hydrogen abstraction. The so-created alkane radicals react further with OH to form an olefin and H₂O. At low temperatures, a regime of high apparent activation energy has been determined for high chloride loadings, while at high temperatures and low chloride loadings, a second regime with lower activation energy was found. It is suggested that the first regime is controlled by reaction kinetics, whereas the second regime is diffusion-controlled. Which of the two regimes predominates is strongly dependent on the reaction temperature and the structure and composition of the catalyst.     

Reaction Densification of α'-SiAlON: 1, Wetting Behavior and Acid-Base Reactions

Phase development during reaction hot pressing of α-Si₃N₄, AlN, Al₂O₃, and M₂O_Z powder mixtures (M = Li, Mg, Ca, Y, Nd, Sm, Gd, Dy, Er, and Yb) forming α'-SiAlON has been studied. The wetting behavior of the ternary eutectic melt of M₂O_z-Al₂O₃-SiO₂ was found to control the reaction sequence during hot pressing. Li, Ca, Mg, Nd, Sm, and Gd were found to preferentially wet and react with Si₃N₄ first, whereas Dy, Er, and Yb preferentially wetted and reacted with AlN first. The intermediate phases are Si rich in the former and Al rich in the latter case. Pearson's principle of acid-base theory, which predicts decreasing basicity of oxides of Li, Ca, Mg, Nd, Gd, Sm, Dy, Er, and Yb and decreasing acidity of oxides of Si and Al, is used to understand these reactions.     

以类水滑石为前驱体制备Ru基CH_4-CO_2重整催化剂

以类水滑石为前驱体,采用共沉淀法制备了不同Ru含量的xRu/Mg(Al)O催化剂(x=1,2,4),采用XRD、H2-TPR和CO脉冲吸附等表征催化剂结构和Ru金属分散度,并评价Ru含量对CH4-CO2重整反应活性与稳定性的影响。XRD与CO脉冲吸附结果表明,Ru含量增加时,还原后Ru金属颗粒的表面活性位数目增加,但分散度降低,Ru金属的粒径增大。活性测试结果表明,Ru质量分数为2%时,催化剂活性最高。Ru质量分数为1%时,催化剂具有较好的稳定性,归属于高分散Ru金属颗粒与Mg(Al)O载体之间的强相互作用。     

Mg、Ce修饰纳米Al_2O_3负载Ni催化剂对CH_4、CO_2重整反应制合成气的影响

考察了助剂Mg、Ce修饰的纳米A l2O3负载N i催化剂对CH4、CO2重整反应制合成气的反应性能影响,采用正交实验筛选催化剂。结果表明,N i含量在9%~13%时,催化剂表现出较好的活性;随Mg含量的增加,反应活性基本呈下降趋势,说明Mg降低了催化剂体系的反应性能;Ce的加入总体上提高了反应活性,但是当Ce含量为3%时,反应活性最好;从不经预还原实验和低温点反应实验推断出,CH4和CO2重整反应中关键反应步骤是CH4的裂解;助剂Ce有利于提高催化剂的稳定性,而Mg却会使催化剂的稳定性下降很快。     

A study of the kinetics of the oxidative coupling of methane over a Li/Sn/MgO catalyst

The rate of reaction of methane with oxygen in the presence of a Li/Sn/MgO catalyst has been studied as a function of the partial pressures of CH₄, O₂ and CO₂ using a well-mixed reaction system which is practically gradientless with respect to gas-phase concentrations. It is concluded that the rate-determining step involves reaction of a molecule of CH₄ adsorbed on the catalyst surface with an adsorbed di-atomic oxygen species. The kinetics are consistent with a Langmuir-Hinshelwood type mechanism involving competitive adsorption of CH₄, O₂ and CO₂ on a single site. A comparison is made with previously published results for the Li/MgO material.     

氧化镁/γ-氧化铝催化蒽醌法工艺 降解物再生过程研究

以γ-氧化铝和六水合硝酸镁为原料,采用等体积浸渍法制备了氧化镁/γ-氧化铝催化剂。X射线衍射（XRD）显示,随着氧化铝含量增加,主要衍射峰位置逐渐向低角度方向偏移,表明在γ-氧化铝载体表面形成了MgAl2O4相。在常压、50 ℃下评价了氧化镁/γ-氧化铝催化剂对蒽醌工作液再生和5,6,7,8-四氢-2-乙基-9, 10-蒽醌（H4EAQ）转化性能。结果表明,氧化镁/γ-氧化铝催化剂对蒽醌工作液中降解物再生和H4EAQ转化效果优于未改性γ-氧化铝,并且随着氧化镁负载量增加蒽醌工作液再生和H4EAQ转化效果增加。当氧化镁负载量达到30%（质量分数）时,氧化镁/γ-氧化铝催化剂对蒽醌降解物再生和H4EAQ转化量较γ-氧化铝分别提高54%和231%。     

