Al_(2)O_(3)负载Pt基催化剂表面动态变化的谱学研究

Spectroscopic Study of Surface Dynamics of Al_(2)O_(3) Supported Pt-Catalysts

明确多相催化剂表面在反应过程的动态变化对催化剂的优化、设计有重要意义.我们通过控制Pt的不同负载量制备了一系列Al_(2)O_(3)负载的Pt/Al_(2)O_(3)催化剂,利用X-射线衍射、X-光电子能谱、球差扫描电镜、CO-探针的红外光谱、低能离子散射谱、程序升温氧化和拉曼光谱等研究Pt/Al_(2)O_(3)的表面结构和反应过程中的变化,以丙烷直接脱氢(PDH)反应为探针,考察反应过程存在“诱导”期的表面动态变化,特别是表面积碳、表面形貌、活性位点等的演化.进而与其催化反应性能关联,发现Pt纳米粒子(NP)和团簇上丙烷易深度脱氢或断裂C-C键生成CH_(4)的同时形成积碳、随后失去活性;而孤立的Pt单原子位点(SAC)上不易生成积碳、是丙烯生成的关键活性位.

Understanding the dynamic changes of heterogeneous catalyst under reaction conditions is very important for improving the catalyst and designing a new catalyst.In present study,a series of Al2O3 supported Pt/Al_(2)O_(3) catalysts were prepared with various Pt loadings.Surface structures and changes were studied by the X-ray diffraction(XRD),X-ray photoemission spectroscopy(XPS),high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM),CO probed Fourier transform infrared spectroscopy(CO-FTIR),low energy ion scattering spectroscopy(LEIS),temperature programmed oxidation of carbon(TPOC)and Raman spectroscopy.Propane dehydrogenation(PDH)was used as a probe reaction.Surface dynamics,especially coke formation,surface morphology and active sites were investigated,and correlated with catalytic performance.It was found that Pt/Al_(2)O_(3) catalysts underwent an‘induction’period for PDH.Propane was easy to deeply dehydrogenate,broke C-C bond on Pt nanoparticles(NP)and clusters to form CH_(4) and coke,resulted in a lower activity.In contrast,the isolated Pt single-atom central sites(SAC)were not easy to form coke,and would mainly be the active sites for propylene formation.