Niobium-substituted octahedral molecular sieve (OMS-2) materials in selective oxidation of methanol to dimethoxymethane

Abstract

The prepared bifunctional Nb-OMS-2 catalysts are promising candidate in partial oxidation of methanol into dimethoxymethane at a lower temperature suggesting that there is an important temperature regime when forming active sites for DMM production.

Soot Combustion over Niobium-Doped Cryptomelane (K-OMS-2) Nanorods—Redox State of Manganese and the Lattice Strain Control the Catalysts Performance

“…In most cases, the extent of Mn substitution in the cryptomelane octahedra with another metal is less than 5% [12]. However, preservation of the molecular sieve structure has been observed even at the doping levels up to 30% [20].…”

“…However, overheating of the K-OMS-2 catalysts, might lead to an excessive K loss, and decrease of the CDPF activity in subsequent cycles of the catalyst operation [17,18]. Improvement of the activity can be obtained by incorporation of other elements (such as Ag, In, Mg, Al, W, V, Fe, Co, Ni, Cu, Zn) into the octahedral molecular sieve matrix [18][19][20][21]. Manganese substitution by other metals affects both the physical and chemical properties of the cryptomelane catalysts [13,20], influencing the aspect ratio of the crystallites, the degree of their aggregation, thermal stability, the Mn 3+ /Mn 4+ ratio, the electric conductivity, and catalytic activity.…”

“…Improvement of the activity can be obtained by incorporation of other elements (such as Ag, In, Mg, Al, W, V, Fe, Co, Ni, Cu, Zn) into the octahedral molecular sieve matrix [18][19][20][21]. Manganese substitution by other metals affects both the physical and chemical properties of the cryptomelane catalysts [13,20], influencing the aspect ratio of the crystallites, the degree of their aggregation, thermal stability, the Mn 3+ /Mn 4+ ratio, the electric conductivity, and catalytic activity. In most cases, the extent of Mn substitution in the cryptomelane octahedra with another metal is less than 5% [12].…”

“…To establish the functionalization ability of K-OMS-2, replacement of Mn by ions of similar ionic radii, as mentioned above, were examined showing that the resultant materials maintain the one dimensional 2 × 2 octahedral framework, which is characteristic of the cryptomelane structure [12,13,[22][23][24][25][26]. However, the substitution of transition metals of larger size for manganese (e.g., Nb, Mo, W for Mn) in the octahedral framework, and its impact on the changes in morphology, particle size, and deSoot activity of the resultant catalytic material has been investigated less intensively [20,21,27]. The introduction of larger elements allows obtaining not only cryptomelane with a larger volume of the channels, when compared to the non-modified material, but also materials in which the charge balance of the octahedral Mn sites is influenced by the presence of the pentaor hexa-valent metal cations within the K-MOS-2 structure.…”

“…The introduction of larger elements allows obtaining not only cryptomelane with a larger volume of the channels, when compared to the non-modified material, but also materials in which the charge balance of the octahedral Mn sites is influenced by the presence of the pentaor hexa-valent metal cations within the K-MOS-2 structure. Furthermore, Wasalathanthri et al [20] reported that incorporation of the Nb ions into the K-OMS-2 framework prevents sintering of cryptomelane crystals during calcination, and promotes the activity of the catalysts in the selective oxidation of methanol.…”