A facile and effective method for the distribution of Mo/HZSM-5 catalyst active centers

Post-steaming treatment of Mo/HZSM-5 catalysts results in more molybdenum species migrating into and residing in the HZSM-5 zeolite channels. This is confirmed by XRF and XPS measurements. H-1 MAS NMR and Si-29 MAS NMR also demonstrate that the number of free Bronsted acid sites decreases in the Mo/HZSM-5 catalysts that underwent post-steaming treatment, compared to untreated Mo/HZSM-5 catalysts. As a result, the deactivation rate constant (kd) on the Mo/HZSM-5 catalyst after post-steaming treatment for 0.5 h is much smaller, and the catalyst therefore shows remarkable stability in the probe reaction of methane dehydro-aromatization. The results suggest that a more beneficial bi-functional balance between active Mo species for methane activation and acid sites for the following aromatization is developed over those Mo/HZSM-5 catalysts that have experienced post-steaming treatment for 0.5 h, in comparison with the untreated Mo/HZSM-5 catalysts.

Cyclopropanation on a highly active heterogeneous catalyst: CuO/TiO2-Al2O3

Some heterogeneous catalysts, cupric oxide supported on different supports, were prepared and employed to catalyze the cyclopropanation of styrene and 2,5-dimethyl-2,4-hexadiene with ethyl diazoacetate (EDA). The catalytic performance for cyclopropanation strongly depends on the nature of the support. A novel catalyst, CUO/TiO2-Al2O3, in which Al2O3 is modified with a monolayer TiO2, is found to be most active and selective for the cyclopropanation reaction. The yields of 93 and 94% cyclopropanes are obtained for styrene and 2,5-dimethyl-2,4-hexadiene at 40 degreesC as the substrates, respectively. The activity and selectivity in cyclopropanes are optimized with a monolayer dispersion of cupric oxide on the corresponding supports. (C) 2002 Elsevier Science B.V. All rights reserved.

In situ IR spectroscopic studies on molybdenum nitride catalysts: active sites and surface reactions

Recent IR spectroscopic studies on the surface properties of fresh Mo2N/gamma-Al2O3 catalyst are presented in this paper. The surface sites of fresh Mo2N/gamma-Al2O3, both Modelta+ (0<δ<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm(-1), due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo2N/gamma-Al2O3 behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo2N/gammaAl(2)O(3) catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo2N/gammaAl(2)O(3) catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites.

A Review of Active Appearance Models

Active appearance model (AAM) is a powerful generative method for modeling deformable objects. The model decouples the shape and the texture variations of objects, which is followed by an efficient gradient-based model fitting method. Due to the flexible and simple framework, AAM has been widely applied in the fields of computer vision. However, difficulties are met when it is applied to various practical issues, which lead to a lot of prominent improvements to the model. Nevertheless, these difficulties and improvements have not been studied systematically. This motivates us to review the recent advances of AAM. This paper focuses on the improvements in the literature in turns of the problems suffered by AAM in practical applications. Therefore, these algorithms are summarized from three aspects, i.e., efficiency, discrimination, and robustness. Additionally, some applications and implementations of AAM are also enumerated. The main purpose of this paper is to serve as a guide for further research.

Functional gold nanoparticle-peptide complexes as cell-targeting agents

In this paper, we report a novel approach using peptide CALNN and its derivative CALNNGGRRRRRRRR (CALNNR(8)) to functionalize gold nanoparticles for intracellular component targeting. The translocation is effected by the nanoparticle diameter and CALNNR8 surface coverage. The intracellular distributions of the complexes are change from the cellular nucleus to the endoplasmic reticulum by increasing the density of CALNNR8 at a constant nanoparticle diameter. Additionally, increasing the nanoparticle diameter at a constant density of CALNNR8 leads to less cellular internalization.

Ethylene polymerization, and the copolymerizations of ethylene with hexene or norbornene with highly active mono(beta-enaminoketonato) vanadium(III) catalysts

Five novel vanadium(III) complexes [PhN = C(R-2)CHC(R-1)O]VCl2(THF)(2) (4a: R-1 = Ph, R-2 = CF3; 4b: R-1 =t-Bu, R-2 = CF3; 4c: R-1 = CF3, R-2 = CH3; 4d: R-1 = Ph, R-2 = CH3; 4e: R-1 = Ph, R-2 = H) have been synthesized and characterized. On activation with Et2AlCl, all the complexes, in the presence of ethyl trichloroacetate (ETA) as a promoter, are highly active precatalysts for ethylene polymerization, and produce high molecular weight and linear polymers. Catalyst activities more than 16.8 kg PE/mmolv h bar and weight-average molecular weights higher than 173 kg/ mol were observed under mild conditions.

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure.

WO3/C hybrid material as a highly active catalyst support for formic acid electrooxidation

The hybrid material based on WO3 and Vulcan XC-72R carbon has been used as the support of Pd nano-catalysts. The resultant Pd-WO3/C catalysts in a large range of WO3 content exhibit excellent catalytic activity and stability for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the uniform dispersion of Pd with less particle sizes on the WO3/C support and the hydrogen spillover effect which greatly accelerates the dehydrogenation of HCOOH on Pd.

Self-assembly of lambda-DNA networks/Ag nanoparticles: Hybrid architecture and active-SERS substrate

In this article, highly rough and stable surface enhanced Raman scattering (SERS)-active substrates had been fabricated by a facile layer by-layer technique. Unique lambda-DNA networks and CTAB capped silver nanoparticles (AgNP) were alternatively self-assembled on the charged mica surface until a desirable number of bilayers were reached. The as-prepared hybrid architectures were characterized by UV-vis spectroscopy, tapping mode atomic force microscopy (AFM) and confocal Raman microscopy, respectively.

Ethanol-induced formation of silver nanoparticle aggregates for highly active SERS substrates and application in DNA detection

A controllable silver nanoparticle aggregate system has been synthesized by adding different amounts of ethanol to cetyltrimethylammonium bromide (CTAB) capped silver nanoparticles (Ag-nps), which could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. This ethanol-induced aggregation can be attributed to preferential dissolution of CTAB into ethanol, which leads a partial removal of the protective CTAB layer on Ag-nps. The optical and morphological properties of these aggregates under various volumes of ethanol were explored via UV-vis spectroscopy and atomic force microscopy.