Most of the TS structures are C I , 43 out of 59, and the rest are C II . Their distribution across sites is reported in Table . All of the C I structures are found within a pocket, typically with large available volume (θ ij = 101 ○ -129 ○ and ϕ ij = 121 ○ -160 ○ ). In the majority of the C II cases, the H 2 O 2 molecule is located at the intersection of two small pockets (θ = 90 ○ -101 ○ and ϕ = 124 ○ -149 ○ ), with the only exception of the 2M site and the ISO site 10, where the C II structures occupy the largest pocket. We use the following notation to identify a TS structure: for instance, "C I (P b ) -1" indicates the TS structure with largest σ angle within the pocket P b and it belongs to category I; while "C II (P a /P b ) -1" indicates a category II TS structure at the intersection between pockets As shown in Table , five different sites (three ISO and two 3M sites) were identified as C I -only sites. It is useful to analyze in detail the individual adsorption and activation energies for each TS configuration in two representative sites, reported in Figure . In this and in the following figures, the reference energy E Site 11 is a 3M type, and 8 TS structures were found, see Figure in the SI for the structures and Figure for the energies. The energy separation in pockets is also roughly respected for ∆E tot ads , although there is some overlap in the energy values at the edges of each pocket group. The grouping follows the available volume: larger volume leads to lower ∆E a . ads and ∆E a are usually in the largest pockets. Furthermore, different configurations can be roughly grouped by pockets in the energy diagrams, which suggests that the pocket volume parameters are important descriptors for site activity. However, other geometric descriptors referring to the orientation within the pocket are needed to characterize the effect of steric hindrance.