Preparation of nano-gold in zeolites for CO oxidation: Effects of structures and number of ion exchange sites of zeolites

Nano-gold was prepared in different types of zeolite (Y beta-and mordenite) in pH-adjusted chloroauric acid solution. The effects of the pore structures and the aluminum content on the loading of gold and on the reaction activity for CO oxidation at 0 degrees C were investigated. The gold loading in each zeolite was strongly related to the aluminum content; it was also affected by the structure of the zeolite. HRTEM results revealed that a few particles of gold around 1 nm in diameter were formed in the cage of Y-type zeolite with less aluminum loading (1.8 wt.%), and there was aggregation of gold species on the exterior surface of the zeolite; in contrast, more particles of gold around 1 nm were formed in Y-type zeolite with more aluminum loading (12.4 wt.%), no aggregation was observed. The results from the temperature-programmed reduction in hydrogen indicated that the gold species were reduced in the smaller pores (in beta and mordenite) only at lower temperatures. Nevertheless, gold was easily sintered in the channels of beta and mordenite during CO oxidation, causing severely reducing the activity. The cage-like pore in Y-type zeolite with 12.4 wt.% aluminum loading prevented the sintering of gold, and its hydrophilic surface favoured the activation of gold species; therefore, this Au/Y catalyst exhibited high catalytic activity and stability for CO oxidation. (c) 2005 Elsevier B.V. All rights reserved.