Course Of Decomposition Research Articles

Will rising atmospheric CO 2 affect leaf litter quality and in situ decomposition rates in native plant communities?

Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO2 concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant species produced in alpine, temperate and tropical communities maintained at elevated CO2 (600-680 μl l-1) was not significantly different from that produced in similar communities maintained at current ambient CO2 concentrations (340-355 μl l-1). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO2 did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO2 was significantly slower than that of litter produced under ambient CO2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil fertilities common in many native ecosystems as atmospheric CO2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO2.

Microbial biomass content, basal respiration and enzyme activities during the course of decomposition of leaf litter in a black alder ( Alnus glutinosa (L.) Gaertn.) forest

Decomposition of leaf litter from a black alder ( Alnus glutinosa (L.) Gaertn.) forest on a fen (peat soil) in Northern Germany was studied at two sites within the forest. The ‘wet’ site was adjacent to a lake and soil was water-saturated throughout most of the year. In contrast, the other site was substantially drier, especially in summer and therefore called the ‘dry’ site. The pH (H 2O) value of the topsoils (horizon below litter) at the wet and dry site was 6.0 and 3.5, respectively. The litter consisted mainly of alder leaves and decomposed at different rates at the two sites. After 12 months, about 40% of the initial litter was decomposed at the dry site compared to 90% at the wet site. The water content of the litter varied seasonally, particularly at the dry site. The pH of the litter was similar to or higher than that in the underlying topsoil and decreased at the dry site after 18 months. The total C content in residual material did not change during the course of decomposition. The microbial biomass content was, with some irregularities, similar throughout the first months and then continually declined. Basal respiration decreased from an initial value of approximately 700 to 100 μg CO 2 g −1 dry litter h −1 after 17 months. β-Glucosidase activity also continuously decreased during litter decomposition; protease activity decreased initially but then tended to increase. The metabolic quotient declined during the course of litter decomposition from a relatively high value to a value almost typical for soils. This decline indicates an increase in the C utilization efficiency of the microbial community as well as a shift from a zymogenous to an autochthonous microflora. Regression analyses were performed to determine correlations between properties and to evaluate factors controlling the decomposition process.

Isotope Discrimination during Decomposition of Organic Matter: A Theoretical Analysis

AbstractStable isotope composition is a powerful characteristic of the development of soil organic matter, but there is a need to understand the causes of and to predict the changes in isotopic composition during organic matter decomposition. We used the continuous quality theory to derive a set of equations to analyze how properties of the litter interact with properties of the decomposers to produce different patterns of isotopic composition. The distribution of isotopes between different chemical fractions in the litter is in itself such that it should lead to increasing depletion of 13C during the course of decomposition. Isotope effects on decomposer growth rate, efficiency, and dispersion in quality increase, on the other hand, 13C concentration. The magnitudes of these effects have to be, in relative terms, considerably greater than that of initial litter chemical composition. The equations derived were also successfully tested on experimentally observed patterns of changes in C isotopic composition in an agricultural soil and some forest soils.

N2O Decomposition over Manganese Oxides

The catalytic decomposition of N2O was studied over four different oxides of manganese—MnO, Mn3O4, Mn2O3, and MnO2. The respective specific activities were 6.3×10−4, 2.5×10−3, 4.8×10−3, and 8.1×10−4μmol/sċm2at 623 K and 0.066 atm of N2O. Apparent activation energies fell between 19 and 27 kcal/mol, and the reaction orders with respect to N2O were between 0.74 and 0.89. XRD patterns showed that pretreatment at 773 K under He converted MnO2into Mn2O3, which gave a specific activity similar to that of the original Mn2O3sample; therefore, MnO2was pretreated under pure oxygen at 645 K prior to reaction to retain the bulk MnO2phase. On the other hand, MnO was oxidized to Mn3O4during the course of N2O decomposition. Thus Mn2O3is the phase associated with the highest catalytic activity. A detailed kinetic study with the most active Mn2O3sample found that the reaction order at 648 K with respect to N2O was near 0.8 over a wide pressure range, and the reaction rate was retarded by oxygen. The experimental data fit a simple Langmuir–Hinshelwood model well and both kinetic and thermodynamic parameters could be determined. The activation energy for the rate determining step—dissociation of adsorbed N2O into N2(g)and adsorbed oxygen—was 31 kcal/mol. Weak N2O adsorption was indicated by heat of adsorption and entropy of adsorption values of 7 kcal/mol and −9 cal/molċK, respectively, while for O2adsorption the respective values were 22 kcal/mol and −26 cal/molċK. Independent Langmuir isotherms for N2O adsorption between 297 and 353 K revealed only reversible adsorption with a heat of adsorption of 5 kcal/mol.

