Catalytic activity of Co-åkermanite and Co-pyroxene in oxidation reactions

Abstract

Two calcium-cobalt silicates were synthesized in which cobalt occupies different structural positions. The crystal phases belong to two main structural silicate types. In the Co-åkermanite structure (Ca 2 CoSi 2 O 7 ), cobalt cations take tetrahedral coordination toward oxygen atoms. In the Co-pyroxene structure of CaCoSi2O6, cobalt displays octahedral coordination. Ca2CoSi2O7 was prepared by solid-phase synthesis and CaCoSi2O6 was prepared by sol-gel method. The synthesis of the phases was confirmed by XRD, FTIR, and EPR data. On the basis of the XPS analysis, it can be concluded that Co 2+ cations exist in the studied silicates. Thus, it is possible to study the catalytic activity of two silicate phases containing Co 2+ cations in different coordinations: tetrahedral and octahedral. It was found that cobalt silicates with crystal structures corresponding to pyroxene and åkermanite possess catalytic activity in the reactions of complete oxidation of CO and toluene. Co-pyroxene exhibits higher catalytic activity than Co-åkermanite, but the higher cobalt content on the surface of Co-pyroxene should also be taken into account. Then, it turns out that catalytically active complexes with Со 2+ ions in tetrahedral coordination are more efficient than those with such ions in octahedral coordination when equal concentrations of cobalt were used on the surface of the catalysts.Résumé : On a réalisé la synthèse de deux silicates de calcium et de cobalt dans lesquels l'atome de cobalt occupe des positions diverses dans la structure. Les phases cristallines appartiennent à deux types principaux de structures de silicate. Dans la structure åkermanite du Ca2CoSi2O7, les cations du cobalt occupent des positions de coordination tétraédrique par rapport aux atomes d'oxygène. Le Ca2CoSi2O7 a été préparé par une synthèse en phase solide alors que le CaCoSi2O6 a été obtenu par méthode sol-gel. Les synthèses des phases ont été confirmées par des données de diffraction des rayons-X (DRX), d'infrarouge à transformée de Fourier (IR-TF) et résonance paramagnétique électronique (RPE). Sur la base d'analyse de données de spectroscopie photoélectronique des rayons-X (SPX), il est possible de conclure que, dans les silicates étudiés, il existe des cations Co 2+ . Il est donc possible d'étudier l'activité catalytique des deux phases de silicate contenant des cations Co 2+ dans des environnements de coordination différents : tétraédrique et octaédrique. On a trouvé que les silicates de cobalt avec une structure cristalline correspondant à celle du pyroxène et de l'åkermanite présentent une activité catalytique dans les réactions d'oxydation complète du CO et du toluène. Le Co-pyroxène possède une activité catalytique plus élevée que celle de la Co-åkermanite; toutefois, on doit tenir compte du fait que la teneur en cobalt est plus élevée sur la surface du Co-pyroxène. Il en découle alors que, pour des concentrations identiques de cobalt à la surface des catalyseurs, les complexes catalytiquement actifs comportant des ions Co 2+ en coordinatio...

The Viscous Behavior of FeOt-Al2O3-SiO2 Copper Smelting Slags

“…The results are comparable with the work done by Mihailova and Mehandjiev [16] and Hofmeister. [17] Olivines including fayalite show FTIR reflectance at 13 different band positions.…”

“…The FTIR analysis in Figure 6 was found to be comparable with the results of others. [15][16][17] The FTIR results of the asymmetric stretching bonds between 1150 and 850 cm À1 show four distinct absorption peaks near 1085, 947, 911, and 873 cm À1 , which correspond to values of nonbridging oxygen per silicon (NBO/Si) of 1, 2, 3, and 4, respectively. [15] NBO/Si represents the oxygen atoms within the silicate structure for which one of the two valence electrons is bonded with a silicon atom and the other is unbonded.…”

Novel Co-akermanite (Ca2CoSi2O7) bioceramics with the activity to stimulate osteogenesis and angiogenesis

“…Wu et al prepared a kind of cobalt-containing mesoporous bioactive glass scaffolds (Co-MBG) and found this Co-MBG enhanced VEGF protein secretion and bone-related gene expression in HBMSCs, but their work did not demonstrate the synergetic effect between Si and Co. And at the same time it is rather difficult to study the synergetic effect of different ions using bioactive glasses duo to their complicated chemical composition. 47,48 Floating zone method is more suitable for growing CAKT single crystalline samples with high purity but low productivity, while solid-state reactions always require longer sintering time or multi-time sintering to obtain pure materials. 46 Previously, CAKT tablets and single crystals were generally prepared by solid-state reactions and floating zone method for investigating their catalytic activity and magnetoelectric properties, respectively.…”

“…37 CAKT will provide a simpler chemical composition compared with bioactive glass for studying the synergistic effects between Si and Co. CAKT with a melilite structure has been reported by Brisi and Abbattista (1960). Mukhopadhyay et al 46 obtained CAKT powders by calcining mixed reagents three times at 1250 o C for 150 h under flowing argon gas, while Mihailova et al 47 fabricated CAKT tablets by solid-state reactions at 1200 o C for 2-3 h but the purity was low. 47,48 Floating zone method is more suitable for growing CAKT single crystalline samples with high purity but low productivity, while solid-state reactions always require longer sintering time or multi-time sintering to obtain pure materials.…”

“…46 Previously, CAKT tablets and single crystals were generally prepared by solid-state reactions and the floating zone method for investigating their catalytic activity and magnetoelectric properties, respectively. 48,49 The floating zone method is more suitable for growing CAKT single crystalline samples with high purity but low productivity, while solid-state reactions always require longer sintering time or multi-time sintering to obtain pure materials. Mukhopadhyay et al 47 obtained CAKT powders by calcining mixed reagents three times at 1250 1C for 150 h under flowing argon gas, while Mihailova et al 48 fabricated CAKT tablets by solid-state reactions at 1200 1C for 2-3 h but the purity was low.…”