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.
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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.
324 citations
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.
127 citations
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
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.
14 citations
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
References
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TL;DR: In this paper, the oxygen storage capacity of cerium oxide (CeO2) containing zirconium oxide(10, 20, 30, 50, 85, 93 mol%) was studied by measuring temperature programmed reduction.
Abstract: The oxygen storage capacity of cerium oxide (CeO2) containing zirconium oxide (10, 20, 30, 50, 85, 93 mol%) (ZrO2) was studied by measuring temperature programmed reduction. On increasing the ZrO2 content, the reduction reaction at 530 °C appeared stronger, and that at 800 °C weaker. A 50CeO250ZrO2 mixture comprised tetragonal ZrO2(CeO2) and cubic CeO2(ZrO2). Whereas the 15CeO285ZrO2 mixture comprised a phase of tetragonal ZrO2(CeO2) which gave a maximum OSC peak. Characterization of the as-prepared and TPR resulting samples were carried out by XRD and SEM.
201 citations
TL;DR: In this article, it was shown that both Bronsted and Lewis acidity centres can exist at the surface of an homo-geneous family of sulfated zirconia catalysts provided sulfate groups (either isolated or, better, polynuclear units) exist on the regular patches of few low-index crystal planes representing the top termination of the scale-like ZrO2 crystallites.
Abstract: Both Bronsted (protonic) and Lewis (aprotic) acidic centres can exist at the surface of an homo-geneous family of sulfated zirconia catalysts, provided sulfate groups (either isolated or, better, polynuclear units) exist on the regular patches of few low-index crystal planes representing the top termination of the scale-like ZrO2 crystallites. The Bronsted/Lewis acidity ratio depends then on (at least) two variables: the surface hydration/dehydration degree, and the highest temperature reached by the system because Bronsted acidity is induced only by the thermally most labile fraction of surface sulfates.
128 citations
TL;DR: In this article, fine powders of zirconia were prepared by employing combustion method with varying fuel to pre-cursor molar ratios, and the catalytic activity was probed with transfer hydrogenation reaction in liquid phase.
Abstract: Fine powders of zirconia were prepared by employing combustion method with varying fuel to pre-cursor molar ratios. The zirconia powders contained more amount of monoclinic phase as the fuel content was increased. This aspect was studied using XRD, IR and UV-vis diffuse reflectance techniques. The surface acid-base properties of these samples were also investigated by indicator titration method. The catalytic activity was probed with transfer hydrogenation reaction in liquid phase. It was found that combustion synthesized zirconia did not provide required active sites for transfer hydrogenation reactions in liquid phase unlike hydrous zirconia.
120 citations
TL;DR: An infrared spectroscopic study was made of the adsorbed species and the gas-phase products from the dehydrogenation and dehydration reactions of 2-propanol over CeO2 catalysts calcined at different temperatures as mentioned in this paper.
Abstract: An infrared spectroscopic study was made of the adsorbed species and the gas-phase products from the dehydrogenation and dehydration reactions of 2-propanol over CeO2 catalysts calcined at different temperatures. The adsorbed species observed included hydrogen-bonded alcohol molecules, alcoholate ions, and carboxylate ions. The dehydrogenation reaction to form acetone was followed by a transformation of this product to give isobutene and methane. The dehydration reaction gave propene as the sole product. Mechanisms for the various surface reactions are proposed which are consistent with the infrared results.
103 citations
TL;DR: In this paper, the propan-2-ol dehydration or dehydrogenation over three simple metal oxides (TiO2, ZrO2 and CeO2) was carried out in helium, dihydrogen or air flow, at temperatures in the (473 −623 K) range.
Abstract: The propan-2-ol dehydration or dehydrogenation over three simple metal oxides (TiO2, ZrO2 and CeO2) was carried out in helium, dihydrogen or air flow, at temperatures in the (473–623 K) range. Propan-2-ol decomposition on metal oxide surfaces has been used as an acid–base test. On TiO2, ZrO2 or CeO2, it appears that propene and acetone formation sites are not specific and it is difficult to deduce surfaces properties from activities and selectivities observed. In helium and dihydrogen, for all the metal oxides, temperature increase always favours propene formation. In air, the three metal oxides used are more active and their selectivity in acetone is more important than in helium or dihydrogen. The results clearly show that propanol transformation cannot be a simple test of acidity. Particularly, on ceria, results suggest that redox property and the high lability of lattice oxygen contribute to products formations, involving oxygen vacancies.
89 citations