Thermal properties of cyanatocopper(II) complexes with pyridine, bipyridine and phenanthroline

The thermal properties of cyanatocopper complexes with pyridine, bipyridine and phenanthroline are described in this paper. It was found that the thermal stabilities of the complexes were found to increase in the order py≪bipy<phen ligands. The significantly higher thermal stability of the complexes with bipyridine and phenanthroline is caused by the presence of dimeric structural units in the crystal structure and intermolecular interactions of the cyanate and heterocyclic ligands. In our preceding papers we have described the thermal decompositions of thiocyanatocopper complexes CuL2(NCS)2 (L=pyridine and its methyl derivates) which are composed of the liberation of ligandsL and redox reactions of thiocyanate ligands with the central Cu(II) atom [1, 2]. The decomposition temperature of thiocyanate ligands depends on the properties of the ligandsL present in the coordination sphere. An analogous course of thermal decomposition was also observed for [Cu(bipy)2(NCX)](NCX) (X=S or Se) [3]. For the phenanthroline complexes [Cu(phen)2(NCX)2] (X=S or Se) the thermal stability was found to increase significantly (by about 140‡C) and the decomposition stoichiometry was also changed [3]. The present paper contains the results of thermoanalytical studies on bipyridine and phenanthroline cyanatocopper complexes, and a comparison of the thermal properties of pyridine cyanato and isothiocyanatocopper complexes.

Stimulating the thermal decomposition of magnesite

This paper deals with the influence of mechanical activation and decrepitation on the process of formation of active MgO in the course of the thermal decomposition of magnesite. It has been confirmed that the activation has a favourable influence on the formation of the porous oxidic product with specific surface area S A 〉 100 m 2 g −1 which comes into existence in the active zone of the decomposition of magnesium carbonate. The effect of decrepitation with secondary fragmentation on the reactant takes place at temperatures above 923 K. The process of forming active MgO was described by the KEKAM equation with a changing exponential factor.

Non-isothermal kinetics of CrO3 decomposition pathways in air

The course of the non-isothermal decomposition of CrO3 in air was explored kinetically, by using a number of widely accepted methods. The credibility of the values obtained from a given kinetic parameter (the reaction order, the activation energy and the frequency factor) was justified on the grounds of (i) a multiple correlation coefficient, and (ii) the merits and demerits of the method adopted. The results obtained may help towards a characterization of the non-isothermal conditions under which the encountered decomposition events and products could be resolved. The study was motivated by the results of previous physicochemical characterization studies [1, 2], in which catalytically important intermediates CrOx(3<x<6) were structurally identified.

Characterization of the decomposition course of Cu(II) 3,5-diisopropyl salicylate hydrate and chemical reactivity of the final products — spectrothermal investigation

The thermal decomposition of Cu(II) 3,5-diisopropyl salicylate hydrate in dry nitrogen was studied thoroughly. Thermal events involved throughout the decomposition range (room temperature up to 600 °C) were monitored by means of thermogravimetry, differential thermal analysis and IR gas-phase analyses. The corresponding activation energy values were determined non-isothermally. Intermediate and final solid products were characterized by X-ray diffractometry and IR spectroscopy. The results showed Cu 2(C 13H 17O 3) 4 · 8H 2O melts at 115 °C, followed by the release of 8 mol of isopropyl alcohol (C 3H 7OH) to yield Cu 2(C 7H 5O 3) 4 (copper salicylate) through two endothermic processes at 130 °C and 210 °C. Subsequently, the copper salicylate released phenol, CO and CO 2 to give CuO as a final product at 250 °C. The IR spectra of the gaseous products revealed that a marked chemical reactivity of the gas/solid interface was present throughout the decomposition course. As a result, C 3H 7OH was involved in dehydrogenation/dehydration reactions over the freshly generated CuO surface, producing acetone and propene in the gas phase. Moreover, the byproduct acetone was involved in bimolecular interactions over the CuO surface, producing CH 4 and (CH 3) 2C = CH 2 (isobutene) in the gas phase.

Effects of metal ions on the thermal decomposition of brown coal

Abstract Pyrolysis experiments of Loy Yang brown coal from Victoria, Australia, were performed to examine the influence of coexisting metal species. Sodium, magnesium, calcium, barium and nickel were loaded either by ion exchange or by impregnation. The metal-loaded samples were heated under helium at the rate of 5°C/min up to 900°C. Exchanged metal ions affected the course of decomposition in various ways. The temperature of maximum rate of weight reduction was lower for sodium, barium and nickel exchanged brown coal than that for acid-washed coal by 50°C, while the presence of magnesium and calcium did not influence the decomposition temperature compared to that for acid-washed coal. The volatile matter yield decreased and the yield of C 1 gases increased with the amount of nickel or calcium loading. The char yields were almost the same regardless of the cations present, but the surface area of chars varied with metal species and metal loading. In particular, the surface area of char obtained from sodium exchanged coal decreased dramatically with increasing sodium content. The influence of impregnated metal species was found to be different somewhat from those of ion exchanged species, suggesting different interaction with coal surfaces.

