Solventless selective self-condensation of cyclopentanone over robust TiO2-SnO2 acid-base bifunctional catalyst

The self-aldol condensation of cyclopentanone (CP) to aviation fuel precursors was studied over various acid-base bifunctional TiO 2 -based catalysts. Combining TiO 2 and SnO 2 improved the catalytic performance and reduced the apparent activation energy, resulting in a selectivity of 97.5 % for 2-cyclopentylidene cyclopentanone (dimer C 10 ) and 2,5-dicyclopentylidene cyclopentanone (trimer C 15 ) (with 79.2 % yield for dimer C 10 ) at a CP conversion of 92.5 %. Response surface methodology (RSM) analysis of the reaction parameters showed that the actual results were in considerable concordance with the predicted ones. The excellent catalytic performance and stability exhibited by the TiO 2 -SnO 2 nanocomposites catalyst were attributed to (i) the nanoscale mixed metal oxide grains (bonded by Ti–O–Sn) and highly dispersed active Ti δ+ species, which facilitated the adsorption and activation of CP; (ii) the increase in surface O C species contributing to the abundance of hydroxyl groups (including M δ+ –O – pairs), which promoted the formation of the enolate intermediates; (iii) the construction of appropriate medium acid-base sites and the Brønsted/Lewis acid sites (BAS/LAS) ratio, which favored the formation of the desired dimer C 10 . Conversely, the TiO 2 -SiO 2 catalyst with plentiful strong acid-base sites induced the successive condensation of CP, which favored the formation of trimer C 15 . Furthermore, a plausible reaction mechanism for the catalytic self-aldol condensation of CP over the TiO 2 -SnO 2 catalyst was proposed. This study developed an efficient and stable TiO 2 -SnO 2 catalyst for CP self-aldol condensation with promising application potential.