Isosynthesis via CO hydrogenation over SO4–ZrO2 catalysts

Catalytic performances of sulfated zirconia catalysts with various contents of sulfur (from 0.1 to 0.75%) on isosynthesis were studied. It was firstly found that undoped-zirconia synthesized from zirconyl nitrate provided higher activity towards isosynthesis reaction (106 μmol kg-cat^?1 s^?1) compared to that synthesized from zirconyl chloride (84.9 μmol kg-cat^?1 s^?1). Nevertheless, the selectivity of isobutene in hydrocarbons was relatively lower. It was then observed that the catalytic reactivity and selectivity significantly improved by sulfur loading. The most suitable sulfur loading content seems to be at 0.1%, which gave the highest reaction rate and selectivity of isobutene. By applying several characterization techniques, i.e. BET, XRD, NH₃- and CO₂-TPD and SEM, it was revealed that the high reaction rate and selectivity towards isosynthesis reaction of sulfated zirconia catalysts are related to the acid–base properties, Zr³⁺ quantity and phase composition.     

Dehydration of 1,4-butanediol over lanthanide oxides

Vapor-phase catalytic dehydration of 1,4-butanediol was investigated over lanthanide oxides at 375 °C. Tetrahydrofuran (THF) and 3-buten-1-ol were competitively produced from 1,4-butanediol: oxides of light rare earth dominantly catalyze cyclization to THF, while oxides of heavy rare earth such as Tb, Er, and Yb effectively catalyze dehydration to 3-buten-1-ol. In particular, Yb₂O₃ shows the most efficient catalytic activity in the formation of 3-buten-1-ol with the selectivity higher than 80 mol%, which depends on the structure of Yb₂O₃.     

Ce-Doped La2O3 based catalyst for the oxidative coupling of methane

The effect of ceria was studied on the oxidative coupling of methane (OCM) with Ce-doped La₂O₃ in a La:Ce molar ratio of 75:25 using two preparation methods. The characterisation techniques used were XRD and XPS. The results revealed high concentration of oxygen vacancies. Different types of ions (Ce^3 + + Ce^4 +) were detected. More surface Ce^3 + and higher ratio [(O₂^2― + O^—)/ O^2―] were obtained in the oxide synthesised by the solvothermal method, affecting the OCM reaction in terms of higher C₂ hydrocarbons selectivity. This was ascribed to the higher relative amount of O^― species on the catalyst surface.     

Methanol-to-olefins over FeHZSM-5: Further transformation of products

The catalytic activity of FeHZSM-5 was investigated for the conversion of both methanol and mixed C₃° + C₄ hydrocarbons. For methanol conversion at WHSV = 1 h^− 1 and 470 °C, 0.35% FeHZSM-5 showed increased selectivity for propylene and C₂⁼–C₄⁼ olefins by 21% and 4%, respectively, compared with HZSM-5. The selectivity of propane and butylene decreased. High temperature favored the conversion of C₃° + C₄ mixture while the selectivity of ethene + propylene achieved a maximum at 470 °C. Improved olefins selectivity for methanol conversion was attributed to FeHZSM-5 with more weak acid but less strong acid amount and to further transformation of the products.     

Rare-earth nitrate additives for the sintering of silicon carbide

Fourteen rare earth elements in their nitrate form were evaluated as sintering additives for β-SiC. All rare earth nitrates transformed to oxides by a reaction with the surface-adsorbed thin SiO₂ during heat treatment, which enhanced the density of the SiC monolith without decomposing SiC. In particular, Sc, Yb, Tm, Er and Ho were quite effective sintering additives; a > 99% relative density was observed by the addition of 5 wt.% rare earth oxide, whereas the other rare earth additives (Lu, Dy, Tb, Gd, Eu, Sm, Nd, Ce and La) revealed 77–92% density. Moreover, a fine 156 nm-sized SiC grain could be acquired by Sc addition, whereas the other additives showed a SiC grain size of approximately 1 μm. The mean hardness and K_Ic of the dense SiC containing rare earth elements were 24–27 GPa and 3.3–5.0 MPa m^1/2, respectively.     

