Adsorption Of Carbon Oxides Research Articles

OXIDATIVE ROASTING OF INDUSTRIAL SPENT CATALYSTS CO-Mo/Al2O3 HYDROPROCESSING WITH LIM

The oxidative roasting of industrial spent catalyst Co-Mo/Al2O3 for the hydrotreatment of diesel fuel with lime in an air atmosphere was studied. Using the data of DTA, TG and X-ray phase analysis, it was found that during roasting, the sulfur and carbon oxides forms CaSO4 and CaCO3, and Mo is converted to calcium molybdate. Using the filtering fixed bed of reagents, the kinetics of roasting was studied. It was found that in the temperature range of 550 – 600 °C with air, supply rate of 3 l/min the process ends in 38 - 44 min for ground and non-ground catalyst. The optimal parameters (lime consumption, temperature, and time of roasting) of the absorption of sulfur oxides during roasting were determined. The degree of sulfur and carbon oxides adsorption is 96 and 36%, respectively. Separation of roasting products using unmilled spent catalyst is proposed into a small fraction (contains a mixture of CaSO4, CaCO3 and CaO) and a coarse (consists of Al2O3, CaMoO4, CoO) fractions, and their separate processing. It has been shown that in the separate processing of roast fractions by a sodium carbonate solution, it is possible to separately obtain alumina (catalyst base) with cobalt oxide, a molybdenum-containing solution, and also a mixture of sulfate, carbonate and oxide calcium. The used method of roasting the spent hydrotreating catalyst with lime will allow hazardous waste of hazard class 3-4 to be disposed of without hazardous waste gas costs. It allows one to obtain, during further processing, molybdenum and cobalt compounds, as well as finely divided alumina.

Hafnium carbide formation in oxygen deficient hafnium oxide thin films

On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO2−x) contaminated with adsorbates of carbon oxides, the formation of hafnium carbide (HfCx) at the surface during vacuum annealing at temperatures as low as 600 °C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfCx surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO2 thin films prepared and measured under identical conditions, the formation of HfCx was not detectable suggesting that the enhanced adsorption of carbon oxides on oxygen deficient films provides a carbon source for the carbide formation. This shows that a high concentration of oxygen vacancies in carbon contaminated hafnia lowers considerably the formation energy of hafnium carbide. Thus, the presence of a sufficient amount of residual carbon in resistive random access memory devices might lead to a similar carbide formation within the conducting filaments due to Joule heating.

Analysis of the electrochemical quartz crystal microbalance response during oxidation of carbon oxides adsorption products on platinum group metals and alloys

The analysis of the electrochemical quartz crystal microbalance (EQCM) signal is presented for the case of oxidation of carbon oxides adsorption products on Pt, Rh, and their alloys. It is demonstrated that the EQCM response can be roughly approximated by the mass balance involving adsorption/desorption of various species (carbon oxides, oxygen, anions, and water molecules) and metal dissolution. The results obtained by the EQCM are in good agreement with the electrochemical data and confirm the domination of CO radicals among the products of CO2 reduction and CO adsorption on Pt-rich electrodes. In the case of Rh-rich electrodes, the existence of additional species (CHO or COH), more reduced than CO, is suggested.

Electrochemical study on the adsorption of carbon oxides and oxidation of their adsorption products on platinum group metals and alloys

CO(2) reduction and CO adsorption on noble metals (Pt, Rh, Pd) and their alloys (Pt-Rh, Pd-Pt, Pd-Rh, Pd-Pt-Rh) prepared as thin rough deposits have been studied by chronoamperometry (CA), cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The influence of alloy surface composition on the values of surface coverage, eps (electron per site) and potential of the oxidation of CO(2) reduction and CO adsorption products is shown. The oxidation of the adsorbate on Pt-Rh alloys proceeds more easily (at lower potentials) than on pure metals. On the other hand, in the case of Pd-Pt and Pd-Rh alloys the adsorbate oxidation is more difficult and requires higher potentials than on Pt or Rh. The analysis of the EQCM signal is presented for the case of adsorption and oxidation of carbon oxide adsorption products on the electrodes studied. The comparison of adsorption parameters and the EQCM response obtained for platinum group metals and alloys leads to the conclusion that reduced CO(2) cannot be totally identified with adsorbed CO.

