## 4 Effect of Heteroatoms-Metal Interaction in the Liquid Phase Oxidation of Benzyl Alcohol  
In the last decades, the liquid phase oxidation of alcohol using noble metals (Pd, Au, Pd, Ru) deposited on carbonaceous supports has been the subject of several studies [98; 99; 100]. Many reports demonstrated that the presence of heteroatoms on the carbon surface can modify the reactivity of the metal. In this section, we will limit the discussion to some examples of the effect of metal-heteroatom interaction in the liquid phase alcohol oxidation. Our group was among the first to show that Au, Pd, and AuPd immobilized on nitrogen functionalized carbon nanofibers exhibited better performance than the same metals supported on pristine carbon in the benzyl alcohol (entry 1-4) [101; 102]. The enhanced performances of N-containing materials were ascribed to the increased metal-support interaction, limiting the leaching and the coarsening of metal NPs [101; 103]. In successive studies, we demonstrated that the amount and the nature of the nitrogen groups have influenced both activity and selectivity [52; 104]. Pd deposited on pyridine-containing carbon nanofibers CNFs (entry 5) resulted more efficient than pyrrole/pyridine-containing ones (entry 6-7). The presence of pyridine resulted in a higher surface basicity compared to pyrrole/pyridine, facilitating the H-abstraction, which is proposed to be the rate-determining step in alcohol oxidation [100]. Moreover, a strong metal-N interaction prevented the agglomeration and sintering of small Pd particles. The metal-support interaction was also verified by the enhanced metal wetting observed. TEM studies showed that small particles better wet the carbon surface, resulting in oval-like particles rather than the round particle shape observed in colloids [52]. [PERSON] et al. demonstrated that B-doped carbon structures are better support that pristine carbon for Pd nanoparticles [105]. The presence of B induced a strong Pd-B interaction, increasing the activity and the durability of the catalyst during the benzyl alcohol oxidation. The effect of carbon dopant on the activity of non-noble metal was also reported. [PERSON] et al. demonstrated the highest activity of cobalt nanoparticles deposited on nitrogen-doped graphitic carbon compared to Co on bare carbon in the veratryl alcohol oxidation [106]. The presence of N showed a positive synergistic effect on Co, influencing the electronic properties of the metal. [PERSON] et al. were among the first to clearly demonstrate that the role of nitrogen on the enhancing activity of cobalt in benzyl alcohol oxidation is due to an electron transfer at the metal/nitrogen-doped carbon interface [107]. Co/N-Carbon catalysts with different nitrogen amounts, in the form of pyridinic and graphitic N (Figure 9b) (Co@NC-0.3, Co@NC-2, Co@NC-4) were prepared using different amounts of C\({}_{3}\)N\({}_{4}\) as the nitrogen source. The catalytic results clearly showed that the activity increases by increasing the nitrogen amount (entry 10-12, Table 1). By a combination of X-ray photoelectron spectroscopy (XPS) and extended X-Ray absorption fine structure (EXAFS) studies, they have proved that the presence of nitrogen can modify the electron density of Co particles, boosting the oxidative properties of the metal (Figure 9f). XPS showed that by increasing the nitrogen amount, the electron density on Co decreases (Figure 9b). As cobalt is in direct contact with N (Figure 9a), there is a flow of electrons (Mott-Schottky effect) at the metal/nitrogen interface from Co to N (Figure 9d) that depends on the nitrogen amount. Nitrogen-containing carbons with a higher flat band potential will accept electrons from cobalt nanoparticles till the Fermi level reaches an equilibrium. Figure 9: Mott–Schottky effect on the catalytic performance of the Co@NC-x catalysts.