Kinetics of the Internal Oxidation of (Mg, Fe)O Solid Solutions

Single crystals of Mg_{1- x} Fe _x O, x = 0.01, have been oxidized in air at temperatures between 1146 and 1389 K to determine the kinetics of the internal oxidation reaction. A two-phase region composed of MgFe₂O₄ precipitates in a (Mg, Fe)O matrix grows inward from the surface as the reaction progresses. The thickness of this layer as a function of time has been determined by optical microscopy; the growth kinetics are parabolic. In addition, an external oxide layer of (Mg, Fe)O grows outward from the original surface. The thickness of this external oxide layer as a function of time was determined by following the displacement of inert markers with Rutherford backscattering spectrometry; the kinetics of the growth of this external layer are also parabolic in time. The parabolic reaction rate constant determined for the growth of the external layer accurately predicts that for the growth of the internally oxidized region.     

含氯芳烃催化加氢脱氯动力学研究

利用加压微反装置在Ｐｄ／Ａｌ２Ｏ３催化剂上研究了邻二氯苯加氢脱氯动力学。     

Influence of precursors of Li2O and MgO on surface and catalytic properties of Li‐promoted MgO in oxidative coupling of methane

The influence of the catalyst precursors (for Li₂O and MgO) used in the preparation of Li‐doped MgO (Li/Mg = 0.1) on its surface properties (viz basicity, CO₂ content and surface area) and activity/selectivity in the oxidative coupling of methane (OCM) process at 650–750 °C (CH₄/O₂ feed ratio = 3.0–8.0 and space velocity = 5140–20550 cm³ g⁻¹ h⁻¹) has been investigated. The surface and catalytic properties are found to be strongly affected by the precursor for Li₂O (viz lithium nitrate, lithium ethanoate and lithium carbonate) and MgO (viz magnesium nitrate, magnesium hydroxide prepared by different methods, magnesium carbonate, magnesium oxide and magnesium ethanoate). Among the Li–MgO (Li/MgO = 0.1) catalysts, the Li–MgO catalyst prepared using lithium carbonate and magnesium hydroxide (prepared by the precipitation from magnesium sulfate by ammonia solution) and lithium ethanoate and magnesium acetate shows high surface area and basicity, respectively. The catalysts prepared using lithium ethanoate and magnesium ethanoate, and lithium nitrate and magnesium nitrate have very high and almost no CO₂ contents, respectively. The catalysts prepared using lithium ethanoate or carbonate as precursor for Li₂O, and magnesium carbonate or ethanoate, as precursor for MgO, showed a good and comparable performance in the OCM process. The performance of the other catalysts was inferior. No direct relationship between the basicity of Li‐doped MgO or surface area and its catalytic activity/selectivity in the OCM process was, however, observed. © 2000 Society of Chemical Industry     

Comparison of Alkali Metal Promoted MgO Catalysts for Their Surface Acidity/Basicity and Catalytic Activity/Selectivity in the Oxidative Coupling of Methane

Alkali metal (viz. Li, Na, K, Rb and Cs) promoted MgO catalysts (with an alkali metal/Mg ratio of 0·1) calcined at 750°C have been compared for their surface properties (viz. surface area, morphology, acidity and acid strength distribution, basicity and base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) to C₂-hydrocarbons at different temperatures (700–750°C), CH₄/O₂ ratios (4·0 and 8·0) in feed, and space velocities (10320 cm³ g⁻¹ h⁻¹). The surface and catalytic properties of alkali metal promoted MgO catalysts are found to be strongly influenced by the alkali metal promoter and the calcination temperature of the catalysts. A close relationship between the surface density of strong basic sites and the rate of C₂-hydrocarbons formation per unit surface area of the catalysts has been observed. Among the catalysts calcined at 750°C, the best performance in the OCM is shown by Li–MgO (at 750°C). © 1997 SCI.     

Propane Oxidative Dehydrogenation Over Ln–Mg–Al–O Catalysts (Ln = Ce, Sm, Dy, Yb)

Ln–Mg–Al mixed oxide catalysts (Ln = Ce, Sm, Dy, Yb) were prepared from layered double hydroxide precursors, characterized using XRD, N₂ adsorption, TG-DTG, EDX, H₂-TPR and CO₂-TPD techniques and tested in the oxidative dehydrogenation of propane in the temperature range 450–600 °C. For all the catalysts the conversion increases with increasing the reaction temperature while the propene selectivity decreases to the benefit of carbon oxides for Ce-based system and of cracking products for the others. The best yields in propene were obtained with Dy- and Sm–Mg–Al–O catalysts. No correlation between the reducibility of the rare-earth cation and the catalytic performances was observed. A linear correlation between the catalyst basicity and the propene selectivity was evidenced.     

