Solid-state 13C NMR analysis of regenerated and coked catalyst under dry and wet hydrotreatment

This study evaluates the efficiency of non-oxidative regeneration strategies for removing coke deposits from spent catalysts. Solid-state nuclear magnetic resonance and Fourier-transform infrared spectroscopy were used to characterize the structural and compositional properties of the coke. A two-step regeneration process combining accelerated solvent extraction (ASE) and hydrotreatment (HT) was applied at pilot scale. The aliphatic carbon content of the coke decreased from 39% in untreated samples to 17% after ASE and further to 3% following wet HT. Dry HT, involving heated hydrogen under pressure, promoted the formation of light hydrocarbons such as methane and ethane by disrupting carbon–catalyst bonds. Wet HT refers to utilizing a mixture of hydrogen and hydrogen sulfide gas under high-temperature and pressure, and dry and wet HT methods removed substantial amounts of coke, while Dry HT proved remarkably effective, eliminating over 72% of the deposited coke. However, HT-severe conditions (HT-S1) increased coke aromaticity. These findings provide practical insights into the development of non-oxidative regeneration protocols for spent refinery catalysts, thereby minimizing catalyst degradation while enhancing coke removal efficiency.