Adsorption states of carbon monoxide on oxygenated Cu(110) faces

Oxygen preadsorption on Cu(110) surfaces strongly reduces the CO desorption peak at 220 K, typical for clean Cu(110) and induces the development of less tightly bound states, which probably correspond to sites on Cu(111) micro-facets, formed in the course of oxygen stimulated surface reconstruction. A smaller part of the CO molecules ( 20%) seems to interact with adsorbed oxygen to give adsorbed CO ₂ ^– which can be stabilized in the presence of CO₂ by formation of van der Waals complexes, e.g. [CO₂ · CO ₂ ^– ]. At increasing temperature this complex decomposes or disproportionates to give desorbing CO and adsorbed CO ₃ ^– . The interpretation is tentative, but some evidence is given to it by TDS from Cu(111), by XPS, STM and SIMS studies and by theoretical calculations.     

The activation of O2 and the oxidative dehydrogenation of C2H6 over SmOF catalyst

The activation of O₂ over SmOF was studied by in situ laser Raman spectrometry and temperature programmed desorption (TPD). When the hydrogen- and helium-treated (1 h for each gas at 973 K) SmOF sample was cooled to 303 K in oxygen, Raman bands which correspond to the existence of O ₂ ^2– , O ₂ ^n– (2 >n > 1), O ₂ ^– and O ₂ ^- (1 > > 0) species were observed. From 303 to 973 K, there was no O₂ desorption but the Raman bands observed at 303 K reduced in intensity and vanished completely at 973 K, even though the sample was under an atmosphere of oxygen. We suggest that as the sample temperature increased, dioxygen species were converted to mono-oxygen species such as O^– which were undetectable by Raman spectrometry. O₂ desorption occurred above 973 K, giving a TPD-peak at 1095 K. When C₂ H₆ was pulsed over the sample pretreated with oxygen and helium at 973 K, C₂H₄ selectivity was 91.8%. We conclude that the mono-oxygen species is responsible for the oxidative dehydrogenation of ethane to ethene.     

CO Oxidation on Gold Surfaces Studied on the Atomic Scale

The interaction of small gold crystal tips with oxygen gas and CO/O₂ gas mixtures was studied by means of field ion microscopy (FIM). High-resolution FIM-images of clean tips were obtained with hydrogen and neon as imaging gas. At temperatures between 300 and 450 K the exposure of a clean Au sample to O₂ gas at 100–1000 mbar, in the absence of an electric field, led to oxygen chemisorption and formation of a surface oxide. The presence of an electric field of 12–15 V/nm was found to enhance the oxidation process. Exposure to CO gas at 300 K led to the removal of the surface oxide. This was associated with the occurrence of a wave front which started in the apex centre and extended to the outskirts of the tip sample. The build-up of the surface oxide and its titration by carbon monoxide was completely reversible. Our results strongly suggest that pure gold crystals are active catalysts for the CO oxidation at 300 K.     

Terpolymerization: A Review

The terpolymer, poly (styrene-acrylonitrile-linalool) has been synthesized by free radical solution polymerization of the electron-donating monomers, linalool (optically active) (LIN) and styrene (STY) with the electron-accepting monomer, acrylonitrile (AN) using benzoyl peroxide (BPO) as an initiator and xylene as diluent at 75°C for 40 minutes. The system follows ideal kinetics. Rp [BPO]^0.5 [LIN]^1.0 [STY]^1.0 [AN]^1.0. ¹H-NMR spectrum of terpolymer has peaks at 7.8–8.0 due to –OH group of LIN and at 7.0–7.7 due to phenyl group of styrene. ¹³C-NMR spectrum of terpolymer has peaks at ppm = 119–120 of –CN, ppm = 129–136 of C₆H₅ and ppm = 75–77 of –C–OH. Bands at 3075 cm^–1, 2240 cm^–1 and at 3500 cm^–1 are observed in the FTIR spectrum of terpolymer, indicates the presence of phenyl, cyanide and hydroxy group respectively. The reactivity ratios, determined by the Kelen–Tüdös method [r ₁ for AN and r ₂ for (LIN + STY)] are 0.11 and 0.005 respectively. It is concluded that the system agrees with theoretical treatment and gives the relative reactivity ratio k ₁₂/k ₁₃=0.748 by treatment of the free radical propagating mechanism. The overall activation energy is 38 kJ/mol. The molecular weight of terpolymer is determined by gel permeation chromatography technique. The value of _w/ > _n is 1.36.     

