Radioisotope tracer study of co-reactions of methanol with ethanol using 11C-labelled methanol over alumina, H-ZSM-5 and Cu-ZSM-5

¹¹C-labelled methanol was introduced for study of co-reaction of methanol with ethanol over alumina, H-ZSM-5 and Cu-ZSM-5 between 200 and 320 °C. The radio-method was applied to distinguish the radio-labelled methanol derivatives and co-products from unlabelled ethanol derivatives during analysis by radio-GC. The co-reaction was compared to ¹¹C-single methanol transformations from the previous work. Besides ¹¹C-dimethyl ether, ¹¹C-methyl ethyl ether as a co-product was formed between 200–240 °C and completely transformed further between 240 and 320 °C over H-ZSM-5 and alumina and partly over Cu-ZSM-5. In view of our results the appearance of ¹¹C-methyl ethyl ether intermediate is related to higher selectivities to form ¹¹C-traced C₃ and C₄–C₅ paraffins compared to the single ¹¹C-methanol transformation over H-ZSM-5 catalyst. These results suggest a modified methanol transformation pathway in the presence of ethanol over H-ZSM-5.     

Promoting Effect of Triglyme on Lean NO<Subscript>x</Subscript> Reduction Over Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Abstract  

The highly oxygenated hydrocarbon triethylene glycol dimethyl ether or triglyme (CH₃O–(C₂H₄O–)₃CH₃) was found to efficiently reduce NO_x under lean conditions over Ag/Al₂O₃, but gave a low NO_x conversion over Cu-ZSM-5. Furthermore, triglyme showed an extraordinary promoting effect when added together with propene as reducing agent for NO_x over Ag/Al₂O₃ at low temperature. This is most likely due to that triglyme promotes the activation of propene.     

Epoxidation of Propylene by Molecular Oxygen Over the Ag–Y2O3–K2O/α-Al2O3 Catalyst

Abstract The Ag/α-Al₂O₃ catalyst modified with rare earth metal oxide (Y₂O₃) and alkali metal oxide (K₂O) for the epoxidation of propylene by molecular oxygen were prepared and characterized by TG-DTA, XRD and XPS. The results show that a small quantity of Y₂O₃ added plays a role of electron and structure-type promoters, and can change the binding energies of Ag3d and restrain the sintering of Ag crystallites during catalyst preparation. The effects of promoters loading, Ag loading, reaction temperature, and calcination atmosphere on the performance of Ag catalyst were investigated. The results show that the loadings of K₂O, Y₂O₃ and Ag, and reaction temperature affect obviously the catalytic performance of Ag–Y₂O₃–K₂O/α-Al₂O₃ for the epoxidation of propylene to propylene oxide. Under the reaction conditions of 0.1 MPa, 245 °C, GHSV of 2000 h⁻¹ and the feed gas of 20%C₃H₆/8%O₂/N₂, the conversion of propylene of 4% and the selectivity to propylene oxide of 46.8% were achieved over the 20%Ag–0.1%Y₂O₃–0.1%K₂O/α-Al₂O₃ catalyst. Graphical Abstract Y₂O₃ plays a role of electron and structure-type promoters in the Ag–Y₂O₃–K₂O/α-Al₂O₃ catalyst, which can change the binding energies of Ag3d and restrain the sintering of Ag crystallites, resulting in obvious improvement of the catalytic performance of Ag–Y₂O₃–K₂O/α-Al₂O₃ for the epoxidation of propylene to propylene oxide by molecular oxygen.      

New water‐tolerant supported molten indium catalyst for the selective catalytic reduction of nitric oxide by ethanol

The catalytic activity and selectivity of indium supported on controlled pore glass (In‐CPG‐SMMC) were investigated and compared with those of H‐ZSM‐5 and In/γ‐Al₂O₃ for the selective catalytic reduction of nitric oxide by ethanol under net oxidizing conditions, in the absence and presence of water vapors. Even though the support of In‐CPG‐SMMC is almost pure silica (94–99% SiO₂, 1–6% B₂O₃, 0.05–0.3% Na₂O), the activity of this catalyst was found to be comparable with that of the conventional catalysts. The presence of steam in the feed enhanced catalyst activity over the entire temperature range studied. At temperatures above 500°C the ability of H‐ZSM‐5 and In/γ‐Al₂O₃ to reduce NO to N₂ was surpassed by the supported indium catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Screening of Catalysts for Acrylonitrile Decomposition

The catalytic decomposition of acrylonitrile over various metal components (Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Pd, Ag, and Pt) supported on several metal oxides (Al₂O₃, SiO₂, TiO₂, ZrO₂, and MgO) and ZSM-5 was studied. The most promising catalyst was Cu-ZSM-5, which exhibited 100% conversion and at least 80% N₂ selectivity above 350 °C.     

