Synthesis, characterization and performance of bifunctional catalysts for the synthesis of menthol from citronellal†
The synthesis of a series of bifunctional catalysts (1 wt% Pt/W-TUD-1 (Technische Universiteit Delft-1) and 1 wt% Pt/WO3/TUD-1) with different tungsten loadings (5–30 wt% WO3) is described. They were characterized using ICP-OES, INAA, N2 physisorption, XRD and TEM. Their catalytic performance (activity and selectivity) was evaluated in the two-step catalytic synthesis of menthol from citronellal using kinetic analysis. Introducing tungsten during the TUD-1 synthesis results in a high WO3 dispersion, essential for the acidity of the catalyst. High tungsten dispersion is also critical for the Pt hydrogenation activity. Therefore, high dispersion combined with optimal tungsten loading resulted in the highest catalytic activity. The best performing catalyst was 1 wt% Pt/W-TUD-1 (silicon to tungsten ratio of 30), with the highest yields of menthol (96%).