Face of vanadyl pyrophosphate

Active Crystal Face of Vanadyl Pyrophosphate for Selective Oxidation of n-Butane... 

Active crystal face of vanadyl pyrophosphate for selective n-butane oxidation catalyst preparation, 157-158 catalyst weight vs. butane oxidation, 162,163/ catalytic activity, 162,1 (At catalytic reaction procedure, 158 experimental description, 157 flow rate of butane vs. butane oxidation, 162,163/ fractured SiOj-CVO PjO scanning electron micrographs, 160,161/ fractured scanning electron... 

Active crystal face of vanadyl pyrophosphate for selective n-butane oxidation—Continued selectivity, 162,164r selectivity vs. face, 165,166/... 

Inumaru K., Okuhara T. and Misono M. (1992). Active Crystal Face of Vanadyl Pyrophosphate for Catalytic Oxidation of n-Butaneto Maleic Anhydride, Chem. Lett., 10, pp. 1955-1958. 

X-ray powder diffraction patterns, 283 Vanadyl pyrophosphate, active crystal face for selective oxidation of n-butane, 156-166 (VO),Pp,... 

Vanadyl pyrophosphate is widely considered to play an important catalytic role in the oxidation of -butane to MA, specifically the (100) face (Figure 18b), which is retained from the topotactic transformation (6,43,84—86) of the catalyst precursor phase (Figure 18a). Furthermore, this active phase has been reported to be an efficient catalyst for the oxyfimctionalization of light paraffins (a) for the oxidation of ethane to acetic acid (3,87), (b) for the oxidation and ammoxidation of propane to acrylic acid (88) and acrylonitrile (89,90), respectively, and (c) for the oxidation of n-pentane to maleic and phthalic anhydrides (90-102). 

The performance of the various crystal faces of (VO)2P207 has been investigated by Inumaru et al. (103), whose samples exposed individual planes. Vanadyl pyrophosphate was deactivated by the surface deposition of Si02, and the crystallites were then fractured to expose various planes, for example, the (021) and (001) faces. The side faces were found to be nonselective as catalysts, with MA formed only on the (100) face. 

Experimental results on pure vanadium phosphate phases and active catalysts suggested that the active catalyst was vanadyl pyrophosphate with domains of on the (100) face (114). The low selectivity of side faces found by Inumaru et al., 115,116) is attributed to the difficulty of the reoxidation of the vanadium to in these planes. Hutchings et al. (117) proposed a couple as the active site, which can be present on the... 

Ebner and Thompson [58] proposed the termination of the surface with pendant H2P207 groups, which surround two vanadyl dimers (type B). Such surface termination may be envisioned by replacing every phosphate tetrahedron facing up in the bulk (200) planes of (V0)2P207 with pyrophosphate groups. In this type of surface termination, the pyrophosphate fence isolates pairs of vanadyl dimers from other pairs, which was proposed to be beneficial for the selectivity to maleic anhydride during n-butane oxidation. 

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