Promoting the hydrogenation of citral via supported bimetallic Zn–Pt catalysts on TiO2

Abstract

In this study, we utilize a promoter, specifically zinc, in varying concentrations to examine its promoting effects. This series of catalysts was prepared using a co-impregnation method involving zinc and platinum on titanium dioxide (TiO₂). The material was then dried at 100 °C and calcinated at 400 °C for 4 hours. The samples were subjected to a prolonged reduction at 300 °C for four hours. The physicochemical characteristics of the x Zn–Pt/TiO₂ P25 samples, each with distinct weight percentages of x Zn, were evaluated using a comprehensive array of analytical techniques. These methods included elemental analysis, X-ray diffraction, nitrogen sorption, hydrogen chemisorption, transmission electron microscopy, and cyclohexane dehydrogenation. This specific reaction has been utilized as a model to evaluate the accessibility of platinum and the degree of zinc coverage. An investigation into the performance and selectivity of the catalysts was conducted during the hydrogenation of citral, which was performed at a temperature of 70 °C and a hydrogen pressure of 7 MPa. The reaction occurred in isopropanol as the solvent and lasted for 120 minutes. A higher concentration of zinc in the materials was correlated with a reduced accessibility of platinum metal within the catalysts. This specific reaction has been utilized as a model to evaluate the accessibility of platinum and the degree of zinc coverage.

Graphical Abstract

The synthesis of x% Zn–Pt/TiO₂ catalysts (x between 0 and 0.3 wt%), for further application in the selective hydrogenation of citral in the liquid phase. The catalytic systems were deeply characterized by several physico-chemical techniques. We clearly evidenced the existence of an interaction between Pt and Zn with the formation problem of alloy, leading to an inhibition of the Pt hydrogenating activity but contributing to a remarkable increase in the selectivity to unsaturated alcohols due to a better activation of the C=O bond of citral. A maximum value of 81% for the unsaturated alcohols selectivity was reached with the bimetallic 0.3% Zn–Pt/TiO₂ catalyst.