Synthesis of aligned La3+-substituted Sr-ferrites via molten salt assisted sintering and their magnetic properties

M-type hexagonal Sr_1−xLa_xFe₁₂O₁₉ (x=0, 0.05, 0.1, 0.15 and 0.2) ferrites were synthesized in a molten salt matrix to avoid the agglomeration of particles and control grain growth. By eliminating the impurity phase, the influence of rare earth La³⁺ ion substitutions on the lattice structure, morphology and magnetic properties has been investigated. The results show that La³⁺ substitutions have a great influence not only on the grain growth but also on the magnetic orientation. The easy magnetization direction <001> was remarkably enhanced in all substituted powders aligned along a 5 kOe magnetic field. The optimal magnetic properties were obtained via magnetic orientation when the substitution is x=0.15, showing a coercivity of 6.25 kOe, a saturation magnetization of 69.5 emu/g and a remanence ratio of 0.71. This will possibly enable a wide-range application to generate rare earth La³⁺ ion substituted Sr-ferrites for bonded magnets via molten salt assisted sintering.     

Adsorption separation of vinyl chloride and acetylene on activated carbon modified by metal ions

This work mainly involved the adsorption separation of vinyl chloride and acetylene on modified activated carbons. Six metal ions with different hardness were loaded on activated carbon respectively. The effect of metal ions on the adsorption separation performance of vinyl chloride and acetylene was investigated. The experimental results shown that the separation factor of C₂H₃Cl to C₂H₂ over modified activated carbon followed the order: Al(III)/AC > Mg(II)/AC > Fe(III)/AC > AC > Zn(II)/AC ≈ Cu(II)/AC > Ag(I)/AC. The effect of the hardness of metal ions on the adsorption capacity of C₂H₂ was more remarkable than that of C₂H₃Cl, thus the separation factor of C₂H₃Cl to C₂H₂ increased with the rising of absolute hardness of the metal ions.     

High selective and stable performance of catalytic aromatization of alcohols and ethers over La/Zn/HZSM-5 catalysts

The catalytic conversions of methanol, ethanol, dimethyl ether and diethyl ether to aromatic hydrocarbons (especially benzene, toluene and xylene) were achieved over 0.8%Zn/0.6%La/HZSM-5 catalyst with a BTX selectivity as high as over 50% at reaction conditions of 710 K, WHSV 0.8 h^?1. The selectivity of BTX hydrocarbons in methanol aromatization reaction could remain 35% in 40 h.     

Studies of dielectric properties of rare earth (Dy,Tb, Eu) doped barium titanate sintered in pure nitrogen

This paper investigated dielectric properties of rare earth (Dy, Tb, Eu)-doped barium titanate sintered in pure nitrogen. The substituting concentration of rare earth (Dy, Tb, Eu) was 2.0 mol%. The doping behaviors of intermediate rare-earth ions (Dy, Tb, Eu) and their effects on the dielectric property of barium titanate were investigated. Eu³⁺ ion was substituted in the A-site of the perovskite lattice. Dy³⁺ and Tb³⁺ ions substituted partially for Ti⁴⁺ site and partially for Ba²⁺ site. The different rare earth element had a crucial effect on dielectric properties of rare-earth-doped BaTiO₃. Among these doped samples, Tb-doped BaTiO₃ had the largest dielectric constant (70,000–80,000); the smallest dielectric loss (less than 4%), and good capacitance-temperature coefficient, which satisfies the X7R specification of the Electronic Industries Association Standards (TCC within ±15% from ?55 °C to 125 °C).     

Electrostatic immobilization of substrate and polyoxotungstate catalyst at the surface of micelles for enhanced reaction efficiency in water

Polyoxometalate (POM)-based micellar catalysts were prepared by assembling the Keggin tri-anion [PW₁₂O₄₀]^3 − and (L)-N-acetylmethioninate salts of Gemini surfactants in water. Contrary to conventional catalytic systems, we propose a new approach in which the POM catalyst and the substrate to be oxidized ((L)-N-acetylmethioninate) are both localized at the surface of micelles by electrostatic interaction before the reaction. The high local concentration of reactants due to their confinement at the surface of micelles enhances the reaction kinetics. Catalyst recovery experiments showed that, after two cycles of reactions, the activity of the catalysts  was not changed.     

