Guard-bed catalyst: Impact of textural properties on catalyst stability and deactivation rate

The hydrodemetallization (HDM) activity and the stability of FeMo supported catalysts have been investigated during the hydroprocessing of heavy crude oil. The prototype FeMo catalysts were developed in this study as guard-bed catalysts. Such type of front catalyst is frequently used in complex hydrotreatment to protect the more vulnerable subsequent catalysts. Various prototype supports were synthesized in this study to produce different textural properties. Such textural properties were generated and optimized by using different support compositions (0−75 wt.% activated carbon in alumina) and following a certain support pretreatment methodology for pore expansion. Both the support composition and the pretreatment methodology have significantly contributed in developing an optimized HDM catalyst with a large pore volume and a distinctive bimodal pore structure. The large pore volume substantially improved the metal retention capacity, while the bimodal pore structure remarkably reduced the diffusion limitation, allowing the large hydrocarbon molecules (i.e., asphaltene) to reach the inner catalytic sites to enhance their conversion rates. The presence of carbon in the catalyst support, even after calcination, considerably reduced coke and metal depositions on pore-mouths and catalytic sites. The textural and the mechanical properties of support indicate that the optimum composition is attained when the carbon-alumina ratio is 1:1 (50/50 wt.%). The role of textual properties on catalyst stability was investigated by comparing fresh and spent catalysts. The characterization of spent catalysts indicates that the bimodal type of pore has stable performance with time-on-stream (TOS).