Interactions NO—CO and O2—NO—CO on CuCo2O4/γ-Al2O3 and on γ-Al2O3- and CuCo2O4/γ-Al2O3-supported Pt, Rh and Pt—Rh catalysts, a transient response study

The interactions NO—CO and O₂—NO—CO have been studied onCuCo₂O₄γ-Al₂O₃ and on γ-Al₂O₃- and CuCo₂O₄γ-Al₂O₃-supported Pt, Rh and Pt—Rh catalysts. The deposition of noble metals (Pt, Rh and Pt—Rh) on CuCo₂O₄γ-Al₂O₃ instead of γ-Al₂O₃ is beneficial in: lowering the temperature at which maximum N₂O is formed and decreasing the maximum N₂O concentration attained; lowering the onset temperature of NO to N₂ reduction, and increasing the N₂ selectivity; preserving the activity towards NO to N₂ reduction on a higher level following the concentration step NO + COO₂+ NO + CO and changing the conditions from stoichiometric to oxidizing (50% excess of oxidants). The reason for this behaviour of the CuCo₂O₄γ-Al₂O₃-based noble metal catalysts is the formation (reversible) of a reduced surface layer on the CuCo₂O₄ supported spinel under the conditions of a stoichiometric NO + CO mixture.     

Synthesis of CoAl2O4 by double decomposition reaction between LiAlO2 and molten KCoCl3

Submicronic CoAl₂O₄ powders were prepared by double decomposition reaction between solid LiAlO₂ and molten KCoCl₃ at 500 °C for 24 h. The reaction mechanism involves the dissolution of LiAlO₂ shifted by the precipitation of CoAl₂O₄ until complete transformation and the reaction leads to powders with a very homogeneous chemical composition. The powders obtained were mainly characterized by XRD, FTIR, ICP, X.EDS, electron microscopy and diffraction and diffuse reflexion. The blue pigments obtained exhibit a high thermic stability allowing their use for the colouring of ceramic tiles.     

Preparation and electrochemical behaviour of {[Ru(bipy)4Cl2Ag]NO3(CHCl3)·6H2O}n obtained from the self-assembly of trans-Ru(bipy)4Cl2 and AgNO3

The synthesis and characterization of Ru(II) and Ru(II)-Ag(I) compounds are described, in view of their potential use in on/off switchable metal-ridge-metal nanodevices. The compound trans-Ru(bipy)₄Cl₂ (1) [bipy, 4,4′-bipyridine] has been prepared by Ru(DMSO)₄Cl₂ (2) (DMSO, dimethylsufoxide) and an excess of bipy. The compound has been fully characterised by physico-chemical, spectroscopic and single crystal X-ray determinations. trans-Ru(bipy)₄Cl₂ has been employed as building block in a self-assembly reaction with AgNO₃ obtaining the inorganic polymer {[Ru(bipy)₄Cl₂Ag]NO₃ (CHCl₃)·6H₂O}_n (3). The self-assembled Ru-Ag compound has been investigated by infrared (IR), ultraviolet (UV) and visible (vis) spectroscopy, elemental analyses, inductively coupled plasma optical emission spectroscopy (ICP-OES) and thermogravimetric analysis coupled with infrared detector (TGA-IR). The electrochemical behaviour of 1 and 3 have been studied by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). 1 and 3 have been tested both as soluble species in non-aqueous solvents and as self-assembled molecules on gold electrodes in aqueous medium. The electrochemical behaviour of the parent compounds trans-Ru(pyz)₄Cl₂ (4) [pyz, pyrazine] and {[Ru(pyz)₄Cl₂Ag]NO₃}_n (5) have been also investigated for comparison.     

Effect of the hydrogen spillover on the selectivity of dibenzothiophene hydrodesulfurization over CoSx/γ-Al2O3, NiSx/γ-Al2O3 and MoS2/γ-Al2O3 catalysts

Dibenzothiophene (DBT) hydrodesulphurization (HDS) reaction at 3 MPa and 325–375 °C on Mo/γ-Al₂O₃ single-bed and Me/γ-Al₂O₃//SiO₂//Mo/γ-Al₂O₃ (Me = Co or Ni) double-bed catalysts were investigated. Results indicate that ratio cyclohexylbenzene (CHB)/biphenyl (BP) or selectivity is higher when using double-beds rather than a single-bed. Synergy in dibenzothiophene hydrodesulphurization on Co//Mo and Ni//Mo double-beds is also detected. Changes in selectivity and conversion are attributed to the action of spillover hydrogen (Hso) formed in the first bed that reaches the second bed.     

