Abstract
Background: Acid catalysis of alkanes is very important as it is the basis of refining. They can be converted into other alkanes or alkenes by isomerization, cracking or alkylation. Heteropolyacids have unique acid–base and redox properties, which render them valuable in a number of applications. Their strong acidity makes them attractive candidates to tackle the current challenges in alkanes. The aim of this review is to describe the state of the art in the transformations of alkanes catalyzed by heteropolyacids with and without addition of noble metal.
Methods: We undertook a structured search of bibliographic databases for peer-reviewed research literature using a focused review question. The quality of retrieved papers was appraised using standard tools. The characteristics of screened papers were described, and a deductive qualitative content analysis methodology was applied to analyze the interventions and findings of included studies using a conceptual framework. Results: More than one hundred and fifty papers were included in the review. After a general introduction describing the polyoxometalates and their properties, the generally admitted mechanisms of activation of alkanes by acid catalysts were described. The review was then presented by type of alkanes, starting from propane to long chain paraffins. The activation of methane by heteropolyacids was also described as it can be considered as the first step of the oxidation of methane, which is actually a very important challenge. Conclusion: Polyoxometalates are active for the isomerization/cracking of alkanes. If the first studies were made on light hydrocarbons the most recent works are done on wax or heavy oil, in order to valorize them in gasoline. The polyoxometalate reacts easily with the alkane and this reaction is not the kinetically limiting step.Keywords: Heteropolyacids, alkanes, isomerization, cracking, alkylation, petroleum chemistry.
Graphical Abstract
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