Synthesis and characterization of S2O82 −/ZnFexAl2 − xO4 solid acid catalysts for the esterification of acetic acid with n-butanol

New spinel-types of S₂O₈^2 −/ZnFe_xAl_2 − xO₄ solid acid catalysts were prepared by sol–gel method. Their catalytic performances for the synthesis of n-butyl acetate were investigated. The catalysts were characterized by means of XRD, IR, XPS, FT-IR of adsorbed pyridine and NH₃-TPD. The experimental results showed that S₂O₈^2 −/ZnFe_xAl_2 − xO₄ solid acid catalysts maintained the spinel structure as well as the support of ZnFe_xAl_2 − xO₄. Fe^3 + ions were well incorporated and highly dispersed into the spinel lattice. S₂O₈^2 −/ZnFe_0.15Al_1.85O₄ exhibited the maximum conversion of acetic acid with 98.2%. Moreover, S₂O₈^2 −/ZnFe_0.15Al_1.85O₄ showed better reusability, which remained above 72.7% conversion of acetic acid even after being used five times.     

Promotional effect of graphite oxide on surface properties and catalytic performance of La1 − xSrxMnO3 (x = 0,0.1) for methane combustion

The effect of graphite oxide (i.e. GO)/La_1 − xSr_xMnO₃ (x = 0,0.1) catalysts on methane combustion in CNG's (compressed natural gas) exhaust was investigated in current work. GO layer was employed to realize a surface modification. The light-off temperature of methane decreased, and reached the full conversion at 540 °C. The prepared catalysts were also characterized by TEM, surface energy, XPS and H₂-TPR techniques. SEM indicated that the La_1 − xSr_xMnO₃ particles grew dispersedly on GO layer, and surface analysis suggested that the introducing of GO can enhance the adsorption of oxygen groups on the surface of the catalysts.     

Preparation of Pd/(Ce1 − xYx)O2/γ-Al2O3/cordierite catalysts and its catalytic combustion activity for methane

A series of (Ce_1 − xY_x)O₂ (x = 0,0.15,0.35,0.5) coatings on γ-Al₂O₃ pre-coated cordierite honeycomb were prepared by sol–gel method, and then palladium was loaded by aqueous solution impregnation deposition with Pd(NO₃)₂ as precursor. The structure and morphology of samples were evaluated and the catalytic combustion activity for methane was also discussed. (Ce_1 − xY_x)O₂ synthesized by sol–gel has a single-phase cubic fluorite structure. Increasing the Y/Ce ratio can significantly improve the inner surface morphology of the honeycomb channels and also the coating mechanical stability, and leads to a considerable improvement in the catalytic activity of the prepared catalysts for methane.     

Synthesis and characterization of Ce–La oxides for the formation of dimethyl carbonate by transesterification of propylene carbonate

A series of cerium–lanthanum catalysts prepared using the co-precipitation method were investigated for transesterification of propylene carbonate (PC) with methanol to produce dimethyl carbonate (DMC). Synthesized catalysts were characterized by XRD, CO₂- and NH₃-TPD, N₂ adsorption/desorption and SEM–EDX techniques. Studies were carried out to study the effect of reaction conditions such as methanol/PC molar ratio (4–12), catalyst dose (2–10 wt.% of PC), reaction time (2–10 h) and temperature (140–180 °C) on the DMC yield. Highest PC conversion and DMC yield of 72% and 74%, respectively, were observed with catalysts having a 1:4 Ce/La molar ratio.     

Bifunctional Pd/Al-SBA-15 catalyzed one-step hydrogenation–esterification of furfural and acetic acid: A model reaction for catalytic upgrading of bio-oil

Al-SBA-15 supported palladium bifunctional catalysts were evaluated for one-step hydrogenation–esterification (OHE) of furfural and acetic acid as a model reaction for bio-oil upgrading. Experimental results show that it is viable to convert these unstable constituents of bio-oil to esters and alcohols through this simple and effective OHE reaction. The results of NH₃–TPD and catalytic performances show that Al-SBA-15 with medium ratio of Si/Al favors the OHE reaction between furfural and acetic acid. It is noteworthy that there is a synergistic effect between the metal sites and the acid sites over composite bifunctional catalyst of 5%Pd/Al-SBA-15 for the OHE reaction.     

