Рентгенівський фазовий аналіз складної каталітичної системи типу xFePO4oyNi3(PO4)2

Abstract

In this work, using the XRD analysis, the phase composition of several experimental series of synthesized catalysts implemented in the complex xFePO4•yNi3(PO4)2 system was first investigated. Catalysts К-1 ‒ К-3 (where К-1 corresponded to a starting composition of 99,5 wt. % FePO4 ‒ 0,5 wt. % Ni3(PO4)2; К-2: 99,0 wt. % FePO4 ‒ 1,0 wt. % Ni3(PO4)2 and К-3: 75,0 wt. % FePO4 ‒ 25,0 wt. % Ni3(PO4)2) are characterized by absence of reflexes which could correspond to initial hydrate FePO4•2H2O or its anhydrous analogue. Despite the fact that it is the composition of these samples that includes the maximum amount of the starting iron (III) orthophosphate. All air-dry catalysts were amorphous. Diffractograms of the four following catalysts К-4 ‒ К-7 (where К-4 corresponds to a starting composition of 50.0 50,0 wt. % FePO4 ‒ 50,0 wt. % Ni3(PO4)2; К-5: 25,0 wt. % FePO4 ‒ 75,0 wt. % Ni3(PO4)2; К-6: 1,0 wt. % FePO4 ‒ 99,0 wt. % Ni3(PO4)2; К-7: 0,5 wt. % FePO4 ‒ 99,5 wt. % Ni3(PO4)2) have significant similarities. Some of the observed reflexes can be attributed to the individual octahydrate of nickel (II) orthophosphate. Almost all the catalysts obtained, after frying under 600ºС, become X-ray amorphous. The only exception is the sample К-1, for which some initial crystallization steps are observed. However, it is impossible to uniquely identify them and attribute them to a single phase. The frying of the test catalyst series at 700ºС temperature results in certainchanges. Thus, samples of К-6 and К-7 acquired signs of partial crystallization. The maximum intensity reflex at 2Θ~30º can be attributed to nickel (II) pyrophosphate, which is formed from dehydrated Ni3(PO4)2•8H2O. At the same time, the catalysts К-4 and К-5 remained X-ray amorphous. Probably, the increase in the content of iron (II) orthophosphate slows down the process of forming crystals of the composition Ni2P2O7. Samples of К-2 and К-3 already show signs of partial crystallization. Obviously, the structure of anhydrous FePO4 begins to form. Although for the catalyst К-1, which has the largest amount of iron (III) orthophosphate, there are no obvious signs of the beginning of crystallization.