Erratum to “Comparative EQCM study on electrooxidation of carbon oxides adsorption products on noble metals and their alloys: Polycrystalline Pd-based systems” [J. Electroanal. Chem. 606 (2007) 117–133

Erratum to “Comparative EQCM study on electrooxidation of carbon oxides adsorption products on noble metals and their alloys: Polycrystalline Pd-based systems” [J. Electroanal. Chem. 606 (2007) 117–133

Comparative EQCM study on electrooxidation of carbon oxides adsorption products on noble metals and their alloys. Polycrystalline Pd-based systems

CO2 reduction and CO adsorption on Pd alloys with Pt and Rh (Pd–Pt, Pd–Rh, Pd–Pt–Rh) have been studied by cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The values of surface coverage, eps (electron per site) and potential of the oxidation of CO2/CO adsorption products depend on alloy surface composition. The oxidation of reduced CO2 on Pd-poor Pd–Pt–Rh alloys proceeds more easily (at lower potentials) than on Pt or Rh. On the other hand, in the case of Pd–Pt and Pd–Rh alloys the adsorbate oxidation is more difficult and requires higher potentials than on pure metals. The EQCM response in CO2/CO adsorption experiments is affected not only by the effects connected with the changes in mass attached to the resonator but also by the non-mass effects including changes in metal–solution interactions and variation of solution density and viscosity in the vicinity of the electrode. The comparison of adsorption parameters suggests that the products of CO2 reduction and CO adsorption on Pd alloys are not identical.

Electrochemical quartz crystal microbalance study on carbon oxides adsorption in the presence of electrosorbed hydrogen on Pd alloys with Pt and Rh

CO 2 and CO adsorption on Pd–Pt and Pd–Rh alloys has been studied by cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). Adsorbed CO 2 inhibits partially hydrogen adsorption on Pt and Rh surface atoms but does not block significantly hydrogen absorption into alloy bulk. In the presence of adsorbed CO both hydrogen adsorption and absorption are strongly suppressed. On electrodes covered with adsorbed CO the oxidation of previously absorbed hydrogen is significantly shifted into higher potentials. The EQCM response in CO 2/CO adsorption experiments is affected by both the effects connected with the changes in mass attached to the resonator and the non-mass effects including changes in metal–solution interactions and variation of solution density and viscosity in the vicinity of the electrode. Differences in the EQCM behavior suggest that the products of CO 2 and CO adsorption on the alloys studied are not totally identical.

Hydrogen insertion into Pd–Pt–Rh alloy limited volume electrodes (LVEs) ☆☆Keynote Lecture.

Limited volume electrodes have been used to examine the processes of hydrogen electrosorption by Pd–Pt–Rh alloys under conditions of cyclic voltammetric (CV) experiments. Hydrogen adsorption and hydrogen absorption signals well separated from surface oxides generation and oxides reduction currents are seen on CV curves recorded in the full potential range. The possibility is demonstrated of simultaneous investigations of bulk processes of hydrogen insertion/removal and surface processes of carbon oxides adsorption. Due to different adsorption characteristics towards CO 2 exhibited by the alloy components hydrogen adsorption and hydrogen absorption signals can be distinguished. Adsorbed CO 2 causes partial blocking of hydrogen adsorbed on Pt and Rh surface atoms. The presence of adsorbed CO 2 on the electrode surface does not influence significantly hydrogen insertion into the alloy. CO adsorption results in a strong inhibition of hydrogen adsorption. Hydrogen insertion into the bulk is not totally blocked but proceeds much slower than in the absence of CO adsorbates.

