Finding optimal surface sites on heterogeneous catalysts by counting nearest neighbors

Abstract

A good heterogeneous catalyst for a given chemical reaction very often has only one specific type of surface site that is catalytically active. Widespread methodologies such as Sabatier-type activity plots determine optimal adsorption energies to maximize catalytic activity, but these are difficult to use as guidelines to devise new catalysts. We introduce "coordination-activity plots" that predict the geometric structure of optimal active sites. The method is illustrated on the oxygen reduction reaction catalyzed by platinum. Sites with the same number of first-nearest neighbors as (111) terraces but with an increased number of second-nearest neighbors are predicted to have superior catalytic activity. We used this rationale to create highly active sites on platinum (111), without alloying and using three different affordable experimental methods.

A DFT Study on the O2 Adsorption Properties of Supported PtNi Clusters

“…Thus, each adsorption site was assigned a GCN value (see Figure 5a). GCN values establish a direct link between geometry and the adsorption map, despite the size, shape and composition of the supported clusters [26][27][28][29][30]. From Figure 5a, it is clear that those adsorption sites having the largest GCN value correspond to namely the FCC and HCP sites (>6), while smaller GCN values (<5) are calculated to sites involving clusters' edges and vertices (see calculated GCN values in Tables S1-S3, in Supplementary Materials).…”

“…A geometrical characterisation of the O 2 adsorption site is done using the generalized coordination number (GCN). Introduced by Sautet and co-workers for monometallic Pt systems, the GCN is a geometrical descriptor as robust as the d-band center, which establishes a direct link between geometry, adsorption map and activity [26][27][28][29]. The GCN can be defined as the coordination number at the adsorption site weighted by the overall coordination of the neighbouring atoms:…”

“…However, due to cluster sizes and geometries, Ni atoms are in some cases located inevitably at cluster surface sites (e.g., TO 25 , Dh 58 ). For all cases considered, we calculated the general coordination number (GCN), a quantity which establishes a link between geometry, adsorption and activity [26][27][28][29]. The GCN can distinguish symmetrically equivalent sites, and it has been recently used to successfully describe O 2 adsorption trends over large (∼2 nm) supported PtNi clusters [30].…”

The effect of size and composition on structural transitions in monometallic nanoparticles

“…Morphology, together with size and composition, determines nanocluster's chemophysical properties, establishing a profound link between structural stability and reliable performance [1][2][3][4]. One of the most clear example is in nanocatalysts, as the adsorption properties depend on the local environment of each site, with less coordinated atoms binding small molecules more strongly.…”

“…One of the most clear example is in nanocatalysts, as the adsorption properties depend on the local environment of each site, with less coordinated atoms binding small molecules more strongly. Changes in the nanoparticle morphology affect the site coordination, hence altering cluster reactivity and selectivity with respect to a given reaction [2,3]. Predicting the extent by which structural fluctuations take place is then a fundamental step in order to quantify and possibly tune their chemophysical properties.…”