Methane steam reforming in the absence and presence of H2S over Ce0.8Pr0.2O2 − δ, Ce0.85Sm0.15O2 − δ and Ce0.9Gd0.1O2 − δ SOFCs anode materials

We report here on the activity and stability of low-content praseodymium–, samarium– and gadolinium–cerium oxide catalysts for the steam reforming of methane under water deficient conditions. These materials display different methane reforming activities, and remain free of praseodymium, samarium and gadolinium oxide phases respectively after use in a reaction gas stream composed of 50% CH₄–5% H₂O – (in the absence and presence of 50 or 200 ppm H₂S) – balance He at 740 °C. The results show that Ce_0.8Pr_0.2O_2 − δ, Ce_0.85Sm_0.15O_2 − δ and Ce_0.9Gd_0.1O_2 − δ are effective catalysts for reforming of methane and H₂S in the feed promotes the catalytic activity. Ce_0.8Pr_0.2O_2 − δ appeared to attain the highest activity for methane reforming, a feature that is associated with the ability of praseodymium to undergo a red–ox (Pr^4 +/Pr^3 +) and spreading action in the cerium oxide host structure, possibly resulting in a red–ox relationship between the components.     

Fabrication of Pt–Cu/RGO hybrids and their electrochemical performance for the oxidation of methanol and formic acid in acid media

Pt–Cu/reduced graphene oxide (Pt–Cu/RGO) hybrids with different Pt/Cu ratios were prepared by the reduction of H₂PtCl₆ and CuSO₄ by NaBH₄ in the presence of graphene oxide (GO). The Pt–Cu nanoparticles were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The reduction of GO was verified by ultraviolet–visible absorption spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Compared to Pt/RGO, the Pt–Cu/RGO hybrids have superior electrocatalytic activity and stability for the oxidation of methanol and formic acid. Thus they should have potential applications in direct methanol and formic acid fuel cells.     

Efficient degradation of <Emphasis Type="Italic">para</Emphasis>-chlorobenzoic acid in water by catalytic ozonation with La–Ce–MCM-41

La–Ce–MCM-41 was directly synthesized by a hydrothermal method and applied as heterogeneous catalyst for the ozonation process of para chlorobenzoic-acid (pCBA). La³⁺ and Ce³⁺ were successfully incorporated into the framework of MCM-41 and the formation of degradation products (p-chlorophenol, p-dihydroxybenzene, maleic acid and oxalic acid) were monitored qualitatively using gas chromatography–mass spectrometer and high performance liquid chromatography. Due to the synergy of bimetal and the fast degradation of accumulated intermediates, total organic carbon (TOC) removal efficiency was significantly improved (92 %) in La–Ce–MCM-41/O₃ process compared with ozonation (40 %) at identical reaction condition. The presence of tert-butanol (TBA) in La–Ce–MCM-41/O₃ process indicated that the oxidation of pCBA was mainly due to the function of hydroxyl radicals in the liquid bulk, and a plausible degradation pathway was proposed. TOC removal slightly decreased from 90 to 86 % after La–Ce–MCM-41 being re-utilized three times, which illustrated that La–Ce–MCM-41 was an efficient of promising catalyst for ozonation of pCBA.     

Effect of Pd loading and precursor on the catalytic performance of Pd/WO3–ZrO2 catalysts for selective oxidation of ethylene

The structure and properties of Pd/WO₃–ZrO₂ (W/Zr = 0.2) catalysts with different Pd loadings and precursors were investigated. The results indicate that Pd/WO₃–ZrO₂ prepared from a PdCl₂ precursor was optimum for high activity and selectivity. Moreover, ethylene conversion increased with the Pd loading. The structure and nature of the catalysts were characterized using X-ray diffraction, BET N₂ adsorption, H₂ temperature-programmed reduction and H₂ pulse adsorption techniques. The results reveal that the higher catalytic performance of Pd/WO₃–ZrO₂ prepared from PdCl₂ could be related to the formation of polytungstate species and the existence of well-dispersed Pd particles.     

Preparation of solid acid catalyst SO42−/TiO2/γ-Al2O3 for esterification: A study on catalytic reaction mechanism and kinetics

In this work, a series of SO₄^2-/TiO₂/γ-Al₂O₃ solid acid catalysts were synthesized by impregnation method, in which nano-TiO₂ was prepared by sol-gel method, and then the nano-TiO₂ sol was loaded on porous γ-Al₂O₃ supporter through impregnation. The structure and property of catalyst were characterized by XRD, N₂-BET, SEM, TEM, XPS, NH₃-TPD, Pyridine-IR and FT-IR. In addition, the catalyst of chelate bidentate coordination acid center model was established. The catalytic performance test was carried out in the esterification of n-butyl alcohol with lauric acid and the catalyst showed excellent activity. The experimental results showed that the medium strength acid sites were more dominant active sites than the strong and weak acid sites for the rapid esterification reaction. Its kinetic behaviors and activation energy were studied for the esterification under the catalytic reaction condition.     

