Design of heterogeneous bifunctional catalyst for upgrading bioethanol through the Guerbet reaction

Ethanol;bifunctional catalyst;metal oxide;acid base;Guerbet;aldol condensation;butanol;biodiesel;titanium oxide;supported copper nano particle

Ibrahim, Malek Yahia Saleh ; Kenis, Paul ; Yang ; Hong

关键词: Ethanol;    bifunctional catalyst;    metal oxide;    acid base;    Guerbet;    aldol condensation;    butanol;    biodiesel;    titanium oxide;    supported copper nano particle;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/88973/IBRAHIM-THESIS-2015.pdf?sequence=1&isAllowed=y

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来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Catalytic conversion of ethanol through the Guerbet reaction to higher carbon number molecules allows efficient transformation of biomass to liquid fuels and commodity chemicals. A selective and stable heterogeneous catalyst is required to render this conversion possible in an economic way. The reaction was found to proceed through two parallel mechanisms on basic magnesia where acetaldehyde, formed from ethanol dehydrogenation, can either couple with itself or with adsorbed ethoxide to form new carbon-carbon bonds and the ethanol to acetaldehyde pressure ratio was found to determine which of these two mechanisms predominates. Amphoteric titania, and acidic alumina were found to have very low ethanol dehydrogenation activity and can only catalyze the Guerbet reaction through the acetaldehyde self-coupling mechanism. Strong acidic sites were found to catalyze alcohol dehydration while strong basic sites were found to catalyze esterification and show poor stability under humid conditions. Mild acid-base sites on titania were found to selectively catalyze acetaldehyde aldol condensation and exhibit high stability under humid conditions.To overcome the low dehydrogenation activity of titania, addition of a metallic function was proposed. Among several metals tested, copper was found to be the most selective catalyst for dehydrogenation either as unsupported powder or supported nanoparticles. A synergetic effect was obtained from deposition of the copper nanoparticles on the titania surface since it was found to facilitate product desorption, a step that was found to be the rate limiting for acetaldehyde aldolization. Supported copper nanoparticles were found to catalyze the undesired alcohol esterification reaction. To suppress this side reaction, alloying copper with gold and promotion with chromium and potassium were found to be beneficial. A hybrid sequential-simultaneous reaction configuration was proposed to allow preliminary alcohol selective dehydrogenation on a monofunctional catalyst followed by simultaneous dehydrogenation, aldolization, and product hydrogenation on a bifunctional catalyst.