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Abstract: Although the conversion of oleaginous biomass to the fatty acid methyl esters (FAMEs) that constitute biodiesel is a mature technology, feedstock availability issues as well as challenges stemming from the high oxygen content of FAMEs have limited the widespread application of biodiesel. Consequently, attention has shifted to processes capable of catalytically deoxygenating oleaginous biomass to afford fuel-like hydrocarbons. Deoxygenation via decarboxylation/decarbonylation (deCO_x) represents a promising alternative to the hydrodeoxygenation (HDO) processes typically employed to achieve this transformation, as deCO_x does not necessitate the high pressures of hydrogen and the problematic sulfided catalysts required by HDO.

To date, the majority of deCO_x reports involve Pd or Pt catalysts, the cost of which may be prohibitive. However, Ni-based catalysts have been shown to be capable of affording comparable results to precious metal-based formulations [1]. Recently, we have observed that the promotion of Ni with other earth-abundant metals – such as Cu – leads to considerable improvements in activity, selectivity and resistance to coking [2]. Results of Temperature Programmed Reduction (TPR) and X-ray Photoelectron Spectroscopy (XPS) measurements suggest that these improvements can be attributed to the ability of the aforementioned metal promoters to improve the reducibility of Ni. This results in an increased amount of Ni⁰, which is believed to be the active phase in the deCO_x reaction.

Ni catalysts promoted in this manner afford remarkable results in the conversion of a wide variety of ­model, waste and/or highly unsaturated lipids – including tristearin, triolein, yellow grease, brown grease, hemp seed oil and algal FAMEs – to fuel-like hydrocarbons [3-6]. Indeed, using a fixed-bed reactor operated using industrially-relevant reaction conditions, close to quantitative yields of diesel-like hydrocarbons are obtained. In addition, as shown in Figure 1, a catalyst employed has displayed remarkable stability and recyclability in a run comprising two 100 h time on stream cycles [5].  

Mentoring has been identified as an effective tool not only for attracting and retaining students from groups traditionally underrepresented in STEM disciplines, but also for improving their academic performance. However, additional benefits could be obtained by housing mentoring initiatives in research centers as opposed to in traditional academic departments. Therefore, a mentoring initiative based at the ��ɫ��Ƶ Center for Applied Energy Research is striving to test this hypothesis [7]. Recently, providing the participating students access to international research opportunities has become a focus of this mentoring program.

References

[1] T. Morgan, D. Grubb, E. Santillan-Jimenez, M. Crocker. Top. Catal., 2010, 53, 820.

[2] R. Loe, E. Santillan-Jimenez, A.F. Lee, M. Crocker, et al. Appl. Catal. B: Environ., 2016, 191, 147.

[3] E. Santillan-Jimenez, R. Pace, T. Morgan, C. McKelphin, M. Crocker, et al. Fuel, 2016, 180, 668.

[4] E. Santillan-Jimenez, R. Loe, M. Garrett, T. Morgan, M. Crocker. Catal. Today, 2018, 302, 261.

[5] R. Loe, M. Maier, M. Abdallah, R. Pace, E. Santillan-Jimenez, M. Crocker, et al. Catalysts, 2019, 9, 123.

[6] R. Loe, K. Huff, M. Walli, R. Pace, Y. Song, E. Santillan-Jimenez, M. Crocker, et al. Catalysts (IN PRESS).

[7] E. Santillan-Jimenez, W. Henderson. 124^th American Society for Engineering Education Annual Conference Proceedings, 2017, Conference Paper ID #17681.

Abstract:

The interface between two fluids is not only important for defining reactivity of dislike materials, but is also applicable for the preparation of stable higher order structures. Recently, the Pentzer lab developed 2D carbon-based nanosheets that assemble at different fluid-fluid interfaces including oil-water, oil-oil, and ionic liquid-water and demonstrated the use of these Pickering emulsions as templates for the preparation of higher order hybrid structures. Graphene oxide (GO) and its functionalized analogues are used as the 2D particle surfactant, and are especially attractive given they have properties distinct and complimentary to the more commonly studied spherical and rod-like counterparts, and because these nanosheets are multifunctional (e.g., antimicrobial, good gas barriers, precursor to electrically conductive nanosheets, etc.).  Recent advances from the Pentzer lab will be reported, including preparation of Janus nanosheets, water-sensitive reactions in oil-in-oil emulsions, GO capsules filled with ionic liquid for supercapacitor electrodes, GO capsules for compartmentalization of phase change materials, and GO coatings for 3D printable polymers to prepare conductive structures. This work makes use of fundamental organic chemistry reactions and thus gives access to unique structures and assemblies of interest for a broad range of applications in a scalable fashion.

