The Effect Of Additive On Catalytic Activity Of VO_x-WO_x/TiO₂Catalysts In The Catalytic Combustion Of Chlorobenzene

A series of studies about the addition of catalyst composition andpreparation technology on basic of V₂O₅-WO₃/TiO₂（V-W/Ti） catalyst wereinvestigated. Chlorobenzene （CB） was chosen as model compound ofchlorined volatileorganic compounds （CVOCs） to evaluate the catalyticactivity in a conventional fixed-bed quartz reactor. The main results are likethe followings:1. Catalysts of different vanadium loading content of V/Ti、V-W/Tiwere prepared by wet-impregnation method using nano-size TiO₂as support.The influence of oxalic acid dosage on catalytic activity was investigated.The results showed oxalic acid for ammonium metavanadate dissolutioncould promote vanadium dispersion. The reduction of the amount of surfaceoxygen and V-O-Ti bonds and the weakening of the binding energy amongthe components catalysts are result from the increase of oxalic acid. Most ofthe vanadium species exist through bridging V-O-V at the expenses ofV-O-Ti bonds, The content of WO₃was increased. In addition, carbonaceousdeposit derived from oxalic acid covered part of the surface active sites.Accordingly, the activity of the catalytic combustion CB of V-W/Ti wasreduced. A certain amount of V、W was completely dispersed on the surfaceof anatase TiO₂of V-W/Ti catalysts by method of water bath in the absenceof oxalic acid. In the promotion of the tungsten, V、W、Ti interact with eachother in the roasting process, the high active species such as V_xTi_yO andV_xW_yO were generated, containing plenty of V-O-Ti bonds, then abundantsurface oxygen were formed. The V-W/Ti catalyst without oxalic acidpossessed the best catalytic activity.2. A series of catalysts of different manganese and vanadium loadingcontent of MnO_x-V₂O₅-WO₃/TiO₂（Mn-V-W/Ti） were prepared by wet-impregnation method, chlorobenzene was chosen to evaluate thecatalytic activity. The results demonstrated that with Doping of Mn contentincreased, the low-temperature activity of the catalyst increased, but whenMn content is high, the catalytic activity declined seriously.Mn-V-W/Ti（0.25）（Mn:（Mn+V）=0.25） catalyst generated Mn（VO₃）_xspecieswith high Mn valence, and catalyst showed excellent low temperaturecatalytic activity. Mn-V-W/Ti（0.75） possessed the worst catalytic activity,that may be due to the formation of Mn（VO3） with poor active. Theinteraction of Mn and V in Mn-V-W/Ti and generated Mn（VO₃）_xspecieswith different Mn valence, which is the main factors for the catalyst activity.3. The honeycomb catalysts were prepared by extrusion forming.Active component Vanadium, tungsten, manganese, appropriate amount ofrare earth and additives were added, supported on TiO₂. The performance ofchlorobenzene catalytic combustion and preparation process of thehoneycomb catalyst were investigated. The results showed that the differentpreparation process, oxalic acid content, doping of rare earth elementscerium, yttrium impacted on the activity of catalysts. Catalysts existed asgranular and uniformly dispersed before activated, Catalyst particles sizeand pore size was significantly increased after activation. V₂O₅、WO₃、VO₂、Mn （VO3）2、PbO were detected, Ce、Y is completely dispersed in catalysts,Mn（VO₃）₂generated by reaction of active component Mn and V and PbOwould lead to decreased a serious decline about activity. Compressivestrength of the activated catalyst also decreased seriously.