Catalysis at the nanoscale may change selectivity.
Among the many virtues ascribed to catalytic nanoparticles, the prospect that the passage from the macro- to the nanoscale may change product selectivity attracts increasing attention. To date, why such effects may exist lacks explanation. Guided by recent experimental reports, we propose that the effects may result from the coupling between the chemical steps in which the reactant, intermediates, and products are involved and transport of these species toward the catalytic surface. Considering as a thought experiment the competitive formation of hydrogen and formate upon reduction of hydrogenocarbonate ions on metals like palladium or platinum, a model is developed that allows one to identify the governing parameters and predict the effect of nanoscaling on selectivity. The model leads to a master equation relating product selectivity and thickness of the diffusion layer. The latter parameter varies considerably upon passing from the macro- to the nanoscale, thus predicting considerable variations of product selectivity. These are subtle effects in the sense that the same mechanism might exhibit a reverse variation of the selectivity if the set of parameter values were different. An expression is given that allows one to predict the direction of the effect. There has been a tendency to assign the catalytic effects of nanoscaling to chemical reactivity changes of the active surface. Such factors might be important in some circumstances. We, however, insist on the likely role of short-distance transport on product selectivity, which could have been thought, at first sight, as the exclusive domain of chemical factors.
Laboratoire d'Electrochimie Moléculaire, Université Paris Diderot, Bâtiment Lavoisier, Sorbonne Paris Cité, Unité Mixte de Recherche Université-CNRS 7591, 75205 Paris Cedex 13, France cyrille.costentin@univ-paris-diderot.fr saveant@univ-paris-diderot.fr.
Cyrille
C
Costentin
Laboratoire d'Electrochimie Moléculaire, Université Paris Diderot, Bâtiment Lavoisier, Sorbonne Paris Cité, Unité Mixte de Recherche Université-CNRS 7591, 75205 Paris Cedex 13, France cyrille.costentin@univ-paris-diderot.fr saveant@univ-paris-diderot.fr.
Jean-Michel
JM
Savéant
electrocatalysis; energy; nanoparticles
Angew Chem Int Ed Engl. 2014 Apr 1;53(14):3558-86
24574053
Chem Rev. 2014 Feb 12;114(3):1709-42
24313306
J Am Chem Soc. 2012 May 2;134(17):7231-4
22506621
J Am Chem Soc. 2014 Feb 5;136(5):1734-7
24417470
Chem Soc Rev. 2013 Mar 21;42(6):2338-56
23165230
Chem Soc Rev. 2014 Nov 21;43(22):7870-86
24745032
J Am Chem Soc. 2010 Jun 9;132(22):7559-67
20469860
J Am Chem Soc. 2012 Dec 12;134(49):19969-72
23171134
J Am Chem Soc. 2015 Apr 15;137(14):4701-8
25812119
Nat Chem. 2009 Apr;1(1):7
21378780
Proc Natl Acad Sci U S A. 2006 Oct 24;103(43):15729-35
17043226
Nanoscale. 2011 May;3(5):2054-73
21399781
J Am Chem Soc. 2007 Sep 12;129(36):10982-3
17705385