Baeyer–Villiger-oxidation of cyclopentanone with aqueous hydrogen peroxide by acid heterogeneous catalysis

Using aqueous hydrogen peroxide containing 30% H₂O₂, solid acid catalysts were compared in their performance as catalysts for the transformation of cyclopentanone to δ-valerolactone. It could be shown that organic ion exchange resins with sulphonic acid groups providing acid functionality are promising catalysts for this reaction. The variation of several reaction parameters was studied in more detail. The obtained results were compared to investigations of zeolites and Nafion^® composite materials.     

Shape selective catalysis in methylation of toluene: Development,challenges and perspectives

Toluene methylation with methanol offers an alternative method to produce p-xylene by gathering methyl group directly from C1 chemical sources. It supplies a “molecular engineering” process to realize directional conversion of toluene/methanol molecules by selective catalysis in complicated methylation system. In this review, we introduce the synthesis method of p-xylene, the development history of methylation catalysts and reaction mechanism, and the effect of reaction condition in para-selective technical process. If constructing p-xylene as the single target product, the major challenge to develop para-selective toluene methylation is to improve the p-xylene selectivity without, or as little as possible, losing the fraction of methanol for methylation. To reach higher yield of p-xylene and more methanol usage in methylation, zeolite catalyst design should consider improving mass transfer and afterwards covering external acid sites by surface modification to get short “micro-tunnels” with shape selectivity. A solid understanding of mass transfer will benefit realizing the aim of converting more methanol feedstock into para-methyl group.

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Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

Supported vanadium oxide catalysts are active in a wide range of applications. In this review, an overview is given of the current knowledge available about vanadium oxide-based catalysts. The review starts with the importance of vanadium in heterogeneous catalysis, a discussion of the molecular structure of vanadium in water and in the solid state and an overview of the spectroscopic techniques enabling to study the chemistry of supported vanadium oxides. In the second part, it will be shown that advanced spectroscopic tools can be used to obtain detailed information about the coordination environment and oxidation state of vanadium oxides during each stage of the life-span of a heterogeneous catalyst. Three topics will be discussed: (1) the molecular structure of supported vanadium oxide catalysts under hydrated, dehydrated and reduced conditions, including the parameters, which influence the molecular structures formed at the surface of the support oxide; (2) elucidation of the active surface vanadium oxide during the oxidation of methanol to formaldehyde, the reaction mechanism and the vanadium oxide---support effect; and (3) deactivation of fluid catalytic cracking (FCC) catalysts by migration of vanadium oxides and the development of a method preventing the structural breakdown of zeolites by trapping the mobile vanadium oxides in an aluminum oxide coating.     

Innovation in solid heterogeneous catalysis for the generation of economically viable and ecofriendly biodiesel: A review

Among the possible options for the transformation of plant oils and animal fats to biodiesel, the alcoholysis process has been frequently selected. The rate of alcoholysis reaction is accelerated using a catalytic material. This article reviews different nature of catalysts utilized to assist the process of biodiesel production. The chemical properties of both homogeneous and heterogeneous catalysts enable their sub-division into acidic and basic materials. The proficiency of several heterogeneous catalytic systems and the possible route of alcoholysis reaction using different materials is systematically discussed. Furthermore, the factors influencing the performance of catalysts are also considered.     

二聚乙烯酮与醇在酸,碱催化下反应规律的探讨

研究了二聚乙烯酮与不同结构的醇在酸，碱催化下的反应规律，并用烷基电子交应的新观战解释了这个规律。     

FT-IR spectroscopic and catalytic study of de-aluminated H-mordenites as environmental friendly catalysts in the hydroxymethylation of 2-methoxyphenol with formaldehyde in aqueous medium

Several de-aluminated H-mordenites, prepared by treating a commercial H-mordenite (HM-16, Engelhard) with aqueous HCl solutions, were characterized and tested as catalysts in the liquid-phase hydroxymethylation of guaiacol with aqueous solutions of formalin, for the production of p-vanillic alcohol (3-methoxy-4-hydroxybenzyl alcohol), the intermediate in vanillin synthesis.

Samples were obtained with Si/Al atomic ratios from 10 to 36; their acidic and hydrophilic properties have been characterized by means of FT-IR spectroscopy of adsorbed probe molecules, namely CO at nominal 77 K, NH₃ and H₂O at room temperature, and ammonia TPD.

De-alumination led to the development of a mesoporous structure, and to a partial structure degradation with the most de-aluminated sample (Si/Al = 36).

