Catalytic wet oxidation of H2S to sulfur on Fe/MgO catalyst

The room temperature wet catalytic oxidation was conducted in a batch reactor with Fe/MgO catalyst. Fe/MgO catalyst was prepared by the dissolution–precipitation method. XRD and temperature-programmed reductions (TPR) indicate that Fe oxide in the Fe/MgO is finely dispersed in the MgO support. The high H₂S removal capacities of Fe/MgO can be explained by the finely dispersed iron oxide MgO. The H₂S removal capacities of Fe/MgO are dependent on oxygen partial pressure (1.0 g H₂S/g_cat in air and 2.6 g H₂S/g_cat in oxygen). The valence state analysis of Fe/MgO catalyst suggests that the H₂S oxidation on Fe/MgO can occur by a redox couple reaction, reducing Fe³⁺ into Fe²⁺ by H₂S and oxidizing Fe²⁺ to Fe³⁺ by O₂.     

Preparation and characterization of MgO powders having Ca or Ba as surface dopants

The tendency of large dopant cations towards surface segregation has here been utilised to prepare high surface area MgO powders carrying Ca²⁺ or Ba²⁺ as surface impurities in amounts equivalent to 0.2 to 5 monolayers of CaO or BaO. Computational approaches had pointed to possibilities for reconstruction of such impurity monolayers into “rumpled” arrangements as a means of minimizing their energies: the rumpled arrangement favoured for Ca²⁺/MgO would have alternate oxygen anions displaced outward from the original (100) plane, whereas that favoured for Ba²⁺/MgO would involve large outward displacement of alternate Ba²⁺ ions. Ions displaced in that way would necessarily feature lower coordination to counter-ions than species on non-rumpled surfaces, and hence could be expected to exhibit higher surface reactivity and/or catalytic activity. This paper presents results of experiments aimed at: (i) preparation of powdered MgO materials having monolayer amounts of CaO or BaO segregated upon their surfaces; and (ii) testing whether such monolayer-doped Ca²⁺/MgO and Ba²⁺/MgO materials exhibit physical and/or chemical properties indicative of the “rumpling” favoured by computations. Chemical comparisons made between surface reactivities of Ca²⁺/MgO and Ba²⁺/MgO versus the pure MgO support include: lability of surface oxide ions, as manifested in ease of heterophase oxygen isotope exchange at 623–873 K, and relative activities for oxidative coupling of methane at 923–958 K. Physical comparisons include: extent and spectral distribution of surface-sensitive luminescence; BET surface areas; X-ray diffraction and scanning electron microscopy.     

Adsorption on perfect and reduced surfaces of metal oxides

Two major chemical processes, acidobasic and redox, track the adsorption mechanism on metal oxides. Molecular and dissociative adsorption on stoichiometric surfaces can be understood as acid–base processes. Clean and anhydrous surfaces of metal oxides have two different active sites: cations and anions. Electron-rich molecules or fragments arising from a heterolytic bond cleavage (Lewis bases) react with Mⁿ⁺, while electron poor ones (Lewis acids) react with O²⁻. The MgO and TiO₂ surfaces clearly appear to be predominantly acidic and molecules that do not dissociate generally bind to the metal cation. The electronic structure, insulating character for the stoichiometric surface, is preserved upon adsorption.

When the initial system does not favor an energy gap (open-shell adsorbates, defective surfaces), the best adsorption mode is via a redox mechanism that restores the situation of an insulator and the highest oxidation states for all the atoms.

For radical adsorption a first solution occurring on irreducible oxides is to couple the electrons and form two opposite ions adsorbed on the two surface sites, as for H₂/MgO, involving an acid–base mechanism. Another possibility occurring on reducible oxide is via an electron transfer to or from the oxide (redox mechanism). The electron transfer occurs from the substrate to the adsorbate for electronegative group (Cl adsorption on O) or the other way around for an electropositive one (NO adsorption on M). The reactivity at surfaces deviating from stoichiometry differs from that on the perfect ones. The difference does not only originate from the modification of the coordination number but also from the electron counting.     

