Nanotech 2011

Fundamental insights into Rh Nanoparticle Sites Responsible for CO Hydrogenation to C1 Hydrocarbons and C2 Oxygenates

N. Kapur, X. Hao, C. Sampara, J. Hyun, B. Shan, J.B. Nicholas, B. Davis, K. Cho
Nanostellar Inc, US

Keywords: advanced materials, catalysis, hydrogenation

Abstract:

Herein, we examine Rh surface defects as the active sites for syngas conversion with in- situ surface characterization, kinetic experimentation and microkinetic modeling. Infra- red spectroscopy and temperature programmed desorption performed with CO flow on Rh nanoparticles indicates the availability of two distinct Rh binding sites (surface defects and (111) facets). We also explore the possibility of Rh surface reconstruction giving rise to under-coordinated sites due to the presence of syngas and high temperature conditions by using X-ray absorption spectroscopy. Microkinetic description of the CO hydrogenation mechanism on Rh defect sites is used to simulate CO conversion, ethanol and methane selectivity trends as a function of temperature and pressure and compared against experimental turnover rates to determine rate limiting reactions and key reactivity descriptors. Our results indicate direct CO dissociation and methylene addition to CO as precursors for catalytic activity and C2 oxygenate formation respectively. A comprehensive understanding of the active sites participating in the CO scission, hydrogenation and C-C coupling reactions will aid Rational Catalyst Design to develop materials with tunable activity and desired product selectivity.
 

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