Aart Kleijn focuses on the rapidly expanding field of sustainable chemistry and energy. The motivation for this work is the issue of climate change, the finite resources of fossil fuels and the political availability of fuels for energy supply. Many processes in chemistry and sustainable energy take place on the outside of and not inside materials, which necessitates special methods of investigation. The aforementioned processes are, for example, catalytic agents (which accelerate chemical reactions in the desired direction), converters of solar energy into chemical products, and energy storage media. Kleijn will be involved in the research in this field taking place at the UvA. He also heads a research programme at the The Foundation for Fundamental Research on Matter (FOM) for Plasma Physics Rijnhuizen.
Kleijn started his career at the FOM Institute AMOLF, where he worked from 1972-1999, with the exception of a short break to work for IBM in the United States. He was leader of two scientific departments at AMOLF. Kleijn was also professor by special appointment of Physics at the University of Amsterdam from 1989-1999. Since 1999, he has been professor of Chemistry at Leiden University. From 2003 to mid-2010, he was also director of the FOM Institute for Plasma Physics Rijnhuizen in Nieuwegein. He is currently director of the Van 't Hoff Institute for Molecular Sciences at the Faculty of Science. Kleijn has approximately 270 scientific publications to his name (spelled as Kleyn) and has held many positions within the national and international scientific community.