New research shows promise for hydrogenating carbon dioxide as liquid fuel
Experimental and chemical theorists with the Department of Chemistry have collaborated on research for hydrogenating carbon dioxide, which could reduce CO2 emissions and recycle CO2 back to liquid fuel. This work, “A Bimetallic Nickel-Gallium Complex Catalyzes CO2 Hydrogenation via the Intermediacy of an Anionic d10 Nickel Hydride,” was published in the Journal of the American Chemical Society.
A bimetallic nickel-gallium catalyst converts CO2 and H2 into formate with high efficiency. The capture of a reactive intermediate, an anionic nickel hydride, is also notable because this is the first anionic nickel hydride to be bottled and crystallized. The hydride donor strength was also found to be as high as the most reactive precious metal hydrides. The reaction between CO2 and H2 to produce formic acid is important because formic acid is an industrial chemical, while CO2 is an abundant and underutilized feedstock. The reaction is also the first step in recycling CO2 back to liquid fuels. The neat reactivity of this nickel catalyst arises from its interaction with gallium because no catalysis is observed for the single nickel analogue. Next, researchers seek to understand the mechanism in detail for improving later generations of catalysts, and to extend the strategy of using Lewis acids like gallium to promote base metal reactivity in other catalytic applications.
The paper abstract reads: “Large-scale CO2 hydrogenation could offer a renewable stream of industrially important C1 chemicals while reducing CO2 emissions. Critical to this opportunity is the requirement for inexpensive catalysts based on earth-abundant metals instead of precious metals. We report a nickel-gallium complex featuring a Ni(0)→Ga(III) bond that shows remarkable catalytic activity for hydrogenating CO2 to formate at ambient temperature (3150 turnovers, initial rate = 9700 h−1), compared with prior homogeneous nickel catalysts. The Lewis acidic Ga(III) ion plays a pivotal role by stabilizing reactive catalytic intermediates, including a rare anionic d10 Ni hydride. The structure of this reactive intermediate shows a terminal Ni−H, for which the hydride donor strength rivals those of precious metal-hydrides. The combined experimental and computational results show that modulating a transition metal center via a direct interaction with a Lewis acidic support can be a powerful strategy for promoting new reactivity paradigms in base-metal catalysis.”
The experimental work was carried out by graduate students Ryan Cammarota and Matt Vollmer in the group of Professor Connie Lu, and the theoretical calculations were conducted by post-doctoral associates Jing Xie, Ph.D. and Jingyun Ye, Ph.D., in the group of Professor Laura Gagliardi. This work is also a collaboration with scientists from the Pacific Northwest National Laboratory (PNNL), including Aaron Appel, Ph.D., Samantha Burgess, Ph.D., and John Linehan, Ph.D. With a Department of Energy Office of Science Graduate Student Research award, Cammarota worked with the PNNL researchers for five months.
The work was supported by the U.S. Department of Energy, Office of Science Graduate Student Research award to Cammarota, Office of Basic Energy Sciences award DE-SC0012702 (Inorganometallic Catalyst Design Center) and by the National Science Foundation (award CHE-1665010 and Graduate Research fellowship to Vollmer).