Irradiation of γ-ray to FSM-16 encapsulated HAuCl4, synthesized via chemical vapor deposition, led to
9 the formation of Au nanowires (2-10 nm diameter and 17-147 nm length). Contrarily, reductive
10 carbonylation of impregnated HAuCl4 with FSM-16 using CO (200 torr)/water (20 torr) for 2 h, followed
11 by irradiation with a high-pressureHglamp at 300Kfor 36 h, resulted in the formation ofAunanoparticles
12 (circular; 8-75 nm diameter). These catalysts have been characterized by XRD, N2-sorpitometry, TEM,
13 UV-vis-DRS, CO-FTIR spectroscopy, and then tested for water-gas shift reaction (WGSR) under
14 feeding conditions of PCO=60 torr and PH2O=5 torr. Evidently, Au nanowires exhibited higher activity
15 (3 times) than Au nanoparticles. It has been shown that the activity depends on Au geometry rather than
16 structural characteristics, such as surface area. In-situ FTIR CO adsorption and UV-vis-DRS evidenced
17 major changes on the surface properties of Au nanowires in exposing different oxidation states as well as
18 inducing electron deficiencies exceeding those on Au nanoparticles. Gold nanowires displayed a surface
19 plasmon resonance peak at 525 nm derivatized from distribution in size and dispersion and rather
20 exceeding that at 484 nm exhibited for gold nanoparticles. It has been shown that Au0 species, including
21 nanowires and small aggregated metallic nanoparticles, contribute significantly, if not predominantly, to
22 theWGSactivity. TheTEMstudy provided evidence that reduction pretreatment ofAu nanowires prior to
23 carrying out the reaction results in elimination of the activity due to sintering (from 35 to 53 nm) as well as
24 to the exhibited change in geometry and thus altering the nature of active centers. |