Effect of sulfur dioxide on nitric oxide adsorption and decomposition on Cu-containing micro- and mesoporous molecular sieves

NO decomposition was studied at different temperatures on copper-exchanged ZSM-5, AlMCM-41 and NbMCM-41 molecular sieves. Cu-ZSM-5 zeolites presented the highest activity. SO₂ poisoning was also performed and Cu–NbMCM-41 was found to be more resistant. IR results of NO and SO₂ coadsorption either at room temperature or at 573 K show evidence that sulfate formation occurred at 573 K and partially prevented NO adsorption on Cu²⁺ in square planar structure in Cu-ZSM-5. Sulfation of Cu–NbMCM-41 was quite low due to niobium incorporated into the lattice. By contrast, niobium present in the extra-lattice position in CuNb-ZSM-5 and CuNb–AlMCM-41 did not protect the catalyst from sulfation. H₂-TPR results suggested that sulfates were formed on copper sites. IR spectra after treatment under SO₂ + O₂ at 673 K indicated that sulfated species were covalently bonded, their structure varying according to the nature of the support. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of calcination behaviors on precipitated iron–manganese Fischer–Tropsch synthesis catalyst

Calcination behaviors play an important role in Fischer–Tropsch (FT) performance over a slurry iron–manganese catalyst. The present study was undertaken to investigate the effects of calcination behaviors (calcination temperature, heating rate and calcination atmosphere) on the textural properties, reduction/carburization behavior, bulk phase structure and FT synthesis performances over precipitated Fe–Mn catalysts. N₂ physisorption, X-ray photoelectron spectroscopy (XPS), H₂ thermal gravimetric analysis (TGA) and M?ssbauer effect spectroscopy (MES) were used to characterize the catalyst. It is found that increasing calcination temperature and heating rate lead to low surface area and high enrichment of Mn on the catalyst surface. High calcination temperature also increased the crystallite size of α-Fe₂O₃ and suppressed the reduction/carburization of the catalysts in H₂ and syngas. Low calcination temperature and low heating rate promoted the further carburization of the catalyst and increased the activity during FT process. High calcination temperature and low heating rate restrained the formation of CH₄, increases C₅⁺ selectivity and improved the selectivity to light olefins. In addition, calcination in argon could improve the carburization and increase FT activity of the catalyst. The present iron–manganese catalyst with lower calcination temperature, lower heating rate and calcined in argon is optimized for its FT performances.     

Thermodynamic features of the Cu-ZSM-5 catalyzed NO decomposition reaction

Over a Cu-ZSM-5 catalyst with a quantified amount of the active Cu²⁺-dimers (Cu²⁺-O^2--Cu²⁺), the kinetics of the catalytic NO decomposition to N₂ and O₂ was derived on the basis of the proposed reaction mechanism, and such thermodynamic data as adsorption enthalpies of NO and O₂ onto the Cu ion dimer sites were evaluated. It was revealed that the enthalpy of the adsorption of NO (δH=-34.1 kcal/mol) onto a reduced Cu⁺-dimer, as the initiating step of NO decomposition catalysis, was higher than that (δH=-27.8 kcal/mol) onto an oxidized Cu²⁺-dimer, or that (δH=-27.4 kcal/mol) of the dissociative adsorption of O₂ onto the two reduced Cu⁺-dimers in neighbor. The strong inhibition effect of gas phase oxygen on the kinetic rate of NO decomposition at 400–600 ‡C could be explained by the thermodynamic predominance of the oxidized Cu²⁺-dimers against the active reduced Cu⁺-dimers on the catalyst even at high temperature and under the low partial pressure of oxygen. It was also found that the maximum catalytic activity at temperatures around 500 ‡C, which was commonly observed in the Cu-ZSM-5 catalyzed NO decomposition reaction, was attributed to the relatively large enthalpy of NO adsorption onto the reduced Cu⁺-dimers as compared to that of the reaction activation energy (=19.5 kcal/mol), resulting in less favored NO adsorption at the higher temperatures than 500 ‡C.     

