Gallagher James R, Childers David J, Zhao Haiyan, Winans Randall E, Meyer Randall J, Miller Jeffrey T
Chemical Science and Engineering Division, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439, USA.
Phys Chem Chem Phys. 2015 Nov 14;17(42):28144-53. doi: 10.1039/c5cp00222b. Epub 2015 Mar 20.
We report the structural evolution of Pd-Zn alloys in a 3.6% Pd-12% Zn/Al2O3 catalyst which is selective for propane dehydrogenation. High signal-to-noise, in situ synchrotron X-ray diffraction (XRD) was used quantitatively, in addition to in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) and extended X-ray absorption fine structure (EXAFS) to follow the structural changes in the catalyst as a function of reduction temperature. XRD in conjunction with DRIFTS of adsorbed CO indicated that the β1-PdZn intermetallic alloy structure formed at reduction temperatures as low as 230 °C, likely first at the surface, but did not form extensively throughout the bulk until 500 °C which was supported by in situ EXAFS. DRIFTS results suggested there was little change in the surfaces of the nanoparticles above 325 °C. The intermetallic alloy which formed was Pd-rich at all temperatures but became less Pd-rich with increasing reduction temperature as more Zn incorporated into the structure. In addition to the β1-PdZn alloy, a solid solution phase with face-center cubic structure (α-PdZn) was present in the catalyst, also becoming more Zn-rich with increasing reduction temperature.
我们报道了对丙烷脱氢具有选择性的3.6% Pd-12% Zn/Al₂O₃催化剂中钯锌合金的结构演变。除了原位漫反射红外傅里叶变换光谱（DRIFTS）和扩展X射线吸收精细结构（EXAFS）外，还定量使用了高信噪比的原位同步加速器X射线衍射（XRD），以跟踪催化剂结构随还原温度的变化。XRD结合吸附CO的DRIFTS表明，β1-PdZn金属间合金结构在低至230°C的还原温度下形成，可能首先在表面形成，但直到500°C才在整个体相中广泛形成，原位EXAFS证实了这一点。DRIFTS结果表明，在325°C以上，纳米颗粒表面变化不大。形成的金属间合金在所有温度下都富钯，但随着还原温度升高，随着更多锌掺入结构中，富钯程度降低。除了β1-PdZn合金外，催化剂中还存在具有面心立方结构的固溶体相（α-PdZn），其也随着还原温度升高而变得更富锌。
