Junlin Zheng

Bio: Junlin Zheng is an academic researcher from Sinopec. The author has contributed to research in topics: Rietveld refinement & Powder diffraction. The author has an hindex of 4, co-authored 5 publications receiving 122 citations.

Elucidation of Adsorbate Structures and Interactions on Brønsted Acid Sites in H-ZSM-5 by Synchrotron X-ray Powder Diffraction.

Abstract: Microporous H-ZSM-5 containing one Bronsted acid site per asymmetric unit is deliberately chosen to host pyridine, methanol, and ammonia as guest molecules. By using new-generation in situ synchrotron X-ray powder diffraction combined with Rietveld refinement, the slight but significant alteration in scattering parameters of framework atoms modified by the guest molecules enables the user to elucidate their adsorption geometries and interactions with the Bronsted acid sites in H-ZSM-5 in terms of atomic distances and angles within experimental errors. The conclusion, although demonstrated in the H-ZSM-5, is expected to be transferable to other zeolites. This approach provides a stepping stone towards the rational engineering of molecular interaction(s) with acid sites in zeolitic catalysis.

Decarboxylation of Lactones over Zn/ZSM-5: Elucidation of the Structure of the Active Site and Molecular Interactions.

Abstract: Herein, we report the catalytic decarboxylation of γ-valerolactone (GVL) over Zn/ZSM-5 to butene, followed by aromatization at high yield with co-feeding of water. An evaluation of the catalytic performance after prolonged periods of time showed that a water molecule is essential to maintain the decarboxylation and aromatization activities and avoid rapid catalyst deactivation. Synchrotron X-ray powder diffraction and Rietveld refinement were then used to elucidate the structures of adsorbed GVL and immobilized Zn species in combination with EXAFS and NMR spectroscopy. A new route for the cooperative hydrolysis of GVL by framework Zn-OH and Bronsted acidic sites to butene and then to aromatic compounds has thus been demonstrated. The structures and fundamental pathways for the nucleophilic attack of terminal Zn-OH sites are comparable to those of Zn-containing enzymes in biological systems.

A New Route for De-carboxylation of Lactones over Zn/ZSM-5: Elucidation of Structure and Molecular Interactions

Abstract: Here, we report a catalytic process of decarboxylating gamma-valerolactone, GVL (the biomass derived lactone as an example) over Zn/ZSM-5 to butene, followed by aromatization at high yield with co-feed water. Evaluation of catalytic performance at prolonged time shows that water molecule is essential in maintaining the decarboxylation/ aromatization activity without rapid deactivation. Synchrotron X-ray diffraction and Rietveld refinement are then used to elucidate the adsorbed structures of GVL and immobilized Zn-species with the support of EXAFS and NMR. A new route of cooperative hydrolysis of GVL by framework Zn-OH and Bronsted acid sites to butene and then to aromatics is for the first time demonstrated. The structures and fundamental pathways for nucleophilic attack of terminal Zn-OH site are comparable to that of reported Zn-containing enzymes in biological systems.

Fast, highly enantioselective and sustainable fluorination of 4-substituted pyrazolones catalyzed by amide-based phase transfer catalysts

Abstract: We developed an amide-based Cinchona alkaloids catalyzed enantioselective fluorination of 4-substituted pyrazolones, the products with a quaternary chiral fluorine-attached carbon centre were afforded in high yields (up to 99%) with...

31P NMR Chemical Shifts of Phosphorus Probes as Reliable and Practical Acidity Scales for Solid and Liquid Catalysts

Abstract: Acid–base catalytic reaction, either in heterogeneous or homogeneous systems, is one of the most important chemical reactions that has provoked a wide variety of industrial catalytic processes for production of chemicals and petrochemicals over the past few decades. In view of the fact that the catalytic performances (e.g., activity, selectivity, and reaction mechanism) of acid-catalyzed reactions over acidic catalysts are mostly dictated by detailed acidic features, viz. type (Bronsted vs Lewis acidity), amount (concentration), strength, and local environments (location) of acid sites, information on and manipulation of their structure–activity correlation are crucial for optimization of catalytic performances as well as innovative design of novel effective catalysts. This review aims to summarize recent developments on acidity characterization of solid and liquid catalysts by means of experimental 31P nuclear magnetic resonance (NMR) spectroscopy using phosphorus probe molecules such as trialkylphosphin...