Reductive amination of n-hexanol to n-hexylamine over Ni–Ce/γ-Al2O3 catalysts

The amination of alkyl alcohols is one of the most promising paths in synthesis of aliphatic amines. Herein, cerium doped nickel-based catalysts were synthesized and tested in a gas-phase amination of n-hexanol to n-hexylamine. It was found that the activity of the Ni/γ-Al₂O₃ catalyst is significantly improved by doping an appropriate amount of cerium. The presence of cerium effectively inhibits the agglomeration of nickel particle, resulting in better Ni dispersion. As Ni particle size plays critical role on the catalytic activity, higher turnover frequency of n-hexanol amination was achieved. Cerium doping also improves the reduction ability of nickel and enhances the interactions between Ni and the catalyst support. More weak acid sites were also found in those cerium doped catalysts, which promote another key step—ammonia dissociative adsorption in this reaction system. The overall synergy of Ni nanoparticles and acid sites of this Ni–Ce/γ-Al₂O₃ catalyst boosts its superior catalytic performance in the amination of n-hexanol.     

Surface alteration of (VO)2P2O7 by α-Sb2O4 as a route to control the n-butane selective oxidation

The catalytic properties of (VO)₂P₂O₇/α-Sb₂O₄ mixed oxides system for n-butane mild oxidation have been investigated on two mechanical mixtures (M1 and M2) of the same well crystallized (VO)₂P₂O₇ (reference vanadyl pyrophosphate) with two different morphologies of α-Sb₂O₄.The M1 mixture of (VO)₂P₂O₇ with α-Sb₂O₄ (1), prepared by oxidation of Sb₂O₃, leads to the oxidative dehydrogenation (ODH) of n-butane, whereas the M2 mixture of (VO)₂P₂O₇ with a commercial α-Sb₂O₄ (2) (Aldrich) with a different morphology improves the maleic anhydride selectivity as compared to the reference (VO)₂P₂O₇ catalyst (synergetic effect). After reaction, no ternary VPSbO phase is detected by XRD and DTA and it was controlled that the two α-Sb₂O₄ oxides are catalytically inactive.The (VO)₂P₂O₇ reference catalyst which produced only maleic anhydride as mild oxidation product shows by XPS a slightly oxidized surface (14% V⁵⁺–86% V⁴⁺).Contamination of the (VO)₂P₂O₇ phase by migration of Sb species occurs after catalytic reaction in the case of the M1 mixture as shown by XPS, LEIS and TEM–EDX analysis. XPS showed that (VO)₂P₂O₇ is partially superficially reduced (86% V⁴⁺–14% V³⁺). This feature is consistent with the decrease of acidity as observed by pyridine adsorption–desorption.In opposition with the M1 mixture, no contamination of the (VO)₂P₂O₇ phase is observed after catalytic reaction in the case of the M2 mixture. The XPS study shows, in this case, that (VO)₂P₂O₇ is partially oxidized (30% V⁵⁺–70% V⁴⁺) at a higher level than for the reference (VO)₂P₂O₇ catalyst. This situation is associated with the increase of selectivity observed for maleic anhydride (synergetic effect).The difference in the catalytic results for the two M1 and M2 mixtures, as compared to the (VO)₂P₂O₇ reference catalyst, can be explained by the alteration of the surface composition of (VO)₂P₂O₇ and the distribution of vanadium oxidation state due to different interaction between Sb₂O₄and (VO)₂P₂O₇, depending on the orientation of the α-Sb₂O₄ crystals.     

Electrolytic reduction behavior of U3O8 in a molten LiCl-Li2O salt

An electrolytic reduction of U₃O₈ in a molten LiCl-Li₂O salt was investigated using the electrochemical techniques of cyclic voltammetry (CV) and chronopotentiommetry (CP). The electrolytic reduction of U₃O₈ powder exhibited a different behavior when the initial current density was higher than for 10 g U₃O₈/batch run. Two kinds of reduction mechanisms, an electro-metallothermic reduction (EMR) and a direct electrochemical reduction (DER) were adopted to explain the resultant behavior. Current efficiencies and reduction products were obtained by a series of constant current runs. Current efficiencies, evaluated for a reduction side, were estimated to be more than 75% throughout a series of constant current runs and lithium uranium oxides (lithium uranates) were detected during the U₃O₈ reduction to metallic uranium.     

