Tailoring the morphology of Pd nanoparticles on CNTs by nitrogen and oxygen functionalization

Abstract

The influence of N and O functionalization of CNT on the morphology of supported Pd-PVA nanoparticles is studied with respect to the catalytic activity in the liquid phase oxidation of benzyl alcohol to benzaldehyde. The impact of specific N and O sites on the carbon surface induced by the high temperature N-functionalization in the temperature range 673-873 K was observed by HRTEM as increased nanoparticles dispersion and enhanced metal wetting at the carbon surface. Those small nanoparticles that stabilized at the N-CNTs surface are beneficial for improving catalytic performance. The interaction of O(2) with the metal surface was studied by microcalorimetry. At 353 K, the PVA shell hinders the dissociative oxygen chemisorption at the surface of the fresh catalyst. Differently, a very high (maximum for Pd/N-CNT873K 750 kJ mol(-1)) and oscillating exothermic differential heat is registered for the washed samples. Such high differential heat on the "washed" sample is due to the sum of oxygen chemisorption and PVA oxidation. Thereby, it is demonstrated that the PVA overlayer suppresses the total combustion reaction pathway. This contribution has highlighted the impact of the dynamic change of morphology of these Pd nanoparticles under the reaction conditions on the catalytic performance and how this is modulated by the nature of the support as well as the PVA. The support with its varying ability to strongly bind Pd regulates the morphology of the nanoparticles on which the sub-surface penetration of O, H, C from the reactants depends, all modulating the electronic structure and thus the reactivity.

Functional carbons and carbon nanohybrids for the catalytic conversion of biomass to renewable chemicals in the condensed phase

“…In the case of Au, the surface topology and interfacial energy seem to dictate the shape of the supported particles. Similar effects on particle shape were observed for Pd when varying the acid-base character of the surface by functionalization with oxygen or nitrogen containing groups [163]. In general, the interaction with the N-containing functional groups promotes the catalytic activity of the metal [164][165][166].…”

Understanding Heteroatom-Mediated Metal–Support Interactions in Functionalized Carbons: A Perspective Review

“…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 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]. Ravat et al demonstrated that B-doped carbon structures are better support that pristine carbon for Pd nanoparticles [105].…”

Sol–gel synthesis of palladium nanoparticles supported on reduced graphene oxide: an active electrocatalyst for hydrogen evolution reaction

“…Cyclic voltammogram of (a) rGO/GCE and (b) PdrGO/GCE in 0.1 M H 2 SO 4 at a scan rate of 5 mV s −1 .synthesis method of Pd-rGO catalyst synthesized in this work with those already reported[37][38][39][40][41][42][43][44][45] in literatures is shown in table 1. As shown, parameters are comparable with other results.To evaluate the electrochemical activity of rGO and PdrGO hybrid, cyclic voltammograms experiments were tested within a potential range from −0.3 to 1.2 V at a scanning rate of 50 mV s −1 in the solution of 0.1 M H 2 SO 4 .…”