Promotional effects of alkali and alkaline earth metals on metal oxide-based catalysts in glycerol upgradation

Abstract

Upgrading glycerol into value-added products (i.e. glycerol carbonate) has been considered as a promising strategy which not only alleviates the extensive accumulation of glycerol caused by the rapidly growth of the biodiesel industry, but also improves the economic profit of the biodiesel process.

Lots of heterogeneous catalysts have been developed for glycerol upgradation to glycerol carbonate via reacting with dimethyl carbonate, but most of the catalysts either contained expensive and limited resources or were synthesized via complicated methods, which obstructs their future industrial implementation for glycerol upgrading. Besides that, the fundamental understanding behind the promotional roles of the dopant such as alkali and alkaline earth metals is still ambiguous which hinders the design of efficient catalysts for application in industry. Thus, the aim of this thesis focuses on two main points: 1. Developing low-cost and high-efficiency catalysts which utilises highly abundant elements such as alkali and alkaline earth metals; 2. Systematically investigating the promotional roles of dopants based on their ionic radii, valence states, the crystallinity, the electronic state, surface basicity, surface area, pore size, and morphology. Overall, three newly developed catalysts – 25 mol% Na/La2O3, 7 wt.% Na/CeO2 and 7 wt.% Li/MgO – have been studied in glycerol upgradation to glycerol carbonate and showed the highest catalytic performance among all developed catalysts in each research chapter, where the glycerol conversion is 87%, 87% and 92% and glycerol carbonate yield is 60%, 65%, and 87%, respectively. In addition, after systematically investigating on the promotion effects of doping alkali and alkaline earth metals on support materials, the similar ionic radius and lower valence state of the dopant compared to their host metals have been found as dominant factors in boosting the catalytic performance of support materials. More thorough discussions are included in each research chapter (Chapter 3, Chapter 4 and Chapter 5).