X 18 B Group 11 promoters Ag and

Зарегистрируйтесь, чтобы просмотреть полный документ!

X 18 B Group 11 promoters Ag and Au facilitate Co reduction and boost Co metal site densities during Fischer-Tropsch synthesis G. Jacobs*, M. C. Ribeiro*, W. Ma*, S. Khalid**, B. H. Davis* *University of Kentucky Center for Applied Energy Research **Brookhaven National Laboratory Fischer-Tropsch synthesis (FT) is used to convert coal, natural gas, and biomassderived syngas – a mixture of CO and H 2 – to a distribution of hydrocarbons that can be upgraded to produce transportation fuels (e. g. , diesel and jet fuels) and chemicals (e. g. , lubricants and waxes). Alumina is often the support of choice for commercial slurry phase Fischer-Tropsch synthesis, due to its high attrition resistance and ability to stabilize small cobalt metal particles. However, due to the strong interaction between the support and cobalt oxides, catalyst activation, which involves reducing the Co 3 O 4 to Co 0 (surface Co 0 being the active site) via Co. O intermediate, can be a challenge. Expensive promoters like Pt are often added to promote reduction. A combination of in-house (e. g. , TPR and H 2 -chemisorption/pulse reoxidation) and synchrotron (e. g. , XANES and EXAFS) methods was employed to characterize the catalysts. A significant improvement in extent of reduction was observed by addition of Cu, Ag, and Au that, for some specific cases, translated to significantly higher Co 0 surface active site densities. Reactor testing using a slurry phase reactor confirmed a 75% increase in CO conversion with a negligible to slight decrease in C 1 selectivity with certain catalysts promoted by Au and Ag. The synchrotron measurements provided key information on oxidation state changes and local atomic structure in order to link the changes in catalyst structure with resulting improvements in performance. Normalized XANES spectra of references and cobalt catalysts after direct reduction of the calcined catalysts at 350 o. C in H 2, including (a) 15%Co/alumina; (b) 1. 63%Cu 15%Co/alumina, (c) 2. 76%Ag-15%Co/alumina; (d) 5. 05%Au 15%Co/alumina; (e) Co 0 foil; and (f) Co. O reference. Group 11 promoter addition significantly facilitates the reduction of Co. O species, and in the cases of Ag and Au, boosting Co 0 surface site densities, leading to higher CO conversion rates on a per gram catalyst basis. Jacobs, G. ; Ribeiro, M. C. ; Ma, W. ; Ji, Y. ; Khalid, S. ; Sumodjo, P. T. A. ; Davis, B. H. , “Group 11 (Cu, Ag, Au) promotion of 15%Co/Al 2 O 3 Fischer-Tropsch synthesis catalysts, ” Applied Catalysis A: General 361 (2009) 137 -151. Work performed on beamline X-18 b.

Скачать презентацию X 18 B Group 11 promoters Ag and

2235fccd44a1fd477f3f2bc1a513d572.ppt

Количество слайдов: 1