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

Abstract

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 Brønsted 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.

Bio-glycerol hydrodeoxygenation to propylene: advancing knowledge on Mo-based catalyst characteristics and reaction pathways under flow conditions

“…In the open literature, catalytic materials having redox sites, such as copper oxide, have been applied for the dehydration reaction of glycerol. 59,60 These results further verify the results obtained in CH 3 OH-TPSR experiments according to which the ratio of the acid/redox sites is significantly lower in the reduced catalyst compared to the fresh one. Performance data suggest that the reduced catalyst with the low acid/redox ratio promotes the complete deoxygenation to propylene while samples with higher ratios lead to partially deoxygenated products in agreement with the work of M. El Doukkali et al 40 Summarizing, catalyst hydrogen pre-treatment step is of utmost importance to obtaining the active sites for the reaction to proceed towards propylene production.…”

“…Thus, as the formation of both is highly favored, it can be assumed that both Lewis and Brønsted active sites co-exist on the catalyst surface which favor almost exclusively the formation of dehydration products. 58,59 Even though the production of both hydroxyacetone and acrolein require the presence of acid sites, their production from redox and/or basic sites is also feasible. In the open literature, catalytic materials having redox sites, such as copper oxide, have been applied for the dehydration reaction of glycerol.…”

Cu/ZrO2 Catalyst Modified with Y2O3 for Effective and Stable Dehydration of Glycerol to Acetol

“…It was reported that increasing the copper oxide dispersion can develop the catalyst acidity and activity for dehydrate glycerol selectively to acetol [ 30 , 31 ]. Generally, the greater acidity the catalyst possesses, the better catalytic performance it exhibits [ 1 , 7 ]. Therefore, it is reasonable to think that the presence of Y 2 O 3 facilitates the Cu dispersion, enhances the acidity, and thus promotes the selectivity for acetol production from glycerol.…”

“…Over the last few decades, determining how to valorize glycerol has been widely investigating since the steep increasing biodiesel production results in an excess supply of glycerol [ 1 ]. Glycerol is a highly reactive molecule as it possesses three hydroxyl functional groups.…”

“…Glycerol is a highly reactive molecule as it possesses three hydroxyl functional groups. Based on the heterogeneous catalysis, glycerol can be converted into many high-added-value products, including selective oxidation to dihydroxyacetone, glyceric acid, hydroxypyruvic acid [ 2 ], mesooxalic acid [ 3 ], tartronic acid or lactic acid [ 4 ], hydrogenolysis to propanediols [ 5 ] or ethylene glycol [ 6 ], catalytic dehydration to acrolein or acetol [ 1 ], etc. Among the derivative production, catalytic dehydration to acetol has been receiving great attention due to the broad use of acetol as a chemical platform [ 7 ].…”