Search

This article reports a novel method for preparing supported NiW hydrodesulfurization (HDS) catalysts with tunable size and morphology of active phases to achieve highly selective HDS performance in hydro-upgrading fluid catalytic cracking (FCC) naphtha. The proposed approach features the combined use of W-based hybrid nanocrystals (HNCs) as the W precursor and the promoting effect optimization of Ni promoter. The W-based HNCs synthesized under mild hydrothermal conditions are monodispersed particles with an average size of ca. 2 nm and show a core–shell structure with W 6 O 19 2− as the inorganic core and short-chain quaternary ammonium cations as the organic shell. The use of W-based HNCs facilitates the formation of highly dispersed W species and WS 2 active phases with enhanced stacking, thus yielding a larger number of accessible Ni–W–S edge sites upon nickel impregnation. Moreover, we found that the advantageous W dispersion in the HNC-derived monometallic catalyst precursor allows further modification of the size and morphology of the active phase via the optimized incorporation of Ni promoter, leading to the formation of Ni–W–S edge sites with a lower percentage of brim sites and thereby resulting in considerably higher selective HDS performance for FCC naphtha than its counterpart prepared by the conventional impregnation method. The proposed approach makes it easy to tune the size and morphology of WS 2 nanoparticles, shedding light on the rational design of supported WS 2 catalysts for FCC naphtha selective HDS. [ABSTRACT FROM AUTHOR]

In this article, we describe a novel strategy for synthesizing hierarchical ZSM-5 zeolites via the nanoscale depolymerization–reorganization of natural aluminosilicate minerals. This strategy involves two important steps: the first is the top-down depolymerization of one aluminum-rich aluminosilicate mineral via a novel submolten salt system and one silicon-rich aluminosilicate mineral via conventional thermal treatment into nanoscale building blocks, and the second is the bottom-up rearrangement and reorganization of nanoscale building blocks in the synthesis system into hierarchical ZSM-5 zeolites. When used as a fluid catalytic cracking catalyst additive, the resulting ZSM-5 zeolite with hierarchical micro–mesoporous structure exhibited high activity and selectivity for valuable products in preliminary oil refining tests. The salient features of the strategy lie in that it neither involves any inorganic aluminum and silicon salts as precursors nor uses any secondary mesoscale template and post-treatment to create mesopores, thus demonstrating itself to be a green route to synthesizing hierarchical zeolites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sn-Beta zeolite with Lewis acid sites is able to activate C-H bond. • Sn-Beta zeolite exhibits high performance in propane dehydrogenation. • Theoretical calculation suggest that the propane dehydrogenation occurs on the Lewis acid sites. The gap between supply and demand of propylene has become more and more evident, because of a large consumption of the downstream products derived from propylene. Propane dehydrogenation (PDH) constitutes an important alternative for the production of propylene, and thus considerable attention has been paid to the development of eco-friendly and cost-efficient catalysts for this process. Herein, we discover that the Sn-Beta zeolite with Lewis acid sites can activate the C-H bond, and exhibits high catalytic performance in the PDH. XRD, STEM, and XPS characterizations confirm that Sn species are incorporated into the zeolite framework, and H 2 -TPR suggests that there is a strong interaction between Sn species and zeolite framework. It is found that the Lewis acid is the active site for dehydrogenation reaction, and the Brønsted acid is responsible for cracking reaction. The dehydrogenation rate/cracking rate is positively proportional to the L/B ratio, and a high L/B ratio is beneficial for the propane dehydrogenation reaction. The Na-Sn-Beta-30 catalyst possessing the highest amount of Lewis acid but the lowest Brønsted/Lewis ratio, exhibits the best performance in the PDH, which delivers propane conversion of 40% and propylene selectivity of 92%. Most importantly, these Sn-Beta zeolites are extremely stable without any detectable deactivation under the harsh reaction condition for 72 h. Density functional theory calculations reveal that both Sn and adjacent O atom or OH group cooperatively act as the active sites. The PDH occurs through the direct reaction mechanism in which hydrogen molecule is produced by the direct coupling of H atom of primary C 3 H 7 motif with the Brønsted proton in closed sites or the proton of water in open sites. It seems that open sites are more reactive than the closed ones, and the intrinsic enthalpy barriers are calculated to be 242 ~ 301 kJ/mol depending on the hydroxylation extents. These efficient Sn-Beta zeolites could provide a new possibility for the development of a new generation of PDH catalysts with a high stability for the production of propylene. [ABSTRACT FROM AUTHOR]

• Pt-Sn/θ-Al 2 O 3 catalysts were prepared from Surface Organometallic Chemistry concept. • Pt-Sn clusters around 0.75 nm are uniformly distributed at the surface of θ-Al 2 O 3. • Pt-Sn catalyst exhibits high performance in propane dehydrogenation reaction. The bimetallic Pt-Sn catalysts are known to be the most efficient ones for propane dehydrogenation reaction; however, the synthesis of bimetallic Pt-Sn nanocluster (below 1 nm) with an alloy structure still remains a formidable challenge. An approach for the controllable synthesis of Pt-Sn nanocluster based on Surface Organometallic Chemistry on oxide concept is developed here, which involves two basic steps: the sequential grafting of Pt(COD)Me 2 and HSnPh 3 at the surface of dehydroxylated θ-Al 2 O leading to the formation of well-defined bimetallic surface compound consisting of [(AlO)Pt(COD)Me] and [(AlO)SnPh 3 ] fragments, and the hydrogenolysis of this surface compound under a mild condition giving rise to the ultra-small bimetallic Pt-Sn cluster around 0.75 nm. The achieved Pt-Sn/θ-Al 2 O 3 catalysts exhibit high activity, selectivity and stability in propane dehydrogenation to propylene. [ABSTRACT FROM AUTHOR]