CuO-ZnO/Al_2O_3-TiO_2催化剂中TiO_2的结构和电子效应

Structural and Electronic Effect of TiO_2 in CuO-ZnO/Al_2O_3-TiO_2 Catalyst

采用XPS,XRD,TPR,TPD和指标反应等方法研究了TiO_2在负载型CuO-ZnO/Al_2O_3-TiO_2催化剂中所起的作用.发现TiO_2起双重作用,即结构效应和电子效应,TiO_2的结构效应主要表现为它改善了CuO在载体上的分布.TiO_2的电子效应表现为它对Cu^0具有吸电子的作用,从而削弱了Cu和S之间的吸附力,使S容易脱除.另外,部分还原形成的Ti^(3+)具有促进CuS中的Cu^(2+)还原为Cu^0的能力,TiO_2的上述效应的综合结果使催化剂的抗硫中毒性能大大增强.

The modification effects of TiO2 on Cu or CuO in supported CuO-ZnO/Al2O3-TiO2 catalyst were studied by XPS, XRD, TPD and test reaction respectively. XPS determination shows that intensity ratio IZn/Icu for TiO2-free catalyst is higher than that for TiO2 containing catalyst, and TPD study shows that the amount of CO and H2 adsorbed for the latter is greater than that for the former. These facts suggest that the TiO2 additive improves the distribution of CuO or Cu on the surface of catalyst. It has been found that there are two binding energy values, i. e. Eb1 = 74. 5 eV and Eb2=77. 6 eV of Al in the CuO-ZnO/A12O3 catalyst. These binding energies may be related to the Eb value of Al in γ-A12O3 and Al in A12O3 which strongly interacts with CuO or of Al in the spinel CuAl2O4 respectively. Whereas it is only one Eb value (e. g. 74. 5 eV) of Al in the CuO-ZnO/Al2O3-TiO2 catalyst. Therefore, it is suggested that TiO2 additive may weaken the interaction between Al2O3 and CuO or inhibit the formation of spinel between Al2O3 and CuO. These experimental bindings may be attributed to the structural effect of TiO2 on the catalyst. TPR study shows that the reduction temperature (Tr) of CuO in CuO-ZnO./Al2O3-TiO2 increases with the content of TiO2. XPS determination shows that the Eb value of Cu in TiO2 containing catalyst (Eb=933. 7 eV) is higher than that in TiO2-free catalyst (Eb=932. 9 eV). These observations may indicate that TiO2 exerts electronic effect on the catalyst. Both the structural effect which improves the distribution of CuO or Cu on the surface of catalyst and the electronic effect which weakens the bond strength of Cu-S of TiO2 containing catalyst cause the S-resistant character of CuO-ZnO/Al2O3-TiO2 catalyst greatly improved.