The Effects of CO2 and H2O on the NO x Destruction Performance of a Model NO x Storage/Reduction Catalyst

The effects of CO₂ and H₂O on the NO _x storage and reduction characteristics of a Pt/Ba/Al₂O₃ catalyst were investigated. The presence of CO₂ and H₂O, individually or together, affect the performance and therefore the chemistry that occurs at the catalyst surface. The effects of CO₂ were observed in both the trapping and reduction phases of the experiments, whereas the effect of H₂O seems limited to the trapping phase. The data also indicate that multiple types of sorption sites (or mechanisms for sorption) exist on the catalyst. One mechanism is characterized by a rapid and complete uptake of NO _x . A second mechanism is characterized by a slower rate of NO _x uptake, but this mechanism is active for a longer time period. As the temperature is increased, the effect of H₂O decreases compared to that of CO₂. At the highest temperatures examined, the elimination of H₂O when CO₂ is present did not affect the performance.     

Efficient Reduction of NO x by H2 Under Oxygen-Rich Conditions over Pd/TiO2 Catalysts: An in situ DRIFTS Study

The H₂/NO/O₂ reaction under lean-burn conditions has been studied by means of in situ DRIFTS, reactor measurements and temperature-programmed desorption with the aim of understanding the very different behavior of Pd/TiO₂ and Pd/Al₂O₃ catalysts. The former deliver very high NO _x conversions (70-80%) with good N₂ selectivity whereas the latter show very low activity. In addition, PdTiO₂ exhibits two distinct NO _x reduction pathways, thus greatly extending the useful temperature range. It is shown that the PdTiO₂ low-temperature channel involves adsorption and subsequent dissociation of NO on reduced (Pd⁰) metal sites. The low activity of PdAl₂O₃ is a consequence of palladium remaining in an oxidized state under reaction conditions. The high-temperature NO reduction channel found with PdTiO₂ is associated with the generation and subsequent reaction of NH _x species.     

Fe-ZSM-5 Catalysts: Preparation in Organic Media, Fe-particle Morphology and NO x Reduction Activity

Fe-ZSM5 catalysts were prepared at room temperature. Iron was incorporated into H-ZSM5 in organic media (toluene) using iron acetyl acetonate. In order to elucidate the catalytic performance of this Fe-ZSM5, reference catalysts were prepared by chemical vapour deposition (CVD) and impregnation in aqueous media (IMW). The various catalysts were characterized structurally and morphologically. Materials prepared in organic media and CVD showed fibrous iron particles, with radius between 10 and 40 Å, highly dispersed on the external zeolite surface. Fractal dimension values suggest that iron particles grow dendritically when iron is incorporated into zeolite by impregnation in organic media. Nuclear magnetic resonance of ¹²⁹Xe adsorbed on catalysts shows that dendrites can penetrate into the zeolite channels. The dispersion of the iron species on the external surface of the zeolite and the presence of iron inside the channels explain the good catalytic performance in the Selective Catalytic Reduction (SCR) of NO. Ammonia and n-decane were employed as reducing agents. The highest NO to N₂ conversion (≈100% at 430 °C) was obtained when ammonia was used. In contrast, n-decane is unable to reach Fe species in channels, and the inner active surface is thus lost.     

稀土配合物[Ln(C3H7NO2)-x-(C3H4N2)(H2O)](ClO4)3(Ln=La,-x-=3;Ln=Pr,Nd,Sm,-x-=2)的合成、表征与热分析

合成了稀土高氯酸盐与咪唑、DL α 丙氨酸的4种配合物晶体。经傅里叶变换红外光谱(FTIR)、元素分析和化学分析测定后确定其组成为[Ln(C3H7NO2)x(C3H4N2)(H2O)](ClO4)3(Ln=La,x=3;Ln=Pr,Nd,Sm,x=2)。用差示扫描量热法(DSC)测定了4种配合物的热分解数据,4个配合物开始熔化分解的温度分别为502 5K,532 4K,495 7K,516 7K,配合物有较高的热稳定性。     

Strong Size Effects in Supported Ionic Nanoparticles: Tailoring the Stability of NO x Storage Catalysts

