Publications

The modification of HZSM-5 zeolite was carried out by nitridation of commercial HZSM-5 zeolites with flowing pure ammonia at high temperature. The modified HZSM-5 zeolites maintained high crystallinity and high specific surface areas of precursors testified by XRD, BET and SEM analysis. Compared with parent HZSM-5, the surface strong acid sites of modified HZSM-5 zeolites decreased severely as characterized by means of NH3-TPD analysis and pyridine-IR spectroscopy shows that nitridation mainly occurred in Brønsted acid sites. The modified HZSM-5 zeolites exhibited much higher selectivity to para-diethylbenzene (DEB) and significantly enhanced stability than parent HZSM-5 when applied in the reaction of ethylbenzene ethylation with ethanol. The reduction of strong acid sites can suppress the isomerization of para-diethylbenzene and improve the para-selectivity. The effects of nitrogen contents in modified zeolites on the conversion and selectivity to p-DEB were also studied. © 2006 Elsevier B.V. All rights reserved.

ZSM-5 zeolite was in-situ synthesized successfully on the surface of honeycomb cordierite substrate, certified by XRD and SEM techniques. Good thermal and hydrothermal stability of ZSM-5/cordierite could be obtained because of the in-situ synthesis method. Copper ion-exchanged ZSM-5/cordierite was studied as catalyst for selective catalytic reduction of nitrogen oxides. For practical reasons, the catalytic testing experiments were preformed on a real lean burn engine. Unburned hydrocarbons and carbon monoxide in the exhaust were directly used as reductants for NOx reduction. Cu-ZSM-5/cordierite exhibited high catalytic activity, and at 673 K the maximal NOx conversion to N2 could reach 50% at gas hourly space velocity (GHSV) of about 25 000 h(-1). Hydrocarbons and carbon monoxide in the exhaust could also be purified at the same time. As expected, Cu-ZSM-5/cordierite catalyst exhibited good duration and antipoison properties. When traces of lanthanum were introduced to Cu-ZSM-5/cordierite catalyst as a modifier, the activated temperature of the catalyst could be decreased and the temperature window with high NOx conversions broadened. Cu-ZSM-5/ cordierite and LaCu-ZSM-5/cordierite were thought as promising automobile exhaust catalysts under lean conditions. Copper is the main active component in the Cu-ZSM-5/ cordierite catalyst and Cu(II), which was found in the catalyst during the proceeding of reaction by XPS, is thought to be essential. On the basis of this, deNOx process over Cu-ZSM-5/cordierite is also discussed.

Ag/TiO2 catalyst with fine size and homogeneous dispersion of coated silver clusters was synthesized by a recently developed pH-controlled photocatalytic process and applied to the photocatalytic reduction of nitrate as an environmentally friendly and low-cost catalyst with formic acid as a hole scavenger. Compared with conventional preparation routes, the as-prepared Ag/TiO2 catalyst in this study shows better catalytic performance: a nitrate conversion of 98% and selectivity for nitrogen of ca. 100%, which can be achieved after 30 min of irradiation. The average activity was calculated to be ca. 24 mmolNO3-gAg-1min-1, which is much higher than that of most of Pd-Cu-based nitrate hydrogenation systems in terms of metal usage, demonstrating its application potential. A similar photocatalytic efficiency and selectivity for nitrogen were also observed for nitrite photocatalytic reduction on this catalyst. The effects of Ag content, hole scavengers, concentration of formic acid, and other anions present in drinking water, such as SO42-, CO32-, and HCO3-, were systematically investigated. © 2005 Elsevier Inc. All rights reserved.

ZSM-5 zeolitic coatings on aluminum have been prepared successfully by in-situ hydrothermal synthesis method and ZSM-5/A1 monolith was formed. The effects of pH value and crystallization time on the in-situ synthesis were discussed.

