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本文以CO为探针,采用红外光谱、电子自旋共振谱、化学吸附及其程序升温脱附等方法,研究了由担载于Al_2O_3和TiO_2上的Pt_3(CO)_3(PPh_3)_4络合物制成的分散型Pt 催化剂的表面性质和金属与载体间的相互作用。实验结果表明,由Pt_3(CO)_(PPh_3)_4/Al_2O_3表面络合物在真空中脱羰基后所得Pt催化剂吸附CO的IR谱带位于1800cm~(-1),2010cm~(-1)左右,分别对应于桥式(B-)和线式(L-)CO吸附态,B/L值与由无机酸制备之催化剂相比较大。当催化剂经过氧化-还原处理后,由于吸附CO 的B/L 值减小而与无机酸制得之催化剂相近。与此相反,对以TiO_2为载体的催化剂,不论在真空抑或CO中脱羰基时,吸附CO的IR谱不出现桥式态。IR与CO化学吸附量测定结果还表明,由TiO_2为载体的Pt催化剂随氢还原温度之升高CO化学吸附量减少,相应地其CO IR谱带强度逐渐减弱并向低波数方向位移,相应的TPD峰位置却向高温方向位移。
In this paper, CO as probe, using infrared spectroscopy, electron spin resonance spectroscopy, chemisorption and temperature programmed desorption and other methods to study supported on the Al2O3 and TiO_2 Pt_3 (CO) _3 (PPh_3) _4 complex The surface properties of dispersed Pt catalysts and the interaction between metal and support were investigated. The experimental results show that the IR band of Pt adsorbed on Pt catalyst prepared by decarboxylation of Pt_3 (CO) _ (PPh_3) _4 / Al_2O_3 surface complex in vacuum is located at 1800cm -1 and about 2010cm -1 , Corresponding to bridge (B-) and linear (L-) CO sorption states, respectively, with B / L values being larger than those prepared with mineral acids. When the catalyst was subjected to oxidation-reduction treatment, the B / L value of adsorbed CO was similar to that of the catalyst prepared from inorganic acid. In contrast, for TiO 2 -supported catalysts, the IR spectra of adsorbed CO did not appear bridged when decarbonylating in vacuum or CO. The results of IR and CO chemisorption also showed that the Pt chemisorption decreased with the increase of hydrogen reduction temperature and the intensity of CO IR band decreased gradually and shifted to the low wave number corresponding to TPD peak position but to high temperature displacement.