Infrared spectroscopy and microcalorimetry studies of CO adsorption on sulfated zirconia supported platinum catalysts

Carbon monoxide adsorption has been investigated on Pt particles supported on a high surface area zirconia and sulfated zirconias. The accessibility of the Pt surface determined from the comparison of H₂ chemisorption and transmission electron microscopy depends on two parameters: the temperature of treatment in air used to dehydroxylate sulfated zirconia, and the temperature of reduction. An oxidative pretreatment at 823 K yields a poor accessibility of Pt (0.03 < H/Pt < 0.05) whatever the temperature of reduction, whereas a Pt dispersion of 0.6 can be obtained by oxidation at 673 K followed by a mild reduction at 473 K. FTIR spectroscopy of adsorbed CO on Pt/ZrO₂ shows besides the normal linear species at 2065 cm^–1, a band at 1650 cm^–1 which is attributed to CO bridged between Pt and Zr atoms. On Pt/ZrO₂-SO ₄ ^2– , all bridged species tend to disappear, as well as the dipole-dipole coupling andv _CO is shifted by 57 cm^–1 to higher frequencies. These results are attributed to sulfur adsorption on Pt which decreases the electron back-donation from Pt to the 2 ^* antibonding orbital of CO. The lower initial heat of CO adsorption observed on Pt/ZrO₂-SO^4/2– supports this proposal.     

CO and NO adsorption on copper-containing zeolite. A theoretical ab initio study

Ab initio calculations were performed to simulate the interaction between CO or NO and copper-containing zeolite at the SCF level. The zeolite catalysts were modelled by a molecular cluster of composition H₈Si₃AlO₄Cu⁺ with = 0, 1. For = 0 the oxidation state of the Cu atom corresponds to 1+ in Cu⁺/zeolite, while for° = 1 it is equal to 2+ in Cu²⁺/zeolite. It was found that only Cu⁺/zeolite should be responsible for CO and NO adsorption from the gas phase. The calculated heats of adsorption compare well with available experimental data and together with adsorption geometries allow us to interpret the observed IR data.     

Isotopic assessment of CO<Subscript>2</Subscript> production through soil organic matter decomposition in the tropics

Values of ¹³C and ¹⁵N of soil organic matter (SOM) under different land cover in Pasir Mayang, Jambi Province, Sumatra Island, Indonesia were examined to apply them as indicators of SOM dynamics and related CO₂ production. The ¹³C and ¹⁵N values of SOM increased with depth in the 0–30 cm layer in the preserved forest, reflecting ¹³C and ¹⁵N richment in SOM through mineralization and immobilization. The degree of vertical enrichment, difference between 0–5 cm and 10–15 cm SOM, was more pronounced in ¹⁵N than in ¹³C at all sites in Pasir Mayang. The ¹³C -SOM profiles fluctuated through clear-cutting the forest and subsequent burning, which was due to input of biomass with higher C/N molar ratio and lower ¹³C value than the original SOM. However, the ¹⁵N-SOM profiles before and after such a drastic event did not change appreciably. The ¹⁵N-SOM became higher as the C/N ratio decreased and as soil sugar content decreased. These observations suggest that ¹⁵N-SOM is a variable that changes with the amount of easily decomposable organic matter (EDOM) in soil. Soil incubation experiments demonstrated a correlation between CO₂ production rate and degree of vertical ¹⁵N-enrichment in SOM, which was applied to field data to estimate CO₂ production through SOM decomposition. A similar analysis was performed with the soils collected at 27 locations in other districts in Jambi Province than Pasir Mayang. In five locations covered by oil palm plantation, CO₂ production through SOM decomposition controlled 70 of variation in CO₂ emission among the locations. In the remaining 22 locations, however, the CO₂ emission was neither related to CO₂ production from SOM nor to ground litter amount. This observation indicated that mechanisms other than dead organic matter decomposition such as root respiration were dominant sources for CO₂ emission in these sites.     

