SiO_2负载铬基催化剂催化四氢萘合成α-四氢萘酮

Synthesis of α-tetralone from tetralin over SiO_3 -supported Cr-based catalysts

以硝酸铬或重铬酸钾为Cr源,采用浸溃法制备了SiO2负载的Cr基催化剂[Cr(Ⅲ)/SiO2和Cr(Ⅵ)/SiO2],并用共浸溃法制备了K2O改性的Cr(Ⅲ)/SiO2催化剂[K-Cr(Ⅲ)/SiO2]。分别以叔丁基过氧化氢和O2作氧化剂,考察了三种催化剂催化四氢萘合成α-四氢萘酮的反应性能。结果表明,以叔丁基过氧化氢作氧化剂时,Cr(Ⅲ)/SiO2表现出最高的反应活性和选择性,K-Cr(Ⅲ)/SiO2与Cr(Ⅵ)/SiO2活性相近。紫外可见漫反射光谱表征结果表明,Cr(Ⅲ)/SiO2具有最高的低价Cr物种(Cr[L])和高价Cr物种(Cr[H])比例,K2O的引入抑制了Cr[L]物种的生成。推测以叔丁基过氧化氢作氧化剂时,四氢萘氧化生成α-四氢萘醇是反应速率控制步骤,Cr[L]物种可能是催化该反应的活性中心。以O2作氧化剂时,Cr(Ⅲ)/SiO2与Cr(Ⅵ)/SiO2催化剂性能相近,说明O2在相界面传质和(或)在催化剂表面吸附可能是反应的控制步骤。

SiO2 supported Cr-based catalysts were prepared by impregnation method using Cr（ NO3 ）3 or KECr2O2（denoted as Cr （ m ）/siO2 or Cr （ Ⅵ）/SiO2, respectively） as the chromium source. For comparison, K2O modified Cr （ Ⅲ ）/SiO2 （ K-Cr method. Catalytic behaviors of the three sorts of （Ⅲ）/SiO2 ） was also prepared by co-impregnation catalysts for oxidation of tetralin to α-tetralone, using tert-butyl hydroperoxide （TBHP） or O2 as the oxidants, were investigated. The results indicated that when TBHP was used as the oxidants, Cr（ Ⅲ ）/SiO2 exhibited the highest activity and the selectivity to ct-tetralone, while K-Cr（ m ）/sio2 and Cr（ VI ）/SiO2 exhibited similar catalytic behavior. The UV-vis results indicated that Cr（ Ⅲ）/SiO2 had the highest low valence Cr species （ Cr[ L] ） to high valence Cr species （Cr[ H]） ratio, and introduction of K2O inhibited formation of Cr[ L]. It was supposed that oxidation of tetralin to α-tetralol was the rate controlling step and might be catalyzed by Cr[ L] species. Cr（ Ⅲ）/SiO2 and Cr（ Ⅵ ）/SiO2 behaved similarly when O2 was used as the oxidant, suggesting that O2 transfer between the phase interfaces and/or adsorption of O2 over the catalysts might be the rate controlling step in this case.