Preparation and characterization of an unusual tetracobalt-complex; X-ray crystal structure of [Co2(CO)5{μ-P,P(μ-PPh2CCPPh2)}][Co2(CO)4{μ-P-(μ-PPh2CCPPh2)}]

The reaction of bis(diphenylphosphino)acetylene(DPPA) with Co₂(CO)₈ in toluene at 80 °C for 24 h resulted in an alkyne-bridged, diphosphine-chelated tetracobalt-complex, [Co₂(CO)₅{μ-P,P-(μ-PPh₂CCPPh₂)}][Co₂(CO)₄{μ-P-(μ-PPh₂CCPPh₂)}] 3. The X-ray structural studies of 3 reveals that it can be regarded as a dimerized form of two DPPA bridged dicobalt complex, [Co₂(CO)₆(μ-PPh₂CCPPh₂)] 1.     

Photoluminescence behavior on Sr2+ modified CaCu3Ti4O12 based ceramics

Sr²⁺ modified CaSr_xCu_3-xTi₄O₁₂ceramic powders with x?=?ranging from 0.00 to 3.00 were prepared by solid-state reaction. The effects of Sr²⁺ CCTO powders were evaluated by X-ray diffraction (XRD) with Rietveld refinement revealing a mixture of multiple phases. The Raman spectroscopy analysis pointed out that Sr²⁺ addition produces an emission in the blue region, associated to TiO₆ clusters. Optical properties by means of PL analysis showed emission near to blue region for the samples with x?=?0.00, x?=?0.15, x?=?0.30, corresponding to oxygen vacancies. The emission in the violet region is associated to deep defects while emission in the other samples is linked to shallow defects typical of disordered crystalline structures. Less prominent emission in the green region with the increase of Sr²⁺ corresponds to less self-trapped charges, less interaction between electron and hole, and donor–acceptor recombination.     

Study of n-hexane isomerization on mixed Al2O3–ZrO2/SO4 catalysts

Mixed oxides of alumina and zirconia having a relative composition of 50, 80 and 100% Zr₂O were synthesized by means of sol–gel methods. The catalysts were sulfated with H₂SO₄ 1N, and were loaded with 0.3% Pt metal using the incipient wetness technique. The characterization of the physicochemical properties was carried out using XRD, N₂-adsorption at 78 K, and SEM. The catalytic properties of the Al₂O₃–ZrO₂ series were studied by means of dehydration of 2-propanol at 180°C and isomerization of n-hexane at 250°C, 1 atm. The sulfated solids presented a high surface acidity and a limited crystallinity, together with high activity for alcohol dehydration (i.e. 2-propanol). On the other hand, the Al₂O₃–ZrO₂ solid solutions (i.e. those having a 20–80% composition) turned out to be the most active ones for the isomerization of n-hexane.     

Processing and microstructure development in Al2O3-SiC ‘nanocomposites’

Composites consisting of Al₂O₃ + 5 vol.% 0·15 μm SiC particles were prepared by pressureless sintering. The optimum conditions for achieving dense and uniform microstructures by conventional ceramic processing are given in detail. The SiC particles were found to strongly inhibit grain growth of the Al₂O₃ matrix. Densification was also significantly retarded by these ultra-fine particles, and possible explanations for this behavior are discussed.     

Bound-state Ni species — a superior form in Ni-based catalyst for CH4/CO2 reforming

The effects of nickel loading, calcination temperature, support, and basic additives on Ni-based catalyst structure and reactivity for CH₄ reforming with CO₂ were investigated. The results show that the structure of the nickel active phase strongly depends on the interactions of the metal and the support, which are related to the support properties, the additives and the preparation conditions. “Free” Ni species can be formed when the interaction is weak and their mobility makes them easily deactivated by coking and sintering. The effect of strong metal-support interaction (SMSI effect) is different for various supports. The formation of solid solution of Ni–Mg–O₂ and the blocking of TiO_x by the partially reduced TiO₂ can both decrease the availability of Ni active sites in Ni/MgO and Ni/TiO₂. The spinel NiAl₂O₄ formed in Ni/γ-Al₂O₃ might be responsible for its high activity and resistance to coking and sintering because it can produce a highly dispersed active phase and a large active surface area as bound-state Ni species when the catalyst is prepared at high calcined temperatures or with low nickel loading. The addition of La₂O₃ or MgO as alumina modifiers can also be beneficial for the performance of the Ni/γ-Al₂O₃ catalyst.     

