424215 Photocatalytically Enhanced Synthesis of Ammonia

Tuesday, November 10, 2015: 1:10 PM
355A (Salt Palace Convention Center)
Pradeep Krishnakumar, Xiaoyin Chen and Johannes W. Schwank, Chemical Engineering, University of Michigan, Ann Arbor, MI

Ammonia has been credited as being the breakthrough discovery of the 20th century as it is used in arguably two of the most important sectors – agriculture and defense. Hence it is imperative that it is produced in an environmentally-friendly and energy-efficient manner. As is known, to produce ammonia, nitrogen and hydrogen are required. The main issue regarding the commercial synthesis of ammonia is the hydrogen source. For this process, hydrogen is generally obtained from methane reforming. This makes the synthesis process extremely energy intensive while also releasing large quantities of CO2 gas into the atmosphere. One solution to this issue is photocatalytic water splitting that can in principle produce hydrogen in a much more environmentally friendly and energy efficient manner. But, photocatalysts that have been tried are not efficient enough to pursue such an idea. Noble metals such as ruthenium have been proposed to be active for photocatalytic ammonia synthesis. So, a potential solution could be that photocatalytic water splitting catalysts such as titania could be doped with noble metals to photocatalytically produce ammonia [1], thereby producing “carbon-free ammonia”. In our research, our endeavor is to find out the optimal conditions and obtain the best catalyst under which maximum ammonia can be synthesized photocatalytically using a flow reactor system. Recent work has shown that it is possible to photocatalytically enhance thermocatalytic reactions up to a temperature regime of about 200 to 300 °C [2].  Here,  we are exploring to what extent it is possible to photocatalytically enhance the dissociative adsorption of nitrogen while simultaneously generating active hydrogen species via photocatalytic water splitting in the gas phase at elevated temperatures, and produce ammonia directly from water vapor and nitrogen.

[1] K. Ranjit, T. Varadarajan and B. Viswanathan, "Photocatalytic reduction of dinitrogen to ammonia over noble-metal-loaded TiO2," Journal of Photochemistry and Photobiology A: Chemistry, vol. 96, pp. 181-185, 1996.

[2] T. A. Westrich, K. A. Dahlberg, M. Kaviany, J.W. Schwank, Journal of Physical Chemicstry C, vol. 115, pp.16537 – 16543, 2011.

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