Synthetic nanodiamonds (SNDs) containing bimetallic Ni(Co)–Fe composites: preparation,characterization and catalytic performance in the reaction of CO2 methanation

Abstract

In this article, we present the preparation, characterization, and catalytic performance of bimetallic Co₉₃Fe₀₇ and Ni₈₀Fe₂₀ active mass loaded on synthetic nanodiamonds (SNDs) in the carbon dioxide (CO₂) methanation. The pristine SNDs possessing a developed specific surface are thermally stable and inert to the reaction mixture of CO₂ and dihydrogen. However, it is shown that 100% conversion of CO₂ into methane can be reached at the lower temperature than that for a massive Co₉₃Fe₀₇ or Ni₈₀Fe₂₀ catalyst when 20?wt.% of the catalyst mass was loaded on the surface of SNDs. The catalytic activity of the prepared bimetallic/SNDs composites is estimated as the minimum temperature at the maximum conversion of CO₂ at atmospheric pressure: it is 325 and 290?°C for Co₉₃Fe₀₇/SNDs and Ni₈₀Fe₂₀/SNDs, respectively. Thermal desorption studies showed that the methanation over Co-Fe/SNDs and Ni-Fe/SNDs catalysts run through the stage of CO₂ dissociation into carbon and oxygen atoms and their subsequent interaction with hydrogen to form methane and water molecules. Scanning electron microscopy studies have shown that the presence of transition metal-rich sites on the surface of the carrier contributes to the improvement of efficiency of the Ni₈₀Fe₂₀ catalyst action.     

Phosphomethylation of p-substituted anilines

Conclusions The phosphomethylation of p-substituted anilines in three-component systems (amine-paraformaldehyde-trialkyl phosphite, diethyl phosphite, or diethyl thiophosphite) proceeds best with trialkyl phosphites, and the yields are 55–95%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 178–180, January, 1982.     

Temperature Hysteresis in Oxidation of CO on Complex Oxide Catalysts

We have used thermal desorption (TD) with mass spectrometric detection of the desorbed species to study the state of the surface of oxide catalysts for oxidation of CO. Detection of weakly bound forms of water and the species H₃O⁺ and HO ₂ ^⋅ in the thermal desorption spectra correlates with the existence of temperature hysteresis in these samples. The data obtained are explained by the reaction occurring in a highly active state via a heterogeneous-homogeneous mechanism, and also by the effect of local superheating. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 323–327, September–October, 2005.     

Physical and Chemical Properties and Activity of Fe–Co–Cu Oxide Catalysts in Oxidation of CO

We have studied the physical and chemical properties and activity of Fe–Co–Cu oxide catalysts in oxidation of CO. We have shown that the high activity of these catalysts is promoted by formation of the Cu₂(OH)₃NO₃ structure, which is modified by hematite clusters. The presence of OH groups is favorable for the formation of active sites for CO oxidation on the surface of the oxide catalysts.     

Kinetic Models of Catalyst Deactivation in Paraffin Dehydrogenation

The results of studying the deactivation of both unpromoted platinum–alumina catalysts and those promoted with K, Li, In, Sn, and W in the dehydrogenation of lower and higher paraffins are discussed. The main reason for catalyst deactivation is found to be coke formation. The rate laws of coke formation and paraffin dehydrogenation in the non-steady-state regime of the reaction are derived. The catalyst sulfuring is found to enhance its stability. The effects of oxygen and water impurities on the reactions and coke formation are studied.     

Refractive index dispersion in Y2O3 thin films obtained by different methods

We have studied refractive index dispersion in Y₂O₃ thin films obtained by stepwise vaporization and high-frequency ion plasma spraying in different atmospheres. We have established that regardless of the method used to obtain the films, the spectral dependence of the refractive index in the visible region of the spectrum is mainly determined by transitions from the band of 2p states of the oxygen, forming the highest unoccupied level of the valance band, to the bottom of the conduction band, formed by the 4d5s states of the ytrrium. For the studied films, we have determined the parameters of the single-oscillator approximation, the dispersion energy, the ionicity of the chemical bond, and the coordination number. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 129–132, January–February, 2006.     

Study of carbon dioxide adsorption on chromium oxide and gallium oxide catalysts on the basis of linear relaxation times

Results of nonstationary experiments on linear relaxation times were used to determine the rates of carbon dioxide adsorption and desorption on chromium oxide and gallium oxide catalysts by various mechanisms. The rate constants were used to calculate nonstationary concentrations of carbon dioxide on the assumption of linear, dissociative, and bimolecular adsorption–desorption mechanisms. A comparison of the calculated and experimental concentrations of carbon dioxide led to a conclusion that the process of its adsorption most probably occurs by the dissociative mechanism.