Based on a well-defined model-catalyst approach, we study the particle size dependent properties of NO _x storage materials. The single-crystal based model systems are prepared on an ordered Al₂O₃ film, on which BaO nanoparticles are grown under ultrahigh-vacuum (UVH) conditions. Particle size and density are characterized by scanning tunneling microscopy (STM). The interaction with NO₂ is probed by molecular beam (MB) methods in combination with time-resolved IR reflection absorption spectroscopy (TR-IRAS). It is found that both, the stability and the formation kinetics of alumina supported barium nitrate nanoparticles show a strong dependence on particle size. Very small BaO particles are rapidly converted into nitrates, however, the resulting aggregates exhibit a strongly reduced thermal stability. Surface and bulk nitrate and nitrate features are identified by means of vibrational spectroscopy. It is concluded that the size dependencies are related to the formation and decomposition of surface-related BaNO _x species the decomposition temperature of which can be tuned over an exceptionally large temperature interval. It is suggested that the stability of these surface NO _x species is strongly modified by the underlying support.     

Structure Characteristics and NO Selective Catalytic Reduction Property of Sn x Zr1-x O2 Solid Solution Catalysts

Novel catalysts, Sn_xZr_1-xO₂ solid solutions, for NO selective catalytic reduction:NO SCR) are reported. They have much higher activity and selectivity than SnO₂ and ZrO₂. Sn⁴⁺ is the main reductive sites as proved by TPR. The dilution of Sn sites by the coexisting Zr causes a suppression of propene combustion and consequently promoted the selective reduction of NO. The rutile structure might be beneficial to NO SCR.     

Enhanced Sulfur Tolerance of Bimetallic PtPd/Al2O3 Catalysts for Hydrogenation of Tetralin by Addition of Fluorine

A series of mono- and bi-metallic Pt-Pd/Al₂O₃ samples with and without F were studied as aromatic hydrogenation catalysts. The effects of changing the order of impregnation of the Pt precursor and F as well as varying the calcination temperature (300–500 °C) were investigated. Temperature programmed reduction (TPR) results demonstrate the presence of a higher fraction of dispersed metal precursor species left on the surface from the impregnation (PtO _x Cl _y ) on the Pt/Al₂O₃ sample calcined at high temperature. The impregnation of F before the Pt precursor significantly decreases the interaction between the metal and the support. However, this decrease is not observed when F is impregnated after the metal precursor. For the bimetallic Pt-Pd catalysts, the sample prepared adding F before the metal show a higher degree of Pt-Pd interaction than either the parent Pt-Pd/Al₂O₃ catalyst or the one prepared with F added later. TPD of ammonia result show the increase in strong acid sites when F is present. Activity tests for tetralin hydrogenation in the presence of 350 ppm dibenzothiophene indicate a better sulfur tolerance for all F-promoted catalysts, especially Pt-Pd.     

UV and Visible Raman Study of Thermal Deactivation in a NO x Storage Catalyst

In situ UV and visible Raman spectroscopy was used to characterize fresh and thermally aged NO _x storage-reduction catalysts, Pt/Ba/Al₂O₃. From the presence, absence, and nature of certain features in the spectra depending on aging temperature, we conclude that sintering, oxide formation, and separation of components occurred in the thermally aged catalysts. As aging temperature increased, less atomic oxygen was generated on platinum but a high temperature form of oxide or more strongly bound oxygen species was formed. This coincided with a loss of oxidation activity with aging temperature. Under UV excitation, observation of the OH stretch of physisorbed H₂O on aged Pt/Ba/Al₂O₃ indicated separation of Pt from γ-Al₂O₃, since this OH band was observed only on γ-Al₂O₃ (and Ba/Al₂O₃) but not on Pt/Al₂O₃. Nitrite/nitro species and NO (adsorbed on Pt) in aged Pt/Ba/Al₂O₃ indicate that Ba-containing particles are behaving somewhat independently from Pt and Al₂O₃, since these NO _x species are observed only on Pt/Al₂O₃ but not on fresh Pt/Ba/Al₂O₃ under NO+O₂ flow. Moreover, barium nitrate particles in aged Pt/Ba/Al₂O₃ are more crystalline, as shown by the intensity, width, and frequency of the nitrate peak, and possible photo-induced nitrite formation under UV excitation. Finally, a NO _x species with a broad peak at ～330 cm^?1 appeared on fresh but not in aged Pt/Ba/Al₂O₃ (or γ-Al₂O₃, Pt/Al₂O₃, and Ba/Al₂O₃) which may indicate proximity of Pt and Ba-containing particles in fresh Pt/Ba/Al₂O₃.     

