SusChEM: Energies of Adsorbed Catalytic Intermediates on Transition Metal Surfaces: Experimental Benchmarks for Computational Catalysis Research

University Of Washington, Seattle WA

Investigators

Abstract

Catalysts are chemicals that provide more efficient and selective pathways for desirable chemical reactions. Transition metal catalysts are particularly useful in the production of bulk chemicals and fuels, and for cleaner fuel combustion and pollution cleanup. For these solid catalysts, metals at the catalyst surface bind the reacting chemicals with just the right strength (or "bond energy") to enable their chemical conversion to the desired products. Too tightly bound, and the product will not desorb but will remain attached to the catalyst surface. Too weakly bound and the reactant will not adsorb, and cannot react catalytically with it. Improving the energetics of such catalysts is essential for producing and using chemicals and fuels with higher energy efficiency and less pollution, as needed for sustainable living into the future. The key to improving the catalysts is to find materials whose surfaces bind the reacting chemicals with the optimum bond energies. In principle, this can be achieved by solving the equations of quantum mechanics (a branch of physics) with computers. Unfortunately, the math is very difficult, so mathematical approximations must be made for even the fastest computers to solve the equations in reasonable times. Experimental measurements of some of the bond energies are needed to compare to the computer results, to assess whether these approximations lead to incorrect bond energies. In this project, Dr. Charles T. Campbell is measuring bond energies for selected chemicals bound to transition metal surfaces, carefully chosen to enable development of new quantum mechanical methods for more accurately predicting such energies, and to improve the basic understanding of the catalyst's action. Improving the energy accuracy of such fast computations is transformative in the field of heterogeneous catalysis, enabling greater reliability in computer-based predictions of better catalyst materials. This research also provides strong interdisciplinary, research-integrated education for numerous young students, scientists and engineers, who get hands-on experience with state-of-the-art measurement instrumentation and its design. Dr. Campbell is involved in extensive outreach to the broader community, through his frequent public lectures, numerous editorships and advisory board memberships, and service to university and external science education initiatives. Late transition metal catalysts and electocatalysts are used in the production of bulk chemicals and fuels, for cleaner fuel combustion and for pollution cleanup. Improving such catalysts is essential for producing and using chemicals and fuels with higher energy efficiency and less pollution, as needed for sustainable living. With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Charles T. Campbell of the University of Washington is measuring the energetics of selected elementary chemical reactions occurring on late transition metal surfaces, carefully chosen to enable development of new theoretical methods for more accurately predicting such energies. This, in turn, improves the basic understanding of catalytic mechanisms, and facilitates the design of better catalysts. Dr. Campbell's calorimetric measurements, which cannot be performed with the same precision elsewhere in the world, are broadening the database of reliable experimental energies of adsorbed catalytic intermediates that can be used by theoreticians as benchmarks to guide development of computational methods with improved accuracy for calculating the energetics of chemical reactions at late transition metal surfaces. While density functional theory (DFT) has been extremely successful in catalysis research, prior results proved that the mean absolute errors in the energies of adsorbed intermediates from DFT exceeds 20 kJ/mol. The experimental database being developed here greatly facilitates ongoing efforts by the theoretical community to improve the energy accuracy of such fast computational methods, while also clarifying the energetic basis for structure-reactivity correlations in transition metal catalysis. These improvements are transformative for catalysis research, enabling greater reliability in computational prediction of reaction rates and mechanisms, and higher success rates in predicting better catalyst and electrocatalyst materials that are essential for sustainable living. This research also provides strong interdisciplinary, research-integrated education for numerous young science and engineering students and postdoctoral researchers, who get hands-on experience with state-of-the-art measurement instrumentation and its design. In addition to mentoring these young people, Dr. Campbell is involved in extensive outreach to the broader community, through his frequent public lectures, numerous editorships and advisory board memberships, and service to university and external science education initiatives.