(132f) Metal Organic Framework Supported Molybdenum Carbide Sorbents for Sulfur Removal

New emissions restrictions limit the sulfur content in transportation fuels.  Sulfur in these fuels not only leads to SO_xemissions, but severely deactivates most catalysts including those used for automotive emissions control and in fuel cells. Sulfur levels need to be reduced to less than 1 ppm to protect these catalysts. Compared to traditional hydrodesulfurization technologies operated at high temperature and high hydrogen partial pressure, selective adsorption of organosulfur compounds directly from the liquid fuel is very attractive strategy for desulfurization due to its low energy requirements (ambient operation conditions) and low operation costs (no hydrogen consumption).

In this paper we describe the synthesis and performance characteristics of a new type of sorbent consisting of early transition metal carbide domains dispersed onto very high surface area metal organic framework (MOF) supports. A wet impregnation method was used to produce these sorbents. The resulting materials were characterized using x-ray diffraction, sorption analysis, elemental analysis, and electron microscopy. Surface areas for the sorbents were greater than 2000 m²/g or more than 70% of the surface area of the fresh MOF-5 support, and Mo loadings were as high as 10 wt%. The incorporation of MoC_x domains increased the adsorption capacities as shown in Table 1. The liquid feed contained organosulfur compounds including thiophene, dibenzothiophene, and/or 4, 6-dimethyl dibenzothiophene, in iso-octane or benzene solvents.

Total and breakthrough dibenzothiophene adsorption capacities for a feed containing 35 ppmw_S ranged up to 2.5 and 0.8 mgS/g_sorbent, respectively. These values are comparable to or superior to those reported for other types of sorbents including those based on zeolite and transition metal oxide supports. The results indicate that functionalized MOFs are promising adsorbents for the organosulfur compounds typically found in transportation fuels.

Table 1. Adsorption results for MOF-5 and MoC_x/MOF5 sorbents at room temperature.

*Corresponding author: Levi T. Thompson: ltt@umich.edu