Response surface study of the performance of lean NOx storage catalysts as a function of reaction conditions and catalyst composition

NO_x storage and reduction (NSR) catalysts containing Pt, Ba and Fe were studied as a function of reaction conditions and catalyst composition using response surface methodology combined with high-throughput experimentation. The concentrations of the reactant gases and the reactor temperature were varied to probe their effect on catalyst performance, as quantified by lean NO_x storage and N₂O production. An empirical model relating the catalyst performance to five reaction condition variables and three metal weight loading variables has also been developed. It was found that the temperature and the concentrations of the reducing agents, i.e. carbon monoxide and ethylene, had the strongest effect on the lean NO_x storage. It was also found that the Pt and Ba weight loadings had a much greater effect than Fe weight loadings on the performance of NSR catalysts. This model provides insight about the factors controlling the NO_x conversion by NSR catalysts and also predicts the optimum catalyst composition for given reaction conditions and vice versa. As an additional study, the relationship between sulfur poisoning, nitrous oxide production, and exotherm generation was also explored.     

Fabrication of platinum nanoparticles and nanowires by electron beam lithography (EBL) and nanoimprint lithography (NIL): comparison of ethylene hydrogenation kinetics

Electron beam lithography (EBL), size reduction lithography (SRL), and nanoimprint lithography (NIL) have been utilized to produce platinum nanoparticles and nanowires in the 20–60-nm size range on oxide films (SiO₂ and Al₂O₃) deposited onto silicon wafers. A combination of characterization techniques (SEM, AFM, XPS, AES) has been used to determine size, spatial arrangement and cleanliness of these fabricated catalysts. Ethylene hydrogenation reaction studies have been carried out over these fabricated catalysts and have revealed major differences in turnover rates and activation energies of the different nanostructures when clean and when poisoned with carbon monoxide. The oxide-metal interfaces are implicated as important reaction sites that remain active when the metal sites are poisoned by adsorbed carbon monoxide.     

NOx reduction performance of lean NOx catalyst and lean NOx adsorber using DME as reducing agent

The deactivation of a commercial Selective Catalytic Reduction (SCR) catalyst, of V₂O₅−WO₃/TiO₂ type, has been studied through comparisons with results from a full-scale biomass combustion plant to that with laboratory experiments. In the latter, the catalyst was exposed to KCl and K₂SO₄ by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means of an electrostatic field. The reactivity of fresh and deactivated samples was examined in the SCR reaction. Chemical and physical characterizations were focusing on internal structures and chemical composition. Deposition of submicrometer sized particles on the monolithic SCR catalyst was shown to induce deactivation with characteristics resembling those obtained in a commercial biomass combustion plant.     

Catalytic reforming of gasoline to hydrogen: Kinetic investigation of deactivation processes

Catalytic reforming of gasoline to a hydrogen-rich gas is a possible route to feed a fuel cell for electricity production on-board a vehicle. To properly design a fuel processor system, knowledge about the kinetics of the different reactions involved in the reforming is needed. Kinetic studies are hampered by the fact that sulfur compounds present in commercial gasoline may lead to a progressive deactivation of the catalyst. We have undertaken such a study with an optically accessible catalytic channel flow reactor enabling concentration profiles and catalyst surface temperatures to be measured. The concentration profiles measured at different times on stream revealed a progressive deactivation of the catalyst. Isothermal reaction rate constants, depending on the time on stream, were derived by fitting a Langmuir–Hinshelwood kinetic model to the experimental species concentration profiles. The modeling results indicated that the steam reforming of higher hydrocarbons was more strongly affected by the presence of sulfur in the feed than the water gas shift reaction and the steam reforming of methane. Carbon formation was inferred from changes in surface emissivity during the experiments. It is suggested that the primary reason for the observed deactivation is due to the presence of sulfur compounds in the feed. The deactivated catalyst would then promote the formation of coke at the surface, i.e. coke formation is probably a consequence of the deactivation and not a cause for it. Although the variability in preparing the coated catalytic plates affected the measured kinetic rate parameters, the observed trends were in general consistent for all runs.     

Research status and prospect of poisoning in denitration catalysts

Denitration catalysts are easily poisoned by complex components of flue gas. As flus gas poisoning was a major cause of catalyst deactivation, low temperature catalysts with strong anti poisoning ability were actively researched. The research status of poisoning in denitration catalysts was summarized, focusing on the poisoning mechanisms of SO2 and H2O, alkali metals (K), alkaline earth metals (Ca, Mg), and heavy metals (Zn) in the industrial flue gas. Despite remarkable advances, the poisoning mechanism of carbon based catalysts remained poorly understood. The poisoning mechanism of heavy metals on carbon based catalysts, especially the poisoning mechanism of zinc, was recommended for future work. The prospects of improving the resistance of catalysts to sulfur and water, alkali and alkaline earth metals, and heavy metal poisoning, were also discussed.     

Pt–Pd bimetallic catalysts for methane emissions abatement

Bimetallic Pd–Pt catalysts with constant 2 wt% metal loading and varying Pt/Pd ratios were prepared, characterized and studied in the catalytic combustion of methane at low temperature under lean conditions in view of their use for CH₄ abatement from lean-burn NGV heavy duty vehicles exhausts. The influence of mild steam ageing featuring long-term use of the catalysts was also addressed together with their tolerance to H₂S. Catalysts were characterised by Transmission Electron Microscopy and Temperature Programmed Oxidation experiments. Experimental data agreed to suggest an interaction between Pd and Pt in Pd-rich catalysts, thus explaining their improved catalytic activity, even after mild ageing, compared to reference Pd/Al₂O₃. This interaction has no effect on the sulfur tolerance.     