Control of oxygen deficiency in Ca1−x La x MnO3−δ and its cathodic properties in alkaline solution

Ceramic samples of composition Ca_0.9La_0.1MnO_3– having various oxygen contents were prepared by a quenching method under nitrogen atmosphere. As the 3 – value decreased from 2.97 to 2.79, the sample conductivity decreased from 10² to 10^–1 S cm^–1. The porous ceramic samples showed good properties as cathode materials in alkaline solution without using conductive material such as graphite, but the discharge capacity decreased with decreasing sample conductivity. The discharge termination is explained by a simple model considering dissipation of the conductive path (high conductivity core) present in the porous sintered ceramic.     

Steam Reforming of Methanol Over Cu/CeO2 Catalysts Studied in Comparison with Cu/ZnO and Cu/Zn(Al)O Catalysts

A series of Ce_1-xCu_xO_2- mixed oxides were synthesized using a co-precipitation method and tested as catalysts for the steam reforming of methanol. XRD patterns of the Ce_1-xCu_xO_2- mixed oxides indicated that Cu²⁺ ions were dissolved in CeO₂ lattices to form a solid solution by calcination at 773K when x < 0.2. A TPR (temperature-programmed reduction) investigation showed that the CeO₂ promotes the reduction of the Cu²⁺ species. Two reduction peaks were observed in the TPR profiles, which suggested that there were two different Cu²⁺ species in the Ce_1-xCu_xO_2- mixed oxides. The TPR peak at low temperature is attributed to the bulk Cu²⁺ species which dissolved into the CeO₂ lattices, and the peak at high temperature is due to the CuO species dispersed on the surface of CeO₂. The Ce_1-xCu_xO_2- mixed oxides were reduced to form Cu/CeO₂ catalysts for steam reforming of methanol, and were compared with Cu/ZnO, Cu/Zn(Al)O and Cu/AL₂O₃ catalysts. All the Cu-containing catalysts tested in this study showed high selectivities to CO₂ (over 97%) and H₂. A 3.8wt% Cu/CeO₂ catalyst showed a conversion of 53.9% for the steam reforming of methanol at 513K (W/F = 4.9 g h mol^-1), which was higher than that over Cu/ZnO (37.9%), Cu/Zn(Al)O (32.3%) and Cu/AL₂O₃ (11.2%) with the same Cu loading under the same reaction conditions. It is likely that the high activity of the Cu/CeO₂ catalysts may be due to the highly dispersed Cu metal particles and the strong metalsupport interaction between the Cu metal and CeO₂ support. Slow deactivations were observed over the 3.8wt% Cu/CeO₂ catalyst at 493 and 513K. The activity of the deactivated catalysts can be regenerated by calcination in air at 773K followed by reduction in H₂ at 673K, which indicated that a carbonaceous deposit on the catalyst surface caused the catalyst deactivation. Using the TPO (temperature-programmed oxidation) method, the amounts of coke on the 3.8wt% Cu/CeO₂ catalyst were 0.8wt% at 493K and 1.7wt% at 513K after 24h on stream.     

Ternary alkali carbonate composition-oxygen solubility relationship under atmospheric and pressurized conditions – a utility model for MCFC

The effect of O₂/CO₂ = 90/10 gas mixtures under pressurized conditions on the diffusion resistance during oxygen reduction was investigated in carbonate melts of variable composition ranging from the eutectics Li–K, Li–Na to ternary Li–Na–K carbonate melts. It was found that pressurization reduced the diffusion resistance of the reactant species in all compositions investigated. This was ascribed to the increase in concentration of the reactive species in the electrolyte. Reaction order plots of Warburg coefficient versus the total pressure in binary melts showed that: (i) mixed diffusion of superoxide ions and CO₂ prevails in lithium rich carbonates, and (ii) mixed diffusion of peroxide ions and CO₂ predominates in potassium rich carbonates. By means of a computerized statistical analysis of the results, a partial cubic model was found to describe the relationship between alkali carbonate compositions, pressure, and Warburg coefficient. The optimum alkali carbonate compositions are: (i) 0.283Li–0.373Na–0.344 K with _app equal to 137.68 cm²s^–0.5 at atmospheric conditions, and (ii) 0.390Li–0.355 Na–0.255 K with _app 87.53 cm² s^–0.5 and 4.2 atm under pressurized conditions.     

