Some new observation on the formation and optical properties of CdS clusters in zeolite-Y

CdS clusters in zeolite-Y have been prepared by the exchange of Cd2+ into the zeolite following by sulfurization with Na2S in solution. Blue-shifts from the bulk caused by quantum size effect and the change of absorption upon CdS loading are observed. Two absorption bands are detected for one of the sample and are assigned to the 1s-1s band and exciton transition, respectively. The exciton feature is more pronounced in the excitation spectrum than in the absorption spectrum, and the luminescence excited at the exciton band is stronger than that at the 1s-1s band. Copyright (C) 1996 Elsevier Science Ltd

New observation on the formation of PbS clusters in zeolite-Y

PbS clusters in zeolite-Y have been prepared with the reaction of Pb2+-ion-exchanged zeolite-Y with Na2S in solution at room temperature. Their absorption spectra show dramatic blue shifts from that of the bulk PbS. Obvious change of both the absorption edges and peak positions upon PbS concentrations have been observed. These phenomena provide evidences that PbS clusters have been formed within the zeolite. The absorption spectra show featureless structure and have no tails near the absorption edges. As the PbS loading density becomes higher, the absorption bands become stronger and sharpen. Order PbS clusters lattice with high quality might be formed in the supercages of zeolite-Y. (C) 1996 American Institute of Physics.

Catalytic performance of MCM-22 zeolite for alkylation of toluene with methanol

MCM-22 zeolite with mid-strong acidity and openings of 10-membered ring channels may obtain a high catalytic activity and selectivity for alkylation of toluene with methanol. The acidic sites, for catalyzing alkylation of toluene with methanol, are weaker than that for catalyzing toluene disproportionation. Compared with silicon as a modifier, modification of MCM-22 with La(NO3)(3) is a promising way to improve the catalytic selectivity of para-xylene. In addition, the experimental results also clearly indicate the characteristics of MCM-22 structure consisting of large intracrystalline cages, some of which may locate on surface of MCM-22. (C) 2004 Elsevier B.V. All rights reserved.

Enlarged area A-type zeolite membranes prepared by vacuum seeding method

High quality A-type zeolite membranes, with enlarged area over 70 cm(2), were successfully synthesized on a tubular alpha-Al2O3 support by applying the vacuum seeding method.

Synthesis of NaA zeolite membrane on a ceramic hollow fiber

NaA zeolite membrane was successfully synthesized on a ceramic hollow fiber with an outer diameter of 400 mum, a thickness of 100 mum and an average pore radius of 0.1 mum. The as-synthesized membranes were characterized by XRD, SEM as well as gas permeation. A continuous C NaA zeolite membrane formed after a three-stage synthesis. The membrane thickness was similar to5 mum. Gas permeation data indicated that a relatively high quality NaA zeolite membrane formed on the ceramic hollow fiber support. (C) 2003 Elsevier B.V. All rights reserved.

Effect of acid strength distribution on conversion of FCC gasoline over a ZSM-5 zeolite catalyst

Acid strength distribution and the distribution of aromatics formed in the FCC gasoline conversion reaction on a ZSM-5 zeolite with different Na contents have been studied. With increasing Na content in the ZSM-5 zeolite, the acid sites determined by NH3-TPD technique, especially the strong acid sites, clearly decrease. When used as catalyst for the aromatization reaction, the transformation of olefins in the FCC gasoline into aromatics is governed directly by the strong acid sites on the ZSM-5 catalyst. Only under the conditions that a ZSM-5 catalyst possesses suitable strong acid sites is reaction temperature favorable for the aromatics formed.