Catalytic combustion of diesel soot on Co, K supported catalysts

Catalysts containing 12% Co and 4.5% K, supported on MgO and CeO₂ have been studied for diesel soot catalytic combustion. It has been found that this reaction occurs by a redox mechanism when Co and K are deposited on any of the above-mentioned supports. On MgO-supported catalysts, CoO_x species are responsible for the supply of oxygen by a redox reaction. In this catalyst, K plays different roles, one of them being the stabilization of the CoO_x particles. On CeO₂-supported catalysts, Co does not significantly improve the activity of the K/CeO₂ catalyst, since in this case the support itself displays redox properties. XPS analyses indicate that the oxygen availability on the surface is much higher on CeO₂ than on MgO. On both CeO₂ and MgO-supported catalysts, K might provide a route for CO₂ release through a carbonate intermediate species. The presence of NO in the gas phase improves the catalytic activity for soot elimination. NO is oxidized to NO₂ on the Co, K/CeO₂ catalyst, and NO₂ is a stronger oxidizing agent than O₂, therefore decreasing the temperature needed to burn the soot.     

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。     

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.     

The oxidative coupling of methane and the oxidative dehydrogenation of ethane over a niobium promoted lithium doped magnesium oxide catalyst

The promoting effect of niobium in a Li/MgO catalyst for the oxidative coupling of methane (OCM) and for the oxidative dehydrogenation of ethane (ODHE) has been studied in some detail. It has been found that a Li/Nb/MgO catalyst with 16 wt % niobium showed the highest activity for the C₂ production in the OCM reaction; the activity at 600 °C was ten times that of the Li/MgO catalyst at the same temperature. The Li/Nb/MgO catalyst was also slightly more active for the ODHE reaction than was the Li/MgO catalyst. However, the Li/Nb/MgO catalyst produced considerably more carbon dioxide in the both reactions. Structural investigation of the catalyst showed that the addition of niobium to the Li/MgO catalyst increased the surface area and gave an increase in the lithium content of the calcined catalysts. Two niobium phases, LiNbO₃ and Li₃NbO₄, were formed; it is shown that the first of these probably causes the increased activity. Ageing experiments showed that the activity of the catalyst was lost if the catalyst was used above 720 °C, the melting point of the lithium carbonate phase. The catalyst showed a decrease of surface area after ageing and a sharp decrease of the amount of the two niobium phases. The addition of carbon dioxide to the feed could not prevent the deactivation of the Li/Nb/MgO catalyst.     

Oxidative coupling of methane with participation of oxide catalyst lattice oxygen

Redox properties of the supported Li₂O/MgO, K₂O/Al₂O₃ and PbO/Al₂O₃ catalysts are studied. New mechanism of the catalyst re-oxidation is suggested. Re-oxidation of the catalyst in the course of steady-state reaction can proceed as an oxidative dehydrogenation of surface OH groups.     

Ti-Al复合载体载锰催化剂同时脱硝脱汞实验

采用溶胶-凝胶法制备了一系列TiO₂、TiO₂-Al₂O₃（TiAl）、MnO₂/TiO₂（MnTi）和MnO₂/TiO₂-Al₂O₃（MnTiAl）样品,在固定床实验装置上研究了MnTi和MnTiAl催化剂的脱硝、脱汞性能,并对相应的样品进行了BET、XRD、H₂-TPR、XPS表征分析。表征结果表明,Al₂O₃掺入TiO₂后能极大提高载体的比表面积,提升催化剂氧化还原性能,且有利于高价态锰离子（Mn³⁺和Mn⁴⁺）和化学吸附氧（O*）在催化剂表面富集。固定床实验结果表明,在反应温度范围内,MnTiAl催化剂脱硝、脱汞性能均优于MnTi催化剂,MnTiAl催化剂在200℃时脱硝、脱汞效率分别高达88.5%和96.1%。MnTiAl脱除烟气Hg⁰过程中,将Hg⁰氧化为Hg²⁺的同时,催化剂表面Mn³⁺、Mn⁴⁺和O*浓度均被消耗,同时烟气中的O₂能将催化剂表面较低价态的锰离子（Mn²⁺和Mn³⁺）重新氧化为高价态锰离子（Mn³⁺和Mn⁴⁺）,并且能补充催化剂表面的化学吸附氧（O*）,进而实现催化剂催化氧化Hg⁰过程。     