Catalytic decomposition of nitrous oxide over perovskite type solid oxide solutions and supported noble metal catalysts

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La_0.8Sr_0.2MO_3– (M=Cr, Fe, Mn, Co or Y), La_1.8Sr_0.2CuO_4– and supported Pd, Pt catalysts. The reaction was carried out in a gradientless recycle reactor at 1 atm pressure with a feed gas containing about 0.5% N₂O (in helium). Among the various solid solutions, La_0.8Sr_0.2CoO_3– showed a maximum N₂O conversion of 90% at 600C. The order of activity observed for N₂O decomposition was La_0.8Sr_0.2CoO_3–>La_0.8Sr_0.2FeO_3–>La_1.8Sr_0.2CuO_4–> La_0.8Sr_0.2MnO_3–La_0.8Sr_0.2CrO_3–La_0.8Sr_0.2YO_3–. The activity of La_0.8Sr_0.2CoO_3– was compared with supported Pd, Pt and also with unsubstituted LaCoO₃ catalysts under similar reaction conditions. Among all the catalysts tested in this study, Pd/Al₂O₃ showed the lowest light-off temperature for N₂O decomposition. The activity of La_0.8Sr_0.2CoO_3– was found to be comparable to Pd/Al₂O₃ catalyst at temperatures above 500 C. The influence of added oxygen (about 4%) in the feed was examined over La_0.8Sr_0.2CoO_3– and Pd/Al₂O₃ catalysts and only in the case of cobalt catalyst was the conversion of N₂O decreased by 13%. By choosing varied sintering conditions, La_0.8Sr_0.2CoO_3– of different BET surface areas were prepared and the light-off temperature was found to decrease with increase in surface area. The results obtained over solid solutions are discussed on the basis of the cation mixed valency and oxygen properties of the catalyst.     

A study of tile drain nitrate - δ<Superscript>15</Superscript>N values as a tool for assessing nitrate sources in an agricultural region

It is important to evaluate tools which provide insight into nitrate (NO^–₃) contamination source identification in watersheds where multiple nitrogen (N) sources are applied. As nitrate-N stable isotopes have been previously used to identify contaminant sources in groundwater environments, the application of the technique to tile drainage outflow was investigated. Nitrate-N isotopic and concentration analyses of tile drain discharges from six different fields with a range of mineral fertilizer N and hog manure applications were conducted to examine general isotopic patterns and their relation to N fertilizer sources. ¹⁵N of NO^–₃ draining fields were compared to ¹⁵N source signatures through a single growing season. The objective was to determine: (a) whether tile drainage water exiting fields receiving different N sources (inorganic mineral N, organic hog manure N, or a combination of the two) had distinct ¹⁵N values, and (b) whether ¹⁵N signatures of sampled tile drain water fell within expected source ranges. Results suggest that isotopic data differed between fields in a manner consistent with differences in NO-3 sources, as fields only fertilized with mineral N had ¹⁵N values consistently lower than fields with hog manure applications. However, all fields showed isotopic values that were enriched in ¹⁵N relative to their sources during the study period. Therefore, although these fields are discharging tile drainage water with distinctive isotopic signatures, the data suggests that a quantitative evaluation of individual NO^–₃ source contributions is not possible within this watershed. Utilization of this tool in source discrimination in other tile drainage waters should only proceed if it can be demonstrated that isotopic fractionations are not altering source signatures.     

