摘要
本文用XPS和XRD考察了由Rh_4(CO)_(12)出发制得的Rh/V_2O_5和Rh/TiO_2两种催化剂的金属载体强相互作用的差别。实验结果表明,1)高温H_2还原的Rh/TiO_2催化剂,经氧处理后即能恢复吸H_2能力。Rh/V_2O_5催化剂在较低温度(473K)H_2还原时Rh就进入SMSI状态,吸H_2能力被完全抑制,373K氧处理并不能使之恢复,吸H_2性质表现出不可逆性。2)与Rh/TiO_2催化剂的TiO_2相比,Rt/V_2O_5催化剂的V_2O_5更易还原,Rh对V_2O_5的还原有明显的促进作用。3)担载在TiO_2上的Rh比在V_2O_5上更易还原。4)还原后,催化剂表层的Rh/V、RH/Ti均有较大幅度的降低。用氧空位模型能较好地说明Rh/TiO_2催化剂的实验结果,而Rh/V_2O_5催化剂的实验结果适于用钒氧化物覆盖模型解释。
The differences in the manifestation of strong metal-support interaction (SMSI) for Rh/V2O5and Rh/TiO2 catalysts were studied by O2 - H2 titration, XPS and XRD. Cluster Rh4(CO)12 was synthesized according to reference(8). The catalysts were prepared by impregnation of the pretreated oxides (V2O5and TiO2) with Rh4 (CO)12 solution. The Rh content of the catalysts was 1 wt%. The samples were decarbonylated by evacuation for 2 h at 473 K, and then reduced in flowing H2 for 2 h at 473. 673 and 873 K respectively. O2-H2 titration, XPS and XRD determination were carried out for the reduced samples.The results show: 1) 373 K oxygen treatment can restore H2 sorption capacity of the high-temperature (873 K) reduced Rh/TiO2 catalyst. For Rh/V2O5 catalyst, after lower-temperature(473 K) reduction, the H2 sorptive property is completely suppressed, Rh is in full SMSI state. The sorptive property can not be restored by 373 K oxygen treatment, and exhibits irreversibility. 2) V2O5 of Rh/ V2O5 catalyst is easier to be reduced than TiO2 of Rh/TiO2, Rh can greatly promote the reduction of V2O5. 3) Rh supported on V2O5 is more difficultly reduced than that on TiO2. 4) Rh/V and Rh/Ti ratios of the surface of the catalysts decreased remarkably after the reduction.The experimental results of Rh/TiO2 and Rh/V2O5 catalysts can be explained by oxygen vacancy model and complete coverage by vanadium oxide overlayer, respectively.
出处
《分子催化》
EI
CAS
CSCD
1992年第5期339-345,共7页
Journal of Molecular Catalysis(China)
关键词
铑
催化剂
金属催化剂
Rhodium catalyst, Rhodium cluster, Strong metal-support interaction.
