(7fh) Structure-Function Correlations of Nanomaterials in Heterogeneous Catalysis

“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 operando 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 and operando 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 strained mixed Ru_xO_y structure.^[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.

Teaching Interests:

“Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime”

- Lao Tzu

My teaching philosophy has been heavily influenced by this Chinese proverb. I strongly believe that teaching is more than delivering knowledge; it is the teacher’s commitment to the society to raise a new generation able to surpass the “mountains” they may face in their lifetime. The general purpose of science and engineering education is to train independent and collaborative problem solvers. On one hand, it is critical for students to be able to gather, understand and utilize information independently because not only is it impractical to learn everything in class but more importantly, most innovative endeavors have no existing formula to follow. On the other hand, collaborative practice has increasingly been adopted as one of the fundamental mechanisms in the scientific community to tackle interdisciplinary challenges. I am also a candid believer of students’ interest being a key prerequisite for any successful science and engineering education. I have adhered to this philosophy throughout my entire career, and would like to see it’s fulfillment in making me a better researcher, teacher, and person. Therefore, inspiring interest, training independent learning ability and promoting collaborative practice are the three pillars of my teaching philosophy. I am confident that I can teach major course in an undergraduate chemical engineering curriculum. I very much look forward to the opportunity to teach and interact with students in Chemical Reaction Engineering, Kinetics, Material Sciences, Electron Microscopy and Interdisciplinary Methods in Heterogeneous Catalysis.

Reference

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

[2] W. Zheng, R. Schloegl, to be submitted.

[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.