Novel Catalytic Properties of Rh Sulfide for the Synthesis of Methanol from CO + H2 in the Presence of H2S

Rh sulfide yielded 800 gkg-cat^–1h^–1 of methanol at 593 K and 5.1 MPa from CO + H₂ (syngas) even in the presence of H₂S 100 ppm in concentration. The obtained space-time yield of methanol was comparable with that obtained with a commercial Cu/Zn/Al catalyst at a conventional reaction condition (523 K and 5.1 MPa) from a feed containing both syngas and CO₂.     

Methanol synthesis on Cu(100) from a binary gas mixture of CO2 and H2

The rate of methanol synthesis over a Cu(100) single crystal from a 1 1 mixture of CO₂ and H₂ has been measured at a total pressure of 2 bar and a temperature range of 483–563 K. At these conditions the apparent activation energy is determined to be 69 kJ mol^–1, and at 543 K the turnover rate is 2.7 × 10^–4 (site s)^–1. A kinetic model for the methanol synthesis is presented. Predictions from this model are in good agreement with the rates of methanol synthesis observed on real catalysts at industrial conditions.     

Formation of Ni(CO)4 during the Interaction between CO and Silica-Supported Nickel Catalyst: an FTIR Spectroscopic Study

The formation of Ni(CO)₄ during interaction of CO with silica-supported highly dispersed nickel metal (d _av4 nm) was investigated by FTIR spectroscopy. At temperatures below 145 K, in addition to linear and bridged nickel carbonyls, CO adsorption on Ni⁰/SiO₂ leads to the formation of Ni(CO) _x (x=2, 3) subcarbonyls (band at ca. 2090 cm^–1) and negligible amounts of Ni(CO)₄ adsorbed on SiO₂ (band at 2048 cm^–1). Up to this temperature CO causes no detectable erosion of the metal surface. Above 145 K the rate of interaction between CO and the nickel particles significantly increases. Until 235 K Ni(CO)₄ mainly remains in the adsorbed state, while at still higher temperatures the equilibrium between adsorbed and gaseous Ni(CO)₄ (band at 2058 cm^–1) is shifted towards the latter. It is assumed that subcarbonyls formed on defect sites of the metal surface are precursors of the nickel tetracarbonyl. Successive adsorption–evacuation cycles of CO at room temperature result in a decrease in the amount of the Ni(CO)₄ formed, probably due to a reduction of the number of defect metal sites. On the basis of ¹²CO and ¹³CO coadsorption, an alternative interpretation of the band at 2048 cm^–1 to species containing isolated Ni(CO)₃ groups is proposed.     

A study of the oxidative coupling of methane over SrO-La2O3/CaO catalysts by using CO2 as a probe

20%SrO-20%La₂O₃/CaO catalyst (SLC-2), prepared by impregnation, has shown 18% CH₄ conversion and 80% C₂-selectivity for the oxidative coupling of methane (OCM) at 1073–1103 K with CH₄O₂ molar ratio=91 and total flow rate of 100 ml/min. Addition of SrO onto La₂O₃/CaO (LC) catalyst strengthens the surface basicity and leads to an increase in CH₄ conversion and C₂-selectivity. Meanwhile, the reaction temperature required to obtain the highest C₂-yield increases with increasing SrO content. The formation of carbonate on the catalyst surface is the main reason for the deactivation of LC and SLC catalysts. If the amount of CO₂ added into the feed is appropriate and the reaction temperature is high enough, there is no deactivation at all. In such case, the added CO₂ will suppress the formation of CO₂ produced via the OCM reaction, therefore, improves the C₂-selectivity. The FT-IR spectra of CO₂ adspecies recorded at different temperatures show that CO₂ interacts easily with the catalyst surface to form different carbonate adspecies. Unidentate carbonate is the main CO₂ adspecies formed on the catalyst surface. On the LC catalyst surface, the unidentate carbonate was first formed on Ca²⁺ cations at room temperature. If the temperature is higher than 473 K, it will form on La³⁺ cations. On the SLC catalyst surface, if the temperature is lower than 573 K, only the unidentate carbonate formed on Ca²⁺ cations could be observed. When the temperature is higher than 673 K, it will then form on Sr²⁺ cations. This suggests that the unidentate carbonate can migrate on the LC and SLC catalyst surface on one hand, and on the other hand, that the surface composition of SLC catalysts is dynamic in nature. On the basis of both the decomposition temperatures of the carbonate species, and the temperature dependence of the value which is the difference of symmetric and asymmetric stretching frequencies of surface carbonates, the in situ FT-IR technique offered two approaches to measure the surface basicity of the SLC catalyst. The results thus obtained are in good agreement with that of CO₂-TPD. The role of the surface basicity of the SLC catalyst is also discussed.     

