The influence of Si/Al ratio on the distribution of OH groups in zeolites with MWW topology

A series of MWW-type zeolites of increasing Si/Al ratio were investigated with respect to their acidic properties. Concentration of the Brønsted acid centers located at the external crystal surface was invariant for the entire series. Ethanol conversion to ethyl-tert-butyl ether, proceeding only at the external surface, was also constant. The OH groups in MWW zeolites were found to be homogeneous with proton affinity value equal to 1142.7 kJ/mol

Heteropoly Acid/Nitrogen Functionalized Onion‐like Carbon Hybrid Catalyst for Ester Hydrolysis Reactions

A novel heteropoly acid (HPA)/nitrogen functionalized onion‐like carbon (NOLC) hybrid catalyst was synthesized through supramolecular (electrostatic and hydrogen bond) interactions between the two components. The chemical structure and acid strength of the HPA/NOLC hybrid have been fully characterized by thermogravimetric analysis, IR spectroscopy, X‐ray photoelectron spectroscopy, NH3 temperature‐programmed desorption and acid–base titration measurements. The proposed method for the fabrication of the HPA/NOLC hybrid catalyst is a universal strategy for different types of HPAs to meet various requirements of acidic or redox catalysis. The hydrophobic environment of NOLC effectively prevents the deactivation of HPA in an aqueous system, and the combination of uniformly dispersed HPA clusters and the synergistic effect between NOLC and HPA significantly promotes its activity in ester hydrolysis reactions, which is higher than that of bare PWA as homogeneous catalyst. The kinetics of the hydrolysis reactions indicate that the aggregation status of the catalyst particles has great influence on the apparent activity.Know your onion‐like carbon: A heteropoly acid (HPA)/nitrogen functionalized onion‐like carbon (NOLC) hybrid catalyst was successfully synthesized. The hydrophobic environment of NOLC effectively prevents the deactivation of HPA in an aqueous system, and the synergistic effect between NOLC and HPA significantly promotes its activity in hydrolysis reactions.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137551/1/asia201500944.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137551/2/asia201500944-sup-0001-misc_information.pd

Heteropolyacid-based materials as heterogeneous photocatalysts

Heteropolyacids (HPAs) that are often used as heteropolyanions are cheap and stable compounds that have been extensively used as acid and oxidation catalysts as a result of their strong Brønsted acidity and ability to undergo multielectron-transfer reactions. HPAs, which are very soluble in water and polar solvents, have been also used as homogeneous photocatalysts for the oxidation of organic substrates in the presence of oxygen, but their use in heterogeneous systems is by far desirable. Dispersing HPAs onto solid supports with high surface area is useful to increase their specific surface area and hence (photo)catalytic activity. Moreover, owing to the high energy gap between the HOMO and LUMO positions of the HPAs, these compounds are activated only by UV light. Consequently, only less than 5 % of the solar light can be used in photocatalytic reactions, which restricts the practical application of HPAs. This microreview is oriented to describe the reported literature on the use of HPA-based materials as heterogeneous photocatalysts for environmental purposes, that is, for the complete or partial oxidation or reduction of organic molecules