A multi-component NOx-trap catalyst consisting of Pt and K supported on γ-Al2O3 was studied at 250 °C to determine the roles of the individual catalyst components, to identify the adsorbing species during the lean capture cycle, and to assess the effects of H2O and CO2 on NOx storage. The Al2O3 support was shown to have NOx trapping capability with and without Pt present (at 250 °C Pt/Al2O3 adsorbs 2.3 μmols NOx/m2). NOx is primarily trapped on Al2O3 in the form of nitrates with monodentate, chelating and bridged forms apparent in Diffuse Reflectance mid-Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. The addition of K to the catalyst increases the adsorption capacity to 6.2 μmols NOx/m2, and the primary storage form on K is a free nitrate ion. Quantitative DRIFTS analysis shows that 12% of the nitrates on a Pt/K/Al2O3 catalyst are coordinated on the Al2O3 support at saturation.
When 5% CO2 was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by 45% after 1 h on stream due to the competition of adsorbed free nitrates with carboxylates for adsorption sites. When 5% H2O was included in a feed stream with 300 ppm NO and 12% O2, the amount of K-based nitrate storage decreased by only 16% after 1 h, but the Al2O3-based nitrates decreased by 92%. Interestingly, with both 5% CO2 and 5% H2O in the feed, the total storage only decreased by 11%, as the hydroxyl groups generated on Al2O3 destabilized the K–CO2 bond; specifically, H2O mitigates the NOx storage capacity losses associated with carboxylate competition. 相似文献
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NOx adsorber catalyst, Pt/K/Al2O3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al2O3 phase with associated hydroxyl groups at the surface, and an alkalized-Al2O3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al2O3 and 65% for the alkalized-Al2O3. NO2 and CO2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al2O3 adsorbs 0.087 μmol CO2/m2and 2.0 μmol NO2/m2, and Pt/K/Al2O3 adsorbs 2.0 μmol CO2/m2and 6.4 μmol NO2/m2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al2O3 during both lean and rich periods of the NOx adsorber catalyst cycle. 相似文献
The frictional behaviors of methyl oleate (MO), methyl palmitate (MP), methyl laurate (ML), and methyl stearate (MSt) as additives
in hexadecane have been examined in a boundary lubrication test regime using steel contacts. It was found that the transient
attributes of coefficient of friction (COF)-time spectra are a sensitive measure of adsorption equilibria. Critical additive
concentrations were defined and used to perform novel and simple Langmuir analyses that provide an order of adsoprtion energies:
MSt>MP>MO≥ML. Application of Langmuir, Temkin, and Frumkin-Fowler-Guggenheim adsorption models via nonlinear fitting of a general cooperative model demonstrates the necessary inclusion of cooperative effects in the applied
model. In agreement with the qualitative features of steady-state COF-concentration plots, MSt modeling requires minimal cooperative
interaction terms. However, MO, MP, and ML data require large attractive interaction terms to be adequately fitted. Primary
adsorption energies calculated via the cooperative model are necessarily decreased, whereas total adsorption energies correlate well with values obtained via critical concentration analyses. These results and comparisons with previous adsorption studies of MO and MSt suggest that
primary (ester-surface) and secondary (alkyl-surface) adsorbate-adsorbent, adsorbate-adsorbare, and (free-additive) adsorpt-adsorpt
interactions collectively determine both the calculated primary and the cooperative interaction energies. 相似文献
The synthesis of the title complexes was achieved via the reaction of
-p-dichlorobenzene-
-cyclopentadienyliron cations with 4,4′-bis(4-hydroxyphenyl)valeric acid to produce the diiron complexes which were then reacted with a number of arylazo dyes to give cationic bis(cyclopentadienyliron)arene complexes containing the arylazo dyes. These iron-containing monomers were subsequently polymerized via nucleophilic aromatic substitution using 1,8-octanedithiol, 4,4′-thiobisbenzenethiol, or bisphenol A to produce the desired coloured cationic organoiron polymers. The weight – average molecular weights were estimated to range from 11,800 to 31,600. UV–vis studies conducted in dimethylformamide (DMF) showed that the metallated polymers exhibited