As to the acidic properties, both Brønsted species in the main channels and in side-pockets were removed, and less acidic hydroxyls formed.

The catalytic performance was affected mainly by samples hydrophilicity that considerably decreased upon de-alumination. In the Si/Al ratio range investigated, a decrease in the number of acidic sites led to a complex catalytic behaviour, with a maximum activity for intermediate Si/Al ratio (=25). A higher concentration of aromatic compounds in the pores of more hydrophobic zeolites (higher Si/Al ratios) also led to a higher selectivity towards heavy, di-arylic by-products. A comparison with commercial H-mordenites having similar Si/Al ratio evidenced that the occurrence of mesoporosity, in strongly de-aluminated samples, also affected the catalytic performance, favouring the formation of bulky di-aryl compounds and leading to lower guaiacol conversion.     

Design and control of acetic acid dehydration system via heterogeneous azeotropic distillation

Acetic acid dehydration is an important operation in the production of aromatic acid, such as terephthalic acid or in the manufacture of cellulose acetate. Although acetic acid and water does not form azeotrope, but using simple distillation to separate these two components is not practical. The reason is because the system has tangent pinch on the pure water end, thus it is more customary in industry to use an entrainer via a heterogeneous azeotropic distillation column system for the separation. In this study, a suitable entrainer is selected from three candidate acetates through rigorous steady-state simulation of this system. Optimum process design and operating condition are determined to keep high-purity bottom acetic acid composition and also keep a small acetic acid loss through top aqueous draw. Furthermore, the overall control strategy of this column system is proposed to hold both bottom and top product specifications in spite of feed rate and feed composition load disturbances. The proposed overall control strategy is very simple requiring only one tray temperature control loop inside the heterogeneous azeotropic column.     

Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst

This letter presents an original approach to the treatment of phenolic aqueous wastes using H₂O₂ with heterogeneous catalysts. The experimental results indicate that the system using Fe-ZSM-5 zeolite with MFI structure is promising since it allows total elimination of phenol and significant total organic carbon (TOC) removal under mild working conditions. Moreover, Fe-ZSM-5 remains active after after successive runs. Compared with processes using homogeneous catalysis, the possibility of induced pollution caused by the metal ions in the solution is avoided.     

多级纳米孔分子筛在非均相催化中的应用现状及发展前景

传统分子筛因其单一的微孔孔道,在工业应用中表现为扩散阻力差、催化易失活,尤其在涉及大分子的反应过程中催化活性较差是阻碍其工业应用的现实难题,通过优化制备路线得到的多级纳米孔分子筛催化材料可有效解决传统分子筛存在的上述应用缺陷。多级纳米孔分子筛相比传统分子筛因其特殊的孔道结构和物化性能,在非均相催化方面具有丰富的催化活性位点、较短的扩散路径、较高的传递效率和较长的催化寿命,特别在涉及非均相催化反应的现代化学工业中展现出重要的潜在应用价值。综述多级纳米孔分子筛在烃类异构化反应、加氢裂化反应、烷基化与酰基化反应、烯烃氧化反应以及甲醇制烃类等反应中的诸多优势及潜在应用。     

Bridging the gap between homogeneous and heterogeneous gold catalysis: supported gold nanoparticles as heterogeneous catalysts for the benzannulation reaction

Gold nanoparticles supported on metal oxides and activated carbon are able to catalyze the benzannulation reaction of o-(phenylethynyl)benzaldehyde and phenylacetylene to 1-benzoyl-2-phenylnaphtalene with high selectivity at 99% conversion. Benzannulation of ortho-alkynyl benzaldehydes is a reaction typically catalyzed by soluble AuCl₃ and, now, we have found that it can also be catalyzed by heterogeneous gold supported catalysts. The heterogeneous catalytic system can be reused several times without loss of activity or selectivities.     

Permeability of sintered microfibrous composites for heterogeneous catalysis and other chemical processing opportunities

Microstructured materials have potential for enhanced mass and heat transfer compared to typical catalyst particulates used in industrial processes. The pressure drop through catalyst-containing materials is a very important reactor design consideration. A model equation to predict porous media permeability (PMP) over the entire range of possible bed voidages is extended to predict properties of sintered metal meshes. A correlation of data for sintered meshes of nickel fibers is presented in the form of a Kozeny constant form drag plot. Comparison of predictions by the PMP equation with data taken on a sintered composite fiber/particle mesh is presented. Use of the PMP equation as a design tool for optimization of media for adsorbents, catalysts, and filters is discussed.     