TiO2纳米管/UV/O3对腐殖酸的降解动力学

用自制的TiO₂纳米管（TNTs）作为催化剂,对腐殖酸进行TNTs/UV/O₃工艺降解研究.从动力学角度分析了光催化、臭氧化的协同作用及催化剂煅烧温度的影响,考察了反应温度、初始pH值、催化剂投加量和臭氧投加量对降解速率的影响,建立了新型动力学模型.结果表明,光催化和臭氧化有很强的协同作用,催化剂最佳煅烧温度为400℃,腐殖酸的TOC降解过程符合零级反应,模型显示当原水pH值为7.35,TNTs投加量0.806g·L^-1,O₃投加量0.49g·h^-1时TNTs/UV/O₃对腐殖酸TOC的降解取得最佳反应速率,当反应温度T为25℃时,最佳k为0.8095mg·L^-1·min^-1,当反应温度T为30℃时,最佳k为0.8231mg·L^-1·min^-1.试验结果和模型结果对比得出试验值基本符合动力学模型.     

Selective oxidation of propylene to acrolein over supported V2O5/Nb2O5 catalysts: An in situ Raman, IR, TPSR and kinetic study

The vapor-phase selective oxidation of propylene (H₂CCHCH₃) to acrolein (H₂CCHCHO) was investigated over supported V₂O₅/Nb₂O₅ catalysts. The catalysts were synthesized by incipient wetness impregnation of V-isopropoxide/isopropanol solutions and calcination at 450 °C. The catalytic active vanadia component was shown by in situ Raman spectroscopy to be 100% dispersed as surface VO_x species on the Nb₂O₅ support in the sub-monolayer region (<8.4 V/nm²). Surface allyl species (H₂CCHCH_2*) were observed with in situ FT-IR to be the most abundant reaction intermediates. The acrolein formation kinetics and selectivity were strongly dependent on the surface VO_x coverage. Two surface VO_x sites were found to participate in the selective oxidation of propylene to acrolein. The reaction kinetics followed a Langmuir–Hinshelwood mechanism with first-order in propylene and half-order in O₂ partial pressures. C₃H₆-TPSR spectroscopy studies also revealed that the lattice oxygen from the catalyst was not capable of selectively oxidizing propylene to acrolein and that the presence of gas phase molecular O₂ was critical for maintaining the surface VO_x species in the fully oxidized state. The catalytic active site for this selective oxidation reaction involves the bridging VONb support bond.     

Transesterification of edible and non-edible oils over basic solid Mg/Zr catalysts

A series of Mg–Zr catalysts with varying Mg to Zr ratios was prepared by co-precipitation method. These catalysts were characterized by BET surface area, X-ray diffraction, X-ray photo electron spectroscopy and temperature programmed desorption of CO₂. The catalytic activity of these catalysts was evaluated for the room temperature transesterification of both edible and non-edible oils to their corresponding fatty acid methyl esters. The catalyst with Mg/Zr (2:1 wt./wt.%) exhibited exceptional activity towards transesterification reaction within short reaction time. The effects of different reaction parameters such as catalyst to oil mass ratio, reaction temperature, reaction time and methanol to oil molar ratio were studied to optimize the reaction conditions. The reasons for the observed activity of these catalysts are discussed in terms of their basicity and other physico-chemical properties.     

Novel low temperature NOx storage-reduction catalysts for diesel light-duty engine emissions based on hydrotalcite compounds

A series of Pt and Pt,Cu supported catalysts were prepared by wet impregnation of Mg–Al supports obtained from hydrotalcite-type (HT) precursor compounds. These novel NO_x storage-reduction (NO_xSR) catalysts show improved performances in NO_x storage than Pt,Ba/alumina NO_xSR catalysts at reaction temperatures lower than 200 °C. These catalysts show also improved resistance to deactivation by SO₂. The effect is attributed to the formation of well dispersed Mg(Al)O particles which show good NO_x storage properties. The promoted low temperature activity is explained by the lower basicity of the Mg(Al)O mixed oxide in comparison to BaO, which induces on one hand a lower inhibition on Pt activity (NO to NO₂ oxidation and/or hydrocarbon oxidation) due to electronic effect, and on the other hand a lower thermal stability of the stored NO_x. The presence of Cu slightly inhibits activity at low temperature, although improves activity and resistance to deactivation at 300 °C. On these catalysts FT-IR characterization evidences the formation of a Pt–Cu alloy after reduction.     

