Methanol Decomposition to Synthesis Gas Over Supported Pd Catalysts Prepared from Hydrotalcite Precursors

Supported Pd catalysts were prepared by solid-phase crystallization (spc) starting from MgAl hydrotalcite anionic clay minerals as the precursors, and were tested for the methanol decomposition to synthesis gas. The precursors based on [Mg₆Al₂(OH)₁₆CO₃ ^2-] · 4H₂O were prepared by coprecipitation from raw materials containing Pd²⁺, Mg²⁺ and Al³⁺ ions as the components of hydrotalcite. The precursors were thermally decomposed and reduced to afford supported Pd catalysts on MgAl mixed oxide. Pd-supported catalysts as a reference were also prepared by the impregnation (imp) method. The spc-Pd catalysts thus prepared afforded highly dispersed Pd metal particles and showed higher activity as well as lower activation energy than the imp-Pd catalysts. When the precursor was prepared under mild conditions, finer particles of Pd metal were formed over the catalyst, resulting in a high activity. In the case of spc-Pd catalysts, carbon monoxide adsorbed on Pd easily desorbed, compared with imp-Pd catalysts. It is likely that the high activity is due to the highly dispersed and stable Pd metal particles and the easy desorption of carbon monoxide.     

Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method

A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N₂ sorption experiments. The basic and metal functions were analyzed by CO₂‐TPD and H₂‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method.     

Structure and analgesic properties of layered double hydroxides intercalated with low amounts of ibuprofen

Ibuprofen‐intercalated layered double hydroxides (LDH‐IBU) have been successfully synthesized via a coprecipitation method with a nominal [Al³⁺]/[Mg²⁺] ratio of 0.5 and a variable molar IBU/([Al³⁺]+[Mg²⁺]) ratio of 0, 0.15, 0.18, 0.24, 0.36, and 0.72. After an accurate determination of the composition, the nature of the intercalated species and the effective intercalation yield from to IBU, it is shown that the synthesis route used allows a good control of the quantity of intercalated IBU within the LDH framework. This results in different samples with full or partial IBU intercalation in the interlayer space in exchange of nitrate anions. The analysis of the X‐ray diffraction basal reflections reveals that the intercalation of IBU in the framework only increases the basal distances with no alteration of the brucite‐type layers. Also, a computational study used to model the positions and shapes of the basal reflections showed that the structure of the nonfully intercalated compounds follows a random interstratification scheme. Finally, three samples ranging from slightly to fully IBU‐intercalated galleries were selected for preliminary in vivo assays. These tests showed a strong tendency that after 24 hours the low yield of IBU‐intercalated compounds are almost as efficient as the fully intercalated sample.     

PVC糊状树脂交联改性新方法

向PVC糊状树脂中添加2-二置换氨基-4、6-二噻茂仲三嗪或其金属盐及水滑石等添加剂进行交联改性,可显著降低其溶胶粘度,提高透明性,改善加工耐热性。     

Alkoxylation reaction catalysed by layered double hydroxides

Layered double hydroxides (LDHs) are extensively studied as precursors for catalysts, following a calcination at high temperatures to yield mixed oxides. However, these materials are less used as layered materials, i.e., without undergoing thermal activation. We have focused in this work on the use of a series of as-synthesised LDHs for the catalytic preparation of glycol ethers, which is a reaction of primary commercial importance. Two main systems are considered, namely the [Cu–Cr] and [Mg–Al] LDHs. The [Cu–Cr–Cl] LDH is obtained by the coprecipitation method, then through the appropriate chimie douce exchange reactions the original chloride anions are replaced by a variety of oxo- and polyoxometallates, (CrO₄)²⁻, (Cr₂O₇)²⁻, (V₂O₇)²⁻, (V₁₀O₂₈)⁶⁻ and (Mo₇O₂₄)⁶⁻. On the other hand, the [Mg–Al] hydrotalcites, intercalated by (V₂O₇)²⁻, (V₁₀O₂₈)⁶⁻ and [Fe^III(CN)₆]³⁻ anions, are obtained by structure regeneration. This was done by rehydration of a commercial calcined material (Kyowa) in aqueous solutions containing the desired anion. The different materials have been fully characterised by conventional analytical techniques to evidence their lamellar properties and chemical nature. They were then tested in the catalytic reaction involving butan-1-ol and one or more units of ethylene oxide to make butyl-monoglycol ether (BMGE), di-glycol ether (BDGE), tri-glycol ether (BTGE), etc. The reactions were carried out between 80 and 120°C, temperature range in which no collapse of the lamellar structure is normally observed. In this paper it is shown that decavanadate exchanged LDHs proved to be very selective catalysts for the preparation of the monoglycol adduct, some samples achieving up to 100% selectivity in the screening tests.     

Decomposition of nitrous oxide over the catalysts derived from hydrotalcite-like compounds

Catalytic decomposition of nitrous oxide into nitrogen and oxygen has been carried out on ‘in situ' thermally calcined hydrotalcites of general formula M(II)–M(III)-CHT where M(II)=Mg, Co, Ni, Cu or Zn and M(III)=Al, Fe or Cr having different M(II)/M(III) atomic ratios. The reaction was performed in a recirculatory static reactor at 50 Torr (133.3 Pa) initial pressure of N₂O in the temperature range 423–773 K. Among the catalysts screened, Ni and Co containing catalysts with Al as the trivalent cation showed good activity (even at 423 K) wherein 50% and 100% conversion was achieved at 463 K and 523 K, respectively. Results on effect of composition for Co–Al system indicated that the activity increased with increase in the active metal ion concentration (Co²⁺), with closer dependence on the surface concentration (as determined by XPS). The observed activity pattern is explained on the basis of redox property and electronic effects. These materials were further evaluated under flow conditions (at Air Products and Chemicals, USA) simulating the industrial process streams (10% N₂O, 2% H₂O, 2% O₂ and balance N₂ and GHSV=18,500). Among the non-precious metal ions investigated, cobalt-based catalysts offered comparable activity similar to metal-exchanged zeolites for removing N₂O from combustion and Nylon-6,6 processes.     

水滑石类稳定剂热稳定效果的影响因素及其使用途径

简要介绍了水滑石的热稳定机理和影响水滑石类热稳定剂热稳定效果的因素,包括合成条件的影响、阴离子插层的影响、阳离子种类的影响以及改性的影响。综述了水滑石类化合物起到热稳定效果的途径,包括与聚氯乙烯(PVC)制备成复合材料、制成PVC助剂等。     

反相气相色谱法探究镁铁水滑石及其改性材料的表面性质

采用反相气相色谱法(IGC)探究司班20(Span-20)、吐温-80(Tween-80)、曲拉通X-100(Triton X-100)分别与十二烷基苯磺酸钠(SDBS)复合改性镁铁水滑石材料(即SDBS/Span-LDHs、SDBS/Tween-LDHs、SDBS/Triton-LDHs)的表面性质, 通过表面吸附自由能(-ΔG⁰)、表面能色散组分(γ_s^d)及酸碱作用自由能(-ΔG^sp)这三个参数探讨材料改性前后的变化。结果表明, 水滑石经改性后的-ΔG⁰值均比未改性材料的值小, 其中SDBS/Triton-LDHs的-ΔG⁰值最小, 说明SDBS/Triton-LDHs材料的稳定性最好, 且水滑石材料改性后碱性减弱, 其中SDBS/Triton-LDHs材料的碱性最弱。此外, 各类水滑石的γ_s^d值均随着温度的升高而减小, 因此, 在制备聚合物/水滑石类材料时, 可提高温度来改善其与聚合物的相容性。     

水滑石焙烧产物脱除低浓度SO2的研究

研究了水滑石焙烧产物吸附低浓度SO2的性能和还原情况。实验表明：在大于600℃吸附温度下,焙烧的水滑石具有较好吸附性能。吸附剂本身制备条件对脱硫性能影响明显。负载Fe2O3后的复合金属氧化物吸附剂Fe2O3／Mg(Al)O吸附性能整Mg(Al)O有明显提高。氢还原是再生吸附剂的合理和可靠的方法。     

吸附脱除氮氧化物的研究进展

综述了吸附脱除氮氧化物的研究进展。重点讨论了以沸石分子筛、氧化铝、水滑石及类水滑石为载体的吸附剂及吸附工艺对氮氧化物脱除效果的影响。