Continuous 2-Methyl-3-butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis

Abstract

In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and 400 °C, 3 h or 600 °C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using various physicochemical techniques. The catalytic performance of red(400 °C)-Pd/γ-Al2O3 and red(600 °C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover to the alumina support and presence or absence of Pd–Al species. High-temperature reduction leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique electronic properties by decreasing the Pdδ− surface concentration via electron transfer from Pd to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol (97%)—an important intermediate for vitamin A synthesis.