Screening of Fe–Cu-Zeolites Prepared by Different Methodology for Application in NSR–SCR Combined DeNOx Systems

The NO_x NH₃-SCR performance of several Cu and Fe catalysts supported on BETA and ZSM-5 zeolites has been studied in single SCR and double NSR–SCR configuration, and the activity related to the nature and reducibility of metal species on the catalyst surface. Intermediate ammonia formed in NSR improved greatly NO_x conversion at the exit of the double NSR–SCR configuration, which was practically totally converted to N₂.     

Lean NOx Reduction with H2 and CO in Dual-Layer LNT–SCR Monolithic Catalysts: Impact of Ceria Loading

A series of monolithic catalysts consisting of a layer of selective catalytic reduction (SCR) catalyst deposited on top of lean NO_x trap (LNT) catalyst were synthesized for lean reduction of NO_x (NO&NO₂) with H₂ and CO. The LNT catalyst exhibited a rather low NO_x conversion below 250 °C due to CO inhibition. The top SCR layer comprising Cu/ZSM5 significantly increased the NO_x conversion at low temperature by its reaction with NH₃ formed during the regeneration phase. The addition of CeO₂ to the LNT layer promoted the water gas shift reaction (CO + H₂O ? H₂ + CO₂). The WGS reaction mitigated the CO inhibition and the generated H₂ enhanced the low-temperature catalyst regeneration. The ceria addition decreased the performance at high temperatures due to increased oxidation of NH₃. The ceria loading was optimized by applying a non-uniform axial profile. A dual-layer catalyst with an increasing ceria loading axial profile improved the performance over a wide (low and high) temperature range.     

Effect of Gas Atmosphere on Catalytic Behaviour of Zirconia, Ceria and Ceria–Zirconia Catalysts in Valeric Acid Ketonization

Ketonization of valeric acid, which can be obtained by lignocellulosic biomass conversion, was carried out in a fixed bed flow reactor over ZrO₂, 5–20 % CeO₂/ZrO₂ and CeO₂ both under hydrogen and nitrogen stream at 628 K and atmospheric pressure. Regardless gas-carrier 10 wt% CeO₂/ZrO₂ was found to show higher catalytic activity compared to zirconia per se as well as other ceria modified zirconia while ceria per se exhibited very low catalytic activity. All catalysts provided higher acid conversion in H₂ than in N₂ whereas selectivity to 5-nonanone was insensitive to gas atmosphere. XRD, FTIR, UV–Vis DRS, XPS, HRTEM methods were applied to characterize catalysts in reduced and unreduced states simulating corresponding reaction conditions during acid ketonization. XRD did not reveal any changes in zirconia and ceria/zirconia lattice parameters as well as crystalline phase depending on gas atmosphere while insertion of ceria in zirconia caused notable increase in lattice parameter indicating some distortion of crystalline structure. According to XPS, FTIR and UV–Vis methods, the carrier gas was found to affect catalyst surface composition leading to alteration in Lewis acid sites ratio. Appearance of Zr³⁺ cations was observed on the ZrO₂ surface after hydrogen pretreatment whereas only Zr⁴⁺ cations were determined using nitrogen as a gas-carrier. These changes of catalyst’s surface cation composition affected corresponding activity in ketonization probably being crucial for reaction mechanism involving metal cations catalytic centers for acid adsorption and COO^? stabilization at the initial step.     

Oxygen Storage Behavior of Ceria–Zirconia-Based Catalysts in the Presence of SO2

This paper investigates the effect of the presence of SO₂ in the dynamics of oxygen storage on ceria and ceria–zirconia. The introduction of SO₂ under reaction conditions at T<873 K negatively affects CO conversion under oscillating conditions on all the supports studied, owing to the formation of sulfate species. Deactivation is observed on all supports and activity is recovered only after desorption of SO₂, which occurs at 950<T<1000 K, depending on catalyst composition (Ce/Zr ratio) and treatment atmosphere. The amount of sulfur adsorbed is higher over solid solutions, reaching a maximum with Ce _x Zr_1–x O₂ (0.5<x<0.68). However this does not adversely affect activity compared to ceria. In the presence of Rh and Pd, reactivation is favored under reaction conditions. More generally, it appears that the removal of sulfates is facilitated in reductive atmospheres (both hydrogen and CO) over mixed oxides. No differences are observed following regeneration under oxidizing conditions.     