Role of ceria in the improvement of SO2 resistance of LaxCe1 − xFeO3 catalysts for catalytic reduction of NO with CO

Perovskite-type catalysts with LaFeO₃ and substituted La_xCe_1 − xFeO₃ compositions were prepared by sol–gel method. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), CO temperature-programmed reduction (CO-TPR), and SO₂ temperature-programmed desorption (SO₂-TPD). Catalytic reaction for NO reduction with CO in the presence of SO₂ has been investigated in this study. LaFeO₃ exhibited an excellent catalytic activity without SO₂, but decreased sharply when SO₂ gas was added to the CO + NO reaction system. In order to inhibit the effect of SO₂, substitution of Ce in the structure of LaFeO₃ perovskite has been investigated. It was found that La_0.6Ce_0.4FeO₃ showed the maximum SO₂ resistance among a series of La_xCe_1 − xFeO3 composite oxides.     

Synthesis of novel hyperbranched poly(ester-amide)s based on acidic and basic amino acids via “AD + CBB′” couple-monomer approach

A series of novel hydroxyl- or methyl ester- terminated hyperbranched poly(ester-amide)s (HBPEAs) based on acidic (l-glumatic acid and l-aspartic acid) and basic amino acids (l-lysine) have been synthesized via the “AD + CBB′” couple-monomer approach. The ABB′ intermediates were stoichiometrically formed through thio-ene reaction benefited from reactivity differences between functional groups. Without any purification, in situ self-polycondensations of the intermediates at elevated temperature in the presence of Ti(OBu)₄, as a catalyst, afforded HBPEAs with high molecular weights. More rapid polymerization rate and much higher molecular weight as well as broader polydispersity were observed for the polymerization process of intermediates based on acidic amino acids than basic amino acids which is related to the catalytic mechanism and structure difference of intermediates. Moreover, polymerization of intermediate derived from l-aspartic acid was carried out faster by comparison with that from l-glumatic acid. The DB values were approximately estimated to be 47%–49% for the polymers derived from l-aspartic acid and l-glutamic acid. The resultant HBPEAs possessed glass transition temperature (T_g) in the range of ?3 to 11 °C, among which those derived from l-lysine shows the highest T_g, and decomposition temperatures at 10% weight loss under air and nitrogen are in close regions of 261–271 °C and 264–268 °C, respectively.     

Oxidation behaviour of pressureless liquid-phase-sintered α-SiC with additions of 5Al2O3 + 3RE2O3 (RE = La,Nd, Y,Er, Tm,or Yb)

The oxidation behaviour of pressureless liquid-phase-sintered (PLPS) α-SiC was investigated as a function of the sintering additives of 5Al₂O₃ + 3RE₂O₃ (RE = La, Nd, Y, Er, Tm, or Yb) by thermogravimetry experiments in oxygen at 1075–1400 °C for up to 22 h. It was found that the oxidation is in all cases passive and protective, with kinetics governed by the arctan-rate law. This is because the PLPS SiC ceramics develop oxide scales having no cracks or open porosity and accordingly prevent the parent material from direct contact with oxygen. In addition, these oxide scales crystallize gradually during the exposure to the oxidizing atmosphere with the attendant reduction in the amorphous cross-section available for oxygen diffusion. It was also found that the rate-limiting mechanism of the oxidation is outward diffusion of RE³⁺ cations from the intergranular phase into the oxide scale, and that the activation energy of the oxidation increases with increasing size of the RE³⁺ cation. It was also observed that the oxidation of PLPS SiC increases with increasing size of the RE³⁺ cation, an effect that is especially marked for cation sizes above 0.9 Å because the oxidation rate becomes several orders of magnitude faster. This trend is attributable to the oxide scales being more crystalline, and containing crystals that are more refractory and amorphous residual phases that are more viscous as the size of the RE³⁺ cation decreases. Finally, implications for the design of PLPS SiC ceramics with superior oxidation resistance are discussed.     

Processing and properties of Bi0.98R0.02FeO3 (R = La,Sm, Y) ceramics flash sintered at ~650°C in <5 s

We show that flash sintering produces single-phase, nanograin-sized polycrystals of isovalent-substituted multiferroic ceramics of complex compositions. Single-phase polycrystals of Bi_0.98R_0.02FeO₃ (R = La, Sm, Y) were produced at a furnace temperature of ~650°C in a few seconds by the application of an electric field of 50 V cm⁻¹, with the current limit set to 40 mA mm⁻². The dielectric and insulating properties compared favorably with expected values. Impedance spectroscopy suggests electrically homogenous microstructure, except for the sample Bi_0.98La_0.02FeO₃ that shows a small grain boundary contribution to the impedance. These results reinforce the enabling nature of flash sintering for ceramics which pose difficulties in conventional sintering because they contain low melting constituents or develop secondary phases during the sintering protocol.     

