High-silica hollow Y zeolite by selective desilication of dealuminated NaY crystals in the presence of protective Al species

High-silica hollow faujasite crystals were obtained by dealumination of standard NaY crystals followed by their selective desilication in the presence of protective aluminum species.

Carboxylic acids to butyl esters over dealuminated–realuminated beta zeolites for removing organic acids from bio-oils

This article describes a novel method to dealuminate and realuminate H-beta zeolites as catalysts for removing organic acids from bio-oils via their esterification reactions with alcohols.

Etherification over Hβ zeolite modified by lanthanum ion exchange combined with low-temperature steam treatment

Lanthanum ion exchange, steam treatment and La/steam combined modification were used to modify Hβ zeolite, and then comparative studies were performed on the influences of single and compound modified methods on the etherification activity.

Synthesis of mesoporous Beta and Sn-Beta zeolites and their catalytic performances

Mesoporous Beta and Sn-Beta zeolites have been successfully synthesized through a hydrothermal templating and a subsequent post-synthetic route, respectively.

Acidity Adjustment of HZSM-5 Zeolites by Dealumination and Realumination with Steaming and Citric Acid Treatments

This article describes a novel method for acidity adjustment of HZSM-5 zeolites with steaming and citric acid treatments and demonstrates the realumination effect of citric acid on HZSM-5 zeolites dealuminated by steaming. A series of modified HZSM-5 zeolites were prepared by streaming and/or acid treatments and characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), (27)Al MAS NMR spectroscopy, hydroxyl infrared spectroscopy (OH-IR), pyridine-adsorbed infrared spectroscopy, and N(2) adsorption in the present investigation. The results showed that compared with single HCl or citric acid treatment, steaming treatment, and steaming/HCl treatments, citric acid treatment after steaming exclusively increased the amount of framework Al due to reinsertion of extraframework Al into the defective sites of the steamed HZSM-5 framework. This realumination effect of the citric acid treatment on the steamed HZSM-5 zeolite, which is reported here for the first time to the best of our knowledge, could nearly recover the pore structure of the steamed zeolite to that of the parent HZSM-5 zeolite and appropriately tailor the amount and strength of different acid sites, which sheds light on optimizing the physicochemical properties of HZSM-5 zeolites. It was also found that the steaming treatment prior to the citric acid treatment was the precondition of the realumination of HZSM-5 zeolites, suggesting that the lattice defect sites generated during steaming were necessary for citric acid to work.

Mechanism of hierarchical porosity development in MFI zeolites by desilication: the role of aluminium as a pore-directing agent

The role of the concentration and the nature of aluminium in the creation of hierarchical porosity in both commercial and synthesized MFI zeolites have been investigated through controlled mesoporosity development by desilication in alkaline medium. Framework aluminium controls the process of framework silicon extraction and makes desilication selective towards intracrystalline mesopore formation. An optimal molar Si/Al ratio in the range 25-50 has been identified; this leads to an optimal mesoporosity centred around 10 nm and mesopore surface areas of up to 235 m(2) g(-1) while preserving the intrinsic crystalline and acidic properties. At lower framework Si/Al ratios the relatively high Al content inhibits Si extraction and hardly any mesopores are created, while in highly siliceous ZSM-5 unselective extraction of framework Si induces formation of large pores. The existence of framework Al sites in different T positions that are more or less susceptible to the alkaline treatment, and the occurrence of re-alumination, are tentative explanations for the remarkable behaviour of Al in the desilication process. The presence of substantial extra framework Al, obtained by steam treatment, inhibits Si extraction and related mesopore formation; this is attributed to re-alumination of the extraframework Al species during the alkaline treatment. Removal of extraframework Al species by mild oxalic acid treatment restores susceptibility to desilication, which is accompanied by formation of larger mesopores due to the enhanced Si/Al ratio in the acid-treated zeolite.