The roles of Cu, Zn and Mn in Cu0.5Zn0.5Mn2O4 spinel-lattice catalyst for methanol decomposition

Cu_0.5Zn_0.5Mn₂O₄ spinel-lattice catalyst has been studied for methanol decomposition by in situ infrared (IR) spectroscopy analysis and micro reactor study. Methoxy species is formed by dissociative adsorption of methanol which subsequently converts into formate species via step-wise dehydrogenation process. The activities of surface intermediates on reduced CuO, ZnO and Mn₂O₃ catalysts are strongly affected by the ease of hydrogen desorption from the site, the strength of C–H bonding and the availability of oxygen. A synergism between Cu and MnO whereby the Cu serves as a sink for reverse hydrogen atoms spillover from MnO has been proposed. The micro reactor analysis correlates well with the IR results.     

Selective oxidation with air on metal catalysts

Oxidation of organic molecules with air on metal catalysts has been known for a long time but there has been a renewed interest in recent years because these catalytic reactions are environmentally safe and could replace stoichiometric oxidations. This paper describes several oxidation reactions conducted either at high temperatures in the gas phase or at moderate temperatures in the liquid phase; in both cases they proceed via a mechanism of oxidative dehydrogenation on the metal surface. Ethylene glycol was converted to glyoxal at 550°C on Ag/SiC catalyst with a 70% yield provided promoters were added to the reaction feed (diethylphosphite or iodine) or deposited on the catalyst (LiPO₄ or H₃PO₄). The promoters improve the conversion and selectivity by modifying the structure and the oxygen concentration on the surface of silver. Oxidation of glyoxal to glyoxylic acid, glucose to gluconic acid and glycerol to various oxygenated derivatives were conducted in water at 60°C in the presence of carbon-supported palladium or platinum catalysts. Bismuth promoter, deposited on the platinum metals by redox reaction, improves the catalyst activity by preventing over-oxidation of the metal surface and favors the oxidation of secondary alcohol functions into keto-derivatives. At higher reaction temperatures, platinum catalysts produce C-C bond rupture with the formation of carboxylic acids with smaller chains. Thus, cyclohexanol was converted into C₆, C₅, and C₄ diacids with a 45% selectivity to adipic acid on Pt/C catalysts at 150°C.     

Pt/Al_2O_3与Pt/MgO-Al_2O_3催化剂制备及其催化氢能载体甲基环己烷脱氢反应性能

以碱共沉淀法制备Mg-Al水滑石,然后采用浸渍法负载活性组分Pt,经焙烧、氢气还原得到Pt/Al_2O_3与Pt/Mg O-Al_2O_3催化剂,采用XRD、N2吸附-脱附、FT-IR、H2-TPR和Py-IR等分析Mg O的加入对Pt/Al_2O_3催化剂结构性能的影响,并在甲基环己烷连续脱氢反应中对比两种催化剂活性。结果表明,Pt/Mg O-Al_2O_3催化剂比表面积小于Pt/Al_2O_3催化剂,且表面基本无酸性活性中心,但表现出与Pt/Al_2O_3催化剂相同的脱氢活性。在Pt负载质量分数2%、催化剂用量0.5 g、甲基环己烷0.1 m L·min-1纯样进料和325℃反应10 h后,原料平均转化率79.9%,脱氢产物只有甲苯,对应的产氢速率192.8 mmol·(g-metal·min)-1,表现出优良的脱氢活性。     

Catalytic hydrogen transfer due to FeSO4 and Co&z.sbnd;Mo in coal liquefaction

The liquefaction behaviour of a Kentucky coal was studied in batch autoclave experiments at 410 °C under either a H₂ or a N₂ atmosphere (≈ 13.8 MPa) for reaction times of up to 2 h. To understand the catalytic roles of FeSO₄ and a Co&z.sbnd;Mo catalyst in coal liquefaction and to assess the feasibility of using FeSO₄ as a model for coal pyrites, effects of impregnation of the coal with FeSO₄ and direct charges of a Co&z.sbnd;Mo catalyst on coal liquefaction and tetralin dehydrogenation were examined. Both catalysts increase the conversion to benzene-soluble material by 7–10%, and improve the selectivity values for conversion to oil and gas. In addition they are also active in the dehydrogenation of tetralin. The dehydrogenation activities of these catalysts correlate with their catalytic activities during coal liquefaction. Analyses of the mean chemical structures and the product distributions of the coal-derived liquid from liquefaction in H₂ and in N₂ atmospheres indicate that:

1. (1) H-transfer from tetralin is the only major mechanism of coal liquefaction; and

2. (2) both pyrrhotite, generated in-situ from FeSO₄, and Co&z.sbnd; Mo catalyst can provide a major liquefaction mechanism by catalysing the H-transfer from the donor solvent to the coal or the coal-derived liquid.

