Umm Al-Qura University, Faculty of Applied Science, Chemistry Department, Makkah, Saudi Arabia.
J Colloid Interface Sci. 2011 Feb 1;354(1):100-8. doi: 10.1016/j.jcis.2010.10.008. Epub 2010 Oct 13.
A facile, previously unexplored, method to synthesize bimetallic Pt-Au nanowires (20nm diameter×120-170nm long) on mesoporous FSM-16 (2.7nm) was fabricated by co-impregnation of H(2)PtCl(6) with HAuCl(4) followed by evacuation at 300K and finally exposure to the CO/H(2)O gas mixture (60:5Torr) at 323K for 1.0h. On the other hand, spherical monometallic nanoparticles of pure Pt (7.0nm diameter) and Au (7-26nm diameter) were synthesized as well, by impregnation, at the same reaction conditions. The catalysts were characterized by in situ FTIR spectroscopy, UV-vis absorption spectroscopy, TEM, TPR and TPCOR. The catalytic activities toward the water-gas shift reaction (WGSR) were also examined under atmospheric pressure and at the margin of 323-373K. The optical absorption spectra showed a remarkable shift and broadening of Pt-Au surface Plasmon resonance band at 515nm apart from those of individual analogue emphasizing bimetallic formation. Results from in situ FTIR spectroscopy indicated that incorporation of Au assisted and stabilized the formation of carbonyl clusters of Pt-Au-CO (2084cm(-1)) and Pt-CO (1888cm(-1)) inside the host FSM-16. The Pt-Au carbonyl clusters built up at the moment of vanishing the linear carbonyl band of the charged Au (Au(+)-CO, 2186cm(-1)) along with a concomitant increase in the reduced gold (Au(0)-CO, 2124cm(-1)) species. TPR profiles showed that the H(2) consumed was higher for Pt/FSM-16 than for Pt-Au/FSM-16 verifying the facile reduction of Pt moieties after addition of Au. The CO adsorption peak maximum, in TPCOR, for Pt/FSM-16 occurred at higher temperature than that of Pt-Au/FSM-16, which exhibited higher amounts of CO(2) produced. The relative decrease in CO bindings on bimetallic surface was responsible for increasing the CO oxidation activity mainly through an association mechanism. Accordingly, the activity of Pt-Au/FSM-16 towards WGS showed a marked increase (8-23 times) compared with those of monometallics emphasizing the dependence of this reaction on the electronic defects of the nanowires. A straightforward reduction mechanism was deduced for Pt-Au alloy formation in view of the results obtained.
通过共浸渍 H(2)PtCl(6) 和 HAuCl(4)，然后在 300K 下抽真空，最后在 323K 下暴露于 CO/H(2)O 气体混合物（60:5Torr）中 1.0h，制备了介孔 FSM-16（2.7nm）上的双金属 Pt-Au 纳米线（20nm 直径×120-170nm 长）的简便、以前未探索过的方法。另一方面，通过浸渍，在相同的反应条件下也合成了纯 Pt（7.0nm 直径）和 Au（7-26nm 直径）的球形单金属纳米粒子。通过原位 FTIR 光谱、紫外可见吸收光谱、TEM、TPR 和 TPCOR 对催化剂进行了表征。在大气压力和 323-373K 的边界条件下，还检查了对水煤气变换反应（WGSR）的催化活性。光学吸收光谱显示，Pt-Au 表面等离激元共振带在 515nm 处发生了明显的位移和展宽，与单个模拟物相比，强调了双金属的形成。原位 FTIR 光谱的结果表明，Au 的掺入有助于并稳定了 Pt-Au-CO（2084cm(-1)）和 Pt-CO（1888cm(-1)）在主体 FSM-16 内的羰基簇的形成。随着带电荷的 Au（Au(+)-CO，2186cm(-1)）的线性羰基带的消失，同时伴随着还原金（Au(0)-CO，2124cm(-1)）物种的增加，Pt-Au 羰基簇得以建立。TPR 曲线表明，Pt/FSM-16 消耗的 H(2)高于 Pt-Au/FSM-16，这验证了 Au 加入后 Pt 部分的还原更容易。在 TPCOR 中，Pt/FSM-16 的 CO 吸附峰最大值出现在比 Pt-Au/FSM-16 更高的温度下，Pt-Au/FSM-16 产生了更高量的 CO(2)。双金属表面 CO 结合的相对减少是增加 CO 氧化活性的主要原因，主要通过缔合机制。因此，与单金属相比，Pt-Au/FSM-16 对 WGS 的活性显著增加（8-23 倍），强调了该反应对纳米线电子缺陷的依赖性。根据获得的结果，推导出了 Pt-Au 合金形成的直接还原机制。
