Effect of reduction temperature on formation and evolution of Ni/Al2O3 Catalysts for hydrogenation of dimethyl terephthalate to dimethyl 1,4-Cyclohexanedicarboxylate

Abstract

The nickel-aluminum composite oxide was synthesized via the co-precipitation and roasting method, and then we explored the profound effect of reduction temperature during activation on formation and evolution of the Ni/Al₂O₃ catalysts. Hereon, the hydrogenation of dimethyl terephthalate (DMT) to dimethyl 1,4-cyclohexanedicarboxylate (DMCD) was a probe reaction for the investigation into the structure–activity relationship of the Ni/Al₂O₃ catalyst. This study leveraged techniques such as TEM, H₂-TPR, XPS, H₂-TPD to examine the impact of reduction temperature on the catalyst’s structure and hydrogenation capabilities. The findings demonstrated that as the reduction temperature increased, so did the reduction degree of Ni²⁺ in the catalyst and the H₂ adsorption sites. However, excessively high reduction temperatures can lead to the sintering of the Ni⁰ particles, thereby increasing grain size, and the optimal reduction temperature was determined to be 550 °C. Smaller grain sizes of the Ni⁰ particle were particularly suitable for saturation hydrogenation of benzene ring. A DMT conversion of 100% and a DMCD selectivity of 91.3% were obtained over the optimized Ni₂Al₁-550 catalyst under the moderate conditions of 150 °C and 5 MPa.

Graphical abstract