Ring-opening reactions of ethylene oxide on Pd(110) surfaces

Ethylene oxide (EO) reactions on Pd(110) surfaces were investigated under ultra-high vacuum conditions using temperature programmed reaction/desorption. EO adsorbed on clean Pd(110) at 120–260 K underwent ring-opening, leading to the formation of methane at 325 K. The ratio of methane to CO produced exhibited a dependence on coverage. Furthermore, deuterium coadsorption experiments produced methane containing up to two deuterium atoms, suggestive of the presence of hydrocarbon species less hydrogen-rich than methyl groups on the surface. There was also evidence of C 2 hydrocarbon dehydrogenation at ca. 450 K, reminiscent of ethylene dehydrogenation on the clean Pd(110) surface. These observations are consistent with the release of CH 2 species in the course of EO decomposition on this surface. However, this is in contrast with acetaldehyde decarbonylation on the clean Pd(110) surface, where decarbonylation appears to lead to the release of methyl species on the surface. Studies of EO decomposition on oxygen-precovered Pd(110) surfaces indicated that the EO oxidation does not proceed via carboxylate intermediates; rather the epoxide decomposes to CO, which combines with oxygen on the surface to produce carbon dioxide. Again, in the light of the oxidation chemistry of acetaldehyde on oxygen-precovered metal surfaces, where acetate intermediates are formed, it is suggested that ring-opening of EO on Pd(110) does not proceed via isomerization to an acetaldehyde intermediate, but occurs by sequential CO and CC scission reactions.

Thermoanalytical investigations of the decomposition course of copper oxysalts

The thermal decomposition course of copper acetate monohydrate (CuAc) was examined on heating up to 600°C at various rates, by TG, DTA and DSC. Non-isothermal kinetic and thermodynamic parameters were determined in air or nitrogen. SEM was used to describe the decomposition course and the solid products were identified by IR and XRD analysis. The results indicated that CuAc was dehydrated at 190°C and then partially decomposed at 220°C, giving rise to CuO in addition to a minor portion of Cu2O and Cu4O3. The last two oxides seemed to facilitate the decomposition of the rest of the anhydrous acetate. Cu2O and Cu4O3 were oxidized in air at >400°C, in a process that did not occur in nitrogen.

Thermoanalytical investigation of the decomposition course of copper oxysalts

Thermoanalytical investigation of the decomposition course of copper oxysalts

Thermal decomposition of rubidium-sodium halidothiocyanatobismuthates(III)

Mono- and binuclear rubidium-sodium halidothiocyanatobismuthates(III) have been prepared. Thermal, chemical and X-ray analyses were used to establish the thermal decomposition course of these complexes. The pyrolysis occurs in three stages connected with the mass loss and exothermic effects. The decomposition temperatures of the title salts are 190–210°C.

Thermal and chemical events in the decomposition course of manganese compounds

Thermogravimetry and differential thermal analysis, infrared spectroscopy (solid phase and gas phase), and X-ray diffraction were used to characterize the pathways of the decomposition of the hydrated acetate, oxalate and nitrate of manganese in air. The non-isothermal activation energy ( ΔE, kJ mol −1) was determined for the thermal processes monitored throughout the decomposition course. The results showed that Mn( CH 3 COO) 2·4 H 2 O dehydrates in three steps up to 130 °C, and then decomposes to a mixture of manganese oxides Mn 3O 4 (major) and Mn 2O 3 (minor) through the intermediates Mn(OH)CH 3COO and/or MnOCH 3COO and MnCO 3. MnC 2 O 4·2 H 2 O dehydrates in one step at 150 °C, and then decomposes via MnCO 3 into Mn 3O 4 (hausmannite structure) at 350 °C. Mn( NO 3) 2·4 H 2 O undergoes stepwise dehydration up to 175 °C, and decomposes above 200 °C via an unstable oxynitrate intermediate yielding MnO 2; this decomposes at about 550 °C to the α-Mn 2O 3 phase.