Vapor-phase dehydration of 1,5-pentanediol into 4-penten-1-ol

Dehydration of 1,5-pentanediol was investigated over ZrO₂ and Yb₂O₃ catalysts at 300–450 °C. 1,5-Pentanediol was converted into 4-penten-1-ol together with tetrahydropyran over monoclinic ZrO₂ at temperatures <400 °C, and the selectivity to 4-penten-1-ol exceeded 50 mol%. Modification of ZrO₂ with Li ions increased the selectivity to 4-buten-1-ol up to 70 mol%. Yb₂O₃ also effectively worked as a catalyst in the dehydration of 1,5-pentanediol into 4-buten-1-ol at temperatures <425 °C. Especially, Yb₂O₃ with cubic structure showed higher than 75 mol% selectivity to 4-penten-1-ol.     

A novel Fe(III) salt-catalyzed monoterpene aerobic oxidation in methyl alcohol

The Fe(III)-catalyzed aerobic oxidation of monoterpenes in CH₃OH has been developed, in which simple Fe(III) salts are used as catalysts in the absence of stabilizing ligands. Remarkably, Fe(NO₃)₃ catalyst efficiently promotes the oxidation of monoterpenes under air or dioxygen. The highest TON and TOF reached 476 and 162 h^− 1, respectively. In general, reactions with 1.0–9.0 mol% of catalyst reached high conversions (ca. 90–99%) and high oxidation products selectivity (ca. 80%). Notably, α-pinene and β-pinene were selectively oxidized into only allylic product, myrtenol methyl ether. The significant breakthroughs of this simple oxidative process are the use of inexpensive Fe(III) salts as catalysts and environmentally-friendly oxidants (air or dioxygen).     

Partial oxidation of methane in BaCe0.1Co0.4Fe0.5O3−δ membrane reactor

A new perovskite material, BaCe_0.1Co_0.4Fe_0.5O_3?δ used as dense oxygen permeable membrane for partial oxidation of methane (POM) reaction was investigated. In order to improve the synergetic effects between membrane and catalyst, LiLaNiO/γ-Al₂O₃ catalyst was directly packed onto the surface of the membrane to carry out POM. In BaCe_0.1Co_0.4Fe_0.5O_3?δ membrane reactor, high oxygen permeation flux, high CH₄ conversion and CO selectivity were obtained. At 950 °C, oxygen flux of 9.5 ml cm^?2 min^?1, CH₄ conversion of 99% and CO selectivity of 93% were achieved with a membrane thickness of 1.0 mm. There was an induction process at the initial stage of POM, which was related to the reduction of NiO to Ni⁰ in LiLaNiO/γ-Al₂O₃ catalyst. Experiments illustrated that higher reaction temperature would shorten the induction time. During continuously operating for 1000 h at 875 °C, no degradation of performance of the membrane reaction was observed. SEM characterization also demonstrated that the membrane disc maintained an integral structure without any cracks after long-term operation.     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

Improvement of the polyoxometalate's performance in the asymmetric oxidation of styrene via combined with chiral ionic liquid

The efficiency and enantioselectivity of polyoxometalate (POM) in the oxidation of styrene with H₂O₂ could be improved via simply combined the POM with the chiral ionic liquids (CILs), which consist of the quaternized alkyl bromide salts (with lengths of C-8, C-12, and C-16) derived from natural chiral S-nicotine. The hybrids showed synergistic advantages between POM and CILs, achieving a complete conversion of styrene after 1 h of mild reaction and a relatively high selectivity for R-(−)-1-phenylethane-1, 2-diol with 72% yield and 96% ee. Further fluorescence analysis illustrated that CILs might serve for the enantiomeric recognition of R- than S-enantiomers.     

The unique behavior of the catalytic system Pd(OAc)2/N-heterocyclic carbene on the telomerization of isoprene with methanol

The catalytic system Pd(OAc)₂/1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (IMes · HCl) promotes the telomerization of isoprene with methanol resulting in methoxy-dimers with a head-to-head coupling of the isoprene units at unprecedented activity and selectivity. Employing 1,3-bis(2,6-di-i-propylphenyl)-4,5-dihydroimidazolium tetrafluoroborate (SIPr · HBF₄) instead of IMes · HCl, new sesquiterpenes are obtained by the trimerization of isoprene.     

