Old Questions, New Paradigms: Tuning Nanocatalytic Reactivity and Selectivity*

Identification and tuning the factors governing reactivity and selectivity have been central productive challenges in catalysis. Attempts were made to uncover organizing concepts, such as the Sabatier principle in the form of volcano plots, seeking correlations between characteristic properties through use of catalytic descriptors, obtained, almost exclusively, from surface science studies of extended catalytic systems. The advent of nanocatalysis brought key assumptions of the above approaches under scrutiny, and critical assessments of the adequacy of the above-noted framework – via systematic theoretical and experimental studies of reactivity, spectroscopy, and microscopic reaction pathways of size-selected supported nanocatalysts and trapped gas-phase clusters – resulted in a paradigm shift. This led to selection of “catalytic tuning knobs” appropriate for the nanoscale, including: non-crystallographic nanocluster structures and their isomers, nanocluster dynamic fluxionality, enhanced nanocluster-support interactions, local work-function and nanocluster charging dependencies on the support-film composition, nanoscale thickness and underlying metal (i.e. a-silica on Pt vs Mo), and atom-by-atom variation of the atomic coordination and the nanocatalyst discrete electronic structure, requiring statistical distribution analysis. Here, size-specific catalytic tuning is illustrated in: structure-sensitive ethylene hydrogenation catalyzed by supported Pt_n (8 < n < 20) clusters [1]; CO oxidation catalyzed by supported gold Au_n (7 < n < 20) [2]; selective methane activation by trapped small gas-phase gold clusters, and temperature-tunable cycles of gold-catalyzed methane conversion to ethylene or formaldehyde [3].
[1] Nat. Commun. 10389 (2016); ACS Catal. 7, 6738 (2017) [2] J. Phys. Chem. A 103, 9573 (1999); Angew. Chem. 42, 1297 (2003); JACS 131, 538 (2009) [3] Angew. Chem. 49, 980 (2010); JPC A 115, 6788 (2011); Angew. Chem. 56, 13406 (2017)