Zinc Addition Influence on the Properties of Pd/Sibunit Catalyst in Selective Acetylene Hydrogenation

Tuning oxygen molecule passivation and transfer on the catalyst surface for highly efficient hydrogen evolution from formaldehyde

In hydrogen evolution reactions (HER), hydrogen-oxygen recombination reaction typically reduces the hydrogen generation rate. However, in the HER from formaldehyde, un-dissociated oxygen molecules can promote hydrogen generation. In this paper, a series of PdZn/g-C3N4 alloy catalysts were synthesized, and by varying the catalyst composition successfully regulated the reactive sites and surface-interface behaviors, thus enhancing the HER rate. Under optimal conditions (1.5 M NaOH, 2.0 M HCHO, Pd1Zn1/g-C3N4), the Pd1Zn1 alloy catalyst exhibits the highest catalytic activity for hydrogen evolution reaction, with a hydrogen evolution rate of 422.86 μmol·h-1. Mechanistic study of hydrogen production from formaldehyde revealed that O2 molecules are converted into reactive oxygen species HOO-, which then react with formaldehyde to produce hydrogen. The adsorption energies of formaldehyde and oxygen molecules, as well as the O2 dissociation energy barrier, vary significantly with the PdZn alloy compositions, affecting O2 chemical behavior, impeding O2 dissociation, and accelerating the transfer of active species. The results of theoretical calculations indicate that on the surface of the Pd1Zn1/g-C3N4 alloy catalyst, oxygen molecules possess an appropriate adsorption energy and a relatively high dissociation energy barrier. This is conducive to the formation of oxygen-containing active species. Meanwhile, the coordination between metal atoms promotes the efficient transfer of photogenerated electrons and prolongs the photoelectron lifetime. Thus, adjusting the PdZn alloy composition can effectively regulate and enhance the catalyst's hydrogen production activity.

Inserting Single-Atom Zn by Tannic Acid Confinement To Regulate the Selectivity of Pd Nanocatalysts for Hydrogenation Reactions

Precisely controlling the selectivity of nanocatalysts has always been a hot topic in heterogeneous catalysis but remains difficult owing to their complex and inhomogeneous catalytic sites. Herein, an effective strategy to regulate the chemoselectivity of Pd nanocatalysts for selective hydrogenation reactions by inserting single-atom Zn into Pd nanoparticles is reported. Taking advantage of the tannic acid coating-confinement strategy, small-sized Pd nanoparticles with inserted single-atom Zn are obtained on the O-doped carbon-coated alumina. Compared with the pure Pd nanocatalyst, the Pd nanocatalyst with single-atom Zn insertion exhibits prominent selectivity for the hydrogenation of p-iodonitrobenzene to afford the hydrodeiodination product instead of nitro hydrogenation ones. Further computational studies reveal that the single-atom Zn on Pd nanoparticles strengthens the adsorption of the nitro group to avoid its reduction and increases the d-band center of Pd atoms to facilitate the reduction of the iodo group, which leads to enhanced selectivity. This work provides new guidelines to tune the selectivity of nanocatalysts with guest single-atom sites.