Selective hydrogenation of dimethyl terephthalate to dimethyl 1,4-cyclohexanedicarboxylate over zeolite-supported Ru catalysts

Dimethyl 1,4-cyclohexanedicarboxylate (DMCD) is an important chemical product, which is widely used in the synthesis of polyester resins, polyamides, and plasticizers. It is generally prepared via dimethyl terephthalate (DMT) selective hydrogenation. Herein, the zeolite (ZSM-5-25/50/100, ZSM-35, MOR, and β)-supported Ru catalysts were prepared and employed for DMT hydrogenation. Compared to the other zeolites, MOR-supported Ru showed the best performance (DMT conversion: 100%, DMCD selectivity: 81.67% at the conditions of 180°C, 4 MPa H₂, 3 h, 2-propanol as solvent, and m(DMT):m(Cat.) = 5:1). After optimizing the reaction conditions, DMT conversion and DMCD selectivity finally reached 100% and 95.09%, respectively, at 140°C, 6 MPa H₂, 4 h, ethyl acetate as solvent, and m(DMT):m(Cat.) = 2.5:1. Furthermore, Ru/MOR exhibited good reusability with no significant decrease after 5 cycles. The employed catalysts were comprehensively characterized by X-ray diffraction (XRD), N₂-physisorption, transmission electron microscopy (TEM), H₂-TPR, NH₃ temperature-programmed desorption (NH₃-TPD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectrometry (ICP-OES), and CO pulse experiment. The results indicated that Ru/MOR had higher Ru dispersion and stronger metal–support interaction. Moreover, Ru/MOR exhibited greater specific surface area and larger pore size, enhancing the adsorption efficiency of the reactants.