Effect of nanostructured supports on catalytic methane decomposition

Abstract

Carbon deposition from catalytic methane decomposition has drawn increasing interest recently. Previously, we have found the carbon formation depends on the crystalline structure of the support, following the trend of Ni/CeO2 > Ni/CaO > Ni/MgO, because Ni supported on MgO is uniformly dispersed and can stabilize high-x CHx intermediates. We have also found that the addition of Pt can inhibit the carbon deposition on Co/Al2O3 because the alloying between Pt and Co results in the better dispersion of Co on the support. Furthermore, it was revealed that by judging the Ni/Mg molar ratio from 1 to 0.25 we could reduce the diameter of deposited carbon nanotubes from 20 to 12 nm, with substantially smaller production rate. All of these previous studies indicated that better dispersion of the supported metal would benefit the decreasing of carbon deposition. Here we present our recent investigation of the effect of support particle size on the carbon deposition. Three different types of 10 wt% Co/Al2O3 catalysts were prepared: Co on commercial Al2O3 (Cat 1), Co on sol-gel-processed Al2O3 (Cat 2), and sol-gel-made homogeneous Co-in-Al2O3 (Cat 3). TEM showed that the diameter of the Co3O4 particles in sol-gel Al2O3 is only around 6 nm, while it is 20-40 nm in the commercial catalyst. By using XRD and FTIR, Co was identified as crystalline Co3O4 in the as-prepared Cat 1 sample, CoAl2O4 in Cat 2, and amorphous Al2O3 in Cat 3, indicating the best dispersion in Cat 3. Methane CO2 reforming was studied on the three catalysts. Longer lifetime was measured for Cat 3 as compared to those on Cat 1 and Cat 2 (>20 h vs. 1 h). The support size effect is discussed.