Douglas M. Ruthven: In Memoriam of a Great Scholar and a Caring Friend

In September 2021, Professor Douglas Morris Ruthven, one of the pioneers of sorption research, passed away completely unexpectedly. The many research areas he has enriched with his contributions include, in particular, the field of diffusion, i.e., the random movement of guest diffusion in nanoporous materials. When NMR diffusometry was first used to study this phenomenon almost half a century ago, discrepancies of up to several orders of magnitude were revealed compared to the values so far generally accepted. Since then, the study of diffusion in nanoporous materials has been a hot topic in sorption research. The essay reports the great merits Doug Ruthven has earned in his life's work in this field. His activities include the refinement of existing and the development of novel measuring techniques just as their application or revealing the governing processes of mass transfer in a given nanoporous host‐guest system. The essay is, above all, a personal thank you from the author to Professor Ruthven for whom initial discrepancies in research results were not cause for quarrels and arguing but for a lifelong friendship. The article is a grateful review by the author of the many years of amicable collaboration with Prof. Dr. Douglas Morris Ruthven, in recognition of his many activities and his influence on the development of science, notably in the utilization and implementation of adsorption and diffusion in chemical technology and engineering.