Catalytic Conversion of Glycerol to Acetol and Acrolein Using Metal Oxides: Surface Reactions, Prospects and Challenges

Glycerol dehydration to acetol and acrolein is an interesting reaction pathway for conversion of biomass-derived products. However, they undergo extensive deactivation due to coke deposition and sintering, requiring the design of stable catalysts. The oxides stand out due to their natural abundance, simple synthesis, low cost and tunable acidic, basic and redox properties. The different studies apply these oxides as pure phase, supported, mixed or doped. However, it is observed that despite the large number of applied oxides in glycerol conversion, few works describe in detail about more complex oxides such as ferrites, hexaferrites, perovskites, among others. This review reports different acid oxides in the glycerol dehydration to acetol and acrolein as well as basic and redox oxides, describing a historical perspective, showing the most important theoretical foundations of heterogeneous catalysis to comprehend surface reactions and mentioning the different possibilities to understanding the different reactional pathway, highlighting the proposal mechanisms that explain the participation of the different active sites on the surface reactions. Furthermore, the sequence of reactions which show the origin of the coke deposited on catalyst surface was presented, emphasizing the main challenges. The role of the Lewis and Bronsted acid-base sites present in the metal oxides and their interactions on glycerol dehydration were described, providing a direction to design catalysts for selective dehydration reactions resistant against coke deposition and sintering.