VOx/SBA-15催化剂上甲苯气相部分氧化

采用等体积浸渍法制备了不同负载量的VOx/SBA-15催化剂。UV-Vis和H2-TPR等表征结果表明，在较低钒负载量下，钒物种的分散程度较高，主要以孤立的VO4 3－以及少量聚合体V－O－V形式存在；钒负载量较高时会有大量的聚合体V－O－V甚至晶相V2O5出现，而且，催化剂的酸性随着钒物种的高度分散而降低。甲苯气相部分氧化反应结果表明，随着钒负载量的提高，苯甲醛的选择性先升后降，CO、CO2等选择性逐渐提高。这是由于催化剂存在大量的聚合体V－O－V和晶相V2O5时，聚集态钒物种表面较多的酸量促使苯甲醛深度氧化。在相同钒负载量下，催化剂VOx/SBA-15的钒物种分散状态优于VOx/MCM-41和VOx/SiO2，从而使得催化剂VOx/SBA-15呈现较高的苯甲醛选择性。

Partial oxidation of toluene over VOx/SBA-15 catalyst

A series of vanadium based catalysts with SBA-15 as support were prepared by incipient wetness impregnation and characterized by XRD, BET, TPR, UV-Vis and NH3-TPD. The reaction of toluene oxidation over VOx/SBA 15 was carried out in a fixed bed reactor under the conditions of 380℃~520℃, 0.15MPa, n(N2)/n(O2)/n(toluene) = 40/10/1, GHSV=600h－1. The results showed that there is an optimal vanadium loading to get highest benzaldehyde selectivity. Vanadium species existed mainly in the form of isolated and polymeric vanadium species at low vanadium loadings; increasing vanadium loadings would cause the formation of V2O5 crystalline. Isolated polymeric vanadium species were shown to be active in partial oxidation of toluene to benzaldehyde, whereas polymeric vanadium species, especially V2O5 crystalline, reduce greatly the selectivity of benzaldehyde in toluene oxidation. A better dispersion of vanadium species over VOx/SBA-15 surface was observed than those over VOx/MCM-41 and VOx/SiO2, this may contribute to its higher benzaldehyde selectivity in toluene oxidation.