Pentane isomerization and disproportionation catalyzed by sulfated zirconia promoted with iron and manganese

Fe- and Mn-promoted sulfated zirconia was used to catalyze the conversion ofn-pentane in a flow reactor at temperatures in the range of –25 to 40C andn-pentane partial pressures in the range of 0.005 to 0.01 atm. The rates of reaction increased with time on stream during an induction period and then decreased rapidly. The predominant reaction at –25C and short times on stream was isomerization to give isopentane; no dibranched products were observed. The selectivity for isomerization decreased and that for disproportionation increased with increasing temperature, with disproportionation becoming predominant at 40C; the principal product was then isobutane. The product distribution data are consistent with acid-base catalysis and carbocation intermediates. However, there appears to be more to the reaction mechanism than acid-base chemistry, and the roles of the iron and manganese promoters are not yet explained.     

Solid superacid catalysis: kinetics of butane isomerization catalyzed by a sulfated oxide containing iron,manganese, and zirconium

Kinetics of the isomerization ofn-butane and of isobutane catalyzed by sulfated zirconium oxide containing 1.5 wt% Fe, 0.5 wt% Mn, and 4.0 wt% sulfate at 60°C are well represented by a Langmuir-Hinshelwood equation accounting for the reaction equilibrium and for adsorption of both butanes. The adsorption equilibrium constants estimated from the kinetics data are nearly the same for the two butanes. The form of the rate equation and the observation that disproportionation accompanies isomerization suggest that the reaction proceeds via a C_g intermediate.     

State of platinum in zirconia and sulfated zirconia catalysts

Platinum is present in a metallic state following activation in air at 725C of both 5 wt% Pt/ZrO₂ and 5 wt% Pt/SO ₄ ^2– /ZrO₂. Reduction of either catalyst at 725C produces a Pt-Zr alloy, and these reduced catalysts, upon recalcination in air at 725C, form metallic Pt crystallites. Likewise, reduction of these uncalcined catalysts at 725C in H₂ leads to a Pt-Zr alloy formation. However, treatment of these uncalcined catalysts in H₂ at 450C does not produce Pt crystallites large enough to detect by XRD.     

Isomerization ofn-butane on sulfated zirconia: Evidence for the dominant role of Lewis acidity on the catalytic activity

The catalytic activity of a ZrO₂/SO₄ catalyst in the isomerization ofn-butane at 423 K is reversibly suppressed by addition of CO. IR analysis of the adsorption of CO indicates that the only -coordination of CO onto coordinatively unsaturated surface Zr⁴⁺ cations occurs in the 300–473 K interval.     

The effect of potassium on the selective oxidation ofn-butane and ethane over Al2O3-supported vanadia catalysts

The catalytic properties of undoped and K-doped (K/V atomic ratio of 0.5) Al₂O₃-supported vanadia catalysts (4.5 wt% of V₂O₅) for the oxidation ofn-butane and ethane were studied. Isolated tetrahedral V⁵⁺ species are mainly observed in both undoped and K-doped samples. The incorporation of potassium decreases both the reducibility of surface vanadium species and the number of surface acid sites. Potassium-free vanadium catalysts show a high selectivity during the oxidative dehydrogenation (ODH) of ethane but a low selectivity during the ODH ofn-butane. However, the presence of potassium on the vanadium catalysts strongly influences their catalytic properties, increasing the selectivity to C₄-olefins fromn-butane and decreasing the selectivity to ethene from ethane. The role of the acid-base characteristics of catalysts on selectivity to ODH reactions is proposed.On leave from the Department of Industrial Chemistry and Materials, V. le Risorgimento 4, 40136 Bologna, Italy.     

Competitive mechanisms ofn-butane isomerization on sulfated zirconia catalysts

Isotopic analysis ofn-butane isomerization over sulfated zirconium oxide, using double¹³C-labelledn-butane, shows that at low temperature this isomerization is an inter-molecular process. Probably, a C₈ surface intermediate is formed which isomerizes and undergoes -fission; the iso-C₄ fragments are desorbed asi-butane. Previously, the same mechanism was indicated for Fe, Mn promoted catalysts. The isomerization rate at 130°C is drastically lowered by gaseous H₂, because the concentration of the unsaturated species, required for the formation of the C₈ intermediate, is low under such conditions. Whereas₁₃C-scrambledi-butane is a true primary product, isotopic scrambling ofn-butane continues after chemical equilibrium betweenn-butane andi-butane has almost been reached; i.e.¹³C scrambledn-butane is a secondary product. Intra-molecular rearrangement of carbon atoms inn-butane precedes intermolecular scrambling. The similarity of the isomerization mechanism over unpromoted sulfated zirconia and Fe, Mn promoted sulfated zirconia is paralleled by an equal strength of the acid sites in both catalysts. The shift in the FTIR band of CO adsorbed on the Lewis sites indicates that these sites, presumably surface Zr⁴⁺ ions, are weaker acids than A1³⁺ in dehydrated alumina.     

