| In this thesis, the effects of adding different weight loadings of potassium to a Ru catalyst supported on gamma-Al2O3 were investigated. Comparisons were made between the activity of the unpromoted Ru-based catalyst and the potassium promoted Ru catalysts. NH3 conversion of 4 wt% Ru/12 wt% K/gamma-Al2O3 at 350°C was 70% as opposed to 60% for 4 wt% Ru/18 wt% K, or 30% for 4 wt% Ru/6 wt% K. The conversion of the unpromoted 4 wt% Ru catalyst was the lowest (∼10%) at 350°C. A correlation has been drawn between catalyst activity and the presence of crystalline phases resulting from potassium promotion. Promoting RuCl 3 with potassium on gamma-Al2O3 led to the formation of KCl and under certain conditions the formation of hollandite (i.e., KRu 4O8) whiskers occurred. The formation of KCl helps to sequester free Cl- ions that would otherwise have a detrimental impact on the catalyst activity. The 4 wt% Ru/12 wt% K/gamma-Al 2O3 and 4 wt% Ru/20 wt% K/gamma-Al2O3 catalysts containing hollandite whiskers showed higher NH3 conversion than the other catalysts tested with fewer or no hollandite whiskers. After exposure to H2 or NH3, hollandite whiskers were reduced to Ru° nanowires. This thesis does not confirm whether hollandite is active for NH3 decomposition. However, it does provide evidence that hollandite is a necessary precursor leading to an active Ru° phase. The morphologies and phases of the supported catalysts after exposure to H2 and NH3 were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The reduction products from pure hollandite crystals and the rate of hollandite reduction at different temperature levels were determined using the thermogravimetric analysis (TGA).;The reduction products of hollandite (i.e., KRu4O8) are KOH and Ru°. As expected, hollandite was reduced more rapidly in H 2 at higher temperatures. After exposure to reaction conditions, hollandite whiskers in the catalysts were reduced forming nanowires with KOH present within the area scanned using SEM. The nanowires were verified as polycrystalline Ru° using selected area electron diffraction (SAED). From the XRD analysis of 4 wt% Ru/10 wt% K/gamma-Al2O3 catalyst, the oxide phases (KRu4O8, K2RuO3, and RuO 2) present initially were completely reduced to Ru° after the catalyst was pretreated with H2 for an hour at 450°C. Therefore, a complete reduction of hollandite and other oxide phases occurred during the H 2 pretreatment step. The 4Ru/10K catalyst showed higher conversion after H2 pretreatment than that of the same catalyst without pretreatment. The conversion for the 4Ru/10K catalyst tested without H2 pretreatment performed no better than the unpromoted 4Ru based catalyst. This suggests that Ru° nanowires and particles are responsible for the higher conversion. In conclusion, hollandite serves as a precursor leading to an active Ru° phase existing in nanowires, but the activity of hollandite prior to reduction is unknown. The surfaces of Ru° nanowires appeared to exhibit nanopores ranging from 2 to 10 nm. It remains to be determined whether the presence of nanopores is responsible for enhancing the conversion. |
