Effect of Zn Contents of W/Zn-Beta Catalysts on Their Catalytic Performance in the Selective Hydrocracking of Tetrahydronaphthalene into Benzene, Toluene, and Xylene

Selectivehydrocracking (HDC) of tetrahydronaphthalene (THN) intolight aromatic hydrocarbons, such as benzene (B), toluene (T), andxylene (X), was performed over bifunctional catalysts with differentZnO contents (W/Zn-Beta) at 400 degrees C and 6 MPa. In this work, thechange of catalytic performance of the bifunctional catalysts withdifferent ZnO contents in selective HDC of THN and the nine-lump reactionkinetic model was investigated. It was found for the first time thatZnO can not only effectively regulate the acid properties of Betazeolite but also react with WO3 to form non-active ZnWO4 crystals, resulting in low HDC activity of the catalyst.At low ZnO contents of the catalyst (<1 wt %), as the interactionof ZnO-Beta is stronger than that of WO3-Beta,the interaction of ZnO-Beta would replace the interaction ofWO(3)-Beta, leading to the agglomeration of WO3 and the dispersions of WO3 on Beta zeolite decrease.As a result, WO3 would be easily reduced to WS2, and the BTX selectivity would increase. At high ZnO contents ofthe catalyst (>= 1 wt %), the strong acid sites of Beta zeolitewould be covered by ZnO. In addition, the excess ZnO would react withWO(3) to form non-active ZnWO4 crystals, and theBTX selectivity would decrease. The W(25)/Zn(1)-Beta-40 catalyst exhibitedmaximal BTX selectivity (45 wt %) at 94% THN conversion. The kineticstudy further indicated that with the increase of ZnO contents, theratio of formation reaction rate of BTX to the over-HDC rate of BTXincreases first and then decreases, and the reaction path selectivityof THN isomerization increases.

Automated summary

Selective hydrocracking (HDC) of tetrahydronaphthalene (THN) into light aromatic hydrocarbons, such as benzene (B), toluene (T), and xylene (X), was performed over bifunctional catalysts with different ZnO contents (W/Zn-Beta) at 400 degrees C and 6 MPa. It was found that ZnO can effectively regulate the acid properties of Beta zeolite and react with WO3 to form non-active ZnWO4 crystals, resulting in low HDC activity of the catalyst.