Pd/silica cluster catalysts: synthesis and reactivity with H2 and C2H4

Silica-supported Pd clusters were characterized by in situ EXAFS spectroscopy. Clusters with an average nuclearity of six atoms were derived from either an inorganic or an organometallic precursor by reduction at 100–150C. Despite the small size of the clusters, EXAFS contributions from the metal-support interface were not detected. These clusters and larger ones formed by reduction at 320C absorb hydrogen on cooling in H₂ to 30C; the resultant interstitial hydride species decompose in vacuo at 30C. Vacuum treatment at 300C removes chemisorbed H₂ yielding bare Pd clusters. In contrast to larger crystallites, the Pd clusters do not react with C₂H₄ at 150 to form interstitial carbide species.     

Response of males to female sex pheromone in the orange wheat blossom midge,Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae)

Males of the orange wheat blossom midge,Sitodiplosis mosellana (Géhin), were attracted by female but not by male extract in a Y-tube bioassay. In laboratory mating experiments, females exhibited typical calling behavior under all conditions tested. At 19C in the dark, males exhibited a high frequency of wing vibration (a courtship behavior) and mating attempts, and 68% of females were mated. However, there was virtually no courtship or mating activity at 17C and 23C (0 and 11% mated, respectively); at 21C, there was an intermediate level (43% mated). Light intensity of 1500 lux (as compared to darkness), or high relative humidity (96%, as compared to 70%) also inhibited mating activity. In trapping experiments in a wheat field, males but not females were caught in significantly greater numbers in traps baited with a solvent extract of virgin females, as compared with unbaited traps, at a trap height of 20 cm. At a trap height of 60 cm above ground, no males were caught. Males did not differentiate between traps baited with two calling females and a solvent extract of two virgin females, and the latter lost little activity over 48 hr under field conditions. There was a daily rhythm of male response to receptive females or female extract each evening between 1700 and 2200 hr CST. The sensitivity of males to environmental conditions and their consequent short daily period of response in the field are thought to be related to their high susceptibility to desiccation and lack of sources of food as adults.     

Alkylation of phenol with 1-propanol and 2-propanol over catalysts derived from hydrotalcite-like anionic clays

Vapour phase alkylation of phenol with 1-propanol and 2-propanol was carried out in a fixed-bed flow reactor over calcined magnesium aluminium hydrotalcites (MgAl-CHT) with Mg/Al atomic ratios 2, 3 and 4. MgAl 3.0-CHT showed higher phenol conversion (80% at 350C, in the alkylation of phenol with 1-propanol. Both O- and C-alkylations were found to be taking place without any skeletal isomerization of the propyl moiety, suggesting an S_N2 type mechanism. Isomorphous substitution of Mg²⁺ by Cu²⁺ or Ni²⁺ in the hydrotalcite framework resulted in the predominant C-alkylation to give 2-n-propylphenol (60–70%) with nearly 40–50% phenol conversion at 350C. When 2-propanol was used as an alkylating agent, the phenol conversion decreased over all these catalysts and the alkylation was noticed exclusively at C-centers. Comparison of the product selectivity at constant phenol conversion revealed that CuAl 3.0-CHT is more selective for 2-n-propylphenol and 2-isopropylphenol in the reaction of phenol with 1-propanol and 2-propanol respectively. The participation of a pair of acid-base sites in the calcined hydrotalcites for the alkylation reaction has been proposed. The acid-base properties of these catalysts have been examined by the decomposition of cyclohexanol as a test reaction. Analysis of the spent catalysts revealed that Cu²⁺ in CuO gets reduced into Cu¹⁺ and metallic copper during the reaction in the case of CuAl-CHT, while MgO and NiO phases of MgAl-CHT and NiAl-CHT are retained.     

Catalytic conversion of methane to benzene over Mo/ZSM-5

Dehydroaromatization of methane to benzene occurs over a 2 wt% Mo/ZSM-5 catalyst at 700C under non-oxidizing conditions. Following an initial induction period, during which CH₄ reactant reduces the original Mo⁶⁺ ions in the zeolite to Mo₂C and deposition of coke occurs, a benzene selectivity of 70% at a CH₄ conversion of 8–10% could be sustained for more than 16 h. X-ray photoelectron spectroscopy and X-ray powder diffraction measurements indicate that the reduced Mo is highly dispersed in the channels of the zeolite. Initial activation of CH₄ reactant occurs on Mo₂C sites, leading to the formation of C₂H₄ as the primary product. The latter then undergoes subsequent oligomerization reactions on acidic sites of the zeolite to form aromatic products.     