Simple, non-catalytic permethylation of catechol derivatives in subcritical and supercritical water

Environmentally benign, non-catalytic, simple, and complete aromatic ring methylation of catechol derivatives by using 1,3,5-trioxane as the source of methyl groups was investigated in subcritical and supercritical water and under solvent-free conditions. Irrespective of the presence of subcritical and supercritical water as a reaction medium, catechol and 4-methylcatechol afforded the permethylation product 3,4,5,6-tetramethylcatechol. Only a small amount of 3,4,5,6-tetramethylcatechol (2% yield) was obtained under solvent-free conditions at 400 °C for 10 min. However, supercritical water considerably accelerated the formation of 3,4,5,6-tetramethylcatechol (13% yield) under the conditions of 400 °C, 10 min, and 0.35 g/mL water density.     

Phenol methylation over nanoparticulate CoFe2O4 inverse spinel catalysts: The effect of morphology on catalytic performance

A series of CoFe₂O₄ nanoparticles have been prepared via co-precipitation and controlled thermal sintering, with tunable diameters spanning 7–50 nm. XRD confirms that the inverse spinel structure is adopted by all samples, while XPS shows their surface compositions depend on calcination temperature and associated particle size. Small (<20 nm) particles expose Fe³⁺ enriched surfaces, whereas larger (50 nm) particles formed at higher temperatures possess Co:Fe surface compositions close to the expected 1:2 bulk ratio. A model is proposed in which smaller crystallites expose predominately (1 1 1) facets, preferentially terminated in tetrahedral Fe³⁺ surface sites, while sintering favours (1 1 0) and (1 0 0) facets and Co:Fe surface compositions closer to the bulk inverse spinel phase. All materials were active towards the gas-phase methylation of phenol to o-cresol at temperatures as low as 300 °C. Under these conditions, materials calcined at 450 and 750 °C exhibit o-cresol selectivities of 90% and 80%, respectively. Increasing either particle size or reaction temperature promotes methanol decomposition and the evolution of gaseous reductants (principally CO and H₂), which may play a role in CoFe₂O₄ reduction and the concomitant respective dehydroxylation of phenol to benzene. The degree of methanol decomposition, and consequent H₂ or CO evolution, appears to correlate with surface Co²⁺ content: larger CoFe₂O₄ nanoparticles have more Co rich surfaces and are more active towards methanol decomposition than their smaller counterparts. Reduction of the inverse spinel surface thus switches catalysis from the regio- and chemo-selective methylation of phenol to o-cresol, towards methanol decomposition and phenol dehydroxylation to benzene. At 300 °C sub-20 nm CoFe₂O₄ nanoparticles are less active for methanol decomposition and become less susceptible to reduction than their 50 nm counterparts, favouring a high selectivity towards methylation.     

Catalytic ozonation of phenolic compounds: The case of gallic acid

The catalytic ozonation of gallic acid has been carried out in the presence of a perovskite type material (LaTi_0.15Cu_0.85O₃). Some of the main operating parameters like temperature, catalyst and ozone doses exerted a positive influence in the ozonation rate. Contrarily, initial gallic acid concentration showed a negative effect in terms of conversion while the optimum working pH was found to be around 2 (3.5 if deactivation is avoided). Addition of tert-butyl alcohol (free radical scavenger) had no effect on the catalytic removal of gallic acid, although its presence decreased the mineralization degree achieved. The catalyst demonstrated a high stability in terms of the acid removal, however, a partial deactivation was experienced in terms of organic carbon elimination if compared the first and second reuses. The catalyst kept its activity after further reutilisations. Due to the moderate regime developed in the homogeneous phase, the process was better simulated by an empirical expression rather than using a detailed model.     

Hypercrosslinked porous polyporphyrin by metal-free protocol: characterization,uptake performance,and heterogeneous catalysis

Through metal-free protocol, hypercrosslinked porous polyporphyrin with permanent porosity was obatined via the Friedel–Crafts alkylation of tetracarbazolylporphyrin using formaldehyde dimethyl acetal as an external cross-linker. Its chemical structure and porosity was well characterized and confirmed. The BET specific surface area value of HCP-TCPP is 1050 m² g^?1 and related dominant pore size is centered at 0.63 nm. The adsorption amount of methanol by HCP-TCPP is high up to 800 mg g^?1 (about 25.0 mmol g^?1) at its saturated vapor pressure, which is higher than that of toluene (600 mg g^?1, 6.5 mmol g^?1). Further study indicates that polymer HCP-TCPP, possessing the high BET specific surface area and total pore volume, exhibits good hydrogen uptake of 3.44 wt % (77 K) and high carbon dioxide uptake of 41.1 wt % (298 K) at 18.0 bar. Besides, the obtained porous polymer can also be used as an effective heterogeneous catalyst for the Knoevenagel condensation between various aldehydes and malononitrile.     

