Alkylation of m-cresol with methanol and 2-propanol over calcined magnesium-aluminium hydrotalcites

Magnesium-aluminium hydrotalcites (MgAl-HTs) with Mg/Al atomic ratio 2,3 and 4 were synthesized bythe coprecipitation method. Vapour phase alkylation of m-cresol with methanol was carried out over these samples calcined at 723K in the temperature range 523–723K at atmospheric pressure. A mixture of O- and C- alkylated products, namely, 3-methyl anisole (3MA), 2,5- and 2,3-dimethylphenols (DMP) and 2,3,6-trimethylphenol (2,3,6-TMP) were obtained. The selectivity of these products depends on the m-cresol/methanol feed ratio, temperature and contact times. The catalytic activity of these catalysts are in the order MgAl 3.0-CHT>MgAl 2.0-CHT>MgAl 4.0-CHT. MgAl 3.0-CHT showed ∼30% selectivity for 2,5-DMP and 40% selectivity for 2,3,6-TMP with ∼40% conversion at 623K or ∼70% conversion at 723K. The alkylation of m-cresol with 2-propanol over MgAl 3.0-CHT at 673K offered nearly 80% selectivity towards thymol with nearly 40% m-cresol conversion.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. I. Strukturelle Eigenschaften von NiO/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. I. Structural Properties of NiO/SiO₂ Catalysts Structural properties of NiO/SiO₂ catalysts prepared by precipitation-deposition and impregnation have been investigated. A nickel-layer-silicate like structure is formed only in the precipitated catalysts showed infrared spectroscopic measurements. After thermal treatment at 723 K by means of magnetic measurements and reflectance spectroscopy besides Ni²⁺ ions in octahedral environment tetrahedral coordinated Ni²⁺ions were found. The part of tetrahedral coordinated Ni²⁺ ions is independent of the NiO-content up to 40 mole % NiO. Nickel oxide is formed above a content of 40 mole %. In the case of the impregnated catalysts nickel oxide cluster are formed on the surface after annealing at 723 K.     

Evolution of Cu-Zn-Si oxide catalysts in the course of reduction and reoxidation as studied by in situ X-ray diffraction analysis, transmission electron microscopy, and magnetic susceptibility methods

The reduced and reoxidized Cu-Zn-Si oxide catalysts as layered copper-zinc hydroxo silicates with the zincsilite structure were studied using in situ and ex situ X-ray diffraction analysis, transmission electron microscopy, and the temperature dependence of magnetic susceptibility. The catalysts were prepared by homogeneous deposition-precipitation. It was found that Cu⁰ particles were formed on the surface of a layered hydrosilicate with the zincsilite structure upon reduction with hydrogen. The reoxidation of the reduced samples with a mixture of oxygen and an inert gas, which contained no more than 0.05 vol % O₂, resulted in the formation of individual Cu₂O and CuO phases; copper ions did not return to the hydrosilicate structure. Catalytic tests of Cu-Zn-Si catalysts in methanol synthesis indicate that the specific catalytic activity of copper metal particles grows linearly with increasing zinc loading. This fact suggests that copper metal particles, which were obtained by the reduction of Cu²⁺ ions from the copper-zinc hydroxo silicate with the zincsilite structure, were responsible for activity in methanol synthesis. Consequently, the ability to return copper ions to a precursor compound in reoxidation with oxygen at low concentrations, which is known for reduced Cu/ZnO catalysts (these catalysts are highly active in methanol synthesis), is not related to the catalytic activity in methanol synthesis.     

