Catalytic effects in propene ammoxidation achieved through substitutions in the M2 phase of the Mo–V–Nb–Te-oxide system

Abstract

M2-type phases M 3 TeO 10 (M = Mo and V), belonging to the Mo-V-Nb-Te-oxide system, were prepared by substituting to various degrees the M-metal with W, Ti, Nb or Fe, and Te with Ce. The compositions were characterized by BET, XRD and XPS and were studied for propene ammoxidation. The variations of the unit cell parameters with substitution reveal that the orthorhombic, pseudo-hexagonal M2 structure is preserved to different degrees depending on the substituent and its amount. It is noted that partial substitution with W, Ti, Ce and Fe all increase the activity of the base composition and that Ce, and especially W, improve the selectivity to acrylonitrile at the expense of acrolein. The results of the activity measurements and the XPS investigation indicate that the site, activating propene and ammonia on the unsubstituted M2 phase is a surface ensemble of Mo and Te. W and Ce were found to be able to mimic the role of Mo and Te, respectively; W mainly via site isolation and electronic effects, Ce via redox effects. V-and Ti-sites are shown to be inactive, having merely the role of structure adjusting elements, and serving as templates to complex the excess Te on the surface.

Active Sites for Propane Oxidation: Some Generic Considerations

“…Although reports exist [23,32] on attempts supported by high-throughput experimentation to improve the function of the M1 phase and to benefit from a suspected synergy [33][34][35] with the related hexagonal M2 [36,37] phase, it is established [38] that a stable and long-term performance can also be achieved with the bare single [39] M1 phase. This gives hope that a detailed understanding of the mode of operation can be obtained based upon accurate oxide crystallography [40] forming the basis of a detailed understanding [41] of the nature of the active site.…”

Preparation, characterization and catalytic behavior for propane partial oxidation of Ga-promoted MoVTeO catalysts

“…Accordingly Ga 3+ has a promoter effect in this type of catalysts. In addition, and although this promoter effect is lower to those generally reported for Nb-containing Mo-V-Te-O samples [6][7][8][9][10][11][12][13][14][15][16][17], the promoter effect is higher to those reported for other modified catalysts [32][33]. Thus, optimizing both V-and Ga-content, it is possible to increases the selectivity to AA.…”

“…Thus, partial substitutions of W for Mo; Ti, Fe for V; Nb for Mo and V; and Ce for Te in M2-phase MoVTeNbO have been achieved and tested in propene ammoxidation [32][33][34]. An improvement in both catalytic activity and selectivity to acrylonitrile was observed over W and Ce-containing catalysts [33].…”

Inhibition of Propylene Oxidation to Acrylic Acid by Amorphous Overlayers on MoV(Nb)TeO Based M2 Catalysts

“…The amorphously overlayered materials and their characterization are reported in [24,25]. The crystalline materials without overlayers are reported in [19-21, 23, 26].…”

“…We have made several attempts to verify this postulate. Thus, partial substitutions were made of V, Te and Mo with Ti, Ce and W, respectively in the M2 phase, with the substituted compositions exhibiting modestly enhanced activity and selectivity over the base in the ammoxidation of propylene to AN [24,25]. In another study we doped M1 and M2 phases with measured (minute) amounts of acidic elements (e.g.…”