Confinement of mesopores within ZSM-5 and functionalization with Ni NPs for deep desulfurization

Abstract

Adsorptive desulfurization of transportation fuels can be affected by high diffusion limitations in porous sorbents due to the existence of larger kinetic dimensions of sulfur compounds and aromatics. In this contribution, we explored that metal based hierarchically ZSM-5-based micro-/mesostructures (MMZ) can overcome such scarcities without compromising the desulfurization activity. The mesopores of MMZ reduces path length for diffusion to the zeolite internal sites, and the metals (here, Ni) not only establish strong interactions but also enhances the adsorption configurations. The MMZ was synthesized by subjecting commercial H form ZSM-5 (SiO2/Al2O3 = 28) via sequential dissolution-self-assembly and doped with Ni via ultrasound-assisted impregnation. The samples were characterized by N2 sorption, NH3-TPD, XRD, H2-TPR TEM, SEM, FT-IR, elemental distribution mapping, and XPS techniques. The results revealed that high surface area up to 831 m2.g−1 and well-ordered mesostructures obtained when ZSM-5 was subjected to dissolution in 1.0 mol.L−1 NaOH solution and re-assembly of Al- or Si-containing species using cetyltrimethylammonium bromide (CTAB) as a template. The sulfur adsorption capacity was improved from 4.8 to 14.1 mg/g after Ni species and up to 10 wt% are highly dispersed over MMZ. The adsorption capacities of samples decrease in the following order 10Ni/MMZ > 5Ni/MMZ > 15Ni/MMZ > MMZ > 10Ni/ZSM-5 and the increased performance may be ascribed to increased surface acidity, well distributed Ni NPs and texture of MMZ. The isotherm data of thiophene adsorption were fitted well by Langmuir isotherm while kinetic study described that the adsorption data followed pseudo-second order model.