Mass transfer during impregnation controls metal accessibility and performance in granular Fe-Mo HDS catalysts.

This study theoretically and experimentally examines the influence of pore size in hydrodesulfurization (HDS) catalyst supports on the mass transfer resistance during the impregnation of active metals into activated carbon. To this end, a catalyst is synthesized by loading an Fe-Mo combination onto both synthetic and commercial mesoporous carbons, in both powder and granular forms. Various analyses, including XRD, FTIR, BET, TPD, TPR, FESEM, EDX, and crash strength tests, are used to determine the characteristics of synthetic catalysts. Followingly, the catalytic performance of the catalysts for removing sulfur-bearing species from naphtha is investigated Finally, the concentration distribution and diffusion coefficients of the active metals within the powder and granular supports were determined using an analytical–numerical approach. The results indicated that when the catalyst is impregnated onto a granular support rather than a powder form, its catalytic performance improves. This improvement occurs even though the dispersion of active metal is reduced. This enhancement is attributed to a higher percentage of accessible active metal on the surface. However, in the case of industrial granular activated carbon with small pore sizes (approximately 2.6 nm), increased pore blockage and agglomeration of active metal occur, leading to reduced metal dispersion and a decline in catalytic performance. Also, Deff Mo and Deff Fe are equal to 4.41*10− 11 m2/s and 5.27*10− 11 m2/s, respectively. The results of the catalyst performance and modeling indicate that the impregnation of active metals after granulation causes more access of the reactants to the active metals and ultimately increases the performance of the catalyst.