The adsorption of carbon oxides on a palladium electrode from acidic solution

The adsorption of carbon oxides from sulfuric acid solution on a palladium electrode was investigated with electrochemical and radiometric methods. It was found that adsorption of CO takes place in the 0.0–0.8 V range. During the CO adsorption the anodic (below 0.15 V vs. SHE) and cathodic (above 0. 15 V vs. SHE) currents are passing through the solution | electrode interface. Mechanisms for the CO adsorption and the final product structure have been proposed. A small amount of adsorbed CO 2 on the surface of the palladium electrode has been observed. A strong correlation between the decrease in the real surface of the palladium electrode and the currents of sorbed hydrogen during its oxidation has been found. 1. Carbon monoxide adsorption on palladium electrode from acidic solution (0.5 M H 2SO 4) occurs at the potentials below 0.9 V (vs. SHE) 2. The main products of CO adsorption on Pd at potentials where no hydrogen absorption occurs are CO species that seem to be mostly bridge bonded to Pd, also a more reduced form of CO adsorption product should exist on the Pd surface. A certain amount of CO species linearly bound is also possible [13–21] 3. The CO adsorption products at potentials where hydrogen absorption occurs, reflect experimental conditions strongly. Probably they are in a more reduced form in comparison with the adsorption products at more positive potentials 4. A decrease of the real palladium surface during CO adsorption and cyclic electrode polarization is observed. 5. Strong correlation between the decrease of the real surface of the palladium electrode and the currents for the sorbed hydrogen oxidation has been found. One of the oxidation peaks related to the sorbed hydrogen oxidation (the smaller at positive potentials) probably corresponds to the oxidation of adsorbed hydrogen. 6. A small amount (almost negligible) of carbon dioxide is adsorbed on the palladium electrode.

Investigation of the water-gas shift reaction using temperature-programmed desorption

The water-gas shift reaction has been investigated by the temperature-programmed desorption (TPD) of reaction components over a commercial low-temperature catalyst. It has been found that the oxidation state (and consequently the activity) of the catalyst is strongly influenced by the composition of the gaseous mixture. The adsorption capacity of catalysts decreases in the order: H 2O ⪢ CO 2⋍CO; hydrogen does not adsorb. The existence of two types of sites for carbon oxides adsorption has been found experimentally. A further type of storage (inactive) sites for water exists. On the basis of experimental results, model equations for TPD of H 2O, CO 2 and CO were derived. Models best fitting the experimental data were based on the assumption of a non-uniform heterogeneous surface of the catalyst.

Characterization of catalysts for methane coupling by means of thermal methods

Abstract The activity of two catalysts for methane coupling, 1% K 2 O/ZnO and 2% Li 2 O/Y 2 O 3 , has been in- vestigated in the temperature range 680–830°C by using temperature-programmed reaction techniques, either following the gas chromatographic response or the electrical conductivity response: in that way it was possible to obtain the progress of the catalytic activity and of the related selectivity to carbon oxides and to C 2 hydrocarbons. Furthermore, temperature-programmed desorption curves have been studied, either performing adsorption of methane and specifically of oxygen, or performing adsorption of carbon oxides and of C 2 hydrocarbons: the results obtained from the two catalysts allow us to deduce that only a small amount of methane and of oxygen are still anchored on the surface of 1% K 2 O/ZnO at the reaction temperatures, while a considerable presence of adsorbed species in the same range of tem- peratures was observed on 2% Li 2 O/Y 2 O 3 . These results, as well as those obtained by the kinetic analysis of the desorption peaks allow us to stress that homogeneous gas-phase processes are markedly prevailing when zinc oxide is used, while heterogeneous processes play an important role when yttrium oxide is used.

Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal oxide surfaces

Published data on the infrared spectra and coordination of carbonate, bicarbonate and formate ions, and of CO 2 in metal complexes are reported. The usual assignments of absorption bands due to products of CO and CO 2 reactive adsorption on metal oxide surfaces are also critically reexamined.