Effect of different dimethylphenols on the interactions with Ni2+-exchanged montmorillonite

The influence of different steric and electronic properties of 2,4-; 2,5-; and 3,5- dimethylphenols (2,4-; 2,5-; and 3,5- DMP, respectively) on Ni²⁺-montmorillonite (Ni²⁺-MMT) (I) were studied. The results of X-ray diffraction show that the observed changes of the basal spacing were due to the intercalation of phenol derivatives into the interlayer space of montmorillonite. The existence of one peak at ~1,633 cm^?1 in the IR spectra of sample Ni²⁺-MMT + 2,4-DMP (II) and Ni²⁺-MMT + 2,5-DMP (III) and shift of this peaks to higher frequency indicate that 2,4-DMP and 2,5-DMP exist in the interlayer space of Ni²⁺-MMT in the protonated form. The two bands at ~1,622 and 1,597 cm^?1 in the sample Ni²⁺-MMT + 3,5-DMP (IV) indicate that 3,5-DMP may be also directly coordinated to Ni²⁺ cations. The different interactions of phenol derivatives in the silicate interlayers will be connected with different position of methyl groups on the phenol ring.     

Untersuchungen an katalytisch aktiven Oberflächenverbindungen. XIII. Struktur und katalytische Eigenschaften von Molybdän-oxid/SiO2-Katalysatoren

Studies on Catalytically Active Surface Compounds. XIII. Structure and Catalytic Properties of Molybdenum Oxide/SiO₂ Catalysts The catalytic properties of Mo oxide/SiO₂ catalysts in the selective oxidation of methanol to formaldehyde are described. It is shown that, independently on the preparation conditions, all catalysts showed relative high activity and selectivity values which were however, not constant during the reaction time. The high initial activity could be stabilized to a limited extent both by prereduction with methanol (but not with hydrogen) and by decreasing the oxygen concentration of the reaction gas. ESR measurements showed that in dependence on the means of reduction (methanol or hydrogen) two different coordinated Mo⁵⁺ ions were formed. Evidence was given by IR spectroscopy that prereduction in methanol caused the formation of methoxy groups stabilizing catalytically active Mo⁵⁺ ions. UV-Vis, ESCA, and electron microscopic measurements showed however, that further aggregation and formation of microcrystallites of MoO₃ took place during the catalytic reaction which caused the observed decrease of the activity.     

Adsorption mechanism of substituted pyridines on silica suspensions: an NMR study

Adsorption isotherms of 2,5-dimethylpyridine (2,5-DMP) on Aerosil 200 silica from water-2,5-DMP binary mixtures are known to exhibit special features indicative of surface phase transitions in the adsorbed layer. We have made similar observations on another substituted pyridine, 2,4,6-trimethylpyridine (2,4,6-TMP). By using 1D and 2D NMR spectroscopy, we investigated adsorbed layers on silica in suspension in water/substituted-pyridine mixtures and demonstrated the existence of adsorbed species specific signals. Comparison of signals with those displayed on NMR spectra of liquid binary mixtures under various pH conditions rules out adsorption via interaction of the surface silanol group and the lone electron pair of the nitrogen atom. A mechanism of adsorption through the interaction of surface siloxane oxygen and the aromatic pi-system is proposed; it is consistent with both thermodynamic measurements and stacking of substituted pyridines within the adsorbed layer.     

Vapour phase synthesis of isobutyraldehyde from methanol and ethanol over mixed oxide supported vanadium oxide catalysts

The vapour phase synthesis of isobutyraldehyde from methanol and ethanol in one step was investigated over titania-silica, titania-alumina, titania-zirconia, titania-silica-zirconia, and magnesia supported vanadium oxide catalysts at 623 K and under normal atmospheric pressure. Among various catalysts the titania-silica binary oxide supported vanadia provided higher yields than the other single or mixed oxide supported catalysts. The high conversion and product selectivity of V₂O₅/TiO₂-SiO₂ catalyst (20 wt% V₂O₅) was related to the better dispersion of vanadium oxide over titania-silica mixed oxide support in addition to other acid-base and redox characteristics. A reaction path for the formation of isobutyraldehyde from methanol and ethanol mixtures over these catalysts was described.     

