Ultradeep adsorption - Desulfurization of gasoline with Ni/Al-SiO ₂ material catalytically facilitated by ethanol

Adsorptive desulfurization of low-sulfur (22 ppmw) gasoline on solids in a liquid-full (no hydrogen) fixed bed was conducted at 503 K. Addition of 3 wt % ethanol to gasoline increased significantly the adsorption rate of sulfur-containing hydrocarbons on Ni/Al-SiO₂ and its sulfur capacity, leading to <0.5 ppmw residual sulfur with a sulfur capacity of 2 wt % (mass of sulfur per mass of sorbent). Three potential routes for improving desulfurization performance of Ni sorbent in the presence of ethanol and its decomposition products containing CO and hydrogen were considered: (i) formation of nickel carbide (Ni₃C) phase with reactivity toward S-organic compounds higher than that of metallic nickel, (ii) reduction of carbon deposits in the presence of hydrogen, and (iii) formation of nickel sulfide nanoparticles in the presence of H₂/H₂S vs adsorbed sulfur/sulfur organics that block the surface of metallic nickel in the absence of EtOH (hydrogen). Catalyst characterization data (N₂ adsorption, XRD, EDX, HRTEM, FTIR, XPS, AES depth profile analysis) indicated that the effect of ethanol on the desulfurization performance was a result of reduction of coke deposition and changing the sulfur uptake mode from adsorption to reactive adsorption with the formation of bulk nickel sulfide phases Ni ₃S₂ and Ni₃S₄. This is facilitated by hydrogen produced from the catalytic decomposition of ethanol that participates in the desulfurization of S-organics and in the formation of nickel sulfide phases.