Hemihydrate precursors

Figure 12.4 Schematic diagram showing the layered structure of hemihydrate precursors in the (a) (100) and (b) (010) directions (both orthogonal to the (001) layer normal direction) [87].

Figure 12.5 (a) XRD pattern, (b) bright-field image and (c) selected area diffraction pattern from the hemihydrate precursor material [94], (Reproduced with permission). 

Our observations on Co-containing materials show that although the dopant is homogeneously distributed in the hemihydrate precursor phase, it has only a very... 

Figure 17.9. In Situ Raman spectra of the transformation of the hemihydrate precursor to crystalline (VO)2P207. Reproduced with permission from Wachs, I., Jehng, J., Deo, G., Weckhuysen, B., Guliants, V. and Benziger, J. (1996). Catal. Today, 32, p. 47, copyright 1996 from Elsevier.

In a recent study on the precipitation conditions for the hemihydrate [62] the influence of several parameters on the morphology of the precipitate formed was studied. The surface area of the precursors formed was... 

The VPO catalysts are prepared by thermal dehydration of its precursor, vanadyl(IV) hydrogen phosphate hemihydrate, VOHPO4 0.5H2O. The catalytic performance of the VPO catalysts depends on (i) the method of V0HP04 ... 

The aim of the present work was to develop a preparation for the vanadyl orthophosphate hemihydrate which makes use of glycols as the organic compounds able to affect its morphology these have been used as additional components, besides isobutanol, in the reducing medium. A further aim of the present work was to understand which are the key aspects in the thermal treatment through the control of which is it possible to transfer morphological features of the precursor to the vanadyl pyrophosphate, and thus to finally affect the catalytic performance. 

The known effect of organic compounds intercalation in the structure of the vanadyl orthophosphate hemihydrate, in the present case glycols having different number of C atoms used in mixture with isobutanol, has been confirmed. The removal of the retained organic fraction during the thermal treatment may lead either to folly amorphous compoimds, or to confounds which exhibit some peculiar features of the precursor, e.g. a... 

Thermal decomposition of the hemihydrate vanadyl orthophoqihate, with partial or total loss of the hydration water, formation of new phases, and elimination of precursor impurities (chlorine ions, organic compounds) as well as of additives employed for powder tabletting in the case that the tablets are prepared before the dehydration stage. 

Vanadium Phosphate Oxide catalysts are well known to perform the mild oxidation of n-butane to maleic anhydride. The preparation of the precursor of this catalyst, the vanadyl phosphate hemihydrate VOHPO4, 0.5 H2O appears to be very important to control the final properties of the VPO catalyst since the transformation precursor/vanadyl pyrophosphate (VO)2P2C>7 which corresponds to the final active phase is topotactic. It thus appears that it is possible to control the morphology of the final catalyst by the control of the morphology of its precursor (1-4). 

In this paper, we use the possibilities of Ip NMR by spin echo mapping to study the conditions of the formation of the hemihydrate VOHPO4, 05 H2O by reduction of VOPO4, 2 H2O with isobutanol. This method of preparation provides a new route for obtaining a precursor with a different morphology with a high development of the (220) X-rays line as compared to the (001) one (7). 

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