Carbon Monoxide Promotes the Catalytic Hydrogenation on Metal Cluster Catalysts.

Ruixuan Qin,Yue Gong,Nanfeng Zheng,Shiguang Mo,Kunlong Liu,Liting Ren,Lin Gu,Gang Fu,Chaofa Xu,Pengxin Liu,Pei Wang

doi:10.34133/2020/4172794

Abstract

Size effect plays a crucial role in catalytic hydrogenation. The highly dispersed ultrasmall clusters with a limited number of metal atoms are one candidate of the next generation catalysts that bridge the single-atom metal catalysts and metal nanoparticles. However, for the unfavorable electronic property and their interaction with the substrates, they usually exhibit sluggish activity. Taking advantage of the small size, their catalytic property would be mediated by surface binding species. The combination of metal cluster coordination chemistry brings new opportunity. CO poisoning is notorious for Pt group metal catalysts as the strong adsorption of CO would block the active centers. In this work, we will demonstrate that CO could serve as a promoter for the catalytic hydrogenation when ultrasmall Pd clusters are employed. By means of DFT calculations, we show that Pdn (n = 2‐147) clusters display sluggish activity for hydrogenation due to the too strong binding of hydrogen atom and reaction intermediates thereon, whereas introducing CO would reduce the binding energies of vicinal sites, thus enhancing the hydrogenation reaction. Experimentally, supported Pd2CO catalysts are fabricated by depositing preestablished [Pd2(μ-CO)2Cl4]2- clusters on oxides and demonstrated as an outstanding catalyst for the hydrogenation of styrene. The promoting effect of CO is further verified experimentally by removing and reintroducing a proper amount of CO on the Pd cluster catalysts.

Highlights

Metal catalysts are widely used in industrial applications
Through systematic density functional theory (DFT) calculations, we revealed that supported ultrasmall Pd clusters interacted too strongly with H atoms as well as reaction intermediates such that the hydrogenation activity was inhibited
It is widely accepted that the hydrogenation of C=C bonds follows the so-called Horiuti-Polanyi (H-P) mechanism, which consists of the successive addition of atomic hydrogen to the substrate

Summary

Introduction

Metal catalysts are widely used in industrial applications. Metal nanoparticles, clusters, and even atomically dispersed metal catalysts have been extensively explored for their high mass-specific activity [1,2,3,4,5]. For a wide range of reactions on metal surfaces, the adsorption energies and activation barriers are typically related to the Brønsted-Evans-Polanyi relationships [6,7,8]. As for metal catalysts with different sizes, their coordinative and electronic properties are often different from each other. Small metal clusters with a large part of coordinative unsaturated sites usually have stronger interaction energy with molecules than that of their larger counterparts [9, 10]. According to the Sabatier principle [11], the optimum catalytic performance can be achieved with a medium interaction energy such that volcano-shaped size-performance relationships would be observed in many heterogeneous catalytic reactions [12,13,14,15,16]

Methods

Results

Conclusion