A molecular level mechanism ofn-butane oxidation to maleic anhydride over vanadyl pyrophosphate

A molecular level mechanism is proposed for the highly selective 14-e^– oxidative transformation ofn-butane to maleic anhydride on the surface of vanadyl pyrophosphate. The mechanism suggests that the dimeric active sites assume at any given time, one of four possible interconvertible states which differ from each other in the number of available oxygen atoms and the formal oxidation states of the individual vanadium atoms. The relative ratios of active sites in each of the four possible states are dictated by the reaction conditions, the redox properties of the reacting gases and the structure of the vanadyl pyrophosphate active surface. A crucial feature of the mechanism is a pseudo-ozonide surface species formed by the interaction of a chemisorbed dioxygen molecule and an adjacent metal-oxo group. This unusual species is responsible for the initial activation of then-butane, which occurs when the chemisorbed dioxygen abstracts an H-atom from the alkane and the adjacent metal-oxo group reacts with the incipient alkyl radical to form an alkoxy group. The proposed mechanism is entirely consistent with literature reports describing the behaviour of (VO)₂P₂O₇ in flow, pulse and TAP reactors.     

Catalytic behaviour and characterisation of CuO1−z(La2O3)z/2 based catalysts deposited on γ-Al2O3 and prepared in situ with 0.0 ⩽z⩽1.00, without and with addition of Pd

(CuO)_1–z(La₂O₃)_z/2 based catalysts with 0.0z1.0 supported on -Al₂O₃ have been prepared in situ and the phases formed have been identified by XRD, SEM and TEM/EDS studies. The catalyst with z=0.5 exhibited the best catalytic activity for oxidation of CO (T ₅₀=295 and 390C with degrees of conversions of 93 and 92% at 450C under rich and lean conditions, respectively) and C₃H₆ (291 and 414C; 93 and 83%) and reduction of NO (405C; 60 and 0%). This catalyst contained appreciable amounts of the perovskite phase LaAl_1–xCu_xO₃ and the enhanced catalytic properties are ascribed to the presence of this phase. Addition of Pd to this catalyst implied that the degree of conversion of NO increased and that the light-off temperatures for all involved gas species decreased. Ageing experiments revealed that LaAl_1–xCu_xO₃ decomposed and that Cu containing Pd particles were formed during this procedure which in turn deteriorated the catalytic properties of the catalyst.     

What defense doesSchouwia purpurea (Cruciferae) have against the desert locust?

A field study of the food eaten by solitary desert locusts was carried out in a winter breeding area in Mauritania. The food eaten, determined by the plant epidermis found in fecal pellets, was compared to the plant's availability in the habitat.Schouwia purpurea, well represented in the diets, was dominant at the study site. Adults had a preference forTribulus terrester. Growth and feeding on these two plants were compared. The high water content ofS. purpurea leaves limited the dry matter eaten and slowed down growth. Glucosinolates were separated and quantified by gas chromatography. There are 132mol/g dry matter in green leaves. In multiple choice tests, with paper disks, glucosinolate extracts were phagostimulant at a low concentration (21mol/g dry matter) and repulsive at a higher one (214mol/ g dry matter). Biting behavior onS. purpurea was recorded and analyzed on video. The importance ofSchouwia purpurea in desert locust habitats and its defenses is discussed.     

Effect of acid/hydrocarbon ratio,temperature and contact time on the isobutane-isobutylene alkylation with trifluoromethanesulfonic acid

The effect of the acid-hydrocarbon ratio and temperature on the isobutane-isobutylene alkylation with trifluoromethanesulfonic acid was studied over the temperature range of 40CT–80C. The effect of acid/hydrocarbon ratios and temperature passes through a maximum giving high quality alkylate of approximately 70% branched C₈ products at –30C, with a catalyst/hydrocarbon ratio of 0.5. The optimum reaction conditions also depend on the induction period and the effect of secondary reactions influenced by contact time. TFSA is a readily recyclable acid without the need for any purification or regeneration.     

