Effect of nanostructured supports on catalytic methane decomposition

Abstract

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/CeO 2 > Ni/CaO > Ni/MgO, because Ni supported on MgO is uniformly dispersed and can stabilize high-x CH x intermediates. We have also found that the addition of Pt can inhibit the carbon deposition on Co/Al 2 O 3 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/Al 2 O 3 catalysts were prepared: Co on commercial Al 2 O 3 (Cat 1), Co on sol-gel-processed Al 2 O 3 (Cat 2), and sol-gel-made homogeneous Co-in-Al 2 O 3 (Cat 3). TEM showed that the diameter of the Co 3 O 4 particles in sol-gel Al 2 O 3 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 Co 3 O 4 in the as-prepared Cat 1 sample, CoAl 2 O 4 in Cat 2, and amorphous Al 2 O 3 in Cat 3, indicating the best dispersion in Cat 3. Methane CO 2 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.