Metal-Support Synergy of Supported Gold Nanoclusters in Selective Oxidation of Alcohols

Lu Liu,Yuan Tan,Xiao Yan Liu,Xingkun Chen,Xuepeng Wang,Chuanqi Huang,Ronghe Lin,Wenshao Yang,Saisai Wang,Huayin Li,Yunjie Ding,Min Zhao

doi:10.3390/catal10010107

Abstract

Gold catalysts have been reported to exhibit good performance in aerobic oxidation of alcohols, but the intrinsic origin of the catalytic reactivity is still illusive. The catalyst preparation method, the morphology of the gold particles, and even the support might be key factors that determine the activity. Here, we prepared a series of gold catalysts with different supports, i.e., the hydrotalcite (HT), ZnO, MgO, Al2O3, and SiO2, by using the atomically controlled Au25 nanoclusters (NCs) as the gold precursor. The characterization results of the X-ray diffraction (XRD), UV-vis and transmission electron microscopy (TEM) show that the gold particles were mostly uniformly distributed on the supports, with a mean particle size within 3 nm. In aerobic oxidation of benzyl alcohol, the MgAl-HT- and Al2O3-supported Au25 NCs display good performances, with turnover frequency (TOF) values of ~2927 and 2892 h−1, respectively, whereas the SiO2-, MgO-, and ZnO-supported analogues show much inferior activity. The high resolution TEM and X-ray photoelectron spectra (XPS) results suggest that the interactions between gold and the supports in different samples are differing, which influences the morphology and the nature of gold. Our results further point to the importance of acid-base property of the support and the metal-support synergy rather than the gold particle size alone in achieving high-performance in selective alcohol oxidation. Moreover, this work provided a good way to design gold catalysts with controllable sizes that is crucial for understanding the reaction process in aerobic oxidation of alcohol.

Highlights

Supported gold catalysts have attracted a lot of attention in the past few decades because of Hutchings and Haruta’s pioneer work [1,2]
A deep understanding of the size effect and support effect would lead to an improvement of supported gold catalysts
We demonstrated that the preparation method applied in this work was suitable for the synthesis of gold catalysts with controllable sizes

Summary

Introduction

Supported gold catalysts have attracted a lot of attention in the past few decades because of Hutchings and Haruta’s pioneer work [1,2]. Catalysts 2020, 10, 107 hydrogenation of fine chemicals [7,8,9,10], C−C cross-coupling reactions [11,12,13], selective oxidation of alcohols [14,15,16,17,18,19,20], etc This remarkable catalytic behavior of gold catalysts renders them potential candidates for both fundamental research and the industrial community. Using O2 as the oxygen source instead of the stoichiometric oxidants has attracted great interest recently with respect to the economic and environmental reasons [17,18,19,20] These processes remain challenging regarding the selectivity issues since the benzyl alcohol could be overoxidized to form acid and other by-products [21,22]. Developing green and sustainable processes with selective heterogeneous catalysts is of great significance

Methods

Results

Conclusion