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Acid–base properties of amphoteric crystalline YNbO4, which is synthesized by co‐precipitation method using a water‐soluble Nb peroxo complex, are adjusted by the impregnation of phosphate groups. The resulting phosphate–YNbO4 materials are tested for glucose dehydration to 5‐hydroxymethylfurfural (HMF). Both activity and selectivity increase by the introduction of phosphate groups, giving the optimal catalyst with five phosphate groups per nm2 of surface (5P‐YNbO4). 5P‐YNbO4 shows ≈50% selectivity at 75% conversion. Pyridine adsorption experiments show that 5P‐YNbO4 exclusively possesses Lewis acidity. NH3‐ and CO2‐temperature programmed desorption measurements confirm that phosphoric acid treatment increases acid strength and acid density with concurrent loss of basicity. Experiments using isotope‐labeled glucose clarify that HMF is formed on 5P‐YNbO4 through the stepwise dehydration reaction mechanism. Recyclability experiments show an accumulation of carbon deposits at the end of each reaction causing deactivation, but the activity can be completely recovered by successive washing with water and subsequent calcination at 400 °C in air.

In recent years, one of the analogous metal organic frameworks (MOFs) with UiO‐66(Zr) topology receiving wider attention is UiO‐66(Ce), which exhibits interesting properties and high thermal and chemical stability. Hence, in the present work, UiO‐66(Ce) is synthesized by adopting an earlier procedure and characterized by series of spectroscopic techniques like UV‐visible (UV‐Vis), Fourier transform infrared (FT‐IR), Raman and scanning electron microscope (SEM) to confirm its structural features and crystallinity using powder X‐ray diffraction (XRD) and these results are in close agreement with other reports. The catalytic performance of UiO‐66(Ce) was evaluated in the Friedel–Crafts alkylation reaction between β‐nitrostyrene and indole to obtain heterocyclic compounds with biological activity. A series of control experiments indicate that Ce4+ located within the framework plays an important role in promoting this reaction and its activity is found to be much superior to that of UiO‐66(Zr). This enhanced activity with Ce4+ compared to Zr4+ is attributed due to the higher oxophilicity of Ce4+, which can readily bind with an oxygen‐containing substrate such as β‐nitrostyrene. The leaching test confirms the heterogeneity of the reaction and the catalyst can be reused three times with identical activity to the fresh solid. UiO‐66(Ce) shows wide substrate scope with high yields of the desired product. A proposed mechanism is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Supported Cu catalysts and bare inorganic oxides have been tested in the reduction of furfural to furfuryl alcohol under hydrogen transfer reaction conditions by using butanol as a donor. Bare oxides like zirconia and alumina were found to be more active than the corresponding supported catalysts and in particular high surface Zirconia gave a quantitative transformation of the aldehyde into alcohol in 2,5 h at 140 °C according to a pure Meerwein‐Ponndorf‐Verley mechanism. Competitive dehydrogenation of the alcohol formed on the surface of Cu catalysts strongly reduces their activity although selectivity to alcohols on zirconia and alumina supported catalysts keeps very high. On the other hand catalysts with a well‐defined Lewis acid character such as highly dispersed Zirconia on Silica allowed to obtain up to 64% yield in 2‐butyl‐furfuryl‐ether under the same conditions. [ABSTRACT FROM AUTHOR]

Tri-esters of fatty acids with polyols can be easily prepared through direct esterification of different acids with the polyol in the presence of amorphous solid acid catalysts. Conversion close to 100% and very high selectivity to triesters can be obtained in the presence of a silica zirconia amorphous catalyst. Activity and selectivity can be due to the presence of very well dispersed Lewis acid sites consisting in tetrahedrally coordinated Zr ions that are resistant to water formed during reaction as shown by FT IR spectroscopy. [ABSTRACT FROM AUTHOR]

The use of metalloenzyme-like zeolites as Lewis acid catalysts for CC bond formation reactions has received increasing attention over the past few years. In particular, the observation of direct aldol condensation reactions enabled by hydrophobic zeolites with isolated framework metal sites has encouraged the development of catalytic approaches for producing chemicals from biomass-derived compounds. The discovery of new Diels-Alder cycloaddition/dehydration routes and experimental and computational studies of Lewis acid catalyzed carbonyl-ene reactions have given a further boost to this rapidly evolving field. [ABSTRACT FROM AUTHOR]

This review deals with the general discussion on green chemistry and catalysis; and solid acid catalysts. Various Lewis and Brønsted solid acid catalysts reported in the last few years for various synthetic protocols have been discussed in this review. [ABSTRACT FROM AUTHOR]

Hf-, Zr- and Sn-Beta zeolites effectively catalyze the coupled transfer hydrogenation and etherification of 5-(hydroxymethyl)furfural with primary and secondary alcohols into 2,5-bis(alkoxymethyl)furans, thus making it possible to generate renewable fuel additives without the use of external hydrogen sources or precious metals. Continuous flow experiments reveal nonuniform changes in the relative deactivation rates of the transfer hydrogenation and etherification reactions, which impact the observed product distribution over time. We found that the catalysts undergo a drastic deactivation for the etherification step while maintaining catalytic activity for the transfer hydrogenation step. 119Sn and 29Si magic angle spinning (MAS) NMR studies show that this deactivation can be attributed to changes in the local environment of the metal sites. Additional insights were gained by studying effects of various alcohols and water concentration on the catalytic reactivity. [ABSTRACT FROM AUTHOR]

Take the straight path: Furfural was converted into γ‐valerolactone (GVL) through sequential transfer‐hydrogenation and hydrolysis reactions catalyzed by zeolites with Lewis and Brønsted acid sites (see picture). Together, Zr‐Beta and Al‐MFI nanosheets generated GVL in 78 % yield without the use of precious metals or molecular H2. This system offers an attractive streamlined strategy for the production of GVL from biomass‐derived molecules. [ABSTRACT FROM AUTHOR]

The selective conversion of furfural into γ‐valerolactone (GVL) through a series of domino‐like reactions catalyzed by zeolites with Lewis and Brønsted acid sites is described by Y. Román‐Leshkov and co‐workers in their Communication on page 8022 ff. Zr‐Beta and Al‐MFI nanosheets generated GVL in 78 % yield without the use of high‐pressure molecular hydrogen or precious metals. [ABSTRACT FROM AUTHOR]