Vapor phase reduction of cyclohexanone to cyclohexanol on CexZr1-xO2 solid solutions
01 Jan 2003-Reaction Kinetics and Catalysis Letters (Kluwer Academic Publishers)-Vol. 78, Iss: 1, pp 151-159
TL;DR: In this article, a possible mechanism of hydride transfer has been proposed with cerium ions as promoters, which showed better catalytic activity compared to pure ZrO2 and the selectivity to cyclohexanol is 98%.
Abstract: Reduction of cyclohexanone to cyclohexanol using propane-2-ol as hydrogen donor has been carried out in vapor phase on CexZr1-xO2 solid solutions synthesized by ombustion synthesized at 302°C. The solid solutions around 0.4 mol% cerium content show better catalytic activity compared to pure ZrO2 and the selectivity to cyclohexanol is 98%. A moderate acid-base and good redox properties of CexZr1-xO2 solid solutions are seen to be responsible for the catalytic activity. A possible mechanism of hydride transfer has been proposed with cerium ions as promoters.
Citations
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TL;DR: This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.
Abstract: Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria-based catalysts have also been developed for different applications in organic chemistry. The redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria-supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring-opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.
298 citations
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TL;DR: In this article, the authors investigated the effect of ceria in composite oxides for cyclohexanol de-hydrogenation and hydrogen transfer reactions, and showed that the presence of the ceria enhances the surface area and acid-base properties.
Abstract: CeO2–ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV–vis–NIR diffuse reflectance, SEM and acid–base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid–base properties facilitating the dehydrogenation process. At low ceria content, the CeO2–ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)–ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2–ZnO catalysts for reactions involving acid–base sites.
118 citations
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TL;DR: In this paper, the nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr 0.5O2 solid solution has been investigated.
Abstract: The nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr0.5O2 solid solution has been investigated. The vibrational study shows additional IR features at 1051 and 957 cm−1 which are correlated to the primary Keggin anions interacting with Lewis sites involving Ce4+ and Zr4+ ions, and thus affecting the P–O and W=Oterminal bonds. The IR study indicates the formation of interfacial Ce4+–O–W and Zr4+–O–W bonds. The chemisorbed Keggin molecular layers on Ce0.5Zr0.5O2 show activity towards conversion of acetophenone to styrene by Meerwein–Ponndorf–Verley reduction followed by dehydration. The activity is correlated with the relative intensities of IR peaks at 1051 and 957 cm−1 of the perturbed Keggin molecular layers.
33 citations
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TL;DR: In this article, the Ba 2+ modified zirconia (Ba/ZrO 2) materials were characterized using XRD, Fourier analysis, UV-vis-DRS, FESEM and HRTEM techniques.
Abstract: Zirconia nanoparticles were synthesized by precipitation, urea hydrolysis, amorphous citrate and combustion synthesis methods. The zirconia surface was subsequently modified by grafting Ba 2+ species. The Ba 2+ modified zirconia (Ba/ZrO 2) materials were characterized using XRD, Fourier analysis, UV-vis-DRS, FESEM and HRTEM techniques. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of Ba 2+ species. Fourier line profile analysis of the XRD peaks revealed that the average crystallite size of the zirconia nanoparticles is in the range of 5-15 nm. The surface area, basicity and barium content of the material depend strongly on the method of synthesis. The Ba/ZrO 2 catalyst prepared by urea hydrolysis method exhibited higher surface area and barium content compared to other samples. The catalytic activity of the Ba/ZrO 2 catalyst was evaluated for synthesis of β-nitro alcohols and 2-amino 2-chromenes. The β-nitro alcohols were synthesized by condensation of aryl aldehydes and nitromethane. Similarly, the 2-amino 2-chromenes were synthesized by condensation of arylaldehydes, α-naphthol and malononitrile. The Ba/ZrO 2 catalyst was found to be highly efficient for synthesis of both classes of compounds providing excellent yield and purity of the products.
11 citations
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TL;DR: In this article, a series of sulfonated polyvinyl alcohol-Zr-pillared clay nanocomposites were synthesized and characterized using XRD, FTIR, Raman, UV-vis and FE-SEM analytical techniques.
Abstract: A series of sulfonated polyvinyl alcohol-Zr-pillared clay nanocomposites were synthesized. A low molecular weight polyvinyl alcohol (PVA) was sulfonated using chlorosulfonic acid. The sulfonated PVA was intercalated inside the parent clay and Zr-pillared clay (Zr-P) matrix. In an alternative approach, the polyvinyl alcohol was initially intercalated into the clay and Zr-P structure followed by in-situ sulfonation inside the clay matrix. The composite materials were characterized using XRD, FTIR, Raman, UV–vis and FE-SEM analytical techniques. Expansion in clay interlayer due to insertion of the polymeric species and the Zr-pillars was observed from XRD study. FTIR and UV–vis study revealed presence of hydrated sulfonic acid clusters in the composite materials. The clay sheets were largely present in an exfoliated state in the clay-polymer composite materials. Insertion of the Zr-pillar imparts structural rigidity and consequent changes in the morphological features. The catalytic activity of the Zr-pillared clay-sulfonated polyvinyl alcohol composite materials has been investigated for synthesis of hexahydropyrimidines by multicomponent condensation of substituted aniline, formaldehyde and β-dicarbonyl compounds. The composite materials were found to be highly active for synthesis of structurally diverse hexahydropyrimidines in high yield and purity.
