Lei Han

A series of phosphorus and rare earth (RE: La, Ce, Y) modified ZSM-5 zeolites were prepared using precipitation method to enhance vanadium (V) resistance and improve light olefin yield in the catalytic cracking of n-dodecane. The modified catalysts were characterized by XRD, TEM, BET, NH3-TPD, XPS, XAS, and UV-Raman spectroscopy. The results show that RE modification significantly enhances V resistance by forming stable vanadates and protecting the zeolite framework. Among the RE elements, Ce exhibited the best performance due to its redox properties and ability to stabilize Ce (III) in the presence of phosphorus. The P/Ce-ZSM-5 sample (P1Ce) demonstrated superior catalytic performance under 3000 ppm V contamination, with a conversion of 88.90% and a total light olefin yield of 26.51%. The synergistic effect of P and Ce facilitates the reduction of V(V) to the less destructive V(IV) species, thereby alleviating framework damage of zeolites and preserving its acidic sites. This study offers a promising strategy for designing V-resistant zeolite catalysts for deep catalytic cracking (DCC) processes.

Stable extra-large-pore zeolites are highly desirable for catalysis and molecular separation, but most remain microporous, limiting their effectiveness for bulky substrates. Among the few extra-large-pore zeolites that exhibit mesoporosity, the pores typically form as elongated, noncircular pore apertures. We report that NJU120-6, a stable silicate zeolite with an intrinsic cylindrical mesoporous system, has the currently largest 36-ring windows with a free diameter of 25.71 angstroms by 19.12 angstroms. NJU120-6 exhibits the lowest framework density of 9.39 silicon atoms per cubic nanometer and a pore volume of 0.66 cubic centimeters per gram. It remains stable up to 1173 kelvin and can incorporate aluminum and titanium, enabling superior performance in catalytic cracking and in liquid-phase alkene oxidation of bulky molecules, respectively.

Featuring engineerable reaction pathway, ordered hierarchical cracking over core-shell structured zeolites (core@shell) plays a pivotal role in achieving the high-efficient conversion of low-value oil fractions into important petrochemical building blocks such as ethylene and propylene. However, the synthesis of core@shell zeolite composites with specific desirable textures is technically challenging. Herein, a novel embryo seed-breeding (ESB) approach was developed to synthesize polycrystalline ZSM-5@Beta core-shell composites (pZ@B) for boosted light olefin production. For the first time, pZ@B composites composed of a polycrystalline ZSM-5 core and a submicron-sized Beta shell was reported, which shows enhanced inner-diffusion properties and improved hydrothermal stabilities than that of conventional ZSM-5@Beta composites. In pZ@B-catalyzed reations, bulky molecules undergone a preliminary cracking into intermediate products within the Beta shell, followed by the direct diffusion into the micropores of the ZSM-5 core where they could be cracked selectively into ethylene and propylene. Compared with physically mixed zeolites and hierarchical ZSM-5, this pZ@B composite showed the highest conversion and yield of ethylene and propylene in the cracking reaction of both decalin and practical industrial heavy oil. The superior catalytic activity of pZ@B can be attributed to the high accessibility of acid sites and the ordered hierarchical cracking space derived from the core-shell structure.