XPS and ISS analysis of Fischer-Tropsch catalysts

Summary The surface compositions of K and Cu containing Fe/Mn oxide catalysts for Fischer-Tropsch synthesis were investigated by XPS and ISS. The surface species after calcination are identified as Fe₂O₃, Mn₂O₃, MnO₂, CuO and most likely KO₂, and after in situ reduction at 723 K Fe⁰, Cu⁰, Fe²⁺ and Fe³⁺ oxides, MnO and KOH. Mn and K are enriched on the surfaces after calcination and reduction; the Cu surface content is approximately equal to the bulk concentration. The K enrichment is especially strong and ISS indicates that potassium is mainly confined to the uppermost layers. The degree of reduction of Fe is strongly dependent on the amount of Cu or K. The change in surface composition during Fischer-Tropsch reaction in the XPS equipment can be correlated to the activity of the catalysts. The pure and Cu containing samples show a constant activity and only a small increase in carbon surface concentration. The K containing catalysts deactivate after a short time and are then totally covered by carbon. On all catalyst surfaces a small amount of carbonate is formed.

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XPS- and ISS-Analyse von Fischer-Tropsch-Katalysatoren

     

Controlling the Catalytic Properties of Copper-Containing Oxide Catalysts

The results of a systematic study of the formation of Cu–Zn, Cu–Zn–Al, Cu–Zn–Cr, Cu–Zn–Si, Cu–Cr, and Cu–Si oxide catalysts with a widely varied ratio between their components are generalized within the chemical approach developed by G.K. Boreskov to establish the quantitative relation between their chemical composition and catalytic activity. Simultaneously, their catalytic properties, such as selectivity and activity, are measured under the same conditions in the methanol synthesis and dehydrogenation and water gas shift reactions, whose common feature is a reductive reaction medium. The activity of Cu–Zn–Al–Cr— Si-oxide catalysts in all the studied reactions is governed by the Cu⁰ nanoparticles formed on their surface in the process of reductive activation. Nanoparticles of different catalysts have similar sizes (3–8 nm). However, the ratios between the catalytic activities per unit of the copper surface area for catalysts with various structures of their oxide support (spinel, wurtzite, zincsilite, or silica type) are appreciably different in each reaction. The relation between the chemical composition of a catalyst and its catalytic activity in a certain reaction is established by the chemical composition of its precursor representing a hydroxo compound, i.e., the nature of the selected cations and the quantitative ratio between them. The decomposition of hydroxo compounds to oxides (and the further activation of oxides) should be performed at medium temperatures, providing the incomplete elimination of ОН^– and CO₃^2- anions, i.e., the formation of anion-modified oxides. The structure of the latter and the type of interaction between Cu⁰ nanoparticles and an oxide support are governed by the structure of the hydroxo precursor compound.     

镁铁和镁铁铝催化剂氢还原过程的研究

以水滑石为前体 ,制备了镁铁和镁铁铝复合氧化物催化剂 ,运用原位穆斯堡尔谱研究了催化剂在H2 气氛中的还原行为。结果表明 :由于Mg、Al的加入和固溶体的形成 ,相对地稳定了FeO物相 ,阻碍了H2 对铁离子的还原 ,使得Fe2 进一步还原为金属Fe0 的能力减弱 ;在还原过程中催化剂首先生成含Fe2 的固溶体FeO MgO或FeO MgO Al2O3,然后再完全还原成金属Fe0。     

Characterization and Activity of Cu‐MnOx/γ‐Al2O3 Catalyst for Hydrogenation of Carbon Dioxide

