Effect of Si content on the performance of direct synthesis of dimethyl ether over slurry CuZnAl catalyst prepared by complete liquid phase technology

The effect of Si content on the performance of slurry CuZnAl catalyst prepared by complete liquid phase technology for direct synthesis of dimethyl ether from syngas was investigated. Among them, catalyst with Si/Al ratio of 0.5 showed the best catalytic performance with the CO conversion of 63.31% and the dimethyl ether selectivity of 72.96%. The catalyst was stable after 480 h reaction. As revealed by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption and desorption characterizations, the introduction of Si promoted the dispersion of Cu species nanoparticles and led to increased specific surface area, which was beneficial for improving the CO conversion. Besides, temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) characterizations showed that an electronic interaction between Cu species and other components of the catalyst (especially, Si species) could inhibit the reduction of Cu species, resulting in the abundant Cu⁺ species on the catalyst surface. This was conducive to the synthesis of methanol and could effectively inhibit the formation of CO₂, which was a by-product of the water-gas shift reaction. Moreover, a large amount of Al species (AlOOH) was enriched on the SA0.5 catalyst surface, which might contribute to the dehydration of methanol to produce dimethyl ether. In conclusion, the synergetic catalysis of Cu⁺ and AlOOH in slurry CuZnAlSi system improved the catalytic activity and dimethyl ether selectivity.