Hydroisomerization of n-hexadecane over Pt/ZSM-48 catalysts: Effects of metal-acid balance and crystal morphology

Abstract

The wirelike, rodlike and corolla-like ZSM-48 zeolites with various SiO2/Al2O3 ratios (SARs) were successfully synthesized and exploited for the hydroisomerization of n-hexadecane (n-C16). The influences of metal-acid balance, acid sites quantity, crystal morphology and textural properties on n-C16 hydroisomerization performance were investigated primarily, via various characterization technique such as XRD, FT-IR, SEM, TEM, N2 physisorption, NH3-TPD, and Py-IR. The CPt/CA ratios of various catalysts were calculated for the quantified expression of the metal-acid balance, and the acid sites quantity was seriously crucial for the consecutive acid-catalyzed reaction after CPt/CA ratios satisfied within an ideal range. Large external surface could accelerate the conversion rate, shorten the diffusional constraints and inhibit the cracking. The superiorities of satisfied CPt/CA values (0.12–0.15), high concentration of acid sites (>230 μmol/g) and large external surface (>120 m2/g) persuaded the Pt/Z(P)80, Pt/Z(H)60 and Pt/Z(H)80 samples to demonstrate wonderful hydroisomerization performance with outstanding yield around 80 wt% and excellent i-C16 selectivity over 91 wt%. Although Pt/Z(W)80 and Pt/Z(R)80 samples owned the relatively small crystal, the gloomy catalytic activity of them was observed due to their relatively low concentration of acid sites and external surface. Moreover, the presence of “key-lock” mechanism was verified by the observations of 7-methyl-pentadecane (7MC15) dominating in isomer products.