The effect of manganese on the dispersion, reduction behavior and active states of surface of supported copper oxide catalysts have been investigated by XRD, temperature‐programmed reduction and XPS. The activity of methanol synthesis from CO₂/H₂ was also investigated. The catalytic activity over CuO‐MnO_x/γ‐Al₂O₃ catalyst for CO₂ hydrogenation is higher than that of CuO/γ‐Al₂O₃. The adding of manganese is beneficial in enhancing the dispersion of the supported copper oxide and make the TPR peak of the CuO‐MnK_x/γ‐Al₂O₃ catalyst different from the individual supported copper and manganese oxide catalysts, which indicates that there exists strong interaction between the copper and manganese oxide. For the CuO/γ‐Al₂O₃ catalyst there are two reducible copper oxide species; α and β peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO‐MnO_x/γ‐Al₂O₃ catalyst, four reduction peaks are observed, α peak is attributed to the dispersed copper oxide species; β peak is ascribed to the bulk CuO; γ peak is attributed to the reduction of high dispersed CuO interacting with manganese; δ peak may be the reduction of the manganese oxide interacting with copper oxide. XPS results show that Cu⁺ mostly existed on the working surface of the Cu‐Mn/γ‐Al₂O₃ catalysts. The activity was promoted by Cu with positive charge which was formed by means of long path exchange function between Cu? O? Mn. These results indicate that there is synergistic interaction between the copper and manganese oxide, which is responsible for the high activity of CO₂ hydrogenation.     

ORTHO-selective phenol methylation over iron-magnesium oxide catalysts

Alkylation of phenol to ORTHO-cresol and 2,6-xylenol with methanol in the presence of iron and iron-magnesium oxide catalysts was investigated. The catalysts displayed high activity and stability. Addition of magnesium oxide to the iron catalyst increases its selectivity towards C-alkylation in ortho-position. It was found that the active phase in the investigated catalysts is highly dispersed magnetite or mixed spinel of Fe(MgFe)O₄ type. It is noticed that if Fe⁺² ions are replaced by Mg⁺² ions in the spinel the basicity of the bifunctional catalyst is augmented, increasing ortho-selectivity of alkylation.     

Active component of supported vanadium catalysts in the selective oxidation of methanol

The structure of catalysts based on vanadium oxide supported on different oxides (SiO₂, γ-Al₂O₃, ZrO₂, and TiO₂) was investigated. Their catalytic properties in the selective oxidation of methanol in a temperature range of 100–250°C were studied. It was shown that the nature of the support determines the structure of the oxide forms of vanadium. The supporting of vanadium on SiO₂ and γ-Al₂O₃ leads to the preferred formation of crystalline V₂O₅; the surface monomeric and polymeric forms of VO_x are additionally formed on ZrO₂ and TiO₂. It was established that the crystalline V₂O₅ oxide is least active in the selective oxidation of methanol; the polymeric forms are more active than monomeric ones. The mechanism of the selective oxidation of methanol to dimethoxymethane and methyl formate on the vanadium oxide catalysts is considered.     

Rapid analysis of the nitrification inhibitor 3,4-dimethylpyrazole phosphate in soil using LC-MS/MS

Nitrate from the biological nitrification of ammonium fertilisers causes environmental damage via groundwater contamination and nitrous oxide emission. To limit nitrate formation, nitrification inhibitors (NIs) are used in conjunction with ammonium-based fertilisers in agricultural land management. The NI 3,4-dimethyl-1H-pyrazole phosphate (DMPP), with an active constituent 3,4-dimethyl-1H-pyrazole (3,4-DMP), is commercially available and its effectiveness and behaviour in soils have been studied. However, only one method for the analysis of 3,4-DMP in soil has been reported and relies on extensive sample preparation to remove matrix interferences prior to HPLC analysis. A new method was developed to allow monitoring of 3,4-DMP residues in soil after appliaction, which utilises the greater selectivity and sensitivity of LC-MS/MS. A 3,4-DMP limit of quantitation of 0.5 ng/g was achieved, which is 10 times more sensitive than the published method, and was achieved using 10,000 times less 3,4-DMP injected on-column, with an injection volume 100 times smaller. Four internal standards were evaluated to improve the accuracy of the extraction method. The isotope-substituted structural isomer 3,5-dimethyl pyrazole-¹⁵N₂ provided the best and most consistent recoveries over the 300-fold concentration range tested. The new method was employed to investigate the persistence and mobility of 3,4-DMP in an agricultural soil. 3,4-DMP had a half-life of 5 days in the top 0.5 cm of soil at normal and double recommended application rates, while half-lives in the 2.5 cm soil profile were 28 and 21 days, respectively. 3,4-DMP mobility in the clay loam soil tested was low, with only 15–25% of applied 3,4-DMP detected below the top 0.5 cm, suggesting the loss of 3,4-DMP was either due to volatilisation or degradation, rather than leaching into the soil profile.     

