Synthesis methodology affecting vanadium titanium silicalite-1 catalyst

Abstract

Vanadium titanium silicalite-1 (V/TS-1) samples (Si/Ti = 50, Si/V = 100) are synthesized by using hydrothermal method. To determine a suitable synthesis method that can control the amounts of titanium and vanadium in the MFI structure of synthesized catalysts, the effects of synthesis methodology (the vanadium salt addition method) and type of vanadium salt (VCl₃, VO(acac)₂and V₂O[subscript 5] ) are investigated. The synthesized catalysts are characterized using various techniques such as XRF, XRD, BET, SEM, FT-IR, NH –TPD and ESR. The catalytic behavior is evaluated using the gas phase oxidation of 2-propanol (8 vol% oxygen, 5 vol% 2-propanol, balanced with argon). The catalytic reaction is carried out in a microreactor at a temperature range 100-500 degree Celsius, atmosphere pressure. This research shows that the vanadium salt addition method and the type of vanadium salt do not significantly affect the MFI structure as well as the reaction pathway. During the synthesis procedure, the vanadium species existing in the part of cation complex when it dissolved in aqueous solution is easier to be incorporated into the TS-1 structure than the ones exist in the part of anion complex. The surface area of the synthesized catalysts decrease inversely with the amount of vanadium incorporated. The NH₃ –TPD results indicate that the synthesized catalysts have two different types of acid site; the weaker one desorbed NH₃ at the temperature range 135-145 degree Celsius and the stronger one desorbed NH₃ at around 222-242 degree Celsius. For catalytic behavior, it is found that the synthesized V/TS-1 catalysts which have the vanadium active species derived from VCl₃ bonded on its surface are active in the 2-propanol oxidation and it can inhibit the dehydration and the combustion of 2-propanol. However, the ones which have the vanadium active species derived from VO(acac)₂ bonded on the catalyst surface do not be active in the 2-propanol oxidation but it can inhibit the 2-propanol combustion. Moreover, it is found that V₂O₅ is not the suitable vanadium source for this synthesis method because V⁵+ tends to stay in the anion complex which is more difficult to be incorporated into the TS-1 structure.