Selective Catalytic Reduction of NO x Over Nano-Sized Gold Catalysts Supported on Alumina and Titania and Over Bimetallic Gold–Silver Catalysts Supported on Alumina

The reduction of NO with octane under lean conditions was examined over gold supported on alumina and titania and over alumina supported bimetallic gold–silver catalysts. The silver loading was either 1.2 or 1.9 wt% whereas 0.3, 1 or 5 wt% gold was used. The catalysts were characterized by means of EDXS, N₂-adsortion, UV–Vis and TEM to correlate recorded results with different preparation methods. UV–Vis measurements indicated that gold was present in the form of fine Au particles, single Au ions and small (Au)_n ^δ+ clusters on the catalysts and silver was mainly present in the form of single Ag ions. The highest NO to N₂ reduction activity was recorded over the 0.3Au–Al₂O₃ catalyst. The Au–TiO₂ catalysts did not result in significant NO to N₂ reduction.     

Enhancement of Pd-Pt/Al2O3 catalyst performance in naphthalene hydrogenation by mixing different molecular sieves in the support

The hydrogenation of naphthalene in hexane was carried out over the catalyst Pd-Pt supported on alumina mixed with different molecular sieves including ZSM-5, Beta, USY and SAPO-11. The catalyst was characterized by N₂ sorption, NH₃-TPD, TPR, and H₂-O₂ titration. The results indicated that the catalyst performance for naphthalene hydrogenation is related to its acid property, pore structure, Pd-Pt dispersion, and metal-support interaction, which may be well regulated by mixing proper molecular sieves in the alumina support. The catalyst Pd-Pt supported on a two-component support of Al₂O₃-SAPO-11 is provided with proper acidity, large pores and moderate metal dispersion; it exhibits excellent performance in the saturated hydrogenation of naphthalene to decalin (over it a complete conversion of naphthalene is observed and the selectivity to decalin exceeds 90% at 260-300 °C).     

Combination of TLC Blotting and Gas Chromatography–Mass Spectrometry for Analysis of Peroxidized Cholesterol

We have established a sensitive and convenient method for analysis of cholesterol hydroperoxides (Chol-OOHs) as trimethylsilyloxyl derivatives using diphenylpyrenylphosphine (DPPP)-thin-layer chromatography (TLC) blotting and gas chromatography–electron ionization–mass spectrometry/selected-ion monitoring (GC–EI–MS/SIM). Chol-OOH standards were prepared by photosensitized oxidation and azo radical-induced peroxidation of cholesterol. Trimethylsilyloxyl derivatives of cholesterol 5α-hydroperoxide (Chol 5α-OOH), cholesterol 7α-hydroperoxide (Chol 7α-OOH), and cholesterol 7β-hydroperoxide (Chol 7β-OOH) could be separated from one another in the SIM chromatogram using a fragment ion with elimination of trimethylsilanol from the molecular ion. This method was used to characterize peroxidized cholesterol from azo radical-exposed human low-density lipoprotein and UVA-irradiated human keratinocytes in the presence of hematoporphyrin. Finally, we succeeded in the quantification of each Chol-OOH isomer present in hairless mouse skin with and without UVA irradiation by use of β-sitosterol hydroperoxide as internal standard. The accumulation of Chol 5α-OOH with Chol 7α/βOOH in the skin indicates that singlet molecular oxygen (¹O₂) participated in the peroxidation of skin cholesterol, because Chol 5α-OOH is known to be a ¹O₂ specific cholesterol peroxidation product. We concluded that the combination of DPPP-TLC blotting and GC–EI–MS/SIM is useful for quantifying peroxidized cholesterol in biological samples and confirming the participation of ¹O₂ in oxidative stress.     

Formation and Migration of NCO Species on Ag/SiO2 Catalyst

The adsorption of HNCO has been investigated on Ag/SiO₂ catalyst by means of FTIR spectroscopy. Adsorption of HNCO on the reduced sample at 190 K produced an absorption band at 2,170 cm⁻¹ attributed to NCO bonded to Ag. Annealing the adsorbed layer under continuous degassing, the 2,170 cm⁻¹ band gradually attenuated and at the same time a spectral feature at 2,300 cm⁻¹ due to Si–NCO developed. From these spectral changes it was inferred that NCO bonded to Ag spilt over onto silica.     

