SYNTHESIS AND STUDY BY MOSSBAUER-SPECTROSCOPY OF LIPSCOMBITE (FE23+FE2+(PO4)(2)(OH)(2)) PARTIALLY SUBSTITUTED BY MANGANESE, COBALT, AND CHROMIUM CATIONS

Recent investigations claimed the use of lipscombite, Fe23+Fe2+(PO4)(2 )(OH)2, as a catalyst for the oxidative dehydrogenation of isobutyric acid. In the present study, the synthesis and characterization by Moss bauer spectroscopy of Mn-, Co-, and Cr-substituted lipscombites are de scribed. It is found that lipscombite substituted by 10%, 20%, and 30% of cobalt and manganese could be prepared while the substitution by c hromium did not exced 20%. Mossbauer spectroscopy along with other phy sicochemical characterization techniques showed that Fe-2-x(3+),M(x)(2 +)Fe2+(PO4)(2-x)(HPO4)(x)(OH)(2) (M = Mn or Co) type solid solutions were obtained instead of Fe-2(3+)Fe(1-x)(2+)M(x)(2+)(PO4)(2)(OH)(2) solid solutions which exist for natural compounds. Chromium-substitute d compounds belonged to a Fe2-x3+Crx3+Fe2+(PO4)(2)(OH)(2) limited so lid solution (x < 0.3). Mn2+, Co2+ and Cr3+ were found to preferential ly occupy in the lipscombite structure two ferric cations sites Fe(3)b and Fe(3)a, which differ by their cationic surrounding.