Improving the selectivity to C4 products in the aldol condensation of acetaldehyde in ethanol over faujasite zeolites

Formation Pathways toward 2‐ and 4‐Methylbenzaldehyde via Sequential Reactions from Acetaldehyde over Hydroxyapatite Catalyst

“…The yield of 2‐butenal decreases with increasing conversion of acetaldehyde (for conversions greater than 15 %), because secondary condensation reactions, which form C 6 and C 8 enal products, consume 2‐butenal. First, aldol condensation of acetaldehyde to 2‐butenal gives 2,4‐hexadienal and subsequent condensation of acetaldehyde to 2,4‐hexadienal produces 2,4,6‐octatrienal . Once formed, 2,4,6‐octratrienal rapidly undergoes electrocyclization and dehydrogenation to produce 2‐MB=O .…”

“…Figure shows that 2‐butenal is the primary product of the aldol condensation of acetaldehyde and that 2‐butenal remains the most abundant product until the conversion of acetaldehyde reaches ≈40 % (0.35 kPa C 2 H 4 O, 1 kPa C 2 H 5 OH, 99 kPa H 2 , 548 K), which agrees with prior investigations . The yield of 2‐butenal decreases with increasing conversion of acetaldehyde (for conversions greater than 15 %), because secondary condensation reactions, which form C 6 and C 8 enal products, consume 2‐butenal.…”

“…Such coupling reactions continue in a series of steps that consume primary products and form larger species . While the cascades of ethanol coupling (Guerbet reaction) processes produce broad distributions of linear and branched alcohols by numerous self‐ and cross‐condensation reactions, narrower product distributions that provide selectivity to specific species emerge if unsaturated aldehydes (and enals) mainly participate in condensation reactions.…”

Synthesis of C4 and C8 Chemicals from Ethanol on MgO‐Incorporated Faujasite Catalysts with Balanced Confinement Effects and Basicity

“…As illustrated in Scheme , the self‐aldol condensation of acetaldehyde produces 3‐hydroxybutanal, which readily dehydrates to form crotonaldehyde. Another well‐known self‐condensation pathway of acetaldehyde is the Tishchenko reaction, which gives ethyl acetate as a product .…”

“…Adjustable molecular confinement when using zeolites as catalysts is a unique tool offered by zeolites to enhance selectivity. Previously, we investigated the aldol condensation of acetaldehyde over faujasite zeolites with varying silicon/aluminum ratios and different types of alkali‐metal cations . We found that the C 4 /(C 6 +C 8 ) product ratio depended on a variety of factors, such as strength, density, and accessibility of basic sites.…”