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H₂-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO₂, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co³⁺ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.     

IR and XPS studies of the reactivity of CO with Ti-H species at the support on Rh/TiO2 catalysts

Incorporation of hydrogen in Rh/TiO₂ samples during high temperature reduction (H₂ at T > 573 K), has been studied by TPD-MS. ESR and NMR data suggest that hydride-like species associated to Ti³⁺ ions at the support are formed, i.e, (Ti-H)³⁺. Rh(3d) XPS peaks (at 311.2, 306.5 eV) remain unchanged after removal of such hydride-like species (by outgassing at 773 K), though it modifies the adsorption capacity for CO and H₂, monitored by i.r. and NMR, thus indicating a SMSI effect which is reversed by outgassing at 773 K the sample. By heating in CO at 373–473 K bands at 1590, 1470 and 1220 cm^-1 are developed only in the samples saturated with hydrogen, while CH₃OH is detected in the gas phase. Experiments using a pulse microreactor in conditions that allow formation of such (Ti-H)³⁺ species, lead to methanol as the only product of syngas reaction. A model is proposed to explain generation of oxygenated compounds on these catalysts, whieh assumes reaction of the hydride-like species at the TiO₂ support with CO molecules either directly interacting with the support or hounded to the rhodium at the metal-support interface.     

酸处理对CuY催化剂孔结构及氧化羰基化性能的影响

对NaY分子筛(n_Si/n_Al=2.65)进行了草酸脱铝处理并作为载体采用液相离子交换法制备CuY催化剂,应用于常压甲醇氧化羰基化合成碳酸二甲酯(DMC)反应。NaY分子筛及其CuY催化剂通过N₂低温吸附-脱附、透射电子显微镜、X射线衍射、²⁹Si固体核磁共振、NH₃吸附程序升温脱附、吡啶吸附红外光谱、H₂程序升温还原、原子吸收等方法进行表征。研究结果表明,酸处理NaY分子筛后,骨架铝被脱除,导致骨架n_Si/n_Al比增加、相对结晶度降低并产生介孔,有利于产物分子的扩散,从而影响催化活性。采用4 h、2 mol·L^-1草酸处理NaY分子筛作为载体制备的CuY催化剂显示出较高的催化性能,DMC时空收率和甲醇转化率分别从103.6 mg·g^-1·h^-1和6.3%增加到184.9 mg·g^-1·h^-1和10.2%。产生的介孔能够促进催化剂中铜活性位的可接近性及反应物分子和产物分子的扩散。     

Monolayer V2O5/TiO2–ZrO2 catalysts for selective oxidation of o-xylene: preparation and characterization

A series of TiO₂?CZrO₂ supported V₂O₅ catalysts with vanadia loadings ranging from 4 to 12 wt% were synthesized by a wet impregnation technique and subjected to various thermal treatments at temperatures ranging from 773 to 1,073?K to understand the dispersion and thermal stability of the catalysts. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area, oxygen uptake, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results of 773?K calcined samples conferred an amorphous nature of the mixed oxide support and a highly dispersed form of vanadium oxide. Oxygen uptake measurements supported the formation of a monolayer of vanadium oxide over the thermally stable TiO₂?CZrO₂ support. The O 1s, Ti 2p, Zr 3d, and V 2p core level photoelectron peaks of TiO₂?CZrO₂ and V₂O₅/TiO₂?CZrO₂ catalysts are sensitive to the calcination temperature. No significant changes in the oxidation states of Ti⁴⁺ and Zr⁴⁺ were noted with increasing thermal treatments. Vanadium oxide stabilized as V⁴⁺ at lower temperatures, and the presence of V⁵⁺ is observed at 1,073?K. The synthesized catalysts were evaluated for selective oxidation of o-xylene under normal atmospheric pressure in the temperature range of 600?C708?K. The TiO₂?CZrO₂ support exhibits very less conversion of o-xylene, while 12 wt% V₂O₅ loaded sample exhibited a good conversion and a high product selectivity towards the desired product, phthalic anhydride.     