Deactivation of a Pt/Silica–Alumina Catalyst and Effect on Selectivity in the Hydrocracking of n-Hexadecane

The deactivation behavior of a bifunctional catalyst consisting of platinum on amorphous silica–alumina was studied in the hydrocracking of n-hexadecane. The initial decline in activity and the change in selectivity were monitored at the following reaction conditions: pressure = 30 bar; temperature = 310 °C; hydrogen-to-hexadecane feed molar ratio = 10. Initially, hexadecane conversion and selectivity to cracking products decreased rapidly with time-on-stream, and stabilized after 40 h on stream. This could be related to an initial loss of metal surface area, which decreased the activity of monofunctional hydrogenolysis generating cracking products. The acidic function seemed to be unaffected under these reaction conditions. The stable catalyst was exposed to a lower hydrogen-to-hexadecane ratio to accelerate deactivation by coking. A decline in the activity of both functions was observed. The activity of the acidic function could be almost completely recovered by oxidative regeneration, while the metal activity was only partially recovered.     

Effect of Tourmaline Addition on the Catalytic Performance and SO2 Resistance of NixMn3−xO4 Catalyst for NH3-SCR Reaction at Low Temperature

Catalysis Letters - NixMn3?xO4 and NixMn3?xO4/T (T represents tourmaline) catalysts with a double-layer hollow structure were prepared by a rigid template method for low-temperature...     

Effect of Temperature and Other Variables on the Optimum Formulation of Anionic Extended Surfactant–Alkane–Brine Systems

Anionic extended surfactants of the alkyl polypropylene oxide sulfate type are found to obey the linear correlation lnS = k ACN for optimum formulation (three-phase behavior) of ionic surfactant–oil–water systems, with a k value essentially the same as for n-alkyl sulfates. The addition of n-pentanol produces a shift in optimum formulation without significant change in k. An increase in temperature is found to produce a decrease in surfactant hydrophilicity, which is opposite to the expected behavior of anionic species. This trend, which is typical of nonionic surfactant behavior, is probably due to the partial hydration of the very first propylene oxide units which are located close to the anionic head group.     

Effect of Zr–Al Co-Doping on Structure and Photocatalytic Performance of ZnO Photocatalyst

利用水热处理结合焙烧的方法分别制备了Zr、Al掺杂及Zr–Al共掺的ZnO光催化剂。研究了制备的光催化剂样品的相结构和光谱性能;以紫外光（λ=254nm）为光源,酸性橙Ⅱ为降解对象,进行光催化活性测试;考察了Zr、Al掺杂对ZnO光催化剂反应活性的影响。研究表明,制备的产物均为六方晶系纤锌矿结构的ZnO;Zr、Al掺杂及Zr–Al共掺的ZnO样品的光催化活性相对于纯ZnO均有较大程度的提高,而且Zr–Al共掺的ZnO的光催化性能明显优于单一掺杂的。Zr–Al共掺可以明显改善ZnO表面状态,使ZnO具有更丰富的表面羟基,同时可以抑制光生电子–空穴对的复合,从而有利于光催化活性和稳定性的提高。     

Optical Properties and Radiation Resistance of Zinc Orthosilicate Obtained by the Hydrothermal–Microwave Method

A hydrothermal–microwave method for the synthesis of zinc orthosilicate is developed. A crystalline phase of zinc orthosilicate, willemite, is synthesized at low temperature and its optical characteristics are determined. The dependence of the diffuse reflection coefficient on the irradiation at low temperatures (90 K) and pressures of 10^–5–10^–6 Pa is studied. The results of gravimetric, X-ray phase, and thermographic studies shows that the microwave synthesis of zinc orthosilicate from water-soluble salts of the initial components accelerates at lower temperatures of willemite formation. The microwave treatment of the initial zinc orthosilicate provides the production of nanodispersed willemite powder at lower temperatures and shorter expositions.     

Spectroscopic Study on the Nature of Active Entities in Copper–Ceria CO-PROX Catalysts

A series of oxidised copper-ceria catalysts with varying copper loadings and prepared by two different methods (impregnation of ceria and coprecipitation of the two components within reverse microemulsions) have been examined with the aim of determining the nature of active entities for the two main (CO and H₂) competing oxidation reactions that take place during preferential oxidation of CO in H₂-rich streams over this type of catalysts. The analysis is mainly based on operando spectroscopic exploration by DRIFTS and XANES as well as in situ analysis by Raman. The results allow establishing a model of the catalytic behaviour of this type of catalysts which can provide keys to control their CO-PROX catalytic properties.     