Life of silicon carbide heaters in argon at high temperatures

Conclusions The electrical heating elements made from silicon carbide in argon age slowly and may operate for more than 300 h at a temperature on the surface of 1700C and more than 200 h at 1800C.The service life of the heating elements made from silicon carbide at 2000C in argon is less by a factor of 20 than at 1800C. At 2000C sublimation of the SiC from the heating element is observed.The presence in the argon atmosphere of up to 11% oxygen does not have a marked influence on the rate of oxidation of the heating elements at 1600C at the surface.Translated from Ogneupory, No. 3, pp. 33–36, March, 1967.     

Spalling resistance of corundum refractories

Conclusions Refractories based on electromelted corundum with an alumina binder are marked by comparatively low spalling resistance. The refractoriness-under-load of 2 kg/cm² is above 1800.The replacement of the alumina binder in these refractories by 10 – 20% kaolin, which causes crystallization of the mullite, helps to improve the spalling resistance. But the softening point here is reduced to 1700.Replacement of the fine-grain electro-melted corundum by finely dispersed alumina promotes active crystallization of the mullite and is accompanied by a further increase in the spalling resistance. The softening point remains low (1670).     

Modification of allelopathic effects ofp-coumaric acid on morning-glory seedling biomass by glucose,methionine, and nitrate

Studies of allelopathy have emphasized primarily the identification and quantification of phytotoxins in soils, with only limited attention directed toward how organic (carbon) and inorganic constituents (nutrients) in the soil may modify the action of such phytotoxins. In the present study, increasing carbon (C) levels (up to 108g C/g soil) supplied as glucose, phenylalanine, orp-hydroxybenzoic acid did not alter morning-glory biomass, but similar C levels supplied as leucine, methionine, orp-coumaric acid were inversely related to morning-glory biomass. Similar joint action and multiplicative analyses were used to describe morning-glory biomass response to various C sources and to generate dose isolines for combinations ofp-coumaric acid and methionine at two NO₃-N levels and for combinations ofp-coumaric acid and glucose at one NO₃-N level. Methionine, glucose, and NO₃-N treatments influenced the inhibitory action ofp-coumaric acid on biomass production of morning-glory seedlings. For example, results from the multiplicative analysis indicated that a 10% inhibition of morning-glory biomass required 7.5gp-coumaric acid/g soil, while the presence of 3.68g methionine/g soil thep-coumaric acid concentration required for 10% inhibition was only 3.75g/ g soil. Similar response trends were obtained forp-coumaric acid and glucose. The higher NO₃-N (14 vs. 3.5g/g) treatments lowered the methionine and increased thep-coumaric acid concentrations required for 10% inhibition of morning-glory biomass. These results suggested that allelopathic interactions in soil environments can be a function of interacting neutral substances (e.g., glucose), promoters (e.g., NO₃-N), and/or inhibitors (e.g., methionine andp-coumaric acid) of plant growth.The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of products named, nor criticism of similar ones not mentioned.     

Production of BL-0.5 lightweight brick with combustible additives

Conclusions Lightweight brick with a bulk density of 0.5 g/cm² made with combustible additives is an effective refractory insulating material and can be used for purposes of insulation at 1000 – 1200.The use of BL-0.5 lightweight refractory for insulating blast furnace blowpipes at a blast temperature of 930 – 950, apart from preserving the ends of the blowpipe and saving heat, creates better conditions for servicing the furnace in the tuyere zone.     

Aphid deterrence by glucose esters in glandular trichome exudate of the wild tomato,Lycopersicon pennellii

Settling of the potato aphid,Macrosiphum euphorbiae, on feeding membranes was deterred by methanolic leaf rinses ofLycopersicon pennellii, or of its F₁ with tomato,L. esculentum. The active compounds in theL. pennellii rinsates were identified as 2,3,4-tri-O-acylglucoses bearing short to medium chain length fatty acids. These compounds are localized in the glandular exudate of the type IV trichomes and may accumulate to levels in excess of 400 g/cm². In choice assays, purified glucose esters fromL. pennellii reduced aphid settling at concentrations as low as 25 g/cm²; at concentrations of 150 g/cm² or more, all aphids avoided treated areas. Glucose esters were also active in deterring aphid settling in no-choice assays. At 100 g/ cm², these esters resulted in increased levels of mortality after 48 hr.     

Abrasion resistance of refractory concretes

Conclusions With the use of abrasion resistant aggregate (corundum or corundum-mullite compositions) the highest abrasion resistance, approximating to that of fired dense chamotte articles) during heating to 1100C is possessed by concretes having a phosphate bond and containing water glass.Concretes based on high-alumina and aluminous cements around the critical temperatures have a low abrasion resistance, but at temperatures above 1100C as a result of the formation of a ceramic bond their abrasion resistance increases.Translated from Ogneupory, No. 4, pp. 41–47, April, 1967.