Acid-base bifunctional catalysis by ZrO2 and its mixed oxides
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.
TL;DR: The present review summarizes the current state of the art in the use of MOFs as solid catalysts according to the type of site, making special emphasis on the more recent strategies to increase the population of these active sites and tuning their activity, either by adapting the synthesis conditions or by post-synthetic modification.
Abstract: Metal organic frameworks (MOFs) are a class of porous crystalline materials that feature a series of unique properties, such as large surface area and porosity, high content of transition metals, and possibility to be designed and modified after synthesis, that make these solids especially suitable as heterogeneous catalysts. The active sites can be coordinatively unsaturated metal ions, substituents at the organic linkers or guest species located inside the pores. The defects on the structure also create these open sites. The present review summarizes the current state of the art in the use of MOFs as solid catalysts according to the type of site, making special emphasis on the more recent strategies to increase the population of these active sites and tuning their activity, either by adapting the synthesis conditions or by post-synthetic modification. This review highlights those reports illustrating the synergy derived from the presence of more than one of these types of sites, leading to activation of a substrate by more than one site or to the simultaneous activation of different substrates by complementary sites. This synergy is frequently the main reason for the higher catalytic activity of MOFs compared to homogeneous catalysts or other alternative solid materials. Besides dark reactions, this review also summarizes the use of MOFs as photocatalysts emphasizing the uniqueness of these materials regarding adaptation of the linkers as light absorbers and metal exchange at the nodes to enhance photoinduced electron transfer, in comparison with conventional inorganic photocatalysts. This versatility and flexibility that is offered by MOFs to optimize their visible light photocatalytic activity explains the current interest in exploiting these materials for novel photocatalytic reactions, including hydrogen evolution and photocatalytic CO2 reduction.
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.
TL;DR: The present review addresses the formation, properties and applications not only of TiO(2) nanotubes but also of related transition metal oxides.
Abstract: Among all one dimensional nanostructures other than carbon, titania nanotubes have gained increasingly more scientific interest due to a successful combination of functional material properties with a well controllable nano-architecture. For self-organized TiO2nanotube arrays not only the simple increase in the specific surface area but also their self-aligned nature leads to a significant enhancement of the performance when used in photoelectrochemistry, photocatalysis, dye-sensitized solar cells, or electrochromic devices. In addition to this, these ordered and size-controlled nanostructured TiO2 surfaces also have material-specific advantages, for example in superhydrophobic/superhydrophilic and biomedical applications. The formation of these vertically oriented nanotube arrays can be achieved by a simple one-step electrochemical self-assembly process. By adjusting the anodization parameters, the geometry such as the tube length or diameter can easily be controlled. The present review addresses the formation, properties and applications not only of TiO2nanotubes but also of related transition metal oxides.
TL;DR: In this article, the specific properties of dispersed and promoted ZrO 2 are presented for the photocatalytic total decomposition of water and a novel application for photocatalysis of water is presented.
Abstract: Examples of the application of ZrO 2 for catalysts and catalyst supports are reviewed. The specificity of the structure and the surface properties including the behavior of surface OH groups are introduced. The catalytic properties of dispersed and promoted ZrO 2 are presented. The novel application to the photocatalytic total decomposition of water is also presented.
TL;DR: Levulinic acid and its esters are converted to γ-valerolactone over metal oxide catalysts by catalytic transfer hydrogenation via the Meerwein-Ponndorf-Verley reaction.
Abstract: Levulinic acid and its esters are converted to γ-valerolactone over metal oxide catalysts by catalytic transfer hydrogenationvia the Meerwein–Ponndorf–Verley reaction.
TL;DR: In this article, the surface properties of binary oxides containing zirconium oxide are characterized and the generation of super acidity on the addition of a small amount of sulfate ion to ZO is elucidated.
Abstract: Zirconium oxide is characterized to be the only one metal oxide which possesses explicitly four chemical properties on the surface; acidic and basic properties and oxidizing and reducing properties. Intriguing and sometimes unique catalytic activities of zirconium oxide itself are discussed in connection with the surface properties. It is also pointed out that zirconium oxide is an interesting and useful catalyst support. Generation of super acidity on the addition of a small amount of sulfate ion to zirconium oxide is elucidated. The surface properties of binary oxides containing zirconium oxide are also characterized.
TL;DR: The results of the coisomerization of 1-butene-d 0 d 8 showed that the reaction involved primarily an intramolecular hydrogen transfer as mentioned in this paper, indicating that the active sites consist of both basic and acidic sites.
Abstract: Acidic, basic, oxidizing, and reducing properties of ZrO2 were measured by the ir spectra of adsorbed pyridine, by CO2 adsorption or the ESR of diphenylnitroxide radical formed from diphenylamine and O2, by the ESR of adsorbed triphenylamine, and by the ESR of adsorbed nitrobenzene, respectively. The variations of these properties with pretreatment temperature of ZrO2 were independent of each other. The maximum concentrations of these sites and the pretreatment temperatures at which the maxima were obtained were 3.9 × 10−8 mole/m2 and 400 °C for acidic sites, 1.7 × 10−7 mole/m2 and 700 °C for basic sites measured by diphenylamine, 1.5 × 10 mole/m2 and 700 °C for oxidizing sites, and 4.3 × 10−8 mole/m2 and 500 °C for reducing sites. Among these properties, it was the basic property with which the activity for isomerization of 1-butene correlated best. The activity was poisoned not only by CO2 but also by NH3 or triethylamine, indicating that the active sites consist of both basic and acidic sites. The results of the coisomerization of 1-butene- d 0 d 8 showed that the reaction involved primarily an intramolecular hydrogen transfer.
TL;DR: In this article, the authors compared the performance of 1,3-butadiene and 2-methyl-1, 3-Butadiene over ZrO2 using H2 and Cyclohexadiene as hydrogen sources and concluded that the sites responsible for the transfer hydrogenation are not the same as those which catalyze hydrogenation with H2.
Abstract: Hydrogenation of 1,3-butadiene and 2-methyl-1,3-butadiene and equilibration reaction of H2D2 were carried out over ZrO2 using H2 and Cyclohexadiene as hydrogen sources. Reaction rates were measured by changing the activation temperature of the catalyst. While the hydrogenation with H2 and H2D2 equilibration reaction gave an optimum activity at 600 °C, another optimum was obtained for transfer hydrogenation at 800 °C. Hence it is concluded that the sites responsible for the transfer hydrogenation are not the same as those which catalyze hydrogenation with H2 and H2D2 equilibration. Product distributions in n-butenes and methylated butenes were compared on ZrO2, ThO2, La2O3, and MgO and were also compared in direct hydrogenation with H2 and transfer hydrogenation with Cyclohexadiene. Assuming an ionic intermediate, selectivity changes in the monoolefins produced over different catalysts and by different hydrogen sources were interpreted in terms of the variation of the anionic character of the intermediate and the shift of anionic to neutral or cationic intermediate, respectively.