Chloromethoxyl and dichloromethoxyl formation on zeolite ZnY,an in situ NMR and flow reactor study

In situ¹³C and²⁷Al MAS NMR and flow reactor studies were used to study the decomposition of dichloromethane and chloroform on zeolite ZnY. The initially formed products were framework-bound chloromethoxyl (from dichloromethane) and dichloromethoxyl (from chloroform) species, analogous to the non-halogenated alkoxyls observed in previous investigations. The principal components of the¹³C chemical shift tensors were: chloromethoxyl, ₁₁ = 116 ppm, ₂₂ = 79 ppm and ₃₃ = 37 ppm; dichloromethoxyl, ₁₁ = 128 ppm, ₂₂ = 91 ppm and ₃₃ = 65 ppm. Formation of both species occurred at 298 K, and each decomposed at 423 K. This decomposition formed HCl which dealuminated the zeolite (as monitored by²⁷Al MAS NMR) causing deactivation (flow reactor studies). Further evidence for the destruction of the zeolite was the NMR observation of CO formation, implying incorporation of oxygen from zinc hydroxyl or framework sites. Although ZnY is shown to be unsuitable for catalytic chlorocarbon destruction, the observation of chloromethoxyl and dichloromethoxyl species is significant, and the formation of halogenated alkoxyl species should be considered in future investigations of halocarbon chemistry on oxides and molecular sieves.     

Oxidative dehydrogenation of ethane over some titanates based perovskite oxides

A series of perovskite catalysts have been tested for the oxidative dehydrogenation of ethane. The composition of these catalysts covered CaTi_1–x Fe _x O_3–, with 0 x 0.4, SrTi_1–x Fe _x O_3–, with 0 x 1.0, as well as mixtures of these. The latter catalysts containing more basic Sr metal showed higher selectivity to ethene than the former catalysts containing Ca. A few catalysts with Co on B-sites in the lattice were tested, but lost their stability above 923 K, resulting in a substantial change in the product selectivity. The perovskites gained activity when Fe was introduced in the lattice to form hypervalent ions (Fe⁴⁺) which are believed to play a role in the catalytic activity of these materials.     

Mechanical relaxation in arimide PM fibres in the temperature range 20–900°K

Conclusions The temperature dependences of the tangent of the mechanical loss angle, tan , the dynamic shear modulus, G', and the velocity of shear waves, c_t, of arimide PM fibre have been studied by the method of free twisting oscillations in the temperature range 20–900°K, at frequencies of 0.2–1 Hz.Relaxation transitions are observed in the tan = f(T) dependence in the temperature regions of 115, 220, 400, and 644°K, with activation energies of 23, 59, 84, and 770 kJ/mole, respectively.Values of the dynamic shear modulus of the investigated fibre have been obtained over a wide temperature range.Translated from Khimicheskie Volokna, No. 4, pp. 41–42, July–August, 1984.     

Properties ofSrMO 3-δ(M=Fe,Co) as oxygen electrodes in alkaline solution

Strontium ferrates and cobaltates with compositions SrFeO_3- (0.060.40) and SrCoO_3- (0.040.30) were synthesized. The dependence of the oxygen electrode properties on the value was examined in 1 mol dm^–3 KOH solution. In the SrFeO_3- series, the samples with 0.24<<0.29, showed the highest activity in both oxygen evolution and reduction reactions. In contrast, no strong dependence on the value was observed in SrCoO_3-, which also showed a high catalytic activity for oxygen evolution.