Effect of steam on the acid strength of H3PW12O40/SiO2 · nH2O and its application in skeletal isomerization of n-butane

The effect of steam on the acid strength of H₃PW₁₂O₄₀ (HPW)/SiO₂ · nH₂O was determined by the Hammett indicators. When the steam content in N₂ was 1.6%, the acidity (H₀ > −13.7) of HPW/SiO₂ · nH₂O could be kept for over 10 h at 300 °C, but for only 2 h when steam was lacking. When it was used as a catalyst for skeletal isomerization of n-butane to isobutane at 300 °C, the HPW/SiO₂ · nH₂O showed stability in the presence of steam (1.6% in feed) better than that without steam, due to a suppression of the loss of crystalline water.     

First example of PMMA-supported and highly luminous color-purity red-light metallopolymer based on a tris-β-diketonate Zn2 +-Eu3 +-complex

Through the copolymerization of a complex monomer [Zn(L)(4-vinyl-Py)Eu(TTA)₃] (2; H₂L = N,N′-bis(salicylidene)cyclohexane-1.2-diamine; 4-vinyl-Py = 4-vinyl-pyridine and HTTA = 2-thenoyltrifluoroacetonate) with MMA (methyl methacrylate), the first example of PMMA-supported and highly luminous (Ф_Eu^L = 63.1%) color-purity red-light metallopolymer poly(MMA-co-2) based on a tris-β-diketonate Zn^2 +-Eu^3 +-complex is obtained.     

Effects of Fe addition on the structure and catalytic performance of mesoporous Mn/Al–SBA-15 catalysts for the reduction of NO with ammonia

Mesoporous Al–SBA-15 has been synthesized by a hydrothermal method and used as a support for Mn/Al–SBA-15, Fe/Al–SBA-15, and Mn–Fe/Al–SBA-15 catalysts. XRD, N₂ sorption, XPS, H₂-TPR and activity tests have been used to assess the properties of catalysts. The Mn–Fe/Al–SBA-15 catalyst exhibited a higher SCR activity than Mn/Al–SBA-15 or Fe/Al–SBA-15 due to a synergistic effect between Mn and Fe. After the addition of Fe, the binding energy of Mn 2p_3/2 on Mn–Fe/Al–SBA-15(573) decreased by about 0.4 eV and the Mn^4 +/Mn^3 + ratio decreased to 1.10. The appropriate Mn^4 +/Mn^3 + ratio may have a great effect on the reduction of NO over Mn–Fe/Al–SBA-15(573) catalyst.     

The catalytic performance and characterization of a durable perovskite-type chloro-oxide SrFeO3–δClσ catalyst selective for the oxidative dehydrogenation of ethane

The catalytic performances and properties of SrFeO_3-0.190 and SrFeO_3-0.382Cl_0.443 catalysts have been investigated for the oxidative dehydrogenation of ethane (ODE). XRD results showed that both catalysts exhibited oxygen-deficient perovskite-type structures. The inclusion of chloride ions in the SrFeO_3-δlattice matrix can significantly enhance ethene selectivity and ethane conversion. The SrFeO_3-0.382Cl_0.443 catalyst showed an ethane conversion of ca. 90%, an ethene selectivity of ca. 70%, and an ethene yield of ca. 63% under the reaction conditions: C₂H₆:O₂:N₂ = 2:1:3.7, temperature 680°C, and space velocity 6000 ml h^-1 g^-1. With the increase of space velocity, ethane conversion decreased, whereas ethene selectivity increased over SrFeO_3-0.382Cl_0.443. Lifetime studies showed that the perovskite-type chloro-oxide catalyst was durable. The results of O₂-TPD and TPR experiments illustrated that the implanted chloride ions caused the oxygen nature of SrFeO_3-δ to change. By regulating the concentration of oxygen vacancies and the Fe⁴⁺/Fe ratio in this perovskite-type chloro-oxide catalyst, one can generate a durable chloro-oxide catalyst for the ODE reaction with excellent performance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and Characterization of Perovskite-Type Oxides La1−xMxCoO3 (M = Ce,Sr) for the Selective CO Oxidation (SELOX)

Perovskite-type oxides La_1?xM_xCoO₃ (M = Ce, Sr) were prepared by citrate method, characterized and evaluated in the selective CO oxidation (SELOX-CO). The insertion of low Cerium or Strontium content generated solids with a single phase related LaCoO₃ perovskite. For higher contents we observed segregation of CeO₂ and SrCO₃. The iso-structural substitution favors the formation of vacancies. The SELOX-CO showed 100 % CO conversion at 200 °C. Higher temperatures favored hydrogen oxidation and methanation.