(6fl) Exploring Structure-Function Correlations of Nanomaterials in Energy Conversion and Storage

“And yet it is only by studying function that we can understand function, so that the kinetic aspect must be allowed to retain its place and assigned its part in the unravelling of the great mystery” – C. N. Hinshelwood, 1947

Catalysis is the science and technology of influencing the rates of chemical reactions, which are at the core of chemical industry. Practical success of catalysis needs the interdisciplinary intersection of chemistry, chemical engineering, and material science. My research interests lie on understanding the mechanism of chemical reactions and the role of catalysts under reaction conditions in order to transform qualitative observations and knowledge into predictive science.

In heterogeneous catalysis, under reaction conditions, active centers produce products. The presence of active centers depends on the local geometry of a catalyst particle, which can be varied by tuning the interactions between catalyst particle and the support. As a first of its kind demonstration of this concept, in my Ph.D. work, the ruthenium-carbon interactions were varied by depositing Ru nanoparticles on carbons with different local geometry and functionalities. Using atomic level TEM analysis, we found that the local disorder of the support induces local disorder to the Ru particle^[1] and influences catalysis as confirmed through the direct observation of the reaction intermediate (adsorbed dinitrogen) using in situ XPS over Ru/C catalyst operating at 400 °C and 0.5 mbar ammonia.^[2]

Identification of active centers requires interdisciplinary characterization techniques. For instance, the high H₂ production from ammonia over Mo₂C was due to the prevalence of highly energetic sites (twin-boundaries, stacking faults, steps and defects) which were confirmed with pre- and post TEM and EELS analysis.^[3] Similarly, in my postdoctoral work on biomass conversion, by combining a series of characterizations of XPS, ex/in situ EXAFS and TEM along with reactivity studies, we have discovered that the high yield of 2,5-dimethylfuran from 5-hydroxymethylfurfural benefits from dual functionality catalytic centers of Ru and RuO₂.^[4,5],

The knowledge gained from realizing the active centers can lead to optimized catalysts. In a first instance, we have modified iron catalysts by alloying Co or Ni leading to enhanced activity and stability for ammonia decomposition.^[6]Furthermore, we have developed a novel route to produce nanosized early transition metal carbide particles embedded in carbon, which show an improvement of ammonia cracking activity and a promotion effect in PEM fuel cells.

Reference

[1] W. Zheng, et al, ChemSusChem, 2010, 3, 226-230.

[2] W. Zheng, R. Schloegl, in preparation.

[3] W. Zheng, R. Schloegl, et al, J. Am. Chem. Soc, 2013, 135, 3458-3464.

[4] J. Jae, W. Zheng, R. Lobo, D. Vlachos, ChemSusChem, 2013, 6, 1158-1162.

[5] J. Jae, W. Zheng, A. Karim, R. Lobo, D. Vlachos, ChemCatChem, 2014, 6, 848-856.

[6] J. Zhang, J. Mueller, W. Zheng, et al, Nano Lett, 2008, 8, 2738-2743.