A review on bi/multifunctional catalytic oxydehydration of bioglycerol to acrylic acid: Catalyst type, kinetics, and reaction mechanism

Acrylic acid, conventionally produced via propylene (non-renewable fossil fuel route), is an industrially important chemical. The bio-based feedstock process employing glycerol (a by-product of biodiesel production) has attracted the attention of researchers due to its non-polluting and renewable characteristics. Bi/multifunctional catalysts using a combination of zeolites, metal oxides, heteropoly acids, and phosphates have been mainly studied for the glycerol oxydehydration process. Bronsted acid sites favour acrolein generation over Lewis acid sites, whereas the redox sites convert the generated acrolein to acrylic acid. So far, the maximum acrylic acid yields of 60% and 59% have been reported on heteropoly acid and mixed metal oxide catalysts, respectively. Some DFT studies also revealed the deprotonation energy of acid sites and further helped in designing efficient catalysts. Despite these accomplishments, catalyst deactivation because of coking and stability remains a major problem. In this paper, various bi/multifunctional catalysts employed in glycerol oxydehydration to acrylic acid are critically reviewed. Different catalyst forms, preparation techniques, reaction kinetics, reaction mechanisms, deactivation, reactivation, process operating parameters, and sustainability are considered. In addition, the challenges associated with each catalyst type and strategies to overcome low yield, deactivation, and future directions are discussed.