Supported gold catalysis derived from the interaction of a Au-phosphine complex with as-precipitated titanium hydroxide and titanium oxide
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Supported gold catalysts derived from interaction of a Au-phosphine complex Au(PPh3)(NO3) (1) with conventional titanium oxide TiO2 and as-precipitated titanium hydroxide Ti(OH)(4)* (*, as-precipitated) have been characterized by means of XRD, XPS, EXAFS, and P-31 CP/MAS-NMR. The Au complex 1 was supported on TiO2 and Ti(OH)(4)* without loss of Au-P bonding at room temperature. The Au complex 1 on TiO2 was readily and completely decomposed to form metallic gold particles by calcination at 473 K, whereas only a small part of the complex 1 on Ti(OH)(4)(*) was transformed to metallic gold particles. By calcination of 1/Ti(OH)(4)* at 573 K the formation of both metallic gold particles and crystalline titanium oxides became notable as evidenced by XRD, XPS and P-31 CP/MAS-NMR. The mean diameter of Au particles in 1/Ti(OH)(4)* calcined at 673 K was less than 30 Angstrom as estimated from Au(2 0 0) diffraction, which was about one-tenth of that for the corresponding 1/TiO2, Thus the as-precipitated titanium hydroxide Ti(OH)(4)* was able to stabilize the Au complex 1 to lead to the simultaneous decomposition of Au complex and Ti(OH);. The catalyst 1/Ti(OH)(4)* calcined at 673 K afforded remarkably high catalytic activity for low-temperature CO oxidation at 273-373 K as compared to the catalyst 1/TiO2. (C) 1998 Elsevier Science B.V. All rights reserved.