Stability of rare earth oxides in a moist environment at elevated temperatures—Experimental and thermodynamic studies: Part II: Comparison of the rare earth oxides

Volatilisation tests enabled to quantify the stability of different rare earth sesquioxides, RE₂O₃ (where RE = Sc, Dy, Er, Yb) and to understand the corrosion process. These tests were carried out at temperatures ranging from 1000 to 1400 °C in moist air with 50 kPa of water at atmospheric pressure, under a flowing gas velocity of 5 cm s^?1. Besides the volatilisation rate, the nature of the volatile gaseous species was determined. The proposed experimental method allowed too to assess the Gibbs free energy of formation of these gaseous volatile species. Finally, the stability of each rare earth oxide under a moist environment at high temperature was compared.     

Alkylimidazolium/alkylpyridinium octamolybdates catalyzed oxidation of sulfides to sulfoxides/sulfones with hydrogen peroxide

β-Mo₈O₂₆ based alkyl imidazolium and pyridinium salts of general formula [Bmim]₄Mo₈O₂₆ (Bmim = 1-butyl-3-methylimidazolium), [Hmim]₄Mo₈O₂₆ (Hmim = 1-hexyl-3-methylimidazolium), [Dhmim]₄Mo₈O₂₆ (Dhmim = 1.2-dimethyl-3-hexylimidazolium) and [Hpy]₄Mo₈O₂₆ (Hpy = 1-hexylpyridinium) have been used as catalysts for the oxidation of sulfides using 30% hydrogen peroxide as oxidant. The examined β-Mo₈O₂₆ salts prove to be highly active and are self-separating. A high selectivity towards either sulfoxides or sulfones can be nicely controlled by variation of the reaction conditions. In both cases, the catalysts can be recycled and reused for several times without significant loss of activity, representing a good stability of the catalysts.     

Two new Keggin-type polyoxometalate-based entangled coordination networks constructed from metal-organic chains with dangling arms

Two new polyoxometalate(POM)-based entangled coordination networks with chemical formula of [Mn₂(H₂O)₂(BBPTZ)₅][SiW₁₂O₄₀] (1) and [Ni₂(H₂O)₂(BBPTZ)₅][SiMo₁₂O₄₀]·6H₂O (2) (BBPTZ = 4.4′-bis(1,2,4-triazol-1-ylmethyl)biphenyl), were prepared in a hydrothermal reaction system. Compounds 1–2 were characterized by elemental analyses, IR spectroscopy, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction. In compound 1, dangling arms thread in quadrangular window of the adjacent 2-D layers, thus resulting in a rare 2-D → 3-D polythreading motif. Compound 2 exhibits a rare 2-D → 3-D zipper-closing motif. Using the degradation of methylene blue (MB) as the model, the photocatalytic activities of compounds 1–2 were investigated. Both compounds show efficient catalytic activity for the degradation of MB with the order of 2 > 1. It is found that the POM species of compounds 1–2 play the main role in the photocatalytic degradation process.     

The influence of laser treatment on hot corrosion behavior of plasma-sprayed nanostructured yttria stabilized zirconia thermal barrier coatings

In this study, the effect of laser glazing on the hot corrosion behavior of nanostructured thermal barrier coatings (TBCs) was investigated. To this end, the hot corrosion test of plasma-sprayed and laser-glazed thermal barrier coatings conducted against 45 wt.% Na₂SO₄ + 55 wt.% V₂O₅ molten salt at 910 °C for 30 h in open air atmosphere. The results obtained from hot corrosion test showed that the reaction between Y₂O₃ and the corrosive salt produced YVO₄, leached Y₂O₃ from YSZ and led to the progressive destabilization transformation of YSZ from tetragonal to the monoclinic phase. The lifetimes of the plasma-sprayed TBCs were enhanced approximately twofold by laser glazing. Reducing the reactive specific surface area of the dense glazed layer with the molten salts and improving the stress accommodation through network cracks produced by laser glazing were the main enhancement mechanisms accounting for TBC life extension.