## 3 Results  
Cetyltrimethylammonium chloride-stabilized gold nanotriangles (CTAC-stabilized Au NTs) were synthetized by a 3 steps procedure [23]: seed preparation, growth and shaping (see Scheme 1 and Materials and Methods section). \"Face-blocking\" growth, i.e., directed growth upon selective adsorption of surfactants to most-favorable facets (capping), was chosen as growth mechanism. By this \"surfactant-templating\", an initial shape yielded above 50% can be achieved by firstly generating CTAC capped single-twinned seeds (<10 nm) and then fast seed adding to a growth solution using ascorbic acid, yielding nanotriangles of 60-150 nm upon depletion-induced purification. The synthesis process yielded mostly triangles, although hexagons and small polyhedral particles are scarcely detected. Characterization by TEM and SEM confirm a regular triangular shape of the synthetized CTAC-stabilized Au NTs (Figure 1). High-resolution TEM show nearly 60% of the total nanoparticle population are gold triangles and confirmed the [111] nature of the planar facets of the nanotriangles (Figure 1a) which are very uniform in size distribution and exhibit an edge length of 71 \(\pm\) 3 nm (Figure 1b) and heights up to 40 nm. Additional TEM images and histogram of Au NTs are depicted in Figure S1 of Supplementary Information. The catalytic performance of the CTAC-stabilized gold nanotriangles was, for the first time, evaluated for the cyclohexane oxidation, in terms of products yield, turnover number (TON, moles of KA oil per mole of catalyst) or frequency (TOF, h\({}^{-1}\), TON/reaction time), catalyst amount, and type of oxidant used (see Table 1 and Figures 2-5). The Au NTs show an effective performance as catalysts for the MW-assisted oxidation of cyclohexane, with aqueous _tert_-butyl hydroperoxide (TBHP), to KA oil, through the formation of cyclohexyl hydroperoxide (primary product), under mild conditions (Scheme 2). Importantly, the cyclic KA oil are the only products detected by gas chromatographic analysis, confirming the high selectivity of the catalytic oxidative system (please see Table 1). This achieved high selectivity (100% selectivity for the conditions of entry 4, Table 1) is of utmost economic importance since it avoids costly separation steps in the KA oil production process. In addition, the mild conditions used also contribute for a sustainability enhancement of the catalytic process. Figure 1: TEM (**a**) and SEM (**b**) images of the obtained CTAC-stabilized Au NTs. The best catalytic conditions consisted of using 20 \(\upmu\)mol of catalyst and TBHP (70% aq. solution) as oxidant under MW irradiation at 50 \({}^{\circ}\)C for 3 h (Table 1 and Figures 2-5). In fact, the amount of catalyst plays a significant role, as shown in Figure 2. The increase from e.g., 10 to 20 \(\upmu\)mol of Au NTs in the reaction medium increases the yield from 5.7 to 13.1%. The ratio of Au NTs surface to volume per mole of catalyst was determined for the different amounts of catalyst used and is presented in Table 2. Calculations were performed using the Equations S1 and S2 (see Supplementary Information) for the area and volume of an equilateral triangle, respectively. The influence of the TON affected by the surface to volume ratio, on the total yield of products was determined (see Figure S2 of Supplementary Information), and it was found to exhibit a considerable dependence of the catalyst amount. Moreover, the presence of nitric acid (a commonly used cyclohexane oxidation promotor [27, 28]) has a slight inhibitory effect on the catalytic activity of CTAC-stabilized Au NTs as depicted in Figure 2 and entries 5-7 or 15 of Table 1. However, sulfuric acid has a much stronger inhibitory effect than nitric acid (compare entries 8 and 7 of Table 1) reducing the obtained KA oil yield to 3.3% and 12.2%, respectively. Possibly, the inhibiting effect observed is due to the cationic surfactant cetyltrimethylammonium chloride (CTAC) when combined with H\({}_{2}\)SO\({}_{4}\).