Qin Xin

Carbon nanotubes as support for cathode catalyst of a direct methanol fuel cell

Colloid Interface Sci 1990;138:590–2.[4] Suzuki T, Kaneko K. Structural change of activated carbon [6] Suzuki T, Kasuh T, Kaneko K. The structural change offibers with desorption by in situ X-ray diffraction. Carbon graphitization-controlled microporous carbon upon adsorp-1988;26:743–5. tion of H O and N . Chem Phys Lett 1992;191:569–73.

UV RESONANCE RAMAN SPECTROSCOPIC IDENTIFICATION OF TITANIUM ATOMS IN THE FRAMEWORK OF TS-1 ZEOLITE

Framework titanium atoms in titanium-substituted silicalite (TS-1) can be identified by UV resonance Raman spectroscopy since the associated Raman bands at 1125, 530, and 490 cm(-1) (see figure) are observed only when the charge transfer transition associated with the framework Ti atoms is excited by a UV laser. Thus, framework Ti atoms can be distinguished from nonframework Ti atoms and other defect sites. This method can be applicable to identifying transition metal atoms in the frameworks of other molecular sieves.

Influence of electrode structure on the performance of a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion(R) membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at I M CH3OH, 2 atm oxygen and 90degreesC yields a current density of 100 mA/cm(2) at 0.53 V cell voltage. The peak power density is 120 mW/cm(2). The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed

Titania-modified Hydrodesulfurization Catalysts .1. Effect of Preparation Techniques On Morphology and Properties of Tio2-al2o3 Carrier

Abstract Samples of titania—alumina of various compositions were prepared by the following methods: precipitation from TiCl4 solution with aqueous ammonia, impregnation, evaporation from titanium isoproxide solution in isopropanol, and grafting by reaction of TiCl4 with a hydroxy group on Al2O3. BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and analytical electron microscopy (AEM) techniques were used to characterize the state of dispersion TiO2 and Al2O3. The results showed that a homogeneous dispersion of TiO2 and Al2O3 could be obtained by the grafting technique. The impregnation method could also result in an almost perfectly homogeneous distribution. For TiO2—Al2O3 samples deposited by precipitation, the coverage of TiO2 was less than 50% monolayer. Temperature programmed desorption (TPD) measurements of ammonia indicated that the acid sites of Al203 modified by TiO2 experienced a strong influence only for the sample prepared by the grafting technique.

Ammonia synthesis over Ru/C catalysts with different carbon supports promoted by barium and potassium compounds

Ammonia synthesis over ruthenium catalysts supported on different carbon materials using Ba or K compounds as promoters has been investigated. Ba(NO3)(2), KOH, and KNO3 are used as the promoter or promoter precursor, and activated carbon (AC), activated carbon fiber (ACF). and carbon molecular sieve (CMS) are used as the support. The activity measurement for ammonia synthesis was carried out in a flow micro-reactor under mild conditions: 350-450 degreesC and 3.0 MPa. Results show that KOH promoter was more effective than KNO3. and that Ba(NO3)(2) was the most effective promoter among the three. The roles of promoters can be divided into the electronic modification of ruthenium, the neutralization of surface functional groups on the carbon support and the ruthenium precursor. The catalyst with AC as the support gave the highest ammonia concentration in the effluent among the supports used, while the catalyst with ACF as the support showed the highest turnover-frequency (TOF) value. It seems that the larger particles of Ru on the carbon supports are more active for ammonia synthesis in terms of TOF value