Spectroscopic characterization of 2-naphthylcarbene

The 308 nm excimer laser flash photolysis of 2-naphthyldiazomethane produces triplet 2-naphthylcarbene (λ_max = 362 nm) which decays with the observed pseudo-first-order rate constants (k_exptl) of 5.54 ± 0.03 × 10⁶; 3.33 ± 0.4 × 10⁶; 1.64±0.02 × 10⁷; and 3.05±0.4 × 10⁶ s^-1 in n-pentane, 2,2,4-trimethylpentane (2,2,4-TMP), benzene and Freon 113 respectively. In hydrocarbon solvents the observed decay of triplet 2-naphthylcarbene is correlated with the pseudo-first-order growth of the 2-naphthylmethyl radical (λ_max = 378 nm). Direct kinetic measurements of the reaction of triplet 2-naphthylcarbene in 2,2,4-TMP with cyclohexane, styrene, methanol and carbon tetrachloride yielded bimolecular quenching rate constants of 1.48 ± 0.04 × 10⁶;4.33 ± 0.1 × 10⁷;7.25 ± 0.5 × 10⁶; and 3.35 ± 0.07 × 10⁶M^-1S^-1. It is also found that 2-naphthylcarbene reacts with acetonitrile (k_q = 5.28 ± 0.1 × 10⁵ M^-1 s^-1) to form a nitrile ylide intermediate with a λ_max = 372 nm. These results are interpreted in terms of a rapid singlet-triplet 2-naphthylcarbene equilibrium.     

On the generation and characterization of the spiro[2,5]octadienyl anion in the gas phase

Three routes have been explored in both a high-pressure chemical ionization (CI) source and a low-pressure Fourier transform ion cyclotron resonance (FT-ICR) cell to generate the spiro[2,5]octadienyl anion in the gas phase: (i) proton abstraction from spiro[2,5]octa-4,6-diene; (ii) expulsion of trimethysilyl fluoride by phenyl ring participation following fluoride anion attack upon the silicon centre of 2-phenylethyl trimethylsilane; and (iii) collisionally induced dissociation (CID) of the carboxylate anion of 3-phenylpropanoic acid via carbon dioxide loss. From comparison of the CID spectra of various reference [C₈H₉]^? ions with those of the [C₈H₉]^? ions which could be generated via the routes (i) and (iii) in the CI source it can be concluded that only the third route yields a [C₈H₉]^?ion whose CID spectrum is not inconsistent with the one expected for the spiro[2,5]octadienyl anion. In the FT-ICR cell [C₈H₉]^? ions are generated along all three routes; their structures have been identified by specific ion-molecule reactions and appear to be different. Route (i) yields an α-methyl benzyl anion, probably due to isomerization within the ion-molecule complex formed. An ortho-ethylphenyl anion is formed along route (ii), presumably due to an intramolecular ortho proton abstraction in the generated trimethylsilyl fluoride solvated 2-phenylethyl primary carbanion. The [C₈H₉]^? ion formed along route (iii) shows reactions similar to those of the 1,1-dimethylcyclohexadienyl anion which is structurally related to the spiro[2,5]octadienyl anion. Furthermore, the [C₈H₉]^? ion generated via route (iii) reacts with hexafluorobenzene under expulsion of only one hydrogen fluoride molecule which contains exclusively one of the original phenyl ring hydrogen atoms. On the basis of all these observations it is therefore quite likely that the spiro[2,5]octadienyl anion is formed by collisionally induced decarboxylation of the 3-phenylpropanoic acid carboxylate anion and can be a long-lived and stable species in the gas phase.