of 412–491 nm. Addition of HCl to the polymer solution caused a bathochromic shift into the range of 515–530 nm. Thermogravimetric analysis (TGA) revealed that the iron moieties were cleaved between 205 and 248 °C while the polyether/thioether backbone degraded between 380 and 613 °C. Differential scanning calorimetry (DSC) showed that the polymers exhibited glass transition temperatures (Tg) ranging from 106 to 184°C.This paper is dedicated to Professor Richard J. Puddephatt in recognition of his outstanding contribution to the field of metal-containing polymers. 相似文献
It has previously been suggested that Al2O3/SiC nanocomposites develop higher surface residual stresses than Al2O3 on grinding and polishing. In this work, high spatial resolution measurements of residual stresses in ground surfaces of alumina and nanocomposites were made by Cr3+ fluorescence microspectroscopy. The residual stresses from grinding were highly inhomogeneous in alumina and 2 vol.% SiC nanocomposites, with stresses ranging from ~ ?2 GPa within the plastically deformed surface layers to ~ +0.8 GPa in the material beneath them. Out of plane tensile stresses were also present. The stresses were much more uniform in 5 and 10 vol% SiC nanocomposites; no significant tensile stresses were present and the compressive stresses in the surface were ~ ?2.7 GPa. The depth and extent of plastic deformation were similar in all the materials (depth ~ 0.7–0.85 μm); the greater uniformity and compressive stress in the nanocomposites with 5 and 10 vol% SiC was primarily a consequence of the lack of surface fracture and pullout during grinding. The results help to explain the improved strength and resistance to severe wear of the nanocomposites. 相似文献
Copolymers of acrylonitrile with a furfuryl alcohol resin have been prepared by a free radical reaction, and have been characterized by n.m.r. and i.r. spectroscopy. Their t.g.a. has been performed in air and in a nitrogen atmosphere, to permit the recognition of a number of stages in the weight loss process. D.s.c., also in air and in nitrogen, has identified a number of exothermic and one endothermic process in the copolymers. Solid state cross-polarization/magic angle spinning 13C n.m.r. spectroscopy and i.r. spectroscopy has been used to obtain some insight into the chemistry of the various chemical changes, which in air are completed by combustion and in nitrogen leave a carbon. 相似文献
In response to carbohydrate deprivation or prolonged fasting the ketone bodies, β‐hydroxybutyrate (βHB) and acetoacetate (AcAc), are produced from the incomplete β‐oxidation of fatty acids in the liver. Neither βHB nor AcAc are well utilized for synthesis of sterols or fatty acids in human or rat liver. To study the effects of ketones on cholesterol homeostasis a novel βHB ester (KE) ((R)‐3‐hydroxybutyl (R)‐3‐hydroxybutyrate) was synthesized and given orally to rats and humans as a partial dietary carbohydrate replacement. Rats maintained on a diet containing 30‐energy % as KE with a concomitant reduction in carbohydrate had lower plasma cholesterol and mevalonate (?40 and ?27 %, respectively) and in the liver had lower levels of the mevalonate precursors acetoacetyl‐CoA and HMG‐CoA (?33 and ?54 %) compared to controls. Whole liver and membrane LDL‐R as well as SREBP‐2 protein levels were higher (+24, +67, and +91 %, respectively). When formulated into a beverage for human consumption subjects consuming a KE drink (30‐energy %) had elevated plasma βHB which correlated with decreased mevalonate, a liver cholesterol synthesis biomarker. Partial replacement of dietary carbohydrate with KE induced ketosis and altered cholesterol homeostasis in rats. In healthy individuals an elevated plasma βHB correlated with lower plasma mevalonate. 相似文献
The Fe2+/Fe3+ ratios of 47 simulated nuclear waste glass samples with ratios varying from 0.01 (oxidized) to 1.6 (reduced) were determined by wet-chemical and Mössbauer spectral analyses. The wet-chemical method involved the spectrophotometric determination of Fe2+ and total iron using remote spectroscopy with fiber optic chemical sensing. Interferences from other species present in these glasses were examined and alternative analytical techniques were investigated. Results of wet-chemical and Mössbauer spectral analysis were comparable; however, the wet-chemical method is probably preferable for the analysis of highly radioactive glasses until such glasses have been shown to have satisfactory Mössbauer spectra. 相似文献