The Role of Nitrogen‐doping in the Catalytic Transfer Hydrogenation of Phenol to Cyclohexanone with Formic Acid over Pd supported on Carbon Nanotubes

Abstract

Highly selective one-step hydrogenation of phenol to cyclohexanone, an important intermediate in the production of nylon 6 and nylon 66, is desirable but remains a challenge. Pd nanoparticles supported on nitrogen-and oxygen-functionalized carbon nanotubes (NCNTs, OCNTs) were prepared, characterized, and applied in the hydrogenation of phenol to cyclohexanone to study the effect of Ndoping. Almost full conversion of phenol with high selectivity to cyclohexanone was achieved over Pd/NCNT under mild reaction conditions using either H 2 or formic acid (FA) as a hydrogen source. The effects of reaction temperature and FA/ phenol ratio and the reusability were investigated. Separate FA decomposition experiments without and with the addition of phenol were performed to investigate the reaction mechanism, especially the deactivation behavior. Deactivation was observed for both catalysts during the FA decomposition, while only Pd/OCNT rather than Pd/NCNT was deactivated in the transfer hydrogenation with FA and the FA decomposition in the presence of phenol, indicating the unique role of N-doping. Therefore, we assume that deactivation is caused by the strongly bound formates on the active Pd sites, suppressing further FA decomposition and/or transfer hydrogenation on Pd. The nonplanar adsorption of phenol on NCNTs via weak OÀ H•••N interactions enables the occurrence of the subsequent hydrogenation by adsorbed formate on Pd.

Palladium Nanoparticles Anchored on COFs Prepared by Simple Calcination for Phenol Hydrogenation

“…The spherical morphology of COF-280 is conducive to the formation of Pd with higher Pd 0 proportion on the catalyst surface (Figures and , Table ), which is in favor of the contact between the reactants and Pd NPs. The current studies suggest that Pd 0 is the active site for the phenol hydrogenation. ,− Furthermore, the abundant mesopores in COF-280 (Figure , Table ) can enhance the mass transfer during the phenol hydrogenation. These aspects together lead to the superior catalytic activity of Pd@COF-280 for the phenol hydrogenation.…”

Insights into the Solvent Effect on the Synthesis of Pd@PC-COFs for Phenol Hydrogenation

“…51 Finally, Pd@PC-COF-NBA has the highest Pd(0) proportion (Figure 8c). The current studies suggest that Pd(0) is the active site for the phenol hydrogenation 13,43,62 and can activate more hydrogen per unit time than Pd(2+), 67 thus promoting the improvement of the catalytic performance. Although Pd@PC-COF-MeOH has the highest-specific surface area (Figure 3f, Table 2), higher Pd content (Table 3), and Pd(0) proportion (Figure 8f), its largest Pd particle size (Figure 4f) offsets the beneficial effects, decreasing the catalytic activity.…”

Hybridization of Palladium Nanoparticles with Aromatic‐Rich SU‐101 Metal‐Organic Framework for Effective Transfer Hydrogenation

“…Among various metal catalysts, Pd is traditionally known for its catalytic activity for hydrogenation reactions. Recently, Pd also proved to be an effective catalyst for transfer hydrogenation reactions [12,21–26] . Transfer hydrogenation involves the use of hydrogen sources such as sodium borohydride, isopropanol, formic acid, and hydrazine [27–30] .…”

“…Recently, Pd also proved to be an effective catalyst for transfer hydrogenation reactions. [12,[21][22][23][24][25][26] Transfer hydrogenation involves the use of hydrogen sources such as sodium borohydride, isopropanol, formic acid, and hydrazine. [27][28][29][30] It avoids direct usage of hazardous H 2 gas at high pressure and temperatures for hydrogenation reactions.…”