Pd Distribution Effect And Preparation Process In Macro-Porous ?-Al₂O₃ Support On CO Coupling Reaction

In this paper, the supported catalyst Pd/?-Al₂O₃ was prepared through the wet immersion method by using precursor impregnation liquid Pd?NO3?2 for the methyl nitrite?MN? carbonyl synthesis of dimethyl oxalic?DMO?. The prepared Pd/?-Al₂O₃ catalyst was evaluated in a gradient-less reactor. The objective is to optimize the processing conditions to improve the MN conversion and the DMO selectivity.The ?-alumina possessing an average pore size of 2.8 ?m was used. The uniform distribution and the egg-shelled distribution with a depth of 40?m were respectively prepared by controlling the p H of precursor impregnation solution at 1.67 and 12.25. Catalyst characterization results show that the palladium particle size is about 2³nm, which are highly dispersed state. It is shown that the uniform distribution generally has a higher reaction performance than the egg-shelled one at low Pd loading?<0.2wt %? conditions. Meanwhile, based on the single particle dynamics, Fick diffusion law and Fourier law for heat transfer, the diffusion kinetics model for the single particle catalyst was constructed. Numerical analysis simulates the concentration variation of components along the radial direction with the change of supports' pore size. It is concluded that, for the macro-porous ?-alumina, a uniform distribution of the active palladium leads to a higher catalyst utilization rate, while the egg-shell distribution palladium is recommended in the case of Knudsen Diffusion or configuration diffusion who possess a relatively high internal diffusion resistance, which means the order of magnitude of supports' pore size attains to 10 nm or much smaller.Besides, according to the experiences and literature review of Pd loading, reduction temperature, and impregnation methods, it is considered that the natural factor on the catalyst activity attributes to the dispersion and particle size of the active component in the support.