Reactions of methylcyclopentane on Rh–Pt catalyst prepared by underpotential deposition of Rh on Pt/SiO2

Rh was deposited on to a well-characterized 3.1% Pt/SiO₂ (InCat-1) parent catalyst by underpotential deposition method to obtain a model Rh–Pt bimetallic catalyst. TEM and EDS was used to determine its mean particle size and bulk composition: the particles of ca. 3 nm contained ca. 60% Pt and 40% Rh. The Rh–Pt catalyst was tested in methylcyclopentane (MCP) reaction between 513 K and 603 K and 60–480 Torr H₂ pressure (with 10 Torr MCP). The parent Pt/SiO₂ as well as a 5% Rh/SiO₂ catalyst were also studied for comparison. Four subsequent treatments with O₂ and H₂ up to T = 673 K were applied on the bimetallic catalyst before the catalytic runs. The overall activity showed positive hydrogen order on all samples, bimetallic Rh–Pt resulting in the lowest TOF values. Ring opening and hydrogenolysis products, as well as unsaturated hydrocarbons were formed from MCP. The selectivity of ring opening products and fragments over Rh–Pt catalyst was between the values observed on Pt and Rh, while the selectivity towards benzene formation was highest on the bimetallic sample, especially at higher temperatures. “Selective” ring opening occurred on all samples, resulting mostly in 2 and 3-methylpentane and less hexane. Different pretreatments with H₂ and O₂ affected slightly the dispersion values and the catalytic behavior of Rh–Pt sample. The selectivities of the Rh–Pt catalyst being between the values observed for Pt/SiO₂ and Rh/SiO₂ indicates that the sample studied represented a real bimetallic catalyst, resembling both components and exhibiting at the same time, new properties in addition to those, characteristic of Pt or Rh. Dedicated to Konrad Hayek.     

The effect of pre-sulfiding of catalysts for the vapour phase catalytic synthesis of thiophenes

A study of catalyst pre-sulfiding for the synthesis of 3-methylthiophene from 2-methylbutanol and carbon disulfide over potassium-promoted chromia–alumina has been performed. Pretreatment with CS₂ results in enhancements in 3MT yield and catalyst lifetime. The benefits observed are ascribed to a combination of enhanced Cr₂S₃ formation and poisoning of sites responsible for side reactions which limit selectivity and result in the formation of deactivating by-products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Decomposition of nitrous oxide in excess oxygen over Co- and Cu-exchanged MFI zeolites

The decomposition of nitrous oxide on several Co- and Cu-ZSM-5 zeolite catalysts was studied in the absence and presence of excess oxygen. Also, the effect of methane addition, as well as catalyst steaming in dry and wet feeds is reported. N₂O decomposition with no oxygen in the feed was proportional to metal loading on both catalysts. Co-ZSM-5 was much more resistant than Cu-ZSM-5 in excess oxygen. The tolerance of Co-ZSM-5 catalysts to excessive amounts of oxygen is high when Co²⁺ is stabilized in the zeolite framework and depends on the catalyst method of preparation. The presence of methane with no oxygen in the feed enhanced N₂O decomposition while the addition of both methane and oxygen to the feed decreased N₂O conversion on all catalysts tested. Co²⁺ ions stabilized by ZSM-5 framework have high hydrothermal stability in comparison to Cu²⁺ -exchanged ZSM-5.     

Study on Copper-based Catalysts for Synthesis of N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine from Reductive Alkylation of p-Nitroaniline with 5-Methyl-2-hexanone

The reductive alkylation of p-nitroaniline with 5-methyl-2-hexanone over copper-based catalysts was investigated. Furthermore, the catalysts were characterized using the techniques of XRD, H₂–N₂O titration, H₂-TPR, NH₃-TPD and pyridine-FTIR. The results showed that the addition of Mn, Ba and La into Cu–SiO₂ catalyst played an important role in the improvement of the selectivity towards N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine (BMPPD). The highest selectivity towards BMPPD over 58CuO–9MnO₂–BaO–1La₂O₃–30SiO₂ (wt.%) catalyst could be ascribed to the best dispersion of copper (i.e., the highest hydrogenation ability) and the most amounts of the surface Lewis acidic sites.     

Reactions of n‐hexane on Pt–Sn/Al2O3 and removal of retained hydrocarbons by hydrogenation

n‐hexane was reacted on two Pt–Sn/Al₂O₃ catalysts, one prepared by coimpregnation (T) the other by using a bimetallic PtSn complex precursor (N). Both catalysts produced isomers, methylcyclopentane fragments and benzene, the aromatic selectivity being higher on catalyst N. The hydrocarbon entities remaining after reaction were removed by hydrogen treatment. They contained methane, C₂–C₅ fragments (not observed on Pt, thus unique for PtSn) and benzene. The possible state and composition of chemisorbed carbonaceous entities during reactions are discussed. More hydrocarbons, including slightly more methane could be hydrogenated off from catalyst N of lower dispersion. The higher overall activity of catalyst N in the presence of more than one C per surface Pt points to its higher coke tolerance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quantification and redox property of the oxygen-bridged Cu<Superscript>2+</Superscript> dimers as the active sites for the NO decomposition over Cu-ZSM-5 catalysts

