Experimental Study on the Deactivation Behavior of NiMo/γ-Al2O3 Catalyst during the Hydrogenation of Methyl Acrylate

It is of great significance to determine the deactivation behavior for the development of highly efficient and stable catalysts. In this work, the deactivation and regeneration experiments were investigated for NiMo/γ-Al₂O₃ catalysts during the hydrogenation of methyl acrylate at 80 °C, 1 MPa H₂, n(H₂)/n(l) = 10, and WHSV = 1 h^–1. Multiple characterization techniques, including XRD, UV–vis DRS, H₂-TPR, XPS, TEM, and TG, were employed for the analysis of deactivated and regenerated catalysts. The fresh catalysts exhibited good catalytic hydrogenation performance with a 99.7% yield of methyl propionate and 1002 h time-on-stream stability; however, the catalytic durability after the first and second regeneration is remarkably decreased to 600 and 299 h. The detailed analysis results demonstrated that the first-stage deactivation of the catalyst was attributed to the deposition of carbonaceous compounds on catalyst surface during the hydrogenation process. While the second- and third-stage deactivation should be caused by carbonaceous accumulation, formation of NiAl₂O₄ through strong interaction between the Ni species and Al₂O₃ support, and sintering of active component particles, which may be due to the loss of molybdenum. Specifically, the catalyst deactivation derived from carbon deposition can be recovered under thermal treatment at 450 °C, but NiAl₂O₄ generation and active component aggregation are irreversible.