Support surface modification induced highly stable precious metal catalyst for efficient CO oxidation

Fudong  Liu, University of Central Florida

Support surface modification induced highly stable precious metal catalyst for efficient CO oxidation

Shaohua Xie,1 Wei Tan,1,2 Samantha Collier,1 and Fudong Liu1,*

1University of Central Florida, Orlando, Florida 32816, United States

2Nanjing University, Nanjing, Jiangsu 210023, China

* Corresponding author: fudong.liu@ucf.edu (F. Liu)

Precious metal catalysts are widely used in automotive exhaust control due to their excellent performance, but superior catalytic performance at low temperature and enhanced stability after severe aging are still required to meet potentially more stringent vehicle emission standards in the future [1]. Ceria is one of the most intensively investigated rare earth oxides, which showed excellent ability of stabilizing precious metals [2, 3]. However, the high cost and low stability of pure CeO2 with low surface area still limited its direct application in industry. Hence, the development of a facile method for generating highly stable CeO2 support for precious metal anchoring is highly demanded for automobile exhaust control.

We herein developed a facile support surface modification strategy for the preparation of thermally stable CeO2/Al2O3 support (CA-T). Comparing to CeO2/Al2O3 support (CA) prepared by traditional incipient wetness impregnation (IWI) method in which mainly bulky CeO2 (ca. > 50 nm) was found on Al2O3 surface, the CeO2 particles with average diameter of ca. 12 nm were well dispersed on Al2O3 surface for CA-T. After loading of Pt by simple impregnation method, it was observed that Pt was atomically anchored on both CA-T and CA. The activated Pt/CA-T catalysts showed much higher CO oxidation activities than activated Pt/CA catalysts not only before but also after aging. In addition, only slight drop in CO oxidation activity was observed for Pt/CA-T after aging at 800 oC (e.g. 12 oC increase for T50), while significant loss was observed in the activity for conventional Pt/CA (e.g. 51 oC increase for T50) and Pt/Al2O3 (e.g. 80 oC increase for T50), suggesting that the Pt/CA-T catalyst generated with support surface modification showed excellent thermal stability. By means of HAADF-STEM, in situ DRIFTS, and EXAFS techniques, it was clearly revealed that Pt single sites anchored to the rich step sites of CeO2 within Pt/CA-T was much more stable than those anchored to the crystal surface of CeO2 within Pt/CA. The excellent low temperature activity of activated Pt/CA-T catalyst for CO oxidation was closely associated with its abundant Pt cluster step sites and Pt-CeO2 interfaces, which facilitated the adsorption of active CO species and outstanding oxygen activation/transfer capacity.

References:

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