For a range of Cu-ZSM-5 catalysts with different Cu-exchange levels on the two kinds of ZSM-5 with different Si/A1 ratios, temperature programmed reduction using CO (CO-TPR) followed by H₂ (H₂-TPR), and temperature programmed desorption of oxygen (O₂-TPD) were conducted using an online mass spectrometer to characterize and quantify the copper species on the catalysts in the calcined state. Copper species on the ZSM-5 were quantitatively characterized as Cu²⁺, (Cu-O-Cu)²⁺ and CuO after calcination in oxygen environment. The N₂ formation activities of the catalysts in the decomposition of NO were well correlated with the quantified catalytic amounts of the Cu²⁺ ions involved in the Cu-dimers, (Cu-O-Cu)²⁺. The mol fraction of the Cu ions present as the Cu-dimers increased at the sacrifice of the isolated Cu²⁺ with increasing Cu ion exchange level, suggesting that the species could be formed between the two Cu²⁺ in close proximity. Oxygen that could be thermally desorbed from the oxidized catalysts in the O₂-TPD was responsible for the reduction of the Cu-dimers. It was concluded that the decomposition of NO over Cu-ZSM-5 catalyst proceeded by the redox of (Cu-O-Cu)²⁺, as active centers. With the temperature programmed surface reaction using N₂O or NO over an oxidized catalyst sample as well as the O₂-TPD, it was possible to estimate the change of the oxidation state of the Cu ions engaged in the Cu-dimers.     

Nitro-fatty Acids Occur in Human Plasma in the Picomolar Range: a Targeted Nitro-lipidomics GC–MS/MS Study

First studies on the occurrence of nitrated fatty acids in plasma of healthy subjects revealed basal concentrations of 600 nM for free/nonesterified nitro-oleic acid (NO₂-OA) as measured by liquid chromatography tandem mass spectrometry (LC–MS/MS). We recently showed by a gas chromatography tandem mass spectrometry (GC–MS/MS) method the physiological occurrence of two isomers, i.e., 9-NO₂-OA and 10-NO₂-OA, at mean basal plasma concentrations of 880 and 940 pM, respectively. In consideration of this large discrepancy we modified our originally reported method by replacing solid-phase extraction (SPE) by solvent extraction with ethyl acetate and by omitting the high-performance liquid chromatography (HPLC) step for a more direct detection and with the potential for lipidomics studies. Intra-assay imprecision and accuracy of the modified method in human plasma were 1–34% and 91–221%, respectively, for added NO₂-OA concentrations in the range 0–3,000 pM. This method provided basal plasma concentrations of 306 ± 44 pM for 9-NO₂-OA and 316 ± 33 pM for 10-NO₂-OA in 15 healthy subjects. Nitro-arachidonic acid and nitro-linolenic acid were not detectable in the plasma samples. In summary, our studies show 9-NO₂-OA and 10-NO₂-OA as endogenous nitrated fatty acids in human plasma in the pM range; HPLC is recommendable as a sample clean-up step for reliable quantification of nitro-oleic acids by GC–MS/MS.     

Influence of Al2O3 support on the activity of Ag/Al2O3 catalysts for SCR of NO with decane

The role of the Al₂O₃ support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated. A series of Ag/Al₂O₃ catalysts were prepared by impregnation method and characterized by N₂ pore size distribution, XRD, UV–Vis, in-situ FT-IR and acidity measurement by NH₃ and pyridine adsorption. The catalytic activity differences of Ag/Al₂O₃ are correlated with different properties of Al₂O₃ supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al₂O₃ (Ag/Al₂O₃ (SG), showed higher NO _x conversion (65% at 400 °C), compared with the respective catalysts made from commercial Al₂O₃ (Ag/Al₂O₃ (GB), Ag/Al₂O₃ (ALO), (∼26 and 7% at 400 °C). The higher surface area, acidity and pore size distribution in sol–gel prepared Al₂O₃ (SG) results in higher NO and hydrocarbon conversion. Based on the UV–vis characterization, the activity of NO reduction is correlated to the presence of Ag_n^δ+ clusters and acidity of Al₂O₃ support was found to be one of the important parameter in promoting the formation and stabilization of Ag_n^δ+ clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al₂O₃ (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of –CN and –NCO intermediate species formation over 4wt% Ag/Al₂O₃ (SG). We conclude that the physico–chemical properties of Al₂O₃ play a crucial role in NO _x conversion over Ag/Al₂O₃ catalysts. Thus, the activity of the Ag/Al₂O₃ catalyst can be tailored by using a proper type of Al₂O₃ support.