     

CrO x /Ti-Al2O3催化剂结构及其催化丙烷脱氢性能

以模板法制备的Ti改性Al₂O₃为载体制备了CrO _x /nTi-Al₂O₃催化剂,考察了Ti含量对催化剂的结构及其催化丙烷脱氢性能的影响。采用X射线衍射（XRD）、N₂吸附-脱附、透射电子显微镜（TEM）、傅里叶变换红外光谱（FTIR）、拉曼光谱、X射线光电子能谱（XPS）、氨气程序升温脱附（NH₃-TPD）、吡啶红外吸附（Py-IR）等方法对催化剂的结构进行了表征。结果表明,CrO _x /nTi-Al₂O₃催化剂具有均匀的泡沫状介孔结构并含有少量微孔,表面积在180~195m²/g;铬主要以Cr⁶⁺和Cr³⁺形式存在,其中Cr⁶⁺主要以单铬酸盐和双铬酸盐形式存在,Cr³⁺以α-Cr₂O₃晶体和高分散Cr₂O₃形式存在,Ti的加入降低了催化剂表面Cr⁶⁺含量,增加了孔道内高分散Cr³⁺含量;Ti的加入降低了弱酸的强度,生成了少量中强酸,并使催化剂中B酸和L酸中心数量明显减少。少量的Ti（0.5%~1.0%TiO₂,质量分数）可明显提高丙烷转化率和丙烯收率,但过多的Ti（>2%TiO₂）则明显降低丙烯选择性而使丙烯收率降低。CrO _x /nTi-Al₂O₃催化剂表面Cr⁶⁺物种可催化丙烷氧化脱氢,本身还原成Cr³⁺后继续催化丙烷直接脱氢,孔道内部的高分散Cr³⁺可催化丙烷直接脱氢反应,二者结合使催化剂保持了较高的催化活性和较好的稳定性。     

Density functional theory and kinetic Monte Carlo simulation study the strong metal–support interaction of dry reforming of methane reaction over Ni based catalysts

Oxide supports modify electronic structures of supported metal nanoparticles,and then affect the catalytic activity associated with the so-called strong metal-support interaction(SMSI).We herein report the strong influence of SMSI employing Ni_4/α-MoC(111) and defective Ni_4/MgO(100) catalysts used for dry reforming of methane(DRM,CO_2+CH_4→2 CO+2 H_2) by using density functional theory(DFT) and kinetic Monte Carlo simulation(KMC).The results show that α-MoC(111) and MgO(100) surface have converse electron and structural effect for Ni_4 cluster.The electrons transfer from a-MoC(111) surface to Ni atoms,but electrons transfer from Ni atoms to MgO(100) surface;an extensive tensile strain is greatly released in the Ni lattice by MgO,but the extensive tensile strain is introduced in the Ni lattice by α-MoC.As a result,although both catalysts show good stability,H_2/CO ratio on Ni_4/α-MoC(111) is obviously larger than that on Ni_4/MgO(100).The result shows that Ni/α-MoC is a good catalyst for DRM reaction comparing with Ni/MgO catalyst.     

The nature of metal oxide on adsorptive and catalytic properties of Pd/MeOx/Al2O3 catalysts

The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide.

The NO dissociation was better on the Pd/MoO₃/Al₂O₃ catalyst than on the Pd/CeO₂/Al₂O₃ and Pd/Nb₂O₅/Al₂O₃ catalysts. The explanation for the very high N₂ production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me^δ+ stoichiometric reaction.

The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N₂ selectivity.     

