Applications superacidic metal oxides

The predominant application of metal oxide catalysts is due to their oxidation and acid-base behavior. In the following, these areas are discussed separately, although it is clear that in many materials, for example, heteropolyacids, which combine both strong acidity and oxidation efficacy (37,38), and the sulfated metal oxides, where controversy exists as to whether the observed low temperature isomerization pathways are catalyzed by superacid or redox mechanisms (39-41), the distinction between acid-base and oxidation properties is somewhat arbitrary. To illustrate their principles, a number of different reaction types are discussed. Dehydrogenation reactions, ammoxidation, and the WGS reaction have been included imder oxidation catalysts since they constitute major industrial applications of metal oxide-based catalysts. In the case of acid-base catalysis, some of the recent activity in the area of biodiesel is described as an illustration of the complementarity of both acid catalysis and base catalysis. There are a number of additional applications of oxides as catalysts, such as in photocatalysis (42), which have not been reviewed here because of limitations of space. Oxidation Activity. 

Different catalysts bring about different types of isomerization of hydrocarbons. Acids are the best known and most important catalysts bringing about isomerization through a carbocationic process. Brpnsted and Lewis acids, acidic solids, and superacids are used in different applications. Base-catalyzed isomerizations of hydrocarbons are less frequent, with mainly alkenes undergoing such transformations. Acetylenes and allenes are also interconverted in base-catalyzed reactions. Metals with dehydrogenating-hydrogenating activity usually supported on oxides are also used to bring about isomerizations. Zeolites with shape-selective characteristics... 

PFSA membranes have excellent chemical inertness and mechanical integrity in a corrosive and oxidative environment, and their superior properties allowed for broad application in electrochemical devices and other fields such as superacid catalysis, gas drying or humidification, sensors, and metal-ion recovery. Here, we refer their important applications in electrochemical devices for energy storage and conversion including PEMFC, chlor-alkali production, water electrolysis, vanadium redox flow batteries, lithium-ion batteries (LIBs), and solar cells. 

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