Characterizations of Cobalt Oxide Nanoparticles within Faujasite Zeolites and the Formation of Metallic Cobalt

Abstract

Cobalt oxide (CoO x ) particles within faujasite zeolites have been synthesized by a procedure comprising (i) ion-exchange of cobalt ions into the zeolite, (ii) precipitation of cobalt ions with sodium hydroxide within the supercages of the zeolite, and (iii) calcination. The materials are characterized by XRD, nitrogen sorption, XPS, TEM-EDS, H 2 -TPR, and O 2titration. The concentration of sodium hydroxide for precipitation and the temperature for calcination are found to be critical in controlling the locations of the CoO x particles. With appropriate conditions, the CoO x particles formed are located and encapsulated in the supercages of faujasite zeolites. The sizes of the CoO x particles are in the range of 0.7-3 nm with a maximum distribution of 1.3-1.5 nm. These particles exist mainly in the state of CoO. On the other hand, higher calcination temperature or higher concentration of sodium hydroxide may lead to the formation of larger Co 3 O 4 particles located outside the supercages of the faujasite zeolites. The CoO x particles encapsulated in the supercages exhibit a broad reduction peak and can be partly reduced to metallic cobalt at temperatures as low as 573 K, while the cobalt cations exchanged into the zeolites can only be reduced at temperatures higher than 773 K. The metallic cobalt formed by the reduction of cobalt oxide within the supercage exhibits superior catalytic activity in Fischer-Tropsch synthesis.

Mesoporous silica supported cobalt oxide catalysts for catalytic removal of benzene

“…The reduction of cobalt oxide on Si-B ended at less than 600°C, and most of the oxide species have been reduced in the first stage, whereas, the reduction of cobalt oxide on Si-A and Si-C were prolonged to much higher temperature, especially for Co/Si-C, the reduction didn't finished even at 1,173 K. In addition, Co/ Si-C has the largest area of the reduction peak in the second stage. It is believed that the second reduction stage is related to the reduction of amorphous cobalt oxide which interacts strongly with the support [19][20][21][22][23]. Thus, we conclude that Si-C interacts more strongly with the supported cobalt oxide.…”

“…Figure 6 displays the H 2 -TPR profiles of the silica supported cobalt oxide catalysts. The reduction of supported cobalt oxide was generally divided into two stages [19][20][21][22][23], namely, the reduction of large crystalline Co 3 O 4 particles at lower temperature and the reduction of surface cobalt oxide species which interact strongly with the support at higher temperature. In our work, the reduction peaks below 773 K can be mainly resulted from the reduction of large Co 3 O 4 crystallites, which involves a two-step process of Co 3 O 4 to CoO and of CoO to Co, and the reduction of this stage is usually separated into two peaks.…”

Catalytic combustion of benzene on Co/CeO2/SBA-15 and Co/SBA-15 catalysts

“…3 displays the TPR profile of Co/SBA-15 and Co/CeO 2 /SBA-15 catalysts. The reduction of supported cobalt oxide was generally divided into two stages [29,30], namely, the reduction of large crystalline Co 3 O 4 particles at lower temperature and the reduction of surface cobalt oxide species that interact with the support at higher temperature. For sample Co/SBA-15, there are two main reduction peaks.…”

Determination of the maximum retention of cobalt by ion exchange in h-zeolites

“…According to Tang et al (2004) and Wang et al (2005), introduction of cobalt ions into zeolites by ion exchange, followed by reduction with sodium hydroxide, is the most convenient method for synthesis of metal nanoparticles encapsulated in zeolites. In this way, the ion exchange method can provide cobalt cations in the pores or cages of a zeolite (Tang et al, 2004).…”

“…In this way, the ion exchange method can provide cobalt cations in the pores or cages of a zeolite (Tang et al, 2004). The smaller cobalt nanoparticles encapsulated inside these pores or cages can exhibit high CO conversion in the FischerTropsch Synthesis (Wang et al, 2005).…”