Acid and base characteristics of molybdenum carbide catalysts

The acid and base properties of a high surface area Mo₂C catalyst were characterized using the temperature programmed desorption of CO₂ and NH₃, the decomposition of isopropyl alcohol (IPA) as a test reaction and monitoring changes in the associated rates and product selectivities on the addition of acid and base site poisons. The Mo₂C catalyst was prepared using the temperature programmed reaction method and passivated prior to exposure to air. Prior to carrying out the temperature programmed desorption experiments and reaction rate measurements, the Mo₂C catalyst was reduced in H₂ at 400 °C. Results obtained for the reduced Mo₂C catalyst were compared with those for MgO, HZSM-5 and 1% Pt/SiO₂ catalysts. The study provided evidence for the presence of both acid and base sites on Mo₂C. The base and acid sites on the Mo₂C catalyst were weaker than those on the MgO and HZSM-5 catalysts, respectively. The base and acid sites were likely created as a consequence of charge transfer from molybdenum to carbon.     

Oxidative dehydrogenation of propane over V2O5-MgO/TiO2 catalyst: Effect of reactants contact mode

The performance of the active catalyst 5%V₂O₅-1.9%MgO/TiO₂ in propane oxidative dehydrogenation is investigated under various reactant contact modes: co-feed and redox decoupling using fixed bed and co-feed using fluid bed. Using fixed bed reactor under co-feed conditions, propane is activated easily on the catalyst surface with selectivities ranging from 30 to 75% depending on the degree of conversion. Under varying oxygen partial pressures, especially for higher than the stoichiometric ratio O₂/C₃H₈ = 1/2, nor the propane conversion or the selectivities to propene and COx are affected. The performance of the catalyst in the absence of gas phase oxygen was tested at 400 °C. It was confirmed that the catalyst surface oxygen participates to the activation of propane forming propene and oxidation products with similar selectivities as those obtained under co-feed conditions. The ability of the catalyst to fully restore its activity by oxygen treatment was checked in repetitive reduction–oxidation cycles. Fluid bed reactor using premixed propane–oxygen mixtures was also employed in the study. The catalyst was proved to be very active in the temperature range 300–450 °C attaining selectivities comparable to those of fixed bed.     

K2O/Al2O3和Na3PO4/MgO固体碱催化合成松香酸蔗糖酯的研究

分别以自制固体碱K₂O/Al₂O₃和Na₃PO₄/MgO为催化剂,1,2-丙二醇为反应溶剂,催化松香与蔗糖合成松香酸蔗糖酯。以酯化率为指标,考察了反应温度、催化剂的负载量、反应时间、松香与蔗糖质量比对松香酸蔗糖酯合成的影响。通过SEM和BET等手段对催化剂进行表征,并对松香酸蔗糖酯的乳化、发泡、表面张力等性能进行测试。结果表明：K₂O/Al₂O₃与Na₃PO₄/MgO比表面积分别为142.52和19.38m²/g;在松香酸蔗糖酯的合成反应中,催化剂K₂O/Al₂O₃的活性高于Na₃PO₄/MgO。K₂O/Al₂O₃为催化剂时,最优合成工艺条件为反应时间2.5h,反应温度125℃,K₂O/Al₂O₃催化剂用量3%,催化剂中K₂O负载量30%,松香和蔗糖质量比1：2,该条件下酯化率达到98%。合成的松香酸蔗糖酯与市场广泛使用的脂肪酸蔗糖酯相比,具有更好的表面活性。     

Oxidative activation of ethane on catalytic modified dense ionic oxygen conducting membranes

A reactor using dense mixed ion electron conducting membranes was successfully studied in the oxidative dehydrogenation of ethane to ethylene. Already bare Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ membranes allowed reasonable operation with yields beyond state-of-the-art steam cracking. The application of a surface catalyst was found to enhance performance even further. Long term stable operation and ethylene yields of about 75% were observed when using membranes with V/MgO micron grain or Pd nano cluster modified surfaces at temperatures of 1040 or 1050 K, respectively. Being one key factor for the performance of the membrane reactor, the influence of the surface catalysts on the oxygen permeation is reported in a detailed study. Parameters for a model describing the oxygen permeation were determined. The nature of the model indicates the importance of the surface exchange for oxygen permeation, explaining in this way the observed enhancement after application of surface catalysts at the permeate side.