Abstract:

Dye-sensitized solar cells have received considerable attention since the advent of mesoporous TiO₂ thin films described by Grätzel and O’Regan [1].  The UNC-Energy Frontier Research Center (EFRC) is interested in these materials for the application in dye-sensitized photoelectrosynthesis cells (DSPECs) that produce fuels that can be used when the sun has set [2]. Recently a kinetic pathway for an unwanted charge recombination reaction between the electrons injected into TiO₂ and an oxidized dye was identified. [2,3] This was accomplished by the rational design of molecules where the distance and driving force were held near parity and only a bridge unit was varied between a xylyl- and a phenyl- thiophene bridge. Spectroscopic analysis revealed that electronic coupling through the phenyl bridge was a factor of ten greater than through the xylyl bridge and this lowered the free energy for electron transfer. [3,4] Dye-sensitization was also utilized to generate a high valent metal oxo species implicated in water oxidation [5] and I-I bonds in terionic iodide complexes.[6]  Background on dye-sensitization and solar energy conversion will be provided that gives context for these most recent advances and suggests new directions for future research and applications.

References:

[1] “A Low- Cost, High Efficiency Solar Cell Based on the Dye- Sensitized Colloidal TiO₂ �󾱱�����” O’Regan, B.; Grätzel, M. Nature 1991, 353, 737.

[2] “Finding the Way to Solar Fuels with Dye Sensitized Photoelectrosynthesis Cells” Brennaman, M.K.; Gish, M.K.; Alibabaei, L.; Dares, C.J.; Dillon, R.J.; Ashford, D.L.; House, R.L.; Meyer, G.J.; Papanikolas, J.M.; Meyer, T.J. J. Am. Chem. Soc. 2016, 138, 13085-13102.

[3] “A Kinetic Pathway for Interfacial Electron Transfer from a Semiconductor to a Molecule” Hu. K.; Blair, A.D.; Piechota, E.J.; Schauer, P.A.; Sampaio, R.N.; Parlane, F.; Meyer, G.J.; Berlinguette, C.P. Nature Chem. 2016, 8, 853-859.

[4] “Kinetics Teach That Equilibrium Constants Shift Toward Unity with Increased Electronic Coupling” Sampaio, R.N.; Piechota, E.J.; Troian-Gautier, L.; Maurer, A.B.; Berlinguette, C.P., Meyer, G.J. Proc. Nat. Acad. Sci. USA 2018, 115, 7248-7253. 

[5] “A High Valent Metal Oxo Species Produced by Photoinduced One Electron, Two Proton Transfer Reactivity” Hu, K.; Sampaio, R.N.; Tamaki, Y.; Marquard, S.; Meyer, T.J.; Meyer, G.J. Inorg. Chem. 2018, 57, 486-494.

[6] “A Ter-Ionic Complex that Forms a Bond Upon Visible Light Absorption” Wehlin, S.A.M.; Troian-Gautier, L.; Sampaio, R.N.; Marcélis, L.; Meyer, G.J. J. Am. Chem. Soc. 2018, 140, 7799–7802.

Zirconium in the Spotlight: New Pathways to Photoluminescent Molecules

Carsten Milsmann

C. Eugene Bennett Department of ��ɫ��Ƶ, West Virginia University

The efficient utilization of sunlight as a carbon-neutral, renewable energy source remains a challenge for scientists across many disciplines. The enormous scope of solar energy conversion on a global scale requires the development of photoactive materials from readily available and economically viable resources. Photoluminescent complexes based on earth-abundant early transition metals or main group elements present an attractive low-cost, low-toxicity alternative to precious metal photosensitizers commonly used in photochemical processes and solar energy conversion. However, the fundamentally different electronic structures of these elements requires the development of new approaches to light-induced charge separation and electron transfer.

This presentation will highlight the Milsmann group’s efforts to establish design principles for the generation of luminescent early transition metal complexes that can undergo photo-induced single electron transfer (SET) reactions upon irradiation with visible light. A particular focus will be on phosphorescent zirconium complexes that exhibit exceptionally long triplet excited state lifetimes. Our results show that these complexes can not only replace precious metal photosensitizers in photoredox catalytic reactions, but may exhibit optical properties that complement those of traditional late metal compounds. In addition, research towards the development of metal-free phosphorescent molecules based on silicon will be discussed.

Abstract:

The structure of graphene oxide (G-O) is still a challenging topic for developing useful and novel applications, where a compatibility, affinity or even covalent linkage is required at the interface. There is still a no consensus about the essential details, especially relating to the epoxy groups as main complexes in the basal plane, as well as the simultaneous presence of G-O sheets and oxidative debris (OD), with large difference in their oxygen content between both entities. The present seminar  deeps on this topic, through the characterization the base-washed G-O (bwGO) sheets, the OD and the humic fraction of the OD obtained by base digestion, when the parent G-O was previously dried or not, and previously sonicated or not. It was found that the presence of lactols at graphene edges as the dominant surface complexes agrees with all the characterization techniques, and also explains the high decrease of oxygen surface coverage in bwGO, where no carboxylic group removal was observed. These findings suggest that the Hummers-Offeman reaction produces a chemical scissor-effect during the water/hydrogen peroxide quenching step, yielding a broad size distribution of G-O sheets, with little in-plane oxidation, and the vast majority of edges being oxidized to form 7-ring lactol-type heterocyclic functionalities. Therefore, OD consists essentially of the very low sheet-size fractions, highly oxidized poly aromatic hydrocarbons, with a very high oxygen:carbon ratio due to the very high edge to weight ratio.