A simple and green in situ hydrothermal method, free of organic templates or zeolite seeds, was examined and introduced by depositing several typical microporous aluminosilicate zeolites (Linde A, Linde Y, mordenite and ZSM-5) on cordierite supports. Such preparative factors as crystallization time, crystallization temperature and basic strength were systematically investigated to discuss their effect on the growth of zeolites on cordierite supports. The as-prepared zeolite/cordierite samples were characterized by various techniques and a supposed in situ growth mechanism of zeolites on supports was given. The aluminium atoms on cordierite supports were activated by OH-and these activated atoms subsequently built a zeolite framework together with the silicon atoms and aluminium atoms of the synthesis gel. Based on this, the in situ deposition of zeolites can be easily extended to other aluminium-containing supports. With respect to pure zeolite powders, the in situ coated zeolites on supports exhibited much better stability and accessibility, which were thought essential for industrial applications. Copper ion-exchanged ZSM-5/cordierite was studied as catalyst for the direct decomposition of NO and selective catalytic reduction of NO by propane in excess oxygen. Cu-ZSM-5/cordierite was found to exhibit an obviously enhanced turnover frequency compared to Cu-ZSM-5 powders, which made it a potential deNOxcatalyst for future applications. © 2005 Elsevier B.V. All rights reserved.

Nitrided HZSM-5 samples which maintained good crystallinity and high specific surface area were prepared by a nitridation process at a high temperature and used in the acid-catalyzed ethylation of ethylbenzene with ethanol to p-diethylbenzene (p-DEB). The selectivity for p-DEB was significantly increased, and the activity of the catalyst was more stable than that of unmodified HZSM-5 zeolite. Three nitrogen-incorporated HZSM-5 zeolite samples, HZSM-5-5N, HZSM-5-10N, and HZSM-5-15N, were obtained by the nitridation of HZSM-5 with pure ammonia at 800°C for 5, 10, and 15 hr, respectively. HZSM-5 was pretreated at a high temperature before the nitridation was performed. The nitrogen contents were detected by alkaline digestion with molten NaOH at 400°C, and the resulting NH3was titrated with H2SO4. HZSM-5 showed a higher initial activity, but the selectivity for p-DEB was lower than that of HZSM-5-10N and there was a rapid decrease in catalytic activity after several hours. In contrast, the selectivity of HZSM-5-10N was enhanced from 52 to 82%, and the conversion of ethylbenzene was comparatively stable during the reaction time.

Solid-supported metal catalysts have been widely used in industrial processes. The morphology of coated metal on the support is usually an important factor affecting the efficiency of the catalyst. In this study, a photocatalytic process is utilized to control the morphology of platinum particles deposited on titania (Degussa P-25). More specifically, the effect of pH on the morphology and the valence state of platinum nanoparticles was systemically investigated. It is found that, via a simple pH-controlled process, various states of platinum (Pt0, PtIIO, or PtIVO2) can be deposited onto the support directly at will. In this paper, the mechanism of morphology control and the key influencing factors at different pH regimes will be discussed. Followed by photodeposition, a H2 thermal treatment process was employed to convert the oxides into metal platinum with narrow size distribution and even coverage on the supporting titania. Various techniques such as transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive analysis of X-rays, and X-ray photoelectron spectroscopy were employed to characterize the prepared titania-supported platinum particles.

ZSM-5 and AlTS-1 zeolites were successfully in situ synthesized on the surface of honeycomb cordierite substrate, certified by XRD and SEM techniques. Strong interaction between zeolite and substrate developed during in situ synthesis, entailing improved hydrothermal stabilities of the zeolites. A series of nonnoble metal ion-exchanged ZSM-5/cordierite and AlTS-1/cordierite were studied as catalysts for the selective reduction of nitric oxide by propane under dry and wet conditions. In the deNOx processes, NOx (ads) and Cx HyOz (ads) were thought as the important reaction intermediates and the formation of them on the catalysts was a key step in deNOx reactions. Based on this, the factors that influence the activities of the catalysts were discussed considering not only the active components but also the supports. As for the active components, the ability to adsorb gas reactants and the oxidative activity are two dominant factors that determined the deNOx activities. As for the supports, the Brønsted acidity and oxidative activity are two important factors that influenced the deNOx activities. From the catalytic testing results, Cu-ZSM-5/cordierite is selected as a promising SCR deNOx catalyst due to its superior deNOx activity and high selectivity. For practical purposes, the catalytic testing of Cu-ZSM-5/cordierite was also preformed on a real lean-burn engine. Hydrocarbons and carbon monoxide in the exhaust were directly used as reductants for NOx reduction. Thus, three main pollutants in the exhaust could be removed simultaneously. As expected, Cu-ZSM-5/cordierite also exhibited a rather good durability due to the in situ synthesis method. © 2004 Elsevier Inc. All rights reserved.