Porous silica-encapsulated gold nanoparticles for high catalytic stability and activity

Abstract

Gold catalysts have received extensive interest because of their high catalytic activity for various key chemical reactions, such as CO oxidation at room temperature and 4-nitrophenol reduction. However, their poor stability significantly hampers practical applications. In the first work, we report a new approach to successfully synthesize a supported gold nanoparticles (AuNPs) catalyst with high stability while maintaining its high activity for room-temperature CO oxidation. The key to this success is immobilizing porous silica-encapsulated AuNPs on SBA-16, i.e., porous silica substrate, provided with enhanced metal-support interaction. The prepared AuNPs catalyst exhibits high activity for CO oxidation at room temperature (with a turn over frequency of 0.74 s$^{-1}$) than previously reported supported AuNPs catalysts, and excellent stability during CO oxidation at room temperature for 500 hours, thermal treatments up to 650 ºC, and storage under ambient conditions. The superior catalytic, thermal, and storage stability are due to encapsulation of immobilized AuNPs within porous silica layers, while the high activity is attributed to enhanced metal-support interaction. In the second work, we applied porous silica encapsulation to the atomically thin gold nanosheets (AuNSs) to provide structural stability in dried powder form. The prepared silica-encapsulated AuNSs exhibit superior catalytic activity for reduction of 4-nitrophenol (with a normalized rate constant of 8.8 x 104 min$^{-1}$gAu$^{-1}$) than previously reported porous silica-encapsulated AuNPs, and excellent catalytic stability by maintaining its catalytic conversion percentage above 97% after six cycles of reduction reactions at 60 ºC. The structural and catalytic stability are due to the presence of porous silica layers on their surface, while the high activity is due to the bilayer atomic structure of AuNSs. This work provides new insights on the synthesis of highly stable gold catalysts, which pave a way for realizing their practical applications.