Characterization of lanthanum oxide formed as a final decomposition product of lanthanum acetylacetonate: thermoanalytical, spectroscopic and microscopic studies

The porous and high surface area of lanthanum oxide was obtained as a final decomposition product of lanthanum acetylacetonate tetrahydrate. The decomposition course in dry nitrogen was thoroughly studied. Thermal processes occurring throughout the decomposition range (100–800 °C) were monitored by thermogravity; differential thermal analysis and infrared spectroscopy gaseous products. These processes were characterized on the basis of the solid products analyses, using X-ray diffractometry and IR-spectrometry. The results showed La(C 5H 7O 2) 3 completely decomposed to La 2O 3 at 730 °C, through amorphous and unstable intermediates La(CH 3COO)(C 5H 7O 2) 2 at 190 °C, La(CH 3COO) 2(C 5H 7O 2) at 225 °C, La(CH 3COO) 3 at 285 °C, La 2(CO 3) 3 at 390 °C and crystalline and stable La 2O 2(CO 3) at 430 °C. Gas phase decomposition products included propyne, acetone, carbon oxides, methane and isobutene. Methane and isobutene resulted from interfacial reactions involving the initial product (acetone). The ultimate products, La 2O 3 at 700 °C and 800 °C, are crystalline porous solids and having a surface area of 21 and 45 m 2/g respectively.

The preparation of yttrium oxide from a Y(N 2H 3COO) 3 · 3H 2O precursor in various atmospheres

The thermal decomposition of yttrium hydrazidocarbonate trihydrate Y(N 2H 3COO) 3 · 3H 2O has been studied in the temperature range 25–1400°C. The influence of inert and oxidative atmospheres, e.g. argon, carbon dioxide and air, on the course of the thermal decomposition was determined. After dehydration to the anhydrous compound, the decomposition proceeds through several decomposition steps to yttrium oxide. In air, a pure high temperature C form of this oxide is isolated at a relatively low temperature, e.g. 708°C. The same end product is obtained in carbon dioxide, albeit at higher temperatures, but in argon the yttrium oxide is mixed with amorphous carbon. The surface area and other particulate properties are substantially dependent on the heating programme of the sample.

Texture assessment of thoria as a final decomposition product of hydrated thorium nitrate and oxycarbonate

Th(NO 3) 4·5H 2O and ThO(CO 3)·0.5H 2O were used as parent compounds for the formation of ThO 2. Thermal processes involved during the course of decomposition up to 500°C in air were monitored by thermogravimetry, differential thermal analysis and infrared (IR) gas phase analysis. Intermediate and final solid products were characterized by IR spectroscopy and X-ray diffractometry. The results showed that Th(NO 3) 4·5H 2O is completely decomposed to ThO 2 at 300°C via three unstable intermediates: Th(OH)(NO 3) 3 at 165°C; ThO(NO 3) 2 at 210°C and ThO 1.75(NO 3) 0.5 at 250°C. Similarly, ThOCO 3·0.5H 2O is completely decomposed to ThO 2 at 300°C via the unstable intermediate ThO 1.5(CO 3) 0.5 at 160°C. Surface texture measurements and scanning electron microscopy showed that ThO 2, the final decomposition product at 500°C of both Th(NO 3) 4·5H 2O and ThO(CO 3)·0.5H 2O is crystalline and has surface areas of 32 m 2 g −1 and 56 m 2 g −1, respectively. ThO 2 formed from the nitrate is mainly microporous. However, ThO 2 obtained from the oxycarbonate contains different types of porosities.

Stages of the synthesis of gallium nitride with the use of urea

Experimental studies have enabled the suggestion of a scheme of the reaction stages of gallium with urea in the temperature range 20 – 1000°C. During studies on the formation of boron nitride with the use of urea and products of its thermal condensation, we have discovered that cyanamide (H 2CN 2) plays a substantial role in those processes [Z. Gontarz and S. Podsiadło, Pol. J. Chem, 58 (1984) 3; A. Górski and S. Podsiadło, Pol. J. Chem., 58 (1984) 13]. As shown in these works cyanamide, formed in the course of the thermal decomposition of urea, is the main nitriding agent in the reactions. We have decided to investigate the processes of the reactions of urea with gallium to form gallium nitride.

Electronegativity force of cations and thermal decomposition of complex fluorides

The thermal decomposition of anhydrous fluoroborates MBF4 (M=Li, Na, K, Rb, Cs) and M(BF4)2 (M=Ca, Sr, Ba) was investigated. The decomposition proceeds according to a simple acid-base mechanism with evolution of BF3. The influence of the acidity of cationic counterions, expressed by the electronegativity force on the course of thermal decomposition was estimated quantitatively.

Stereospecific course of a transannular CH insertion process

The steric course of the catalytic decomposition of the chiral diazoxazepanedione 1 to 2-pyrrolone 3 was clarified by the X-ray diffraction study of the enantiomerically pure pyrrolidine 5, obtained by reductive cleavage of the unisolated intermediate bicyclic compound 2.