Fuel quality and operational issues for polymer electrolyte membrane (PEM) fuel cells

Polymer electrolyte membrane (PEM) fuel cells are susceptible to degradation due to the catalyst poisoning caused by CO present in the fuel above certain limits. Although the amount of CO in the fuel may be within the permissible limit, the fuel composition (% CO₂, CH₄, CO and H₂O) and the operating conditions of the cell (level of gas humidification, cell temperature and pressure) can be such that the equilibrium CO content inside the cell may exceed the permissible limit leading to a degradation of the fuel cell performance. In this study, 50 cm² active area PEM fuel cells were operated at 55–60 °C for periods up to 250 hours to study the effect of methane, carbon dioxide and water in the hydrogen fuel mix on the cell performance (stability of voltage and power output). Furthermore, the stability of fuel cells was also studied during operation of cells in a cyclic dead end / flow through configuration, both with and without the presence of carbon dioxide in the hydrogen stream. The presence of methane up to 10% in the hydrogen stream showed a negligible degradation in the cell performance. The presence of carbon dioxide in the hydrogen stream even at 1–2% level was found to degrade the cell performance. However, this degradation was found to disappear by bleeding only about 0.2% oxygen into the fuel stream.     

SnO2-TiO2薄膜载体对Au-Pt纳米颗粒电化学性能的影响

采用真空镀膜法在玻碳(GC)电极表面修饰SnO2-TiO2薄膜, 在SnO2-TiO2/GC复合电极表面组装Au-Pt双金属纳米颗粒, 制得Au-Pt/SnO2-TiO2/GC复合电极. 通过循环伏安法(CV)研究了SnO2-TiO2薄膜载体对Au-Pt双金属纳米颗粒电化学性能的影响; 采用扫描电镜(SEM)及X射线光电子能谱(XPS)对Au-Pt在SnO2-TiO2薄膜沉积的形貌及结构进行了表征. 研究结果表明, 10 nm的Au-Pt双金属纳米颗粒均匀地组装于SnO2-TiO2薄膜表面; SnO2-TiO2薄膜载体改善了复合电极抗CO中毒能力; Au-Pt双金属合金的形成提高了Pt 对甲醇氧化的电催化能力, SnO2-TiO2薄膜载体又使Pt纳米粒子d空轨道增多, 提高了Au-Pt双金属纳米颗粒的稳定性和催化性能.     

贝类体内麻痹性贝类毒素的提取方法研究

采用浓度系列为0.04、0.07、0.10、0.15、0.20、0.25、0.30、0.40、0.50、0.70、1.0 mol/L的HCl和HAc溶液作为提取液,分别取10 mL提取液与10 g栉孔扇贝性腺混合,在沸水浴中加热5 min提取麻痹性贝类毒素(PSP);同时采用0.3 mol/L HAc和0.2 mol/L HCl,于冰水浴中进行超声波提取麻痹性贝类毒素5~30 min。提取完成后将混合物于4℃冷冻离心机内离心5 min(3500 r/min),取上清液并以0.1 mol/L NaOH或5 mol/L HCl调整至pH为2.0~4.0。经超滤膜过滤后的提取液以高效液相色谱柱后衍生荧光检测法进行毒素分析,研究毒素组分间的转化关系和提取效率,并与超声波提取法进行了比较。结果表明,采用0.04~0.25 mol/L HCl和0.04~1.0 mol/L HAc从贝肉中提取PSP毒素,各毒素组分浓度差异不大,当HCl浓度大于0.25 mol/L时,N-磺酰氨甲酰基类毒素C1浓度急剧降低,HCl浓度大于0.5 mol/L时,N-磺酰氨甲酰基类毒素C2和GTX5浓度急剧降低,三者在酸度过大的情况下分解或转化为膝沟藻毒素-2(GTX2),膝沟藻毒素-3(GTX3)和石房蛤毒素(STX)。在相同浓度酸的情况下,超声波提取液中C1毒素的浓度显著低于沸水浴提取法,但C2的浓度略高于沸水浴提取液。     

Ruthenium(III) acetylacetonate: A homogeneous catalyst in the hydrolysis of sodium borohydride

Ruthenium(III) acetylacetonate was employed for the first time as homogeneous catalyst in the hydrolysis of sodium borohydride. Ruthenium(III) acetylacetonate was not reduced by sodium borohydride under the experimental conditions and remains unchanged after the catalysis. Poisoning experiments with mercury and trimethylphosphite provide compelling evidence for the fact that ruthenium(III) acetylacetonate is indeed a homogenous catalyst in the hydrolysis of sodium borohydride. Kinetics of the ruthenium(III) acetylacetonate catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration, and temperature. The hydrogen generation was found to be first order with respect to both the substrate concentration and catalyst concentration. The activation parameters of this reaction were also determined from the evaluation of the kinetic data: activation energy; E_a = 58.2 ± 2.6 kJ mol⁻¹, the enthalpy of activation; ΔH^# = 55.7 ± 2.5 kJ mol⁻¹ and the entropy of activation ΔS^# = 118 ± 5 J mol⁻¹ K⁻¹. Ruthenium(III) acetylacetonate was found to be highly active catalyst providing 1200 turnovers over 180 min in hydrogen generation from the hydrolysis of sodium borohydride before deactivation.     