Pt-based anode catalysts for direct ethanol fuel cells

Abstract In the present work, several carbon supported PtSn and PtSnRu catalysts were prepared with different atomic ratios and tested in direct ethanol fuel cells (DEFC) operated at lower temperature ( T =90 °C). XRD and TEM results indicate that all of these catalysts consist of uniform nano-sized particles of narrow distribution and the average particle sizes are always less than 3.0 nm. As the content of Sn increases, the Pt lattice parameter becomes longer. Single direct ethanol fuel cell tests were used to evaluate the performance of carbon supported PtSn catalysts for ethanol electro-oxidation. It was found that the addition of Sn can enhance the activity towards ethanol electro-oxidation. It is also found that a single DEFC of Pt/Sn atomic ratio≤2, “Pt 1 Sn 1 /C, Pt 3 Sn 2 /C, and Pt 2 Sn 1 /C’’ shows better performance than those with Pt 3 Sn 1 /C and Pt 4 Sn 1 /C. But even adopting the least active PtSn catalyst, Pt 4 Sn 1 /C, the DEFC also exhibits higher performance than that with the commercial Pt 1 Ru 1 /C, which is dominatingly used in PEMFC at present as anode catalyst for both methanol electro-oxidation and CO-tolerance. At 90 °C, the DEFC exhibits the best performance when Pt 2 Sn 1 /C is adopted as anode catalysts. This distinct difference in DEFC performance between the catalysts examined here is attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. It is thought that −OH ads , surface Pt active sites and the ohmic effect of PtSn/C catalyst determines the electro-oxidation activity of PtSn catalysts with different Pt/Sn ratios.

Studies on performance degradation of a direct methanol fuel cell (DMFC) in life test

A 75 h life test of a direct methanol fuel cell (DMFC) at a low current density of 100 mA cm−2 was carried out. Electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to characterize the membrane electrode assembly (MEA) during the life test. The EIS results showed that the high frequency cell impedance of the MEA increased from 0.26 ohm cm2 at the beginning of the life test to 0.37 ohm cm2 at the end. SEM images of the MEA in cross-section apparently demonstrated the delamination of the electrodes from the membrane after the life test. TEM analysis of the electrocatalysts in the pre- and post-test cell revealed that the agglomeration of the metal particles in the anode was more serious than in the cathode. The results indicate that the agglomeration of electrocatalysts together with the delamination of the MEA concurrently contribute to the performance degradation of the DMFC.

Adsorption and oxidation of ethanol on colloid-based Pt/C, PtRu/C and Pt3Sn/C catalysts: In situ FTIR spectroscopy and on-line DEMS studies

The interaction of colloid-based, carbon supported Pt/C (40 wt%), PtRu/C (45 wt%) and Pt3Sn/C (24 wt%) catalysts with ethanol and their performance for ethanol electrooxidation were investigated in model studies by electrochemical, in situ infrared spectroscopy and on-line differential electrochemical mass spectrometry measurements. The combined application of in situ spectroscopic techniques on realistic catalysts and under realistic reaction (DEMS, IR) and transport conditions (DEMS) yields new insight on mechanistic details of the reaction on these catalysts under the above reaction and transport conditions. Based on these results, the addition of Sn or Ru, though beneficial for the overall activity for ethanol oxidation, does not enhance the activity for C-C bond breaking. Dissociative adsorption of ethanol to form CO2 is more facile on the Pt/C catalyst than on PtRu/C and Pt3Sn/C catalysts within the potential range of technical interests (<0.6 V), but Pt/C is rapidly blocked by an inhibiting CO adlayer. In all cases acetaldehyde and acetic acid are dominant products, CO2 formation contributes less than 2% to the total current. The higher ethanol oxidation current density on the Pt3Sn/C catalyst at these potentials results from higher yields of C2 products, not from an improved complete ethanol oxidation to CO2.

Novel synthesis of highly active Pt/C cathode electrocatalyst for direct methanol fuel cell

A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of approximately 2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent.

Titania-modified hydrodesulfurization catalysts: II. Dispersion state and catalytic activity of molybdena supported on titania-alumina carrier

A series of molybdena catalysts supported on titania-modified alumina carrier was characterized by X-ray diffraction (XRD), analytical electron microscopy (AEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). The results show that the type of Mo6+ species depends upon the coverage of titania on alumina. The molybdenum atomic concentration was improved when most of the surface of alumina was occupied by titania. TPR profiles of molybdena/titania-alumina exhibit two peaks at 680-710 K and 1090-1100 K. The amount of hydrogen consumption in the TPR process increases with a rise in titania content, which suggests that titania promotes the reduction of molybdena to much lower valency. The XPS data is in agreement with the TPR results. The measurements of the activity of the catalyst in hydrodesulphurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene indicate that titania-modified alumina supports can improve the HDS primary activity of the catalyst.