Supported Ru based ammonia synthesis catalysts

Aslan, Mustafa Yasin
Ru/C type ammonia synthesis catalysts are known to be poisoned by hydrogen. In order to elucidate a mechanism for hydrogen poisoning, H2 adsorption and spillover on Ru based ammonia synthesis catalysts were investigated. Supported Ru catalysts and Na promoted Ru catalyst were prepared by incipient wetness impregnation of Ru(NO)(NO3)3 on SiO2, SBA-15, CNT and Vulcan supports. Dispersion value of the catalysts was determined via H2 chemisorption and Transmission Electron Microscopy (TEM) characterization techniques. Over SBA-15 support, the dispersion of the catalyst determined by two different characterization techniques were in agreement. On the other hand, over CNT and SiO2 supports dispersion measured by TEM characterization method was higher than H2 chemisorption method. H2 chemisorption measurements performed over extended periods of time were used to determine the spilled over hydrogen amounts over Ru/Vulcan and Na-Ru/Vulcan catalysts at 375 torr and 10 torr H2 pressure at room temperature. By using H2 uptake data measured for extended periods of 6 – 24 hours, diffusion coefficient of hydrogen species over Vulcan support was calculated assuming a point source diffusion mechanism. Coefficient of diffusion for Ru/Vulcan and Na-Ru/Vulcan was found as 1.39 x 10-14 cm2/sec and 1.23 x 10-14 cm2/sec, respectively at 375 torr. Similarly, at 10 torr, diffusion coefficients of Ru/Vulcan and Na-Ru/Vulcan catalysts were determined as 1.51 x 10-15 cm2/sec and 1.81 x 10-15 cm2/sec, respectively.


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In this study, the process economics of ammonia synthesis over Co3Mo3N was investigated by searching for an optimum feed stoichiometry. From ammonia synthesis rate measurements at atmospheric pressure and 400 °C over Co3Mo3N, it was found that the rate was independent of H2: N2 stoichiometry for stoichiometries above 0.5: 1. For H2: N2 stoichiometries below 0.5: 1, there was a linear dependency of ammonia synthesis rate on the H2: N2 stoichiometry. Static measurements of hydrogen adsorption isotherms at 25,...
Citation Formats
M. Y. Aslan, “Supported Ru based ammonia synthesis catalysts,” M.S. - Master of Science, Middle East Technical University, 2012.