非晶态CeO_2@TiO_2催化剂的结构、性质及其选择催化还原脱硝性能

采用自发沉积法制备了非晶态Ce O_2@Ti O_2催化剂,通过XRD、Raman光谱、TEM、N_2吸附、H_2-TPR、NH_3-TPD及FTIR等手段表征了催化剂结构和表面性质,研究了Ce O_2@Ti O_2在选择催化还原脱NO反应中的催化性能。结果表明,非晶态Ce O_2@Ti O_2催化剂中Ce与Ti间存在很强的相互作用,能够在原子水平上相互结合,表现出与晶态结构截然不同的还原特性,具备更强的氧化还原能力。同时,与浸渍法制备的Ce O_2/Ti O_2相比,Ce O_2@Ti O_2还具有更大的比表面积和更强的表面酸性,因而具有更加优异的脱硝性能。在175℃下NO转化率即达到80%以上,在200-400℃脱硝率稳定在96.0%-99.4%;同时,H_2O和SO_2的阶跃应答实验表明,Ce O_2@Ti O_2具有很强的抗水和抗SO_2毒化能力。     

燃煤烟气中砷对V_2O_5-WO_3/TiO_2 SCR脱硝催化剂性能的影响

通过将商业V_2O_5-WO_3/TiO_2脱硝催化剂暴露于含As_2O_3烟气中,制备了砷中毒催化剂,并运用X射线衍射(XRD)、比表面积(BET)、NH3化学吸附、傅里叶变换红外光谱(FT-IR)、X射线光电子能谱等技术表征分析了砷对催化剂性能的影响,并提出了催化剂砷中毒机理。结果表明,砷对催化剂具有严重的毒害作用,As_2O_3会吸附在催化剂表面,并被催化剂氧化形成As_2O_5覆盖层,减小催化剂比表面积,减少催化剂V活性位,阻止催化剂对NH3的吸附,造成催化剂失活。     

On-Line Photoionization Mass Spectrometric Study on Behavior of Ammonia Poisoning on H-Form Ultra Stable Y Zeolite for Catalytic Pyrolysis of Polypropylene

In this work, pyrolysis photoionization time-of-flight mass spectrometry (Py-PI-TOFMS) was applied to study the behavior of ammonia poisoning on H-form ultra stable Y (HUSY) zeolite for the catalytic pyrolysis of polypropylene (PP). Firstly, ammonia poisoning on HUSY was performed to obtain the suitable catalysts with different strength and amounts of acid sites. Secondly, online photoionization mass spectra for the pyrolysis products of PP and HUSY with various acid strength were recorded at different pyrolysis temperatures. Finally, the formation curves of various pyrolysates of PP/HUSY with the increase of temperature were determined. Our results indicate that the formation temperatures, yields and selectivity of the pyrolysis products of PP demonstrate obvious relationship with the acid strength of HUSY.     

Solid-phase extraction-fluorimetric high performance liquid chromatographic determination of domoic acid in natural seawater mediated by an amorphous titania sorbent

The feasibility of using sol-gel amorphous titania (TiO₂) as a solid-phase sorbent for the pre-concentration of domoic acid (DA), a potent amnesic shellfish poisoning (ASP) toxin, directly from seawater was explored. The sol-gel titania material is able to adsorb DA from seawater, via the formation of ester-linkage between the carboxylic moieties of DA and the Ti-OH groups on the sorbent surface, at low pH and desorb it at high pH. The chemisorption process is not significantly interfered by the seawater matrix. The optimum pH values for the adsorption and desorption of DA were found to be pH 4 and 11, respectively. The optimal sorbent loading for the batch-type solid-phase extraction of DA was 0.67 mg-TiO₂ ng-DA⁻¹ and adsorption equilibrium was achieved in 2 h at room temperature. The desorbed DA in 500 μL of 0.1 M alkaline borate buffer can be directly derviatized by 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) in aqueous media for fluorimetric HPLC quantification. Analyte recovery, repeatability and detection limit of this titania SPE-fluorimetric HPLC determination are 89%, 6.2% and 120 pg-DA mL⁻¹ (n = 7, P < 0.05), respectively, for a sample volume of 30 mL. This titania SPE technique should also be applicable to the pre-concentration of other polar carboxylate- and phosphonate-containing biomolecules and pharmaceuticals in complex and interfering environmental sample matrices.     

Enzymatic hydrolysis of esterified diarrhetic shellfish poisoning toxins and pectenotoxins

Okadaic acid (OA) and dinophysistoxins-1 and -2 (DTX1, DTX2), the toxins responsible for incidents of diarrhetic shellfish poisoning (DSP), can occur as complex mixtures of ester derivatives in both plankton and shellfish. Alkaline hydrolysis is usually employed to release parent OA/DTX toxins, and analyses are conducted before and after hydrolysis to determine the concentrations of nonesterified and esterified toxins. Recent research has shown that other toxins, including pectenotoxins and spirolides, can also exist as esters in shellfish, but these toxins cannot survive alkaline hydrolysis. A promising alternative approach is enzymatic hydrolysis. In this study, two enzymatic methods were developed for the hydrolysis of 7-O-acyl esters, “DTX3,” and the carboxylate esters of OA, “diol-esters.” Porcine pancreatic lipase induced complete conversion of DTX3 to OA and DTXs within one hour for reference solutions. The presence of mussel tissue matrix reduced the rate of hydrolysis, but an optimized lipase concentration resulted in greater than 95% conversion within four hours. OA-diol-ester was hydrolyzed by porcine liver esterase and was completely converted to OA in less than 30 min, even in the presence of mussel tissue matrix. Esters and OA/DTX toxins were all monitored by LC–MS. Further experiments with pectenotoxin esters indicated that enzymatic hydrolysis could also be applied to esters of other toxins. Enzymatic hydrolysis has excellent potential as an alternative to the conventional alkaline hydrolysis procedure used in the preparation of shellfish samples for the analysis of toxins.