Catalytic conversion of liquid phase citral and citronellal hydrogenations to menthols over metal-12- tungstophosphoric acid supported mesoporous clay catalysts

In this work, we designed novel-based catalysts composed of metals and tungstophosphoric acid supported mesoporous clay through wetness impregnation and reduction methods for getting good activity and selectivity of menthols from catalytic hydrogenations of citral and citronellal. Clay was treated with 4 M HCl and then doped with 12-tungstophosphoric acid and Pd/Ni metals through wetness impregnation method. These catalysts were activated through hydrogen reduction method and applied in high-pressure hydrogenation reactions at optimum reaction conditions. Nickel-doped catalysts showed a good catalytic activity in liquid-phase citral hydrogenation and produced 56% menthols (e.g., selectivity). Similarly, Ni-doped and Pd-doped catalysts could produce 98% and 82% menthols yield/selectivity from citronellal hydrogenation with excellent catalytic activity (e.g., fast conversion), respectively. The catalytic activity and selectivity were connected with balanced metal–acid sites ratio (strong Lewis and medium Bronsted acid-sites) and the presence of mesopores. This multistage reaction was possible in the presence of strong Lewis and medium Brønsted acid sites along with metal active sites.