配合物Ni(C_6H_6NO_3S)_2(H_2O)_4的合成、表征及热稳定性

用常温挥发法合成了一个新颖的单核配合物Ni(C6H6NO3S)2(H2O)4,并利用红外光谱、元素分析、热重分析及X-射线单晶衍射法对其结构进行了表征。结果表明,该配合物晶体属于单斜晶系,P121/n1空间群,晶胞参数为:a=1.191 2 nm,b=0.633 nm,c=1.224 nm,β=108.936°,Z=2,R1=0.027 1,wR2=0.100 7。在标题配合物中,每个Ni2+与4个H2O分子的氧原子及来自两个邻氨基苯磺酸的两个氮原子配位,形成一个畸变的八面体构型。在该配合物中,磺酸基的氧原子没有配位,这表明在该体系下,H2O的配位性能优于磺酸基氧原子。     

Effective Model for Prediction of N2O and NH3 Formation During the Regeneration of NO x Storage Catalyst

In this paper we propose an effective global kinetic model that allows prediction of N₂O and NH₃ formation during the reduction of stored NO _x in dependence on the composition of the rich mixture (H₂/CO/C₃H₆), actual operating temperature, and length of regeneration period. A bench flow reactor equipped with a high-speed FTIR was used to measure dynamic evolution of gas components during periodic lean/rich operation of a fully formulated NSRC catalyst (PtPdRh/Ba/Ce–Zr/Mg–Al/Al₂O₃).     

草酸盐热分解法制备介孔CeO_2催化剂及其脱硝性能研究

用热分解法,对草酸铈进行缓慢热分解,制备出比表面积较高,孔道分布均匀的介孔结构CeO2材料。此法无需引入表面活性剂做造孔模板,步骤简单,成本较低。通过TG-DSC,XRD,N2吸附-脱附,扫描电镜和透射电镜等法对材料的结构和形貌进行表征。此外,还对在不同焙烧温度下制备的介孔CeO2材料进行了氨气选择性催化还原(SCR)脱硝性能测试,结果表明500℃焙烧制备的介孔CeO2的催化活性最好,在275~425℃温度范围之间,NO的转化率维持在100%。     

Effect of Ceria on the Storage and Regeneration Behavior of a Model Lean NO x Trap Catalyst

In this study the effect of ceria addition on the performance of a model Ba-based lean NO _x trap (LNT) catalyst was examined. The presence of ceria improved NO _x storage capacity in the temperature range 200–400 °C under both continuous lean and lean-rich cycling conditions. Temperature-programmed experiments showed that NO _x stored in the ceria-containing catalyst was thermally less stable and more reactive to reduction with both H₂ and CO as reductants, albeit at the expense of additional reductant consumed by reduction of the ceria. These findings demonstrate that the incorporation of ceria in LNTs not only improves NO _x storage efficiency but also positively impacts LNT regeneration behavior.     

Effect of Pt and Ba content on NO x Storage and Reduction Over Pt/Ba/Al2O3

Effects of Pt and Ba content of Pt/Ba/Al₂O₃ on NO _x storage reduction (NSR) catalyst were investigated by means of kinetic analysis of surface nitrates using in situ FT/IR. Turnover frequencies of both storage and reduction of nitrate were significantly enhanced at higher Ba content, while those were higher at lower Pt content below 0.2 wt%.     

CuO/Al2O3吸附SO2后的氢再生及一体化回收硫磺：表征与机理

吸附SO2饱和的CuO/Al2O3可在400℃下的尾气循环过程中用还原剂H2对其再生. 在热重仪上进行程序升温还原再生实验,以考察尾气循环过程中吸附剂上Cu和S的相态变化. DTG曲线上分别于280和330℃处出现失重峰,表明吸附剂上的CuSO4在H2气氛中依次被还原为CuO和Cu. XPS表征结果则显示吸附剂上CuS由SO2和Cu反应生成. 在400℃、进口气H2/SO2摩尔比为1.5时的硫磺制备过程中,以H2再生后的CuO/Al2O3作催化剂,可获得50%以上的硫磺产率,表明在吸附剂的H2再生过程中生成的CuS是硫磺制备过程的催化剂.