Theoretical study of the side reactions of ethanol-to-butadiene conversion on MgO catalyst: formation of diethyl ether, ethyl acetal, 1,3-butanediol, methyl ethyl ketone, n -butanol, butanal, and acetone

To understand the mechanistic details of the catalytic conversion of ethanol to 1,3-butadiene on metal oxides, both the main reaction and the side reactions should be clarified. Seven side reactions on an MgO catalyst were examined using density functional theory calculations. They were: the condensation of ethanol involving dehydration, which generates diethyl ether; condensation between ethanol and acetaldehyde, which generates ethyl acetal; reduction of acetaldol, which generates 1,3-butanediol (1,3-BDO); dehydration of 1,3-BDO, which generates methyl ethyl ketone; hydrogenation of crotonaldehyde, which generates n -butanol; isomerization of crotyl alcohol, which generates butanal; and dehydrogenation and decarboxylation of acetaldol, which generate acetone. Because the ethanol-to-butadiene conversion proceeds via several reaction steps, which are catalyzed on Lewis acidic and/or basic sites, increasing the efficiency of a reaction step in the main reaction path would also increase side reaction paths of other reaction steps.