Effect of the addition of transition metals to Pt/Ba/Al2O3 catalyst on the NOx storage-reduction catalysis under oxidizing conditions in the presence of SO2

The NO_x storage-reduction catalysis under oxidizing conditions in the presence of SO₂ has been investigated on Pt/Ba/Fe/Al₂O₃, Pt/Ba/Co/Al₂O₃, Pt/Ba/Ni/Al₂O₃, and Pt/Ba/Cu/Al₂O₃ catalysts compared with Pt/Ba/Al₂O₃, Pt/Fe/Al₂O₃, Pt/Co/Al₂O₃, Pt/Ni/Al₂O₃, Pt/Cu/Al₂O₃ and Pt/Al₂O₃ catalysts. The NO_x purification activity of Pt/Ba/Fe/Al₂O₃ catalyst was the highest of all the catalysts investigated in this paper after an aging treatment. That of the aged Pt/Ba/Co/Al₂O₃ and Pt/Ba/Ni/Al₂O₃ catalysts was essentially the same as that of the aged Pt/Ba/Al₂O₃ catalyst, while that of the aged Pt/Ba/Cu/Al₂O₃ and Pt/Cu/Al₂O₃ catalysts was substantially lower than the others.

The Fe-compound on the aged Pt/Ba/Fe/Al₂O₃ catalyst has played a role in decreasing the sulfur content on the catalyst after exposure to simulated reducing gas compared with the Pt/Ba/Al₂O₃ catalyst without the Fe-compound. XRD and EDX show that the Fe-compound inhibits the growth in the size of BaSO₄ particles formed on the Pt/Ba/Fe/Al₂O₃ catalyst under oxidizing conditions in the presence of SO₂ and promotes the decomposition of BaSO₄ and desorption of the sulfur compound under reducing conditions.     

Transient analysis of carbon monoxide poisoning and oxygen bleeding in a PEM fuel cell anode catalyst layer

The presence of carbon monoxide in the fuel stream hinders the performance of a polymer electrolyte membrane (PEM) fuel cell, known as carbon monoxide (CO) poisoning. Introducing oxygen in the fuel stream lessens CO poisoning. Since CO poisoning is a phenomenon that occurs over a substantial period of time, a transient model has been developed in this study, taking into account the effect of CO concentration, operating pressure and temperature, as well as oxygen bleeding on the performance of the cell. It is found that at a lower CO concentration the poisoning effect takes a much longer time to reach the steady state, even though for a better steady state anode performance. A higher operating temperature results in a better steady state performance, but the performance drops faster toward the steady state value at higher temperature. A higher operating pressure leads to an enhanced performance over the entire transient history, although the benefit diminishes as pressure is increased. Even with a small amount of oxygen (0.5%) introduced into the fuel stream, the anode performance can be improved significantly. Finally, it is observed that the use of pure hydrogen interspersed in carbon monoxide containing fuel improves the anode performance. However, performance recovery when operating on pure hydrogen is much slower than the performance degradation due to the CO poisoning.     

神经元N受体α4β2亚型在激动剂作用下功能失敏后再激活及宾赛克嗪的拮抗作用

目的: 研究神经元N受体α4β2亚型在激动剂持续作用下,功能失敏后再激活,以及宾赛克嗪的拮抗作用。方法: 在转染后稳定表达神经元N受体α4β2亚型的SH-EP1细胞株上,以烟碱为工具药,通过喷射给药,采用膜片钳全细胞记录技术进行研究。结果: 快速给予1mmol/L浓度的烟碱,可诱发一内向电流,该电流快速激活达到峰值后,在激动剂持续作用下迅速失敏至基线附近。当激动剂去除后可再次记录到一内向电流,该电流可被新型胆碱受体拮抗剂宾赛克嗪所阻断。结论: SH-EP1细胞株转染表达的神经元N受体α4β2亚型在高浓度激动剂持续作用下发生功能失敏,当激动剂去除后可再度激活,此再激活过程可被新型胆碱受体拮抗剂宾赛克嗪所拮抗。     

Determination of histamine and histamine-forming bacteria in tuna dumpling implicated in a food-borne poisoning

An incident of food-borne poisoning causing illness in seven victims, due to ingestion of tuna dumpling, occurred in March 2006, in Chiayi Prefecture, southern Taiwan. The leftovers of the victims’ tuna dumpling and the five other tuna dumpling samples from five other retail stores were collected and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, aerobic plate count (APC), total volatile basic nitrogen (TVBN), total coliform (TC) and Escherichia coli in all samples ranged from 6.08 to 6.43, 0.46% to 0.81%, 5.90 to 8.95 log CFU/g, 6.38 to 21.29 mg/100 g, 750 to 8000 most probable number (MPN)/g, and <3 to 1000 MPN/g, respectively. The suspected tuna dumpling contained 160.8 mg/100 g of histamine greater than the hazard action level of 50 mg/100 g set by the US Food and Drug Administration (FDA) for tuna fish. Given the allergy-like symptoms of the victims and the high histamine content in the suspected tuna dumpling, this food-borne poisoning was strongly suspected to be due to histamine intoxication. In addition, although thirteen histamine-producing bacteria strains capable of producing 8.1–19.7 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH), were identified as Enterobacter sp. (three strains), Pantoea agglomerans (two strains), Klebsiella variicola (four strains) and Serratia marcescens (four strains), by 16S rDNA sequencing with PCR amplification, they were not determined to be the main contributors to histamine accumulation in suspected tuna dumpling.