NSF-BSF: Steering Selectivity in Aldol Reactions by Control of Relative Effective Reaction Rates in Porous Catalysts

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This project, funded under the National Science Foundation (NSF) and US-Israel Binational Science Foundation (BSF) collaborative opportunity NSF 17-520, focuses on the study of catalysis to make chemical processes more environmentally friendly by reducing chemical waste. The chemical transformation of interest is the aldol condensation, which results in a new bond between two carbon atoms. Aldol condensation is an essential reaction in many syntheses of bulk, fine, and specialty chemicals. This reaction shows promise for upgrading biomass-derived feedstocks to fuels or chemicals. The objective is to steer this chemical reaction to give the desired product without generating a multitude of side products. The approach is to develop new solid catalysts and, by varying their surface chemical composition and pore morphology, tune their chemical and physical properties for optimal performance. The new knowledge and fundamental understanding emerging from this collaborative work between the University of Massachusetts Amherst and the Technion-Israel Institute of Technology will serve to better direct aldol condensations and other similarly complex and pivotal chemical reactions. In addition, the project will contribute to U.S. competitiveness in chemical manufacturing of biorenewable products and will promote training of a diverse workforce skilled in biomass processing. Aldol reactions consist of two sequential steps, addition and subsequent dehydration. Cross aldol condensations, particularly those involving unsymmetrical ketones, can lead to a multitude of primary and secondary products. The central hypothesis of this project is that selectivity in aldol reactions, which is governed by relative effective reaction rates, can be tuned by tailoring the active surface sites and effectiveness factors. While theory on the influence of transport limitations on the selectivity in parallel and sequential reactions has been outlined long ago, there are few realizations of these concepts in complex liquid phase reactions. This research project rigorously tests the practical viability of these concepts by manipulating surface chemistry and pore structure of the catalysts. The main catalyst platform is layered double hydroxides, because they allow for a wide and independent variation of chemical and physical properties; that is, acid-base and pore characteristics can be tailored. Porous model materials serve to independently investigate transport limitations. Reactant complexity and reaction conditions are varied to ensure broad validity of the findings. The project benefits from complementary expertise and instrumental capability at the U.S. institution and at Technion in Israel. Student training will include visits of the partner laboratory and a subject-relevant graduate course. The participation of women in science is sought to be broadened through appropriate recruiting efforts and outreach activities targeting female high school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.