Effect of Modification with Vanadium or Carbon on Destructive Sorption of Halocarbons over Nanocrystalline MgO: The Role of Active Sites in Initiation of the Solid-State Reaction

Abstract

Small amounts of vanadium or carbon added to nanocrystalline MgO aerogels were shown to promote their activity in destructive sorption of CF2Cl2 and CFCl3 halocarbons. This reaction is characterized by a prolonged induction period, which is considerably shortened after the addition of the studied promoters. It was demonstrated that the promoting effect of finely dispersed carbon did not depend on its location relative to the MgO nanoparticles. Approximately the same results were obtained when carbon was deposited as a thin layer on the surface of the MgO nanoparticles, when activated carbon was physically mixed with the nanocrystalline MgO or when it was located separately in the reactor. The modifying agents are believed to have a catalytic effect on the reaction of nanocrystalline MgO with halocarbons, accelerating the formation of active sites on the surface of the MgO nanoparticles. Electron-acceptor sites are shown to be possible candidates for the role of such active sites. The concentration of weak electron-acceptor sites tested by electron paramagnetic resonance (EPR) using anthracene as a spin probe increases during the induction period, reaching a well-defined maximum during the active stage of the reaction. Electron-acceptor sites of medium strength characterized by direct ionization of anthracene after adsorption were observed on the surface only during the active stage of the reaction. The studied reaction appears to be one of the first solid-state reactions where the role of surface active sites has been identified.

Nanocrystalline carbon coated alumina with enhanced phase stability at high temperatures

“…For instance, nanocrystalline mesoporous oxides with nanoparticle sizes under 10 nm oen have unusually high reactivity in many chemical reactions. This property leads to their use as efficient catalysts [1][2][3] and destructive sorbents [4][5][6][7][8][9][10] for the neutralization of various toxic compounds. However, the products resulting from their solidstate reactions are usually not nanocrystalline.…”

“…19,23 Earlier we have reported that the carbon coating deposited on the surface of the oxide nanoparticles can act as a nanoreactor shell. On the one hand, such coating can be penetrable for the reactant molecules from the gas 7,10,24,25 or liquid 26 phases making it possible to initiate various catalytic or solid-state reactions inside the nanoreactor. Moreover, the carbon coating prevents sintering of nanoparticles inside the shell during the temperature increase and stabilizes their sizes.…”

Combination of nanophotocatalysis with electro-Fenton-like process in the removal of phenol from aqueous solution: GC analysis and response surface approach

“…Klabunde et al have done a lot of research on the synthesis and application of magnesium oxide. For example, they were investigated the effect of the crystallites of magnesium oxide on the catalytic performance and the effect of vanadium and carbon doping on the adsorption properties of magnesium oxide [18,19]. Using SBA-15 and CMK-3 as hard template, mesoporous MgO was synthesized in Tiemann's report [20].…”

Study of MgO transformation into MgF2 in the presence of CF2Cl2•

“…32,54,55 A strong signal of TNB radical anions characterized by anisotropic splitting on a nitrogen atom with A zz = 27.2 G was observed on the AP-MgO sample after activation in nitrogen flow without any reaction. 56 Its intensity on activated AP-MgO before reaction was about 6×10 18 g -1 . The concentration of electrondonor sites gradually decreased during reaction with CF 2 Cl 2 (Fig.…”