Fischer–Tropsch Synthesis: Studies on the Effect of Support Doping with Si,Mn and Cr on the Selectivity to Alcohols in Ceria Supported Cobalt Catalysts

Mn and Cr doped CeSi mixed oxides were used as supports for Co and tested for CO hydrogenation. Co/CeSi was found to be more active and significantly more selective to n-alcohols/olefins. An increasing selectivity to n-alcohols and decreasing selectivity to olefins as a function of time on stream was also observed, suggesting a trade-off between those two products. Addition of Mn led to similar behavior, although at slightly lower conversions. Addition of Cr, however, considerably suppressed n-alcohol formation, while it kept selectivities to olefins within a 20–30 % range over more than 250 h of testing, indicating either higher alcohol dehydration activity, or that the presence of Cr ions lowered the hydrogenating activity of Co. The present work indicates that enhanced contact area between Co and the reducible support is likely a key factor for enhancing selectivity to alcohols.     

Analysis of the Coupling of HC–SCR by Ethanol and NH3–SCR on Real Engine Emissions

Selective catalytic reduction by ethanol on silver-based catalysts was proved to be very effective to abate the nitrogen oxides emitted at the exhaust of an automotive engine. Moreover, the selectivity to ammonia of this reaction may be exploited to further enhance the NOx reduction using a dedicated transition metal exchanged zeolite catalyst. This coupling between HC– and NH₃–SCR is called Dual SCR. In order to control the silver-based catalyst efficiency via ethanol injection, a NOx sensor is located downstream of it, as usually done for urea–SCR on series vehicles. Furthermore, based on the cross-sensitivity of this NOx sensor, large amounts of ammonia were estimated that would help to reduce the remaining NOx on the zeolite based catalyst. However, when measured by FTIR technique, the concentrations of ammonia produced by the HC–SCR catalyst were surprisingly not as high as expected, while large amounts of acetaldehyde were detected and, in a lesser extent, formaldehyde and hydrogen cyanide. NOx were partly reduced over the iron-exchanged zeolite catalyst, improving the overall deNOx efficiency by up to 15 points, while acetaldehyde to formaldehyde ratio reversed and ammonia concentration remains unchanged. The cross-sensitivity of the NOx sensor was further investigated on synthetic gas bench. If its partial dependence on the ammonia concentration is rather well known, the influence of aldehydes and hydrogen cyanide in presence of ammonia had not yet been investigated. The NOx sensor’s signal remains unchanged whatever the aldehydes concentration and a strong sensitivity to the hydrogen cyanide was highlighted.     

Effect of chromium on the kinetics of the contact melting and the graphite-to-diamond transformation in the Co–Fe–C system

We have studied the effect of chromium concentration in alloys of the Co–Fe system on their interaction with graphite at p, T parameters of thermodynamic stability of diamond. It has been found that addition of chromium to the alloys stabilizes the Me₃C-type carbide, as a result, the structure of a layer of a contact melting at the alloy–graphite interface is identical to a horizontal section of the metastable phase diagram of the Fe–C system. It is shown that addition of chromium to the Co–Fe–C system lowers the eutectic melting temperature by 80–100 K. In this case, the coefficient of carbon diffusion in the melt increases by ∼20–30%. An increased surface activity of a Cr-containing melt with respect to graphite is noted, which is the reason of intensive intrusion of the melt deep into a graphite layer along the grain boundaries. As a result, the number of nucleating diamond crystals and the degree of the graphite→diamond transformation increases.     

High Resistance of Cu–Ferrierite to Coke Formation During NH3-SCR in the Presence of n-Decane

Selective catalytic reduction of NO _x by NH₃ over Cu–FER and Cu–ZSM-5 in the presence of n-decane and SO₂ was investigated. NO _x conversion over Cu–ZSM-5 decreased in the presence of n-decane, owing to inhibition of the active sites by coke formation. In contrast, coke formation was negligible over Cu–FER, which maintained its NO _x conversion activity even in the presence of decane. Coke formation was negligible over H–ZSM-5 and H–FER supports, which suggests that Cu species were involved in coke formation. Temperature-programmed reduction by H₂ and electron spin resonance spectroscopy indicated that [Cu–O–Cu]²⁺ was probably the Cu species involved in coke formation over Cu–ZSM-5.     

Effect of ultrasonic vibration on the structure and composition of the interface regions in Ва–W–Ti–O ceramics

A study of Ba–W–Ti–O ceramics has shown that the structure and composition of their interface regions differ from those in the grain bulk owing to the diffusion of tungsten atoms to the grain surface during sintering. They are determined by the conditions of compacting of dry nanopowders (compaction pressure and power of ultrasonic action) and vary in a nonmonotonic way. Increasing the pressure during dry static compacting and exposure to ultrasound result in the formation of a complex structure of fragments and boundaries between them, increase the acoustic density and lead to a decrease in the intergranular boundary thickness to the values that are sometimes comparable to the lattice constant of the boundary material.