On the plasma-chemical synthesis and/or regeneration of ultradispersed catalysts for ammonia production

The equilibrium compositions of multi-component heterogeneouse systems N–Al–O–Ca–Mg, Cu–Zn–Al–O and Fe–Al–K–Ca–Si–O in gaseous and condensed state are established. Further, we have developed a three-dimentional model dealing with the motion, heating, melting and evaporation (thermal destruction) of micron-size particles—(5–60 μm—Fe, Fe₂O₃, Fe₃O₄, FeO, Ni, NiO, Cu, Al, Al₂O₃, CaO, Mg, MgO) in an axial-symmetric plasma-chemical reactor (PCR). Based on the model calculations, we have designed and build plasma-chemical installations and used them to study the mechanisms of preparation of catalysts (and regeneration of spents of deactivated catalysts) for reforming of natural gas (steam conversion of CH₄), for low-temperature steam conversion of CO and for synthesis of NH₃.

A physical-chemical analysis of plasma-chemically synthesised (PCS) and/or regenerated ultra-dispersed catalysts in electric-arc low-temperature plasma conditions has been performed by X-ray structural and phase analysis, electron microscopy, Mössbauer spectroscopy, derivatographic, thermal-magnetic, chemical and analytical methods, by studing the dynamics and kinetics of formation of the active surface due to the reduction (the “plasma” catalysts undergo reduction 2–5 times faster than their respective commercial analoges and show activity by 15–20% higher than that of the conventional catalysts).     

Li~+/MgO上交叉偶联作用的研究

采用Li+/MgO催化剂研究了Li含量、反应温度、原料气组成对甲烷和甲苯催化氧化交叉偶联成乙苯或苯乙烯 (即C8)反应的影响 ,对几种Li含量催化剂上各影响因素引起的差异进行了考察。结果表明 ,其活性中心也主要是Li+O- ,合适的L酸点是本交叉偶联反应中反应物的吸附中心 ,Li+O- 和L酸点是决定偶联反应产物C2 和C8的主要因素。偶联可能主要按游离基机理进行     

Dealumination kinetics of composite ZSM-5/mordenite zeolite during steam treatment: An in-situ DRIFTS study

To get a better understanding of structural deactivation of ZSM-5/MOR during the catalytic cracking of n-heptane in the steam atmosphere, a comprehensive mechanism of hydrothermal dealumination was proposed through in-situ diffuse reflectance Fourier transform infrared spectroscopy(DRIFTS) in this work. The mechanism can be divided into two steps: firstly, the hydrolysis of four Al\\O bonds, and secondly, the self-healing of Si\\OH bonds accompanied with partial condensation of the extra-framework Al species. Accordingly, the kinetics of dealumination process has also been fully discussed. In the IR spectra, the range of 3450–3850 cm~(-1) could be deconvolved to distinguish the hydroxyl groups on the different position and calculate the consumption of each hydroxyl group during the reaction. Based on results from the in-situ DRIFTS, the kinetics of dealumination was hence developed and also in well agreement with the kinetics of deactivation of ZSM/MOR catalysts during the reaction in the presence of little coke deposits.     

甲烷二氧化碳重整镍基催化剂的研究

采用浸渍法制备不同组成催化剂Ni-M/γ-Al₂O₃（M=Zr、Co、Mg、Nd）,通过固定床反应装置考察不同助剂、助剂含量和反应温度对催化剂活性的影响,并对催化剂进行X射线衍射表征。结果表明,14Ni-5Mg/γ-Al₂O₃的催化活性较好,随着反应温度的升高,甲烷转化率和CO收率均升高,反应温度升至800 ℃时,甲烷转化率达97.54%。采用共沉淀法制备载体、浸渍法制备的催化剂14Ni/MgO-Al₂O₃,在反应温度800 ℃、压力1.013 kPa、n(CO₂)∶n(CH₄)=1.2和催化剂用量0.5 g条件下,CO收率高于14Ni-5Mg/γ-Al₂O₃催化剂,但甲烷转化率略低。     

Kinetic study of higher alcohol synthesis directly from syngas over CoCu/SiO2 catalysts

Higher alcohol synthesis (HAS) directly from syngas is one of the most promising approaches for utilizing nonoil resources cleanly and efficiently. A series of bimetallic CoCu catalysts with different Co/Cu ratios were prepared using a SiO₂ support. The structure of Cu modified Co catalysts was characterized using HRTEM, in/ex situ X‐ray diffraction, and temperature‐programmed reduction. It was evidenced that nanoscale metal particles were formed and the reduction of Co oxide at above 673 K. Meanwhile, the interaction between Co and Cu on the surface was assumed to be responsible for the enhanced selectivity to HAS. The intrinsic kinetics for this reaction was performed over a CoCu/SiO₂ catalyst under realistic conditions. The kinetic parameters, including apparent activation energies and reaction orders, were calculated through power‐law models. With the combination of chain growth probability and kinetics, the effect of temperatures on the reaction mechanism and the Cu promotional effects on Co catalysts were elaborated. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1797–1809, 2014