11 citations
References
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TL;DR: A statistical survey of industrial processes using solid acid-base catalysts is presented in this paper, where the number of processes such as alkylation, isomerization, amination, cracking, etherification, etc.
Abstract: A statistical survey of industrial processes using solid acid–base catalysts is presented. The number of processes such as alkylation, isomerization, amination, cracking, etherification, etc., and the catalysts such as zeolites, oxides, complex oxides, phosphates, ion-exchange resins, clays, etc., are 127 and 180, respectively. The classification of the types of catalysts into solid acid, solid base, and solid acid–base bifunctional catalysts gives the numbers as 103, 10 and 14, respectively. Some significant examples are described more in detail. On the basis of the survey, the future trend of solid acid–base catalysis and the fundamental research promising for industrial success are discussed.
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TL;DR: In contrast to these extensive studies of heterogeneous acidic catalysts, fewer efforts have been given to the study of heterogenous basic catalysts as mentioned in this paper. But these studies have been continuous and progressed steadily, and they have never been reviewed in the chemical Reviews before.
Abstract: Heterogeneous acid catalysis attracted much attention primarily because heterogeneous acidic catalysts act as catalysts in petroleum refinery and are known as a main catalyst in the cracking process which is the largest process among the industrial chemical processes. In contrast to these extensive studies of heterogeneous acidic catalysts, fewer efforts have been given to the study of heterogeneous basic catalysts. The types of heterogeneous basic catalysts are listed in Table 1. Except for non-oxide catalysts, the basic sites are believed to be surface O atoms. The studies of heterogeneous catalysis have been continuous and progressed steadily. They have never been reviewed in the chemical Reviews before. It is more useful and informative to describe the studies of heterogeneous basic catalysis performed for a long period. In the present article, therefore, the cited papers are not restricted to those published recently, but include those published for the last 25 years. The paper first describes the generation of basic sites before describing methods used in the characterization of basic surfaces. These are indicator methods, temperature programmed desorption (TPD) of CO{sub 2}, UV absorption and luminescence spectroscopies, TPD of H{sub 2}, XPS, IR of CO{sub 2}, IR of pyrrole, and oxygen exchange betweenmore » CO{sub 2} and the surface. The paper then discusses studies on the catalysis by heterogeneous basic catalysts. Some of these reactions are dehydration, dehydrogenation, hydrogenation, amination, alkylation, ring transformation, and reactions of organosilanes. Catalysts discussed are single component metal oxides, zeolites, non-oxide types, and superbasic catalysts. 141 refs.« less
882 citations
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TL;DR: In this paper, the importance of acid-base bifunctional catalysis by ZrO2 and its mixed oxides is emphasized, and industrial applications of Zr O2 catalysts are demonstrated.
Abstract: Examples of acid-base bifunctional catalysis by ZrO2 and its mixed oxides are summarized. The hydrogenation of olefins, carbon monoxide and aromatic carboxylic acids over ZrO2 are also examples of acid-base bifunctional catalysis which occur by heterolytic splitting of a hydrogen molecule (H2) into a proton (H+) and a hydride ion (H−) on the acid-base pair sites. Industrial applications of ZrO2 catalysts are demonstrated, the importance of acid-base bifunctional catalysis by ZrO2 and its mixed oxides being emphasized.
274 citations
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TL;DR: In this paper, the authors investigated the preparation of high surface area, three-way catalysts (TWC)-like, ceria-zirconia mixed oxide and showed that under basic conditions cationic surfactants effectively incorporate into hydrous oxides of cerium and zirconium.
Abstract: The study investigates the preparation of high surface area, three-way catalysts (TWC)-like, ceria–zirconia mixed oxide. It is shown that under basic conditions cationic surfactants effectively incorporate into hydrous oxides of cerium and zirconium. The presence of cerium inhibits the action of alkyl-trimethyl-ammonium salts as true templating agents and there is no formation of a regular pore structure. The elimination of surfactants upon calcination gives rise to the formation of high surface area, fluorite-structured CeO2–ZrO2 solid solution characterized by a fairly good compositional homogeneity. Surface areas in excess of 230 m2/g were obtained after calcination at 723 K, which drop to ca. 40 m2/g following treatment at 1173 K.
200 citations