Sintering of α-Al2O3/quartz, and α-Al2O3/cristobalite related to mullite formation

Cristobalite and quartz react differently in mixtures with α-Al₂O₃ at 1415°C. With cristobalite, an eutectic liquid forms in accordance with the metastable phase equilibrium diagram for α-Al₂O₃-SiO₂ (cristobalite) in the absence of mullite. With quartz, a liquid first forms on the surfaces of quartz because of the occurence of an intermediate liquid phase on transformation of quartz to cristobalite. These liquids act as precursors to the formation of mullite by reacting with α-Al₂O₃. Mullite was detected earlier in the cristobalite-containing mixtures under similar firing conditions because the growth of mullite becomes significant with the formation of the eutectic liquid at the α-Al₂O₃-cristobalite interface since it is already saturated with Al₂O₃. The kinetics of sintering are affected by the rates of the step reactions.     

η-Al2O3与γ-Al2O3在CS2催化水解反应中的性能比较

通过制备高纯度的前驱体湃铝石获得了η-Al₂O₃材料,采用XRD验证了η-Al₂O₃与γ-Al₂O₃在晶相结构上的差异,比较了两者的表面形貌、织构及酸碱性能,结果显示,η-Al₂O₃与γ-Al₂O₃的比表面积相当,但η-Al₂O₃具有更弱的弱碱位和较少的强碱位,并拥有丰富的中等强度酸性位。将η-Al₂O₃与γ-Al₂O₃作为催化剂应用于CS₂水解反应,结果表明,在(200~450) ℃测试温度范围内,η-Al₂O₃催化剂对CS₂的水解活性始终优于γ-Al₂O₃,两种催化剂上CS₂反应的浓度效应也明显不同,推测与它们的酸碱性质影响了对CS₂的吸附能力有关,导致两者催化CS₂水解反应遵循了不同的机制。     

Hydrodeoxygenation of methyl esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts

Wood-derived bio-oil contains high amounts of compounds with different oxygen-containing functional groups that must be removed to improve the fuel characteristics. Elimination of oxygen from carboxylic groups was studied with model compounds, methyl heptanoate and methyl hexanoate, on sulphided NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ catalysts in a flow reactor. Catalyst performances and reaction schemes were addressed. Aliphatic methyl esters produced hydrocarbons via three main paths: The first path gave alcohols followed by dehydration to hydrocarbons. Deesterification yielded an alcohol and a carboxylic acid in the second path. Carboxylic acid was further converted to hydrocarbons either directly or with an alcohol intermediate. Decarboxylation of the esters led to hydrocarbons in the third path. No oxygen-containing compounds were detected at complete conversions. However, the product distributions changed with time, even at complete conversions, indicating that both catalysts deactivated under the studied conditions.     

Adsorption and interaction of NO, C3H6 and O2 on Pt, Zr, Nb-MCM-41—FTIR study

Adsorption of NO, O₂ and C₃H₆ on the MCM-41 matrices with Nb and Zr loaded with Pt has been studied by the FTIR spectroscopy to characterize these materials as catalysts in the selective reduction of NO with propene. Two types of the catalysts have been studied differing by the methods of Zr and Nb introduction: either by one-pot (group 1) or by post-synthesis impregnation (group 2) and hence by the location of Nb and Zr in the framework (group 1) or extra framework (group 2). It has been found that the positions of these metals in the MCM-41 matrix determine the platinum dispersion, acidic–basic properties and influence the interaction of NO + O₂ + C₃H₆ with the catalyst surfaces. The fact that the Pt dispersion is much higher in group 2 materials has been revealed by results of XRD patterns and TEM images. According to the explanation proposed, the presence of Lewis acid–base pairs in the group 2 of catalysts has strongly activated chemisorption of propene, whereas Lewis basicity, characterized by 2-PrOH dehydrogenation on the samples containing transition metals introduced during the synthesis (group 1), has enhanced chemisorption of nitrite species on platinum. It has been proved that nitrite species have not been stored on Pt/Zr/MCM-41 samples, whereas they have been stabilized on Pt/Zr/Nb/MCM-41 containing BrØnsted acidic centres.     

Conductivity of highly concentrated aqueous electrolyte solutions: NH4NO3 + H2O + LiNO3 system

Conductivity of ammonium nitrate + water (2 moles per NH₄NO₃) + lithium nitrate mixtures containing up to 0.225 stoichiometric mole fraction of lithium nitrate, at the temperatures ranging between 295—345 K, has been measured. At a given composition the variation of conductivity with temperature could be expressed by the equation.

Where A and B are empirical constants. Conductivity—composition isotherms are non-linear, indicating the change in the ordering tendency of the system.