Journal of Materials Science, Vol.42, No.11, 4066-4075, 2007
Synthesis of ZSM-5 zeolite of improved bulk and surface properties via mixed templates
Hydrothermally synthesized ZSM-5 zeolites using tetrapropyl-ammonium bromide (TPA-Br), Xylitol (Xy) and tetrapropyl-ammonium bromide + Xylitol templates; those compared with that of the parent having the same Si/Al molar ratio (64) and purchased from Mobil, were characterized with several physicochemical techniques including N-2 adsorption, XRD, TG/DSC, FTIR and pyridine-FTIR. The effect of various templates on the crystallinity, crystallites size, surface properties and thermal stabilities of the produced ZSM-5 were investigated. ZSM-5 synthesized using TPA-Br + Xy; of S-BET = 393 m(2) g(-1), exhibited a crystallinity percentage comprises of 1.42% when compared with that of the parent (taken at 100% crystallinity) and measured as well a crystallites size of 61 nm exceeding that derived from Xy (41 nm) that measured the lowest crystallinity percentages (71%), lowest S-BET (303 m(2) g(-1)) and highest yield (65%) between all samples. The former sample showed high thermal stability (till 1,000 degrees C) when compared with that derived from TPA-Br, as illustrated from TG/DSC thermograms that provided a criteria on decreasing the pore radius as a result of enclosing appreciable amounts of TPA(+) and Xy inside narrow pores of ZSM-5. This sample also indicated a hydrophobic tendency when compared with that devoted from TPA-Br. Pyridine adsorption measurements showed that addition of Xy to TPA-Br stimulate the existence of basic sites in addition to acidic ones (mainly Bronsted ones) that was in the middle between that derived from Xy and TPA-Br templates. More informations on the textural properties, morphologies, vibrational tetrahedral co-ordination T(Si or Al)-O modes and acidity were evaluated and discussed.