ISSN:
1089-7550
Quelle:
AIP Digital Archive
Thema:
Physik
Notizen:
The Co-ZSM-5 and Co-ThO2-ZSM-5 catalysts are a particularly promising group of bifunctional zeolite catalysts used for the conversion of synthesis gas to gasoline-range hydrocarbons. Catalytic properties of these materials, such as activity and selectivity, depend upon the amount of the cobalt on the medium-pore zeolite ZSM-5, as well as upon the presence of promoters such as ThO2. These studies were undertaken to ascertain the effect of thoria upon the magnetic and structural nature of these catalysts. Zero-field nuclear magnetic resonance measurements have been made on a series of zeolite cobalt and cobalt-thoria catalysts with three different concentrations of Co (3, 6, and 9 wt. %). The catalysts were prepared by making physical admixtures of precipitated cobalt, or cobalt-thoria, and ZSM-5. The amount of thoria introduced ranged from 0.5 to 1.5 wt. %. After reduction of the catalyst samples, the normal metallic cobalt resonance line at 213.0 MHz (fcc) and the fault lines at 215.5 and 218.6 MHz were observed. In the unpromoted catalysts, a line at 210.7 MHz, which is lower than the fcc line frequency, and another line at 221.6 MHz, which is higher than the hcp line frequency, were observed. When the promoter thoria was added, there was a systematic absence of the hcp line in the unused catalyst. Previous catalytic tests had shown that small amounts of the promoter thoria (0.4 wt. %) significantly increase the liquid hydrocarbon yields. The change in catalytic behavior can be related to the changes in crystallite species and crystallite size.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.338421
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