Discrimination of rival kinetic models in heterogeneous catalysis by the dynamic behaviour of products

The transient response method has been applied to discriminate between rival kinetic models derived from the conventional Hougen-Watson procedure in heterogeneous catalysis, by using some old data for the NO-CO reaction, dehydrogenation of sec-butanol, hydrogenation of phenol, and dehydrogenation of tert-butanol. A computer technique is commonly used for the simulation of the transient response curves of products caused by the concentration jump of reactants in a flow type reactor. The shapes of the calculated response curves are of various characteristic types (depending on the given model) which allow for easy discrimination between rival kinetic models. The difficulty of the discrimination in some particular models is also discussed.     

One-step extraction/methylation method for determining the fatty acid composition of processed foods

In a one-step extraction/methylation (OSM) method for determining individual fatty acids (FA) in processed food products, freeze-dried samples, containing 10–50 mg fat, were transmethylated without prior fat extraction with a mixture of methanol-HCl/toluene. After washing the organic phase the formed FA methyl esters were ready for separation by gas-liquid chromatography (GLC). The relative standard deviation for total FA content was <3.5%, regardless of the food type analyzed. Furthermore, the FA composition of selected fatty foods as obtained by the OSM procedure was almost identical with the FA composition of the pure fats extracted by the Soxhlet procedure and with chloroform-methanol, respectively. The OSM method is inexpensive and simple to perform and is, therefore, well suited for nutrient labeling studies, especially in situations where many samples have to be analyzed for their total FA content.     

镁-三苯胺基MOF的制备及光/Lewis酸协同催化

利用水热法将具有Lewis酸性的Mg2+ 和光敏性的三苯胺三羧酸（H3TCA）自组装，构筑了金属有机框架（metal-organic framework; MOF）Mg-TCA，并通过SC-XRD表征了其晶体结构。UV-vis、FL、CV等测试表明Mg-TCA在可见光区（> 400 nm）具有良好的吸收，其激发态氧化还原电位为-1.95 V (vs. SCE)。以苯乙烯类化合物（0.2 mmol）为底物，NHPI活性酯（0.3 mmol）为自由基前体，Mg-TCA（0.01 mmol）为催化剂，DMSO（2 mL）为溶剂和氧化剂，氮气保护，在405nm的LED下照射24 h，反应以30%~82%的产率生成相应的α-烷基苯乙酮。催化剂Mg-TCA可以重复使用3次并且仍保持活性和晶态结构。机理研究表明在反应过程中发生了光/Lewis酸协同催化，Mg-TCA中具有Lewis酸性的镁节点对NHPI活性酯的吸附作用拉近了其与光催化中心三苯胺的距离，从而提升了催化反应的效率。     

Solvent Influence on the Hydrodeoxygenation of Guaiacol over Pt/SiO2 and Pt/H‐MFI 90 Catalysts

Second generation biofuels are produced in the bioliq® process at the Karlsruhe Institute of Technology via gasification of pyrolysis oil and synthesis of gasoline from the emerging synthesis gas. An alternative strategy is the direct upgrading of the pyrolysis oil by hydrodeoxygenation (HDO). The present study reports on the HDO of guaiacol as one of the phenolic compounds strongly abundant in such mixtures. Special focus was laid on the solvent influence using Pt‐based catalysts. Higher HDO ability was seen using nonpolar solvents and acidic supports. Characterization of the catalysts before and after the test showed that the solvent did not only influence the reactivity, but also the catalyst stability.     

Stability and performance of silica gel-supported triphenylpyrylium cation as heterogeneous photocatalyst

Pyrylium salts are known to be good photocatalysts in aqueous solutions, able to achieve the photodegradation of several phenolic pollutants. Nevertheless, they exhibit a limited stability in these media. The rate of the hydrolytic reaction depends on the pH of the solution, the intensity of irradiation and the pyrylium concentration. Silica gel plates have been employed as inorganic support of the pyrylium cation in order to improve its stability and performance as a heterogeneous catalyst. The resulting material has been tested using ferulic acid as a model compound. Important degradation yields have been achieved (up to 80% after 6 h of solar irradiation). The catalyst is stable under these conditions and can be easily recovered for further use.