60th Annual Report on Research 2015

The overall objective of this proposed work is to elucidate the electronic effect on palladium-based catalysts for the electro-oxidation of formate in alkaline media. During this grant, we have successfully begun to develop a fundamental understanding of this chemistry, and we have published two peer-reviewed manuscripts specifically related to this objective. We have also submitted two proposals to NSF chemical catalysis in 2013 and 2014, and the proposals were scored VG/G. We have revised and are re-submitting this proposal to a different program October 2015. This NSF proposal is very similar to the PRF-funded work, and it would represent a significant expansion of the PRF-funded work.

In addition, we have also expanded on the overall objective by making the important discovery that palladium-based bimetallic catalysts significantly promote the electrochemical oxidation rate of alcohols in alkaline media, particularly polyols that can be derived from biologically renewable sources. We have published two peer-reviewed manuscripts on this work, and I am working toward submitting a second proposal to a different program at NSF to determine the fundamental reason for this increase in oxidation rate. We know the electronic effect (present work) is a factor, but the polyol oxidation rate can be significantly increased as a result of other fundamental factors, which we would like to explore. In addition to our publications and submitted proposals, students have given presentations on this work in my group meetings, at department poster sessions, at Spring 2014 ACS, at Spring 2015 ACS, and at two workshops in Pullman, WA.

The first specific aim of this proposed work is to synthesize and characterize carbon supported palladium-based bimetallic nanoparticle catalysts using the metal adatoms Fe, Co, Ni, Cu, and Zn. Students have successfully used a technique in a beaker and synthesized at least one metal:metal ratio of each Pd-M catalyst. We initially found the most significant catalytic efficiency enhancement with Pd-Cu, so we have performed the majority of our work on this catalyst. We are now moving toward spending more time on Pd-Ni, finding that it exhibits significantly different behavior than Pd-Cu.

The second specific aim is to analyze the electrochemical behavior of each bimetallic catalyst. We have completed our work studying formate oxidation on the Pd-Cu catalyst and are beginning now to extend our efforts to the other metals and poly alcohol molecules, discovering that even more interesting behavior is observed on them.

The third, and most significant, specific aim is to correlate the enhanced oxidation rate of formate with evidence of the electronic effect on palladium. We have used X-ray Photoelectron Spectroscopy (XPS) to detect a d-band shift and binding energy shift induced by the strain effect and charge transfer effect between the palladium and first-row transition metal. We have found that Cu induces this electronic effect on Pd in a Pd87Cu13 catalyst such that the d-band center and binding energies shift sufficiently to speed the electrochemical oxidation rate on formate and ethanol. We have also found similar behavior in Pd-Ni. Thus we were successful in confirming that the electronic effect is present in two of the metals. In addition, we have found that these same catalysts promotes the electrochemical oxidation rate even more significantly on polyalcohols such as glycerol and ethylene glycol. This can be attributed to both the electronic effect and the bi-functional effect (whereby both Pd and M participate in the rate determining step). Our results confirm that the electronic effect is present with the polyols but more work must be done to determine how much is contributed from both effects.

This proposal is part of a collaboration that has developed with Drs. Su Ha and Louis Scudiero at Washington State University, where the XPS analysis is performed. In August 2014 and August 2015, I visited WSU for one week with two students each year from my research lab (Tom Copenhaver and Fabian Munoz in 2014; Omar Muneeb and Jose Estrada in 2015). Each PI and student gave an oral presentation. The PIs met for several hours each day to discuss our research and proposals, and the students met to perform and discuss research. This was an outstanding opportunity for me and my students; one of my students has decided to pursue a graduate education in chemistry as a result of this visit.

This grant funding has provided a great opportunity for me and my students to develop our research skills on high quality work. We have been able to dig much deeper into the fundamental role of the electronic effect on palladium-based catalysts. I have travelled with students to ACS and Pullman, WA, for outstanding opportunities to disseminate our work and meet with existing and potential collaborators. In addition, the funding for PI and student salary permitted us to spend a significant amount